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Showing 1401 - 1600 of 1720 Journals sorted alphabetically
West African Journal of Applied Ecology     Open Access  
Western Undergraduate Research Journal : Health and Natural Sciences     Open Access  
Wetlands     Hybrid Journal   (Followers: 25)
Wildlife Biology     Open Access   (Followers: 14)
Wildlife Research     Hybrid Journal   (Followers: 15)
Wiley Interdisciplinary Reviews - System Biology and Medicine     Hybrid Journal   (Followers: 5)
Wiley Interdisciplinary Reviews : Developmental Biology     Hybrid Journal   (Followers: 3)
Wiley Interdisciplinary Reviews : Membrane Transport and Signaling     Hybrid Journal  
Wiley Interdisciplinary Reviews : RNA     Hybrid Journal   (Followers: 3)
World Crop Pests     Full-text available via subscription   (Followers: 1)
World Mycotoxin Journal     Full-text available via subscription   (Followers: 6)
Xenobiotica     Hybrid Journal   (Followers: 10)
Yeast     Hybrid Journal   (Followers: 9)
Zebrafish     Hybrid Journal   (Followers: 1)
Zeitschrift für Evidenz, Fortbildung und Qualität im Gesundheitswesen     Full-text available via subscription   (Followers: 6)
Zeitschrift für Naturforschung C : A Journal of Biosciences     Open Access   (Followers: 2)
Биологический вестник МГПУ имени Богдана Хмельницкого     Open Access   (Followers: 1)

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Journal Cover Medical Engineering & Physics
  [SJR: 0.784]   [H-I: 76]   [9 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1350-4533
   Published by Elsevier Homepage  [3038 journals]
  • Identification of ankle plantar-flexors dynamics in response to electrical
           stimulation
    • Authors: Hossein Rouhani; Milos R. Popovic; Michael Same; Ya Qi Li; Kei Masani
      Pages: 1166 - 1171
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Hossein Rouhani, Milos R. Popovic, Michael Same, Ya Qi Li, Kei Masani
      Modeling the muscle response to functional electrical stimulation (FES) is an essential step in the design of closed-loop controlled neuroprostheses. This study was aimed at identifying the dynamic response of ankle plantar-flexors to FES during quiet standing. Thirteen healthy subjects stood in a standing frame that locked the knee and hip joints. The ankle plantar-flexors were stimulated bilaterally through surface electrodes and the generated ankle torque was measured. The pulse amplitude was sinusoidally modulated at five different frequencies. The pulse amplitude and the measured ankle torque fitted by a sine function were considered as input and output, respectively. First-order and critically-damped second-order linear models were fitted to the experimental data. Both models fitted similarly well to the experimental data. The coefficient of variation of the time constant among subjects was smaller in the case of the second-order model compared to the first-order model (18.1%vs. 79.9%, p <0.001). We concluded that the critically-damped second-order model more consistently described the relationship between isometric ankle torque and surface FES pulse amplitude, which was applied to the ankle plantar-flexors during quiet standing.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.07.011
       
  • Ability of electrical stimulation therapy to improve the effectiveness of
           robotic training for paretic upper limbs in patients with stroke
    • Authors: Hiroyuki Miyasaka; Abbas Orand; Hitoshi Ohnishi; Genichi Tanino; Kotaro Takeda; Shigeru Sonoda
      Pages: 1172 - 1175
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Hiroyuki Miyasaka, Abbas Orand, Hitoshi Ohnishi, Genichi Tanino, Kotaro Takeda, Shigeru Sonoda
      We investigated whether untriggered neuromuscular electrical stimulation (NMES) can increase the effectiveness of shoulder and elbow robotic training in patients with hemiparesis. Thirty subacute stroke patients were randomly equally allocated to robot only (RO) and robot and electrical stimulation (RE) groups. During training, shoulder and elbow movements were trained by operating the robotic arm with the paretic arm, and the robotic device helped to move the arm. In the RE group, the anterior deltoid and triceps brachii muscles were electrically stimulated at sub-motor threshold intensity. Training was performed (approximately 1h/day, 5 days/week for 2 weeks) in addition to regular rehabilitation. Active range of motion (ROM) values of shoulder flexion and abduction, and Fugl-Meyer assessment (FMA) scores were measured before and after training. Active shoulder ROM was significantly better after than before training in the RE group; however, no such improvement was noted in the RO group. FMA scores were significantly better in both groups, and there was no significant difference between the groups. Untriggered NMES might increase the effectiveness of shoulder and elbow robotic training in patients with hemiparesis. Additionally, NMES at a sub-motor threshold during robotic training might facilitate activation of paretic muscles, resulting in paralysis improvement.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.07.010
       
  • FES-induced co-activation of antagonist muscles for upper limb control and
           disturbance rejection
    • Authors: Antônio Padilha L. Bó; Lucas O. da Fonseca; Ana Carolina C. de Sousa
      Pages: 1176 - 1184
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Antônio Padilha L. Bó, Lucas O. da Fonseca, Ana Carolina C. de Sousa
      Control systems for human movement based on Functional Electrical Stimulation (FES) have shown to provide excellent performance in different experimental setups. Nevertheless, there is still a limited number of such applications available today on worldwide markets, indicating poor performance in real settings, particularly for upper limb rehabilitation and assistance. Based on these premises, in this paper we explore the use of an alternative control strategy based on co-activation of antagonist muscles using FES. Although co-contraction may accelerate fatigue when compared to single-muscle activation, knowledge from motor control indicate it may be useful for some applications. We have performed a simulation and experimental study designed to evaluate whether controllers that integrate such features can modulate joint impedance and, by doing so, improving performance with respect to disturbance rejection. The simulation results, obtained using a novel model including proprioceptive feedback and anatomical data, indicate that both stiffness and damping components of joint impedance may be modulated by using FES-induced co-activation of antagonist muscles. Preliminary experimental trials were conducted on four healthy subjects using surface electrodes. While the simulation investigation predicted a maximum 494% increase in joint stiffness for wrist flexion/extension, experiments provided an average elbow stiffness increase of 138% using lower stimulation intensity. Closed-loop experiments in which disturbances were applied have demonstrated that improved behavior may be obtained, but increased joint stiffness and other issues related to simultaneous stimulation of antagonist muscles may indeed produce greater errors.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.07.004
       
  • Feedback control of electrical stimulation electrode arrays
    • Authors: C.T. Freeman; K. Yang; J. Tudor; M. Kutlu
      Pages: 1185 - 1194
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): C.T. Freeman, K. Yang, J. Tudor, M. Kutlu
      Electrical stimulation electrode arrays are an emerging technology that enables muscles to be artificially contracted through the activation of their associated motor neurons. A principal application of electrical stimulation is to assist human motion for orthotic or therapeutic purposes. This paper develops a framework for the design of model-based electrode array feedback controllers that balance joint angle tracking performance with the degree of disturbance and modeling mismatch that can exist in the true underlying biomechanical system. This framework is used to develop a simplified control design procedure that is suitable for application in a clinical setting. Experimental results evaluate the feasibility of the control design approach through tests on ten participants using both fabric and polycarbonate electrode arrays.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.07.002
       
  • EEG-based BCI for the linear control of an upper-limb neuroprosthesis
    • Authors: Carmen Vidaurre; Christian Klauer; Thomas Schauer; Ander Ramos-Murguialday; Klaus-Robert Müller
      Pages: 1195 - 1204
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Carmen Vidaurre, Christian Klauer, Thomas Schauer, Ander Ramos-Murguialday, Klaus-Robert Müller
      Assistive technologies help patients to reacquire interacting capabilities with the environment and improve their quality of life. In this manuscript we present a feasibility study in which healthy users were able to use a non-invasive Motor Imagery (MI)-based brain computer interface (BCI) to achieve linear control of an upper-limb functional electrical stimulation (FES) controlled neuro-prosthesis. The linear control allowed the real-time computation of a continuous control signal that was used by the FES system to physically set the stimulation parameters to control the upper-limb position. Even if the nature of the task makes the operation very challenging, the participants achieved a mean selection accuracy of 82.5% in a target selection experiment. An analysis of limb kinematics as well as the positioning precision was performed, showing the viability of using a BCI–FES system to control upper-limb reaching movements. The results of this study constitute an accurate use of an online non-invasive BCI to operate a FES-neuroprosthesis setting a step toward the recovery of the control of an impaired limb with the sole use of brain activity.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.06.010
       
  • The adaptive drop foot stimulator – Multivariable learning control of
           foot pitch and roll motion in paretic gait
    • Authors: Thomas Seel; Cordula Werner; Thomas Schauer
      Pages: 1205 - 1213
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Thomas Seel, Cordula Werner, Thomas Schauer
      Many stroke patients suffer from the drop foot syndrome, which is characterized by a limited ability to lift (the lateral and/or medial edge of) the foot and leads to a pathological gait. In this contribution, we consider the treatment of this syndrome via functional electrical stimulation (FES) of the peroneal nerve during the swing phase of the paretic foot. A novel three-electrodes setup allows us to manipulate the recruitment of m. tibialis anterior and m. fibularis longus via two independent FES channels without violating the zero-net-current requirement of FES. We characterize the domain of admissible stimulation intensities that results from the nonlinearities in patients’ stimulation intensity tolerance. To compensate most of the cross-couplings between the FES intensities and the foot motion, we apply a nonlinear controller output mapping. Gait phase transitions as well as foot pitch and roll angles are assessed in realtime by means of an Inertial Measurement Unit (IMU). A decentralized Iterative Learning Control (ILC) scheme is used to adjust the stimulation to the current needs of the individual patient. We evaluate the effectiveness of this approach in experimental trials with drop foot patients walking on a treadmill and on level ground. Starting from conventional stimulation parameters, the controller automatically determines individual stimulation parameters and thus achieves physiological foot pitch and roll angle trajectories within at most two strides.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.06.009
       
  • Neuro-fuzzy models for hand movements induced by functional electrical
           stimulation in able-bodied and hemiplegic subjects
    • Authors: Eukene Imatz-Ojanguren; Eloy Irigoyen; David Valencia-Blanco; Thierry Keller
      Pages: 1214 - 1222
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Eukene Imatz-Ojanguren, Eloy Irigoyen, David Valencia-Blanco, Thierry Keller
      Functional Electrical Stimulation (FES) may be effective as a therapeutic treatment for improving functional reaching and grasping. Upper-limb FES models for predicting joint torques/angles from stimulation parameters can be useful to support the iterative design and development of neuroprostheses. Most such models focused on shoulder or elbow joints and were defined for fixed electrode configurations. This work proposes the use of a Recurrent Fuzzy Neural Network (RFNN) for modeling FES induced wrist, thumb, and finger movements based on surface multi-field electrodes and kinematic data from able-bodied and neurologically impaired subjects. Different combinations of structure parameters comprising fuzzy term numbers and feedback approaches were tested and analyzed in order to see their effect on the model performance for six subjects. The results showed mean success rates in the range from 60% to 99% and best success rates in the range from 78% to 100% on test data for all subjects. No common trend was found across subjects regarding structure parameters. The model showed the ability to successfully reproduce the response to FES for both able-bodied and hemiplegic subjects at least with one of the tested combinations.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.06.008
       
  • A novel motion sensor-driven control system for FES-assisted walking after
           spinal cord injury: A pilot study
    • Authors: Gustavo P. Braz; Michael F. Russold; Che Fornusek; Nur Azah Hamzaid; Richard M. Smith; Glen M. Davis
      Pages: 1223 - 1231
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Gustavo P. Braz, Michael F. Russold, Che Fornusek, Nur Azah Hamzaid, Richard M. Smith, Glen M. Davis
      This pilot study reports the development of a novel closed-loop (CL) FES-gait control system, which employed a finite-state controller that processed kinematic feedback from four miniaturized motion sensors. This strategy automated the control of knee extension via quadriceps and gluteus stimulation during the stance phase of gait on the supporting leg, and managed the stimulation delivered to the common peroneal nerve (CPN) during swing-phase on the contra-lateral limb. The control system was assessed against a traditional open-loop (OL) system on two sensorimotor ‘complete’ paraplegic subjects. A biomechanical analysis revealed that the closed-loop control of leg swing was efficient, but without major advantages compared to OL. CL automated the control of knee extension during the stance phase of gait and for this reason was the method of preference by the subjects. For the first time, a feedback control system with a simplified configuration of four miniaturized sensors allowed the addition of instruments to collect the data of multiple physiological and biomechanical variables during FES-evoked gait. In this pilot study of two sensorimotor complete paraplegic individuals, CL ameliorated certain drawbacks of current OL systems – it required less user intervention and accounted for the inter-subject differences in their stimulation requirements.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.06.007
       
  • A patient-controlled functional electrical stimulation system for arm
           weight relief
    • Authors: C. Klauer; S. Ferrante; E. Ambrosini; U. Shiri; F. Dähne; I. Schmehl; A. Pedrocchi; T. Schauer
      Pages: 1232 - 1243
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): C. Klauer, S. Ferrante, E. Ambrosini, U. Shiri, F. Dähne, I. Schmehl, A. Pedrocchi, T. Schauer
      A patient-driven control strategy for Functional Electrical Stimulation (FES), which amplifies volitionally-initiated shoulder abductions, is proposed to improve stroke patients’ rehabilitation. Based on the measured abduction angle, a FES-induced muscle recruitment is generated that yields a pre-specified percentage of this angle – yielding arm weight relief. To guarantee the correct recruitment also under fatigue and uncertain muscle activation we employ feedback control of the recruitment level determined by filtering the FES-evoked electromyogram. Filter parameters are user-optimized to obtain a linear relation between filter output and angle with a good signal-to-noise ratio. The auto-tuned recruitment controller (RC) was tested on five healthy subjects and compared to direct stimulation (DS) while muscle fatigue progressively occurred. Results showed a more linear relation between recruitment level and angle than between non-controlled stimulation intensity and angle ( R 2 = 0.93 vs. R 2 = 0.79 , angular range of 54°). After 6 min of stimulation, abduction decreased by 42% ± 14 for DS and by 0% ± 12 for RC, showing an effective compensation of fatigue. RC yielded significant smaller errors than DS in generating desired angles (0.23% ± 5.9 vs. 14.6% ± 9.7). When FES-induced arm weight support was provided, a mean reduction of the volitional effort (determined by Electromyography) of 78% was achieved compared to angular tracking without FES. First experiments with one acute stroke patient are also reported.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.06.006
       
  • A novel method of using accelerometry for upper limb FES control
    • Authors: Mingxu Sun; Laurence Kenney; Christine Smith; Karen Waring; Helen Luckie; Anmin Liu; David Howard
      Pages: 1244 - 1250
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Mingxu Sun, Laurence Kenney, Christine Smith, Karen Waring, Helen Luckie, Anmin Liu, David Howard
      This paper reports on a novel approach to using a 3-axis accelerometer to capture body segment angle for upper limb functional electrical stimulation (FES) control. The approach calculates the angle between the accelerometer x-axis and the gravity vector, while avoiding poor sensitivity at certain angles and minimizing errors when true acceleration is relatively large in comparison to gravity. This approach was incorporated into a state-machine controller which is used for the real-time control of FES during upper limb functional task performance. An experimental approach was used to validate the new method. Two participants with different upper limb impairments resulting from a stroke carried out four different FES-assisted tasks. Comparisons were made between angle calculated from arm-mounted accelerometer data using our algorithm and angle calculated from limb-mounted reflective marker data. After removal of coordinate misalignment error, mean error across tasks and subjects ranged between 1.4 and 2.9°. The approach shows promise for use in the control of upper limb FES and other human movement applications where true acceleration is relatively small in comparison with gravity.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.06.005
       
  • Stimulation map for control of functional grasp based on multi-channel EMG
           recordings
    • Authors: Lana Popović Maneski; Ivan Topalović; Nenad Jovičić; Suzana Dedijer; Ljubica Konstantinović; Dejan B. Popović
      Pages: 1251 - 1259
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Lana Popović Maneski, Ivan Topalović, Nenad Jovičić, Suzana Dedijer, Ljubica Konstantinović, Dejan B. Popović
      Transcutaneous activation of muscles with electrical stimulation has limited selectivity in recruiting paralyzed muscles in stroke patients. However, the selectivity could be increased by the application of smaller electrodes and their appropriate positioning on the skin. We developed a method for selecting the appropriate positions of the stimulating electrodes based on electromyography (EMG). The EMG activity maps were estimated from signals recorded with two electrode arrays and two 24-channel wearable amplifiers positioned on the nonparetic and paretic forearms. The areas where the difference between the EMG maps obtained from the nonparetic and paretic arms was significant were identified as the stimulation sites. The stimulation was applied through array electrodes with magnetic holders and two wearable stimulators with four output channels each. The measures of functionality included joint angles measured with goniometers (hand opening) and grasp force measured with a multi-contact dynamometer (grasping). The stimulation protocol comprised co-activation of flexors and extensors to stabilize the wrist joint and prevent pronation/supination.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.06.004
       
  • Comparison of calibration methods for accelerometers used in human motion
           analysis
    • Authors: Alexis Nez; Laetitia Fradet; Pierre Laguillaumie; Tony Monnet; Patrick Lacouture
      Pages: 1289 - 1299
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Alexis Nez, Laetitia Fradet, Pierre Laguillaumie, Tony Monnet, Patrick Lacouture
      In the fields of medicine and biomechanics, MEMS accelerometers are increasingly used to perform activity recognition by directly measuring acceleration; to calculate speed and position by numerical integration of the signal; or to estimate the orientation of body parts in combination with gyroscopes. For some of these applications, a highly accurate estimation of the acceleration is required. Many authors suggest improving result accuracy by updating sensor calibration parameters. Yet navigating the vast array of published calibration methods can be confusing. In this context, this paper reviews and evaluates the main measurement models and calibration methods. It also gives useful recommendations for better selection of a calibration process with regard to a specific application, which boils down to a compromise between accuracy, required installation, algorithm complexity, and time.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.08.004
       
  • Bayesian fusion algorithm for improved oscillometric blood pressure
           estimation
    • Authors: Mohamad Forouzanfar; Hilmi R. Dajani; Voicu Z. Groza; Miodrag Bolic; Sreeraman Rajan; Izmail Batkin
      Pages: 1300 - 1304
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Mohamad Forouzanfar, Hilmi R. Dajani, Voicu Z. Groza, Miodrag Bolic, Sreeraman Rajan, Izmail Batkin
      A variety of oscillometric algorithms have been recently proposed in the literature for estimation of blood pressure (BP). However, these algorithms possess specific strengths and weaknesses that should be taken into account before selecting the most appropriate one. In this paper, we propose a fusion method to exploit the advantages of the oscillometric algorithms and circumvent their limitations. The proposed fusion method is based on the computation of the weighted arithmetic mean of the oscillometric algorithms estimates, and the weights are obtained using a Bayesian approach by minimizing the mean square error. The proposed approach is used to fuse four different oscillometric blood pressure estimation algorithms. The performance of the proposed method is evaluated on a pilot dataset of 150 oscillometric recordings from 10 subjects. It is found that the mean error and standard deviation of error are reduced relative to the individual estimation algorithms by up to 7 mmHg and 3 mmHg in estimation of systolic pressure, respectively, and by up to 2 mmHg and 3 mmHg in estimation of diastolic pressure, respectively.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.08.003
       
  • Accurate harmonic phase tracking of tagged MRI using locally-uniform
           myocardium displacement constraint
    • Authors: Safaa M. ElDeeb; Ahmed S. Fahmy
      Pages: 1305 - 1313
      Abstract: Publication date: November 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 11
      Author(s): Safaa M. ElDeeb, Ahmed S. Fahmy
      Harmonic phase (HARP) tracking is one of the most commonly used techniques for estimating the myocardium regional function from tagged cardiac Magnetic Resonance Imaging sequences. Nevertheless, tag fading and phase distortion can severely limit the tracking accuracy of the technique. In this work, we propose to modify the HARP tracking algorithm to impose a constraint of locally uniform displacement field while tracking the different myocardium points. A numerical contracting phantom and a dataset of 11 patients are used to study the performance of the proposed technique at the different cardiac phases, slices, and regions. The results show that the proposed method improves the tracking accuracy and the reliability of the conventional HARP technique.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.08.002
       
  • Energy flow analysis of amputee walking shows a proximally-directed
           transfer of energy in intact limbs, compared to a distally-directed
           transfer in prosthetic limbs at push-off
    • Authors: R.A. Weinert-Aplin; D. Howard; M. Twiste; H.L. Jarvis; A.N. Bennett; R.J. Baker
      Abstract: Publication date: Available online 8 November 2016
      Source:Medical Engineering & Physics
      Author(s): R.A. Weinert-Aplin, D. Howard, M. Twiste, H.L. Jarvis, A.N. Bennett, R.J. Baker
      Reduced capacity and increased metabolic cost of walking occurs in amputees, despite advances in prosthetic componentry. Joint powers can quantify deficiencies in prosthetic gait, but do not reveal how energy is exchanged between limb segments. This study aimed to quantify these energy exchanges during amputee walking. Optical motion and forceplate data collected during walking at a self-selected speed for cohorts of 10 controls, 10 unilateral trans-tibial, 10 unilateral trans-femoral and 10 bilateral trans-femoral amputees were used to determine the energy exchanges between lower limb segments. At push-off, consistent thigh and shank segment powers were observed between amputee groups (1.12W/kg vs. 1.05W/kg for intact limbs and 0.97W/kg vs. 0.99W/kg for prosthetic limbs), and reduced prosthetic ankle power, particularly in trans-femoral amputees (3.12W/kg vs. 0.87W/kg). Proximally-directed energy exchange was observed in the intact limbs of amputees and controls, while prosthetic limbs displayed distally-directed energy exchanges at the knee and hip. This study used energy flow analysis to show a reversal in the direction in which energy is exchanged between prosthetic limb segments at push-off. This reversal was required to provide sufficient energy to propel the limb segments and is likely a direct result of the lack of push-off power at the prosthetic ankle, particularly in trans-femoral amputees, and leads to their increased metabolic cost of walking.

      PubDate: 2016-11-11T17:14:03Z
      DOI: 10.1016/j.medengphy.2016.10.005
       
  • Towards bioreactor development with physiological motion control and its
           applications
    • Authors: Marcus Stoffel; Wolfgang Willenberg; Marzieh Azarnoosh; Nadine Fuhrmann-Nelles; Bei Zhou; Bernd Markert
      Abstract: Publication date: Available online 9 November 2016
      Source:Medical Engineering & Physics
      Author(s): Marcus Stoffel, Wolfgang Willenberg, Marzieh Azarnoosh, Nadine Fuhrmann-Nelles, Bei Zhou, Bernd Markert
      In biomedical applications bioreactors are used, which are able to apply mechanical loadings under cultivation conditions on biological tissues. However, complex mechanobiological evolutions, such as the dependency between mechanical properties and cell activity, depend strongly on the applied loading conditions. This requires correct physiological movements and loadings in bioreactors. The aim of the present study is to develop bioreactors, in which native and artificial biological tissues can be cultivated under physiological conditions in knee joints and spinal motion segments. However, in such complex systems, where motions with different degrees of freedom are applied to whole body parts, it is necessary to investigate elements of joints and spinal parts separately. Consequently, two further bioreactors for investigating tendons and cartilage specimens are proposed additionally. The study is complemented by experimental and numerical examples with emphasis on medical and engineering applications, such as biomechanical properties of cartilage replacement materials, injured tendons, and intervertebral discs.

      PubDate: 2016-11-11T17:14:03Z
      DOI: 10.1016/j.medengphy.2016.10.010
       
  • The coupling between peripheral microcirculation and slow breathing
    • Authors: Zehava Ovadia-Blechman; Benjamin Gavish; Danit Levy-Aharoni; David Shashar; Vered Aharonson
      Abstract: Publication date: Available online 2 November 2016
      Source:Medical Engineering & Physics
      Author(s): Zehava Ovadia-Blechman, Benjamin Gavish, Danit Levy-Aharoni, David Shashar, Vered Aharonson
      Vasomotion (rhythmic changes in arteriolar diameter) is believed to enhance tissue perfusion at low oxygenation levels. We hypothesized that slow breathing and vasomotion may correlate temporally (“coupling”), especially at low oxygenation levels. We paced down spontaneous breathing to about 5 or 6breaths/min in 14 healthy subjects using device-guided breathing (DGB), and continuously monitored respiration, transcutaneous oxygen pressure (“oxygenation”), and skin capillary blood flow ("microflow”) using a laser Doppler flowmeter. The coupling was expressed by cross-correlation calculated in 1-min time windows. Our main results illustrated that: (1) coupling increased gradually upon slowing breathing down in a subgroup, in which initial oxygenation was lower than a threshold of 30mmHg (0.3±0.2 vs. 0.07±0.2, P <10−6); (2) during DGB changes in oxygenation elicited opposite (relative) changes in microflow, with 4-fold higher sensitivity for low initial oxygenation relative to high (regression slope −0.094±0.010mmHg−1 vs. −0.020±0.002mmHg−1, P <10−6); (3) at low initial oxygenation, we observed larger coupling and (relative) microflow changes in younger subjects, and greater oxygenation changes in females (P <10−6 for all); (4) pulse pressure changes from before to after DGB were reduced by increased oxygenation changes during DGB (−5.5±7.4mmHg, r =−0.73, P <0.001). In conclusion, the present methodology can provide the variation trend of respiration–vasomotion coupling during DGB that may characterize microcirculation behavior at tissue oxygenation below a measurable threshold. The potential association of these trends and thresholds with pathologies or specific conditions of the cardiopulmonary system, and the possible role played by the neural sympathetic activity in that coupling, deserve further studies.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.10.009
       
  • A computational assessment of the hemodynamic effects of crossed and
           non-crossed bifurcated stent-graft devices for the treatment of abdominal
           aortic aneurysms
    • Authors: Florian Stefanov; Tim McGloughlin; Liam Morris
      Abstract: Publication date: Available online 20 October 2016
      Source:Medical Engineering & Physics
      Author(s): Florian Stefanov, Tim McGloughlin, Liam Morris
      There are several issues attributed with abdominal aortic aneurysm endovascular repair. The positioning of bifurcated stent-grafts (SG) may affect SG hemodynamics. The hemodynamics and geometrical parameters of crossing or non-crossing graft limbs have not being totally accessed. Eight patient-specific SG devices and four pre-operative cases were computationally simulated, assessing the hemodynamic and geometrical effects for crossed (n = 4) and non-crossed (n = 4) configurations. SGs eliminated the occurrence of significant recirculations within the sac prior treatment. Dean's number predicted secondary flow locations with the greatest recirculations occurring at the outlets especially during the deceleration phase. Peak drag force varied from 3.9 to 8.7N, with greatest contribution occurring along the axial and anterior/posterior directions. Average resultant drag force was 20% smaller for the crossed configurations. Maximum drag force orientation varied from 1.4° to 51°. Drag force angle varied from 1° to 5° during one cardiac cycle. 44% to 62% of the resultant force acted along the proximal centerline where SG migration is most likely to occur. The clinician's decision for SG positioning may be a critical parameter, and should be considered prior to surgery. All crossed SG devices had an increased spiral flow effect along the distal legs with reductions in drag forces.
      Graphical abstract image

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.09.011
       
  • Beyond the front end: Investigating a thigh worn accelerometer device for
           step count and bout detection in Parkinson's disease
    • Authors: A. Godfrey; R. Morris; A. Hickey; S. Del Din
      Abstract: Publication date: Available online 22 October 2016
      Source:Medical Engineering & Physics
      Author(s): A. Godfrey, R. Morris, A. Hickey, S. Del Din
      Free-living ambulation with accelerometer-based devices is an attractive methodology to assess habitual behaviour within Parkinson's disease (PD). However, slowness of movement can contribute to difficulty in quantifying ambulatory/walking outcomes within this group by these devices. This study investigates the use of a commercial accelerometer device (activPAL™) in those with moderate PD to understand its proprietary software (inbuilt algorithm) limitations. The values provided by the proprietary software are evaluated in comparison to novel algorithms on the same raw data to examine limitations for use within this cohort. The bespoke algorithms help to alter sensitivity in outcomes stemming from the same accelerometer data while also highlighting how slight changes in algorithms can drastically inflate/deflate values. In general, results show that the proprietary software generally quantifies lower values of outcomes (step and bout count), which is similar to previous findings. Variations in algorithm functionality highlight large heterogeneity in bout and step counts resulting from a lack of how they are defined within the literature. The novel alternative ambulatory algorithms presented here should be considered for use on raw data from the activPAL™ in those with moderate/severe PD.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.09.023
       
  • Biomechanical optimization of the angle and position for surgical
           implantation of a straight short stem hip implant
    • Authors: Gillian E. Cook; Saeid Samiezadeh; Zachary Morison; Mina S.R. Aziz; Habiba Bougherara; Radovan Zdero; Emil H. Schemitsch
      Abstract: Publication date: Available online 2 November 2016
      Source:Medical Engineering & Physics
      Author(s): Gillian E. Cook, Saeid Samiezadeh, Zachary Morison, Mina S.R. Aziz, Habiba Bougherara, Radovan Zdero, Emil H. Schemitsch
      Conservative hip implants preserve healthy bone for revision surgeries and improve physiological loading; however, they have little supporting biomechanical data with respect to their 3D orientation during implantation. This study endeavored to determine the optimal 3D orientation of a straight short stem hip implant within the proximal femur that would yield a stress distribution most similar to an intact femur. Synthetic femurs were implanted with a stem in one of seven maximum angles or positions and axially loaded, with resultant strain values used to validate a finite element model. Design of experiments was used to analyze the range of potential implant orientations under three gait cycle loading conditions. A global optimal orientation of 9.14° valgus, 2.49° anteversion, 0.48mm posterior position, and 0.23mm inferior position was found to yield stress distributions most similar to the intact femur across the gait cycle range. In general, it was determined that the valgus orientation was optimal throughout the gait cycle, consistently exhibiting a stress distribution more similar to that of the intact femur. Minimal levels of anterior/posterior and inferior positioning were seen to be beneficial in achieving more physiological stresses in specific regions of interest within the proximal femur, while the anteverted orientation was only beneficial in loading under flexion. Overall, orthopaedic surgeons should aim to implant straight short stem hip implants in valgus up to 10°, with an otherwise neutral position and version, unless some degree of deviation would be beneficial for a patient-specific reason. This work has implications for the best surgical placement of straight short stem hip implants to yield maximal biomechanical stability.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.10.002
       
  • Progress in anterior chamber angle imaging for glaucoma risk prediction
           – A review on clinical equipment, practice and research
    • Authors: Shinoj V.K.; Xun Jie Jeesmond Hong; Murukeshan V.M.; Baskaran M.; Aung Tin
      Abstract: Publication date: Available online 24 October 2016
      Source:Medical Engineering & Physics
      Author(s): Shinoj V.K., Xun Jie Jeesmond Hong, Murukeshan V.M., Baskaran M., Aung Tin
      The visualization capabilities of various ocular imaging instruments can generally be categorized into photographic (e.g. gonioscopy, Pentacam, RetCam) and optical tomographic (e.g. optical coherence tomography (OCT), photoacoustic (PA) imaging, ultrasound biomicriscopy (UBM)) methods. These imaging instruments allow vision researchers and clinicians to visualize the iridocorneal angle, and are essential in the diagnosis and management of glaucoma. Each of these imaging modalities has particular benefits and associated drawbacks in obtaining repeatable and reliable measurement in the evaluation of the angle. This review article in this context summarized recent progresses in anterior chamber imaging techniques in glaucoma diagnosis and follow-up procedures.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.09.014
       
  • An active simulator for neonatal intubation: Design, development and
           assessment
    • Authors: Ilaria Baldoli; Selene Tognarelli; Ferdinando Vangi; Davide Panizza; Rosa T. Scaramuzzo; Armando Cuttano; Cecilia Laschi; Arianna Menciassi
      Abstract: Publication date: Available online 3 November 2016
      Source:Medical Engineering & Physics
      Author(s): Ilaria Baldoli, Selene Tognarelli, Ferdinando Vangi, Davide Panizza, Rosa T. Scaramuzzo, Armando Cuttano, Cecilia Laschi, Arianna Menciassi
      This study describes the technical realization and the pre-clinical validation of a instrumented neonatal intubation skill trainer able to provide objective feedback for the improvement of clinical competences required for such a delicate procedure. The Laerdal® Neonatal Intubation Trainer was modified by applying pressure sensors on areas that are mainly subject to stress and potential injuries. Punctual Force Sensing Resistors (FSRs) were characterized and fixed on the external side of the airway structure on the dental arches and epiglottis. A custom silicone tongue was designed and developed to integrate a matrix textile sensor for mapping the pressure applied on its whole surface. The assessment of the developed tool was performed by nine clinical experts who were asked to practice three intubation procedures apiece. Median and maximum forces, over threshold events (i.e. 2N for gingival arch sensors and 7N for epiglottis and tongue sensors respectively) and execution time were measured for each trainee. Data analysis from training sessions revealed that the epiglottis is the point mainly stressed during an intubation procedure (maximum value: 16.69N, median value: 3.11N), while the analysis carried out on the pressure distribution on the instrumented tongue provided information on both force values and distribution, according to clinicians' performance. The debriefing phase was used to enhance the clinicians’ awareness of applied force and gestures performed, confirming that the present study is an adequate starting point for achieving and optimizing neonatal intubation skills for both residents and expert clinicians.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.10.008
       
  • Studying the magnetic stimulation of nervous tissues: A calculation
           framework to investigate stimulation areas
    • Authors: Simona Valentini; Iacopo Portaccio; Dino Accoto
      Abstract: Publication date: Available online 3 November 2016
      Source:Medical Engineering & Physics
      Author(s): Simona Valentini, Iacopo Portaccio, Dino Accoto
      The electromagnetic stimulation of nervous tissue has represented an alternative to electrical stimulation since the 1980s. The growing number of potential applications has led to an increasing interest in the development of modeling tools that can help the design of novel electromagnetic stimulators. In this context, the aim of this paper is to provide a versatile calculation framework to investigate the properties of the electric field generated by a plurality of miniature coils, arranged in cuff configuration. Furthermore, the capability of the miniature coils to elicit a neuronal response in specific portions of the (peripheral) nerve will be investigated. Starting from Jefimenko’s equations, a model was implemented in MATLAB. It calculates the electromagnetic field induced by coils, with arbitrary shape and spatial orientation, and the activating function around the coils through simple numerical integration. By studying the activating functions, it is possible to determine where the neurons can be excited. The model was validated by comparison with FEM simulations. A dimensional analysis was conducted to compare in terms of shape and depth of the stimulation volumes different coil geometries, regardless of design parameters such as current, number of turns and coil sizes.The dimensionless groups identified according to Buckingham’s theorem provide a direct estimate of the stimulation depth reached within the nerve.The calculation tools developed in this paper can be used in the design of coils to quickly compare different geometries and spatial distribution of coils in order to identify the optimal configurations for the specific application addressed by the designer.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.10.012
       
  • Reducing temperature elevation of robotic bone drilling
    • Authors: Arne Feldmann; Jasmin Wandel; Philippe Zysset
      Abstract: Publication date: Available online 24 October 2016
      Source:Medical Engineering & Physics
      Author(s): Arne Feldmann, Jasmin Wandel, Philippe Zysset
      This research work aims at reducing temperature elevation of bone drilling. An extensive experimental study was conducted which focused on the investigation of three main measures to reduce the temperature elevation as used in industry: irrigation, interval drilling and drill bit designs. Different external irrigation rates (0 ml/min, 15 ml/min, 30 ml/min), continuously drilled interval lengths (2 mm, 1 mm, 0.5 mm) as well as two drill bit designs were tested. A custom single flute drill bit was designed with a higher rake angle and smaller chisel edge to generate less heat compared to a standard surgical drill bit. A new experimental setup was developed to measure drilling forces and torques as well as the 2D temperature field at any depth using a high resolution thermal camera. The results show that external irrigation is a main factor to reduce temperature elevation due not primarily to its effect on cooling but rather due to the prevention of drill bit clogging. During drilling, the build up of bone material in the drill bit flutes result in excessive temperatures due to an increase in thrust forces and torques. Drilling in intervals allows the removal of bone chips and cleaning of flutes when the drill bit is extracted as well as cooling of the bone in-between intervals which limits the accumulation of heat. However, reducing the length of the drilled interval was found only to be beneficial for temperature reduction using the newly designed drill bit due to the improved cutting geometry. To evaluate possible tissue damage caused by the generated heat increase, cumulative equivalent minutes (CEM43) were calculated and it was found that the combination of small interval length (0.5 mm), high irrigation rate (30 ml/min) and the newly designed drill bit was the only parameter combination which allowed drilling below the time-thermal threshold for tissue damage. In conclusion, an optimized drilling method has been found which might also enable drilling in more delicate procedures such as that performed during minimally invasive robotic cochlear implantation.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.10.001
       
  • Three-dimensional finite element analysis of a newly developed aliform
           internal fixation system for occipitocervical fusion
    • Authors: Sui-Xiang Liao; Jian-Hua Wang; Yong-Qiang Zheng; Guan Zheng; Ge-Jing Wei; Hong Xia; Xiao-Hua Chen
      Abstract: Publication date: Available online 28 October 2016
      Source:Medical Engineering & Physics
      Author(s): Sui-Xiang Liao, Jian-Hua Wang, Yong-Qiang Zheng, Guan Zheng, Ge-Jing Wei, Hong Xia, Xiao-Hua Chen
      For patients with occipital malformation, it is difficult to obtain reliable stability using three screws on the midline. A new aliform occipitocervical internal fixation system was designed. The occiput was fixed with 3, 7, or 11 screws, and a three-dimensional finite element model of the system was established. A compressive preload of 40N combined with a pure moment of 1.5Nm was applied to simulate normal flexion, extension, lateral bending, and axial rotation. The stress distribution across the screws on the occiput and the occipital displacement produced by the newly developed system were compared with those produced by the DePuy SUMMIT system. Compared with the SUMMIT system (control group), in the new system, the maximum stress on the occiputs fixed with 3 screws (group A) and 7 screws (group B) increased by 16.5% and 15.0%, respectively. In contrast, the maximum stress on the occiput fixed with 11 screws (group C) decreased by 15.6%. In addition, the maximum occipital displacements under extension decreased by 10.0%, 11.4%, and 11.8% in the A, B, and, C groups, respectively. Our results indicate that both group A and the control group exhibited sufficient strength and instant stability; however, group C exhibited the highest stability and the lowest maximum von Mises stress.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.08.011
       
  • Model-dependent and model-independent approaches for evaluating hepatic
           fibrosis in rat liver using shearwave dispersion ultrasound vibrometry
    • Authors: Haoming Lin; Xinyu Zhang; Yuanyuan Shen; Yi Zheng; Yanrong Guo; Ying Zhu; Xianfen Diao; Tianfu Wang; Siping Chen; Xin Chen
      Abstract: Publication date: Available online 1 November 2016
      Source:Medical Engineering & Physics
      Author(s): Haoming Lin, Xinyu Zhang, Yuanyuan Shen, Yi Zheng, Yanrong Guo, Ying Zhu, Xianfen Diao, Tianfu Wang, Siping Chen, Xin Chen
      This study assesses gradations of hepatic fibrosis in rat livers using both model-dependent and model-independent approaches. Liver fibrosis was induced in 37 rats using carbon tetrachloride (CCl4); 6 rats served as the controls. Shear wave velocity as a function of frequency, referred to as velocity dispersion, was measured in vitro by an ultrasound elastography method called shearwave dispersion ultrasound vibrometry (SDUV). For the model-dependent approach, the velocity dispersion data were fit to the Voigt model to solve the viscoelastic modulus. For the model-independent approach, the pattern of the velocity dispersion data was analyzed by linear regression to extract the slope and intercept features. The parameters obtained by both approaches were evaluated separately using a receiver operating characteristic (ROC) curve analysis. The results show that, of all the parameters for differentiating between grade F0–F1 and grade F2–F4 fibrosis, the intercept had the greatest value for the area under the ROC curve. This finding suggests that the model-independent approach may provide an alternative method to the model-dependent approach for staging liver fibrosis.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.10.007
       
  • Modification of the Grood and Suntay Joint Coordinate System equations for
           knee joint flexion
    • Authors: Danè Dabirrahmani; Michael Hogg
      Abstract: Publication date: Available online 1 November 2016
      Source:Medical Engineering & Physics
      Author(s): Danè Dabirrahmani, Michael Hogg
      Since its introduction, the Grood and Suntay Joint Coordinate System (JCS) has been embraced by the International Society of Biomechanics (ISB) and been widely used for biomechanical reporting. There is, however, a limitation in its ability to provide correct flexion values over a wide range of clinically relevant flexion angles. This technical note addresses the limitation of the JCS equations and introduces a new set of equations to overcome this problem.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.10.006
       
  • Biomechanical analysis of combining head-down tilt traction with vibration
           for different grades of degeneration of the lumbar spine
    • Authors: Sicong Wang; Lizhen Wang; Yawei Wang; Chengfei Du; Ming Zhang; Yubo Fan
      Abstract: Publication date: Available online 3 November 2016
      Source:Medical Engineering & Physics
      Author(s): Sicong Wang, Lizhen Wang, Yawei Wang, Chengfei Du, Ming Zhang, Yubo Fan
      In recent years, a combination of traction and vibration therapy is usually used to alleviate low back pain (LBP) in clinical settings. Combining head-down tilt (HDT) traction with vibration was demonstrated to be efficacious for LBP patients in our previous study. However, the biomechanics of the lumbar spine during this combined treatment is not well known and need quantitative analysis. In addition, LBP patients have different grades of degeneration of the lumbar spinal structure, which are often age related. Selecting a suitable rehabilitation therapy for different age groups of patients has been challenging. Therefore, a finite element (FE) model of the L1–L5 lumbar spine and a vibration dynamic model are developed in this study in order to investigate the biomechanical effects of the combination of HDT traction and vibration therapy on the age-related degeneration of the lumbar spine. The decrease of intradiscal pressure is more effective when vibration is combined with traction therapy. Moreover, the stresses on the discs are lower in the “traction+vibration” mode than the “traction-only” mode. The stress concentration at the posterior part of nucleus is mitigated after the vibration is combined. The disc deformations especially posterior disc radial retraction is improved in the “traction+vibration” mode. These beneficial effects of this therapy could help decompress the discs and spinal nerves and therefore relieve LBP. Simultaneously, patients with grade 1 degeneration (approximately 41–50 years old) are able to achieve better results compared with other age groups. This study could be used to provide a more effective LBP rehabilitation therapy.

      PubDate: 2016-11-05T16:20:44Z
      DOI: 10.1016/j.medengphy.2016.10.004
       
  • A theoretical computerized study for the electrical conductivity of
           arterial pulsatile blood flow by an elastic tube model
    • Authors: Hua Shen; Yong Zhu; Kai-Rong Qin
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): Hua Shen, Yong Zhu, Kai-Rong Qin
      The electrical conductivity of pulsatile blood flow in arteries is an important factor for the application of the electrical impedance measurement system in clinical settings. The electrical conductivity of pulsatile blood flow depends not only on blood-flow-induced red blood cell (RBC) orientation and deformation but also on artery wall motion. Numerous studies have investigated the conductivity of pulsatile blood based on a rigid tube model, in which the effects of wall motion on blood conductivity are not considered. In this study, integrating Ling and Atabek's local flow theory and Maxwell–Fricke theory, we develop an elastic tube model to explore the effects of wall motion as well as blood flow velocity on blood conductivity. The simulation results suggest that wall motion, rather than blood flow velocity, is the primary factor that affects the conductivity of flowing blood in arteries.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.013
       
  • Stress shielding in periprosthetic bone following a total knee
           replacement: Effects of implant material, design and alignment
    • Authors: Qing-Hang Zhang; Andrew Cossey; Jie Tong
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): Qing-Hang Zhang, Andrew Cossey, Jie Tong
      Periprosthetic bone strain distributions in some of the typical cases of total knee replacement (TKR) were studied with regard to the selection of material, design and the alignments of tibial components to examine which conditions are more forgiving than the others to stress shielding post a TKR. Four tibial components with two implant designs (cruciate sacrificing and cruciate retaining) and material properties (metal-backed (MB) and all-polyethylene (AP)) were considered in a specimen-specific finite element tibia bone model loaded in a neutral position. The influence of tibial material and design on the periprosthetic bone strain response was investigated under the peak loads of walking and stair descending/ascending. Two of the models were also modified to examine the effect of selected implant malalignment conditions (7° posterior, 5° valgus and 5° varus) on stress shielding in the bone, where the medio-lateral load share ratios were adjusted accordingly. The predicted increases of bone density due to implantation for the selected cases studied were also presented. For the cases examined, the effect of stress shielding on the periprosthetic bone seems to be more significantly influenced by the implant material than by the implant geometry. Significant stress shielding is found in MB cases, as opposed to increase in bone density found in AP cases, particularly in the bones immediately beneath the baseplate. The effect of stress shielding is reduced somewhat for the MB components in the malaligned positions compared with the neutral case. In AP cases, the effect of stress shielding is mostly low except in the varus position, possibly due to off-loading of lateral condyle. Increases in bone density are found in both MB and AP cases for the malaligned conditions.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.018
       
  • Discrete sensors distribution for accurate plantar pressure analyses
    • Authors: Laetitia Claverie; Anne Ille; Pierre Moretto
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): Laetitia Claverie, Anne Ille, Pierre Moretto
      The aim of this study was to determine the distribution of discrete sensors under the footprint for accurate plantar pressure analyses. For this purpose, two different sensor layouts have been tested and compared, to determine which was the most accurate to monitor plantar pressure with wireless devices in research and/or clinical practice. Ten healthy volunteers participated in the study (age range: 23–58 years). The barycenter of pressures (BoP) determined from the plantar pressure system (W-inshoe®) was compared to the center of pressures (CoP) determined from a force platform (AMTI) in the medial-lateral (ML) and anterior-posterior (AP) directions. Then, the vertical ground reaction force (vGRF) obtained from both W-inshoe® and force platform was compared for both layouts for each subject. The BoP and vGRF determined from the plantar pressure system data showed good correlation (SCC) with those determined from the force platform data, notably for the second sensor organization (ML SCC= 0.95; AP SCC=0.99; vGRF SCC=0.91). The study demonstrates that an adjusted placement of removable sensors is key to accurate plantar pressure analyses. These results are promising for a plantar pressure recording outside clinical or laboratory settings, for long time monitoring, real time feedback or for whatever activity requiring a low-cost system.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.021
       
  • Evaluation of the SMALL nail: Drive technology and behavior in situ
    • Authors: L.H. Dünnweber; R. Rödl; G. Gosheger; F.M. Schiedel
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): L.H. Dünnweber, R. Rödl, G. Gosheger, F.M. Schiedel
      Although clear advances have been made during the last 5 years, practical difficulties persist for patients and surgeons in procedures for intramedullary lengthening of long bones. In particular, precise adjustment of the desired amount of lengthening and technically reliable checking of the length actually achieved are problematic. An intramedullary nail with a new type of drive that exploits the shape memory effect has been constructed. The drive technology and the behavior of the intramedullary nail in situ were evaluated in a cadaver experiment. Three shape memory alloy limb lengthening (SMALL) nails were implanted in a body donor. The SMALL nail contains a spring coupled to a shape memory element consisting of a nickel–titanium alloy. This shape memory element “remembers” its initial state before the lengthening through the spring and can return to it when it is warmed. A cartridge heater inside the lengthening nail is warmed using transcutaneous induction with high-frequency energy via a subcutaneously implanted coil. For evaluation, two SMALL nails were implanted into the femora (antegrade on the left and retrograde on the right) and one SMALL nail was implanted into the left tibia. Lengthening by 50mm was attempted using repeated activation of the drive mechanism. At the same time, test parameters for temperature increases and cooling periods were continually monitored and the data were subsequently analyzed. The nail's mechanism worked in principle, but was inadequate in view of success rates (number of lengthening steps attempted versus number of lengthening steps achieved) of 21% for the SMALL nail in the tibia and left femur and 14% for the nail in the right femur. The temperature values measured during the distraction experiments show that high-frequency energy induction in the SMALL nail gives no cause for concern for patients.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.020
       
  • Anisotropic abdominal aortic aneurysm replicas with biaxial material
           characterization
    • Authors: Sergio Ruiz de Galarreta; Raúl Antón; Aitor Cazon; Gorka S. Larraona; Ender A. Finol
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): Sergio Ruiz de Galarreta, Raúl Antón, Aitor Cazon, Gorka S. Larraona, Ender A. Finol
      An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta at least 1.5 times its normal diameter. The criterion of maximum diameter is still used in clinical practice, although numerical studies have demonstrated the importance of other biomechanical factors. Numerical studies, however, must be validated experimentally before they can be clinically implemented. We have developed a methodology for manufacturing anisotropic AAA replicas with non-uniform wall thickness. Different composites were fabricated and tested, and one was selected in order to manufacture a phantom with the same properties. The composites and the phantom were characterized by biaxial tensile tests and a material model was fit to the experimental data. The experimental results were compared with data from the literature, and similar responses were obtained. The anisotropic AAA replicas with non-uniform wall thickness can be used in benchtop experiments to validate deformations obtained with numerical simulations or for pre-intervention testing of endovascular grafts. This is a significant step forward considering the importance of anisotropy in numerical simulations.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.010
       
  • Motor unit firing rates and synchronisation affect the fractal dimension
           of simulated surface electromyogram during isometric/isotonic contraction
           of vastus lateralis muscle
    • Authors: Luca Mesin; Davide Dardanello; Alberto Rainoldi; Gennaro Boccia
      Abstract: Publication date: Available online 12 October 2016
      Source:Medical Engineering & Physics
      Author(s): Luca Mesin, Davide Dardanello, Alberto Rainoldi, Gennaro Boccia
      During fatiguing contractions, many adjustments in motor units behaviour occur: decrease in muscle fibre conduction velocity; increase in motor units synchronisation; modulation of motor units firing rate; increase in variability of motor units inter-spike interval. We simulated the influence of all these adjustments on synthetic EMG signals in isometric/isotonic conditions. The fractal dimension of the EMG signal was found mainly influenced by motor units firing behaviour, being affected by both firing rate and synchronisation level, and least affected by muscle fibre conduction velocity. None of the calculated EMG indices was able to discriminate between firing rate and motor units synchronisation.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.022
       
  • Fully automatic segmentation of femurs with medullary canal definition in
           high and in low resolution CT scans
    • Authors: Diogo F. Almeida; Rui B. Ruben; João Folgado; Paulo R. Fernandes; Emmanuel Audenaert; Benedict Verhegghe; Matthieu De Beule
      Abstract: Publication date: Available online 15 October 2016
      Source:Medical Engineering & Physics
      Author(s): Diogo F. Almeida, Rui B. Ruben, João Folgado, Paulo R. Fernandes, Emmanuel Audenaert, Benedict Verhegghe, Matthieu De Beule
      Femur segmentation can be an important tool in orthopedic surgical planning. However, in order to overcome the need of an experienced user with extensive knowledge on the techniques, segmentation should be fully automatic. In this paper a new fully automatic femur segmentation method for CT images is presented. This method is also able to define automatically the medullary canal and performs well even in low resolution CT scans. Fully automatic femoral segmentation was performed adapting a template mesh of the femoral volume to medical images. In order to achieve this, an adaptation of the active shape model (ASM) technique based on the statistical shape model (SSM) and local appearance model (LAM) of the femur with a novel initialization method was used, to drive the template mesh deformation in order to fit the in-image femoral shape in a time effective approach. With the proposed method a 98% convergence rate was achieved. For high resolution CT images group the average error is less than 1mm. For the low resolution image group the results are also accurate and the average error is less than 1.5mm. The proposed segmentation pipeline is accurate, robust and completely user free. The method is robust to patient orientation, image artifacts and poorly defined edges. The results excelled even in CT images with a significant slice thickness, i.e., above 5mm. Medullary canal segmentation increases the geometric information that can be used in orthopedic surgical planning or in finite element analysis.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.019
       
  • Rôle of contrast media viscosity in altering vessel wall shear stress and
           relation to the risk of contrast extravasations
    • Authors: Sophia Sakellariou; Wenguang Li; Manosh C Paul; Giles Roditi
      Abstract: Publication date: Available online 8 October 2016
      Source:Medical Engineering & Physics
      Author(s): Sophia Sakellariou, Wenguang Li, Manosh C Paul, Giles Roditi
      Iodinated contrast media (CM) are the most commonly used injectables in radiology today. A range of different media are commercially available, combining various physical and chemical characteristics (ionic state, osmolality, viscosity) and thus exhibiting distinct in vivo behaviour and safety profiles. In this paper, numerical simulations of blood flow with contrast media were conducted to investigate the effects of contrast viscosity on generated vessel wall shear stress and vessel wall pressure to elucidate any possible relation to extravasations. Five different types of contrast for Iodine fluxes ranging at 1.5–2.2gI/s were modelled through 18G and 20G cannulae placed in an ideal vein at two different orientation angles. Results demonstrate that the least viscous contrast media generate the least maximum wall shear stress as well as the lowest total pressure for the same flow rate. This supports the empirical clinical observations and hypothesis that more viscous contrast media are responsible for a higher percentage of contrast extravasations. In addition, results support the clinical hypothesis that a catheter tip directed obliquely to the vein wall always produces the highest maximum wall shear stress and total pressure due to impingement of the contrast jet on the vessel wall.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.016
       
  • Advances in Functional Electrical Stimulation modelling and control
    • Authors: Thomas Schauer; Christopher Freeman
      Abstract: Publication date: Available online 4 October 2016
      Source:Medical Engineering & Physics
      Author(s): Thomas Schauer, Christopher Freeman


      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.004
       
  • Improved Rubin–Bodner model for the prediction of soft tissue
           deformations
    • Authors: Guangming Zhang; James J. Xia; Michael Liebschner; Xiaoyan Zhang; Daeseung Kim; Xiaobo Zhou
      Abstract: Publication date: Available online 4 October 2016
      Source:Medical Engineering & Physics
      Author(s): Guangming Zhang, James J. Xia, Michael Liebschner, Xiaoyan Zhang, Daeseung Kim, Xiaobo Zhou
      In craniomaxillofacial (CMF) surgery, a reliable way of simulating the soft tissue deformation resulted from skeletal reconstruction is vitally important for preventing the risks of facial distortion postoperatively. However, it is difficult to simulate the soft tissue behaviors affected by different types of CMF surgery. This study presents an integrated bio-mechanical and statistical learning model to improve accuracy and reliability of predictions on soft facial tissue behavior. The Rubin–Bodner (RB) model is initially used to describe the biomechanical behavior of the soft facial tissue. Subsequently, a finite element model (FEM) computers the stress of each node in soft facial tissue mesh data resulted from bone displacement. Next, the Generalized Regression Neural Network (GRNN) method is implemented to obtain the relationship between the facial soft tissue deformation and the stress distribution corresponding to different CMF surgical types and to improve evaluation of elastic parameters included in the RB model. Therefore, the soft facial tissue deformation can be predicted by biomechanical properties and statistical model. Leave-one-out cross-validation is used on eleven patients. As a result, the average prediction error of our model (0.7035mm) is lower than those resulting from other approaches. It also demonstrates that the more accurate bio-mechanical information the model has, the better prediction performance it could achieve.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.008
       
  • Probabilistic finite element method for large tumor radiofrequency
           ablation simulation and planning
    • Authors: Bin Duan; Rong Wen; Yabo Fu; Kian-Jon Chua; Chee-Kong Chui
      Abstract: Publication date: Available online 4 October 2016
      Source:Medical Engineering & Physics
      Author(s): Bin Duan, Rong Wen, Yabo Fu, Kian-Jon Chua, Chee-Kong Chui
      A challenging problem of radiofrequency ablation (RFA) in liver surgery is to accurately estimate the shapes and sizes of RFA lesions whose formation depends on intrinsic variations of the thermal–electrical properties of soft tissue. Large tumors, which can be as long as 10 cm or more, further complicate the problem. In this paper, a probabilistic bio-heating finite element (FE) model is proposed and developed to predict RFA lesions. Uncertainties of RFA lesions are caused by the probabilistic nature of five thermal–electrical liver properties: thermal conductivity, liver tissue density, specific heat, blood perfusion rate and electrical conductivity. Confidence levels of shapes and sizes of lesions are generated by the FE model incorporated with the mean-value first-order second-moment (MVFOSM) method. Based on the probabilistic FE method, a workflow of RFA planning is introduced to enable clinicians to preoperatively view the predicted RFA lesions in three-dimension (3D) within a hepatic environment. Accurate planning of the RFA needle placements can then be achieved based on the interactive simulation and confidence level selection.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.08.007
       
  • A mathematical method for precisely calculating the radiographic angles of
           the cup after total hip arthroplasty
    • Authors: Jing-Xin Zhao; Xiu-Yun Su; Ruo-Xiu Xiao; Zhe Zhao; Li-Hai Zhang; Li-Cheng Zhang; Pei-Fu Tang
      Abstract: Publication date: Available online 5 October 2016
      Source:Medical Engineering & Physics
      Author(s): Jing-Xin Zhao, Xiu-Yun Su, Ruo-Xiu Xiao, Zhe Zhao, Li-Hai Zhang, Li-Cheng Zhang, Pei-Fu Tang
      We established a mathematical method to precisely calculate the radiographic anteversion (RA) and radiographic inclination (RI) angles of the acetabular cup based on anterior–posterior (AP) pelvic radiographs after total hip arthroplasty. Using Mathematica software, a mathematical model for an oblique cone was established to simulate how AP pelvic radiographs are obtained and to address the relationship between the two-dimensional and three-dimensional geometry of the opening circle of the cup. In this model, the vertex was the X-ray beam source, and the generatrix was the ellipse in radiographs projected from the opening circle of the acetabular cup. Using this model, we established a series of mathematical formulas to reveal the differences between the true RA and RI cup angles and the measurements results achieved using traditional methods and AP pelvic radiographs and to precisely calculate the RA and RI cup angles based on post-operative AP pelvic radiographs. Statistical analysis indicated that traditional methods should be used with caution if traditional measurements methods are used to calculate the RA and RI cup angles with AP pelvic radiograph. The entire calculation process could be performed by an orthopedic surgeon with mathematical knowledge of basic matrix and vector equations.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.007
       
  • Comparison of algorithms to quantify muscle fatigue in upper limb muscles
           based on sEMG signals
    • Authors: Lorenz Kahl; Ulrich G. Hofmann
      Abstract: Publication date: Available online 7 October 2016
      Source:Medical Engineering & Physics
      Author(s): Lorenz Kahl, Ulrich G. Hofmann
      This work compared the performance of six different fatigue detection algorithms quantifying muscle fatigue based on electromyographic signals. Surface electromyography (sEMG) was obtained by an experiment from upper arm contractions at three different load levels from twelve volunteers. Fatigue detection algorithms mean frequency (MNF), spectral moments ratio (SMR), the wavelet method WIRM1551, sample entropy (SampEn), fuzzy approximate entropy (fApEn) and recurrence quantification analysis (RQA%DET) were calculated. The resulting fatigue signals were compared considering the disturbances incorporated in fatiguing situations as well as according to the possibility to differentiate the load levels based on the fatigue signals. Furthermore we investigated the influence of the electrode locations on the fatigue detection quality and whether an optimized channel set is reasonable. The results of the MNF, SMR, WIRM1551 and fApEn algorithms fell close together. Due to the small amount of subjects in this study significant differences could not be found. In terms of disturbances the SMR algorithm showed a slight tendency to out-perform the others.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.009
       
  • A new 3D center of mass control approach for FES-assisted standing: First
           experimental evaluation with a humanoid robot
    • Authors: J. Jovic; V. Bonnet; C. Fattal; P. Fraisse; Ch. Azevedo Coste
      Abstract: Publication date: Available online 28 September 2016
      Source:Medical Engineering & Physics
      Author(s): J. Jovic, V. Bonnet, C. Fattal, P. Fraisse, Ch. Azevedo Coste
      This paper proposes a new control framework to restore the coordination between upper (functional) and lower (paralyzed) limbs in the context of functional electrical stimulation in completely paraplegic individuals. A kinematic decoupling between the lower and upper limbs controls the 3D whole-body center of mass location and the relative foot positions by acting only on the lower-limb joints. The upper limbs are free to move under voluntary control, and are seen as a perturbation for the lower limbs. An experimental validation of this paradigm using a humanoid robot demonstrates the real-time applicability and robustness of the method. Different scenarios mimicking the motion of a healthy subject are investigated. The proposed method can maintain bipedal balance and track the desired center of mass trajectories under movement disturbances of the upper limbs with an error inferior to 0.01 m under any conditions.

      PubDate: 2016-10-01T11:48:04Z
      DOI: 10.1016/j.medengphy.2016.09.002
       
  • Hybrid robotic systems for upper limb rehabilitation after stroke: A
           review
    • Authors: Francisco Resquín; Alicia Cuesta Gómez; Jose Gonzalez-Vargas; Fernando Brunetti; Diego Torricelli; Francisco Molina Rueda; Roberto Cano de la Cuerda; Juan Carlos Miangolarra; José Luis Pons
      Abstract: Publication date: Available online 29 September 2016
      Source:Medical Engineering & Physics
      Author(s): Francisco Resquín, Alicia Cuesta Gómez, Jose Gonzalez-Vargas, Fernando Brunetti, Diego Torricelli, Francisco Molina Rueda, Roberto Cano de la Cuerda, Juan Carlos Miangolarra, José Luis Pons
      In recent years the combined use of functional electrical stimulation (FES) and robotic devices, called hybrid robotic rehabilitation systems, has emerged as a promising approach for rehabilitation of lower and upper limb motor functions. This paper presents a review of the state of the art of current hybrid robotic solutions for upper limb rehabilitation after stroke. For this aim, studies have been selected through a search using web databases: IEEE-Xplore, Scopus and PubMed. A total of 10 different hybrid robotic systems were identified, and they are presented in this paper. Selected systems are critically compared considering their technological components and aspects that form part of the hybrid robotic solution, the proposed control strategies that have been implemented, as well as the current technological challenges in this topic. Additionally, we will present and discuss the corresponding evidences on the effectiveness of these hybrid robotic therapies. The review also discusses the future trends in this field.

      PubDate: 2016-10-01T11:48:04Z
      DOI: 10.1016/j.medengphy.2016.09.001
       
  • Experimental investigation and statistical modeling of temperature rise in
           rotary ultrasonic bone drilling
    • Authors: Vishal Gupta; Pulak M. Pandey
      Abstract: Publication date: Available online 14 September 2016
      Source:Medical Engineering & Physics
      Author(s): Vishal Gupta, Pulak M. Pandey
      Thermal necrosis is one of the major problems associated with the bone drilling process in orthopedic/trauma surgical operations. To overcome this problem a new bone drilling method has been introduced recently. Studies have been carried out with rotary ultrasonic drilling (RUD) on pig bones using diamond coated abrasive hollow tools. In the present work, influence of process parameters (rotational speed, feed rate, drill diameter and vibrational amplitude) on change in the temperature was studied using design of experiment technique i.e., response surface methodology (RSM) and data analysis was carried out using analysis of variance (ANOVA). Temperature was recorded and measured by using embedded thermocouple technique at a distance of 0.5mm, 1.0mm, 1.5mm and 2.0mm from the drill site. Statistical model was developed to predict the maximum temperature at the drill tool and bone interface. It was observed that temperature increased with increase in the rotational speed, feed rate and drill diameter and decreased with increase in the vibrational amplitude.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.012
       
  • A review of the design and clinical evaluation of the ShefStim array-based
           functional electrical stimulation system
    • Authors: Laurence P. Kenney; Ben W. Heller; Anthony T. Barker; Mark L. Reeves; Jamie Healey; Timothy R. Good; Glen Cooper; Ning Sha; Sarah Prenton; Anmin Liu; David Howard
      Abstract: Publication date: Available online 14 September 2016
      Source:Medical Engineering & Physics
      Author(s): Laurence P. Kenney, Ben W. Heller, Anthony T. Barker, Mark L. Reeves, Jamie Healey, Timothy R. Good, Glen Cooper, Ning Sha, Sarah Prenton, Anmin Liu, David Howard
      Functional electrical stimulation has been shown to be a safe and effective means of correcting foot drop of central neurological origin. Current surface-based devices typically consist of a single channel stimulator, a sensor for determining gait phase and a cuff, within which is housed the anode and cathode. The cuff-mounted electrode design reduces the likelihood of large errors in electrode placement, but the user is still fully responsible for selecting the correct stimulation level each time the system is donned. Researchers have investigated different approaches to automating aspects of setup and/or use, including recent promising work based on iterative learning techniques. This paper reports on the design and clinical evaluation of an electrode array-based FES system for the correction of drop foot, ShefStim. The paper reviews the design process from proof of concept lab-based study, through modelling of the array geometry and interface layer to array search algorithm development. Finally, the paper summarises two clinical studies involving patients with drop foot. The results suggest that the ShefStim system with automated setup produces results which are comparable with clinician setup of conventional systems. Further, the final study demonstrated that patients can use the system without clinical supervision. When used unsupervised, setup time was 14min (9min for automated search plus 5min for donning the equipment), although this figure could be reduced significantly with relatively minor changes to the design.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.005
       
  • Morphology based anisotropic finite element models of the proximal femur
           validated with experimental data
    • Authors: W.S. Enns-Bray; O. Ariza; S. Gilchrist; R.P. Widmer Soyka; P.J. Vogt; H. Palsson; S.K. Boyd; P. Guy; P.A. Cripton; S.J. Ferguson; B. Helgason
      Abstract: Publication date: Available online 15 September 2016
      Source:Medical Engineering & Physics
      Author(s): W.S. Enns-Bray, O. Ariza, S. Gilchrist, R.P. Widmer Soyka, P.J. Vogt, H. Palsson, S.K. Boyd, P. Guy, P.A. Cripton, S.J. Ferguson, B. Helgason
      Finite element analysis (FEA) of bones scanned with Quantitative Computed Tomography (QCT) can improve early detection of osteoporosis. The accuracy of these models partially depends on the assigned material properties, but anisotropy of the trabecular bone cannot be fully captured due to insufficient resolution of QCT. The inclusion of anisotropy measured from high resolution peripheral QCT (HR-pQCT) could potentially improve QCT-based FEA of the femur, although no improvements have yet been demonstrated in previous experimental studies. This study analyzed the effects of adding anisotropy to clinical resolution femur models by constructing six sets of FE models (two isotropic and four anisotropic) for each specimen from a set of sixteen femurs that were experimentally tested in sideways fall loading with a strain gauge on the superior femoral neck. Two different modulus–density relationships were tested, both with and without anisotropy derived from mean intercept length analysis of HR-pQCT scans. Comparing iso- and anisotropic models to the experimental data resulted in nearly identical correlation and highly similar linear regressions for both whole bone stiffness and strain gauge measurements. Anisotropic models contained consistently greater principal compressive strains, approximately 14% in magnitude, in certain internal elements located in the femoral neck, greater trochanter, and femoral head. In summary, anisotropy had minimal impact on macroscopic measurements, but did alter internal strain behavior. This suggests that organ level QCT-based FE models measuring femoral stiffness have little to gain from the addition of anisotropy, but studies considering failure of internal structures should consider including anisotropy to their models.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.010
       
  • Numerical prediction of peri-implant bone adaptation: Comparison of
           mechanical stimuli and sensitivity to modeling parameters
    • Authors: Marco Piccinini; Joel Cugnoni; John Botsis; Patrick Ammann; Anselm Wiskott
      Abstract: Publication date: Available online 15 September 2016
      Source:Medical Engineering & Physics
      Author(s): Marco Piccinini, Joel Cugnoni, John Botsis, Patrick Ammann, Anselm Wiskott
      Long term durability of osseointegrated implants depends on bone adaptation to stress and strain occurring in proximity of the prosthesis. Mechanical overloading, as well as disuse, may reduce the stability of implants by provoking bone resorption. However, an appropriate mechanical environment can improve integration. Several studies have focused on the definition of numerical methods to predict bone peri-implant adaptation to the mechanical environment. Existing adaptation models differ notably in the type of mechanical variable adopted as stimulus but also in the bounds and shape of the adaptation rate equation. However, a general comparison of the different approaches on a common benchmark case is still missing and general guidelines to determine physically sound parameters still need to be developed. This current work addresses these themes in two steps. Firstly, the histograms of effective stress, strain and strain energy density are compared for rat tibiae in physiological (homeostatic) conditions. According to the Mechanostat, the ideal stimulus should present a clearly defined, position and tissue invariant lazy zone in homeostatic conditions. Our results highlight that only the octahedral shear strain presents this characteristic and can thus be considered the optimal choice for implementation of a continuum level bone adaptation model. Secondly, critical modeling parameters such as lazy zone bounds, type of rate equation and bone overloading response are classified depending on their influence on the numerical predictions of bone adaptation. Guidelines are proposed to establish the dominant model parameters based on experimental and simulated data.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.008
       
  • Effects of implant drilling parameters for pilot and twist drills on
           temperature rise in bone analog and alveolar bones
    • Authors: Yung-Chuan Chen; Chih-Kun Hsiao; Ji-Sih Ciou; Yi-Jung Tsai; Yuan-Kun Tu
      Abstract: Publication date: Available online 16 September 2016
      Source:Medical Engineering & Physics
      Author(s): Yung-Chuan Chen, Chih-Kun Hsiao, Ji-Sih Ciou, Yi-Jung Tsai, Yuan-Kun Tu
      This study concerns the effects of different drilling parameters of pilot drills and twist drills on the temperature rise of alveolar bones during dental implant procedures. The drilling parameters studied here include the feed rate and rotation speed of the drill. The bone temperature distribution was analyzed through experiments and numerical simulations of the drilling process. In this study, a three dimensional (3D) elasto-plastic dynamic finite element model (DFEM) was proposed to investigate the effects of drilling parameters on the bone temperature rise. In addition, the FE model is validated with drilling experiments on artificial human bones and porcine alveolar bones. The results indicate that 3D DFEM can effectively simulate the bone temperature rise during the drilling process. During the drilling process with pilot drills or twist drills, the maximum bone temperature occurred in the region of the cancellous bones close to the cortical bones. The feed rate was one of the important factors affecting the time when the maximum bone temperature occurred. Our results also demonstrate that the elevation of bone temperature was reduced as the feed rate increased and the drill speed decreased, which also effectively reduced the risk region of osteonecrosis. These findings can serve as a reference for dentists in choosing drilling parameters for dental implant surgeries.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.009
       
  • Termination of atrial spiral waves by traction into peripheral non 1:1
           conducting regions – A numerical study
    • Authors: Amit Rozner; Sharon Zlochiver
      Abstract: Publication date: Available online 7 September 2016
      Source:Medical Engineering & Physics
      Author(s): Amit Rozner, Sharon Zlochiver
      Atrial ablation has been recently utilized to treat atrial fibrillation (AF) by isolation or destruction of arrhythmia drivers. In chronic or persistent AF patients these drivers often consist of one or few rotors at unknown locations, and several ablations are commonly conducted before arrhythmia is terminated. However, the irreversible damage done to the tissue may lead to AF recurrence. We propose an alternative strategy to terminate rotor activity by its attraction into a non 1:1 conducting region. The feasibility of the method was numerically tested in 2D models of chronic AF human atrial tissue. Left-to-right gradients of either acetylcholine (ACh) or potassium conductance were employed to generate regions of 1:1 and non 1:1 conduction, characterized by their dominant frequency (DF) ratios. Spiral waves were established in the 1:1 conducting region and raster scanning was employed using a stimulating probe to attract the spiral wave tip. The probe was then linearly moved towards the boundary between the two regions. Successful attraction of spiral waves to the probe was demonstrated when the probe was <8mm from the spiral wave tip. Maximal traction velocity without loss of anchoring increased in a non-linear way with increasing values of ACh. Success rate of spiral wave termination was over 90% for regional DF ratios of as low as 1:1.2. Given that normally much higher ratios are measured in physiological atrial tissues, we envision this technique to provide a feasible, safer alternative to ablation procedures performed in persistent AF patients.

      PubDate: 2016-09-08T19:50:19Z
      DOI: 10.1016/j.medengphy.2016.08.006
       
 
 
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