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 Biomedical Engineering, IEEE Transactions on   [SJR: 1.201]   [H-I: 138]   [32 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 0018-9294    Published by IEEE  [191 journals]
• IEEE Engineering in Medicine and Biology Society
• Abstract: Presents a listing of the editorial board, board of governors, current staff, committee members, and/or society editors for this issue of the publication.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

• IEEE Transactions on Biomedical Engineering (T-BME)
• Abstract: These instructions give guidelines for preparing papers for this publication. Presents information for authors publishing in this journal.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

• IEEE Transactions on Biomedical Engineering Handling Editors
• Abstract: Presents a listing of the editorial board, board of governors, current staff, committee members, and/or society editors for this issue of the publication.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

• A Review of In-Body Biotelemetry Devices: Implantables, Ingestibles, and
Injectables
• Authors: Asimina Kiourti;Konstantina S. Nikita;
Pages: 1422 - 1430
Abstract: Objective: We present a review of wireless medical devices that are placed inside the human body to realize many and different sensing and/or stimulating functionalities. Methods: A critical literature review analysis is conducted focusing on three types of in-body medical devices, i.e., 1) devices that are implanted inside the human body (implantables), 2) devices that are ingested like regular pills (ingestibles), and 3) devices that are injected into the human body via needles (injectables). Design considerations, current status, and future directions related to the aforementioned in-body devices are discussed. Results: A number of design challenges are associated with in-body devices, including selection of operation frequency, antenna design, powering, and biocompatibility. Nevertheless, in-body devices are opening up new opportunities for medical prevention, prognosis, and treatment that quickly outweigh any design challenges and/or concerns on their invasive nature. Conclusion: In-body devices are already in use for several medical applications, ranging from pacemakers and capsule endoscopes to injectable microstimulators. As technology continues to evolve, in-body devices are promising several new and hitherto unexplored opportunities in the healthcare. Significance: Unobtrusive in-body devices are envisioned to collect a multitude of physiological data from the early years of each individual. This big-data approach aims to enable a shift from symptom-based medicine to a proactive healthcare model.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

• Passive BCI in Operational Environments: Insights, Recent Advances, and
Future Trends
• Authors: Pietro Aricò;Gianluca Borghini;Gianluca Di Flumeri;Nicolina Sciaraffa;Alfredo Colosimo;Fabio Babiloni;
Pages: 1431 - 1436
Abstract: Goal: This minireview aims to highlight recent important aspects to consider and evaluate when passive brain–computer interface (pBCI) systems would be developed and used in operational environments, and remarks future directions of their applications. Methods: Electroencephalography (EEG) based pBCI has become an important tool for real-time analysis of brain activity since it could potentially provide covertly—without distracting the user from the main task—and objectively—not affected by the subjective judgment of an observer or the user itself—information about the operator cognitive state. Results: Different examples of pBCI applications in operational environments and new adaptive interface solutions have been presented and described. In addition, a general overview regarding the correct use of machine learning techniques (e.g., which algorithm to use, common pitfalls to avoid, etc.) in the pBCI field has been provided. Conclusion: Despite recent innovations on algorithms and neurotechnology, pBCI systems are not completely ready to enter the market yet, mainly due to limitations of the EEG electrodes technology, and algorithms reliability and capability in real settings. Significance: High complexity and safety critical systems (e.g., airplanes, ATM interfaces) should adapt their behaviors and functionality accordingly to the user’ actual mental state. Thus, technologies (i.e., pBCIs) able to measure in real time the user's mental states would result very useful in such “high risk” environments to enhance human machine interaction, and so increase the overall safety.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

• Real-Time Model-Based Fault Detection of Continuous Glucose Sensor
Measurements
• Authors: Kamuran Turksoy;Anirban Roy;Ali Cinar;
Pages: 1437 - 1445
Abstract: Objective: Faults in subcutaneous glucose concentration readings with a continuous glucose monitoring (CGM) may affect the computation of insulin infusion rates that can lead to hypoglycemia or hyperglycemia in artificial pancreas control systems for patients with type 1 diabetes (T1D). Methods: Multivariable statistical monitoring methods are proposed for detection of faults in glucose concentration values reported by a subcutaneous glucose sensor. A nonlinear first principle glucose/insulin/meal dynamic model is developed. An unscented Kalman filter is used for state and parameter estimation of the nonlinear model. Principal component analysis models are developed and used for detection of dynamic changes. K-nearest neighbor classification algorithm is used for diagnosis of faults. Data from 51 subjects are used to assess the performance of the algorithm. Results: The results indicate that the proposed algorithm works successfully with 84.2% sensitivity. Overall, 155 (out of 184) of the CGM failures are detected with a 2.8-min average detection time. Conclusion: A novel algorithm that integrates data-driven and model-based methods is developed. The proposed method is able to detect CGM failures with a high rate of success. Significance: The proposed fault detection algorithm can decrease the effects of faults on insulin infusion rates and reduce the potential for hypo- or hyperglycemia for patients with T1D.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

• Image-Based Biophysical Simulation of Intracardiac Abnormal Ventricular
Electrograms
• Authors: Rocío Cabrera-Lozoya;Benjamin Berte;Hubert Cochet;Pierre Jaïs;Nicholas Ayache;Maxime Sermesant;
Pages: 1446 - 1454
Abstract: Goal: In this paper, we used in silico patient-specific models constructed from three-dimensional delayed-enhanced magnetic resonance imaging (DE-MRI) to simulate intracardiac electrograms (EGM). These included electrically abnormal EGM as these are potential radiofrequency ablation (RFA) targets. Methods: We generated signals with distinguishable macroscopic normal and abnormal characteristics by constructing MRI-based patient-specific structural heart models and by solving the simplified biophysical Mitchell–Schaeffer model of cardiac electrophysiology (EP). Then, we simulated intracardiac EGM by modeling a recording catheter using a dipole approach. Results: Qualitative results show that simulated EGM resemble clinical signals. Additionally, the quantitative assessment of signal features extracted from the simulated EGM showed statistically significant differences (p $PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Fast Numerical Simulation of Focused Ultrasound Treatments During Respiratory Motion With Discontinuous Motion Boundaries • Authors: Michael Schwenke;Joachim Georgii;Tobias Preusser; Pages: 1455 - 1468 Abstract: Objective: Focused ultrasound (FUS) is rapidly gaining clinical acceptance for several target tissues in the human body. Yet, treating liver targets is not clinically applied due to a high complexity of the procedure (noninvasiveness, target motion, complex anatomy, blood cooling effects, shielding by ribs, and limited image-based monitoring). To reduce the complexity, numerical FUS simulations can be utilized for both treatment planning and execution. These use-cases demand highly accurate and computationally efficient simulations. Methods: We propose a numerical method for the simulation of abdominal FUS treatments during respiratory motion of the organs and target. Especially, a novel approach is proposed to simulate the heating during motion by solving Pennes’ bioheat equation in a computational reference space, i.e., the equation is mathematically transformed to the reference. The approach allows for motion discontinuities, e.g., the sliding of the liver along the abdominal wall. Results: Implementing the solver completely on the graphics processing unit and combining it with an atlas-based ultrasound simulation approach yields a simulation performance faster than real time (less than 50-s computing time for 100 s of treatment time) on a modern off-the-shelf laptop. The simulation method is incorporated into a treatment planning demonstration application that allows to simulate real patient cases including respiratory motion. Conclusion: The high performance of the presented simulation method opens the door to clinical applications. Significance:The methods bear the potential to enable the application of FUS for moving organs. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • A Novel Method for Continuous, Noninvasive, Cuff-Less Measurement of Blood Pressure: Evaluation in Patients With Nonalcoholic Fatty Liver Disease • Authors: Trine M. Seeberg;James G. Orr;Hanne Opsahl;H. O. Austad;Morten H. Røed;Steffen H. Dalgard;David Houghton;David E. J. Jones;Frode Strisland; Pages: 1469 - 1478 Abstract: Objective: One promising approach for a continuous, noninvasive, cuff-less ambulatory blood pressure (BP) monitor is to measure the pulse wave velocity or the inversely proportional pulse transit time (PTT), based on electrical and optical physiological measurements in the chest area. A device termed IsenseU-BP+ has been developed for measuring continuous BP, as well as other physiological data. The objective of this paper is to present results from the first clinical evaluation with a wide range of patients. The study was set up to verify whether IsenseU-BP+ can be used to measure raw signals with sufficient quality to derive PTT. Methods: The test protocol, run 23 times on 18 different patients with nonalcoholic fatty liver disease, includes both supine measurement at rest as well as measurements during indoor cycling. Changes in PTT were compared with the BP changes measured using validated reference sensors. Results: IsenseU-BP+ measured signals with good quality during rest on 17 of 18 patients despite the high diversity in age, body shape, and body mass index. Evaluation during cycling was difficult due to a lack of good reference measurements. Conclusion: IsenseU-BP+ measures PTT with high quality during supine rest and exercise and could therefore be suitable for deriving noninvasive continuous BP, although evaluation during exercise was limited due to inaccurate reference BP measurements. Significance: Continuous, noninvasive measurement of BP would be highly beneficial in a number of clinical settings. Systems currently considered as the gold standard for the investigation of hypertension carry considerable limitations, which could be overcome by the method proposed here. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Algorithmic Principles of Remote PPG • Authors: Wenjin Wang;Albertus C. den Brinker;Sander Stuijk;Gerard de Haan; Pages: 1479 - 1491 Abstract: This paper introduces a mathematical model that incorporates the pertinent optical and physiological properties of skin reflections with the objective to increase our understanding of the algorithmic principles behind remote photoplethysmography (rPPG). The model is used to explain the different choices that were made in existing rPPG methods for pulse extraction. The understanding that comes from the model can be used to design robust or application-specific rPPG solutions. We illustrate this by designing an alternative rPPG method, where a projection plane orthogonal to the skin tone is used for pulse extraction. A large benchmark on the various discussed rPPG methods shows that their relative merits can indeed be understood from the proposed model. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Efficient Descriptor-Based Segmentation of Parotid Glands With Nonlocal Means • Authors: Christian Wachinger;Matthew Brennan;Greg C. Sharp;Polina Golland; Pages: 1492 - 1502 Abstract: Objective: We introduce descriptor-based segmentation that extends existing patch-based methods by combining intensities, features, and location information. Since it is unclear which image features are best suited for patch selection, we perform a broad empirical study on a multitude of different features. Methods: We extend nonlocal means segmentation by including image features and location information. We search larger windows with an efficient nearest neighbor search based on kd-trees. We compare a large number of image features. Results: The best results were obtained for entropy image features, which have not yet been used for patch-based segmentation. We further show that searching larger image regions with an approximate nearest neighbor search and location information yields a significant improvement over the bounded nearest neighbor search traditionally employed in patch-based segmentation methods. Conclusion: Features and location information significantly increase the segmentation accuracy. The best features highlight boundaries in the image. Significance: Our detailed analysis of several aspects of nonlocal means-based segmentation yields new insights about patch and neighborhood sizes together with the inclusion of location information. The presented approach advances the state-of-the-art in the segmentation of parotid glands for radiation therapy planning. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Continuous Blood Viscosity Monitoring System for Cardiopulmonary Bypass Applications • Authors: Shigeyuki Okahara;Zu Soh;Satoshi Miyamoto;Hidenobu Takahashi;Shinya Takahashi;Taijiro Sueda;Toshio Tsuji; Pages: 1503 - 1512 Abstract: This paper proposes an algorithm that estimates blood viscosity during cardiopulmonary bypass (CPB) and validates its application in clinical cases. The proposed algorithm involves adjustable parameters based on the oxygenator and fluid types and estimates blood viscosity based on pressure-flow characteristics of the fluid perfusing through the oxygenator. This novel nonlinear model requires four parameters that were derived by in vitro experiments. The results estimated by the proposed method were then compared with a conventional linear model to demonstrate the former's optimal curve fitting. The viscosity$(\eta _{e})$estimated using the proposed algorithm and the viscosity$(\eta)$measured using a viscometer were compared for 20 patients who underwent mildly hypothermic CPB. The developed system was applied to ten patients, and$\eta _{e}$was recorded for comparisons with hematocrit and blood temperature. The residual sum of squares between the two curve fittings confirmed the significant difference, with p < 0.001.$\eta _{e}$and$\eta $showed a very strong correlation with$R^{2}$= 0.9537 and p < 0.001. Regarding the mean coefficient of determination for all cases, the hematocrit and temperature showed weak correlations at 0.33 ± 0.14 and 0.22 ± 0.21, respectively. For CPB measurements of all cases,$\eta _{e}$was more th-n 98% distributed in the range from 1 to 3 mPa⋅s. This new system for estimating viscosity may be useful for detecting various viscosity-related effects that may occur during CPB. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Muscle Activity Map Reconstruction from High Density Surface EMG Signals With Missing Channels Using Image Inpainting and Surface Reconstruction Methods • Authors: Parviz Ghaderi;Hamid R. Marateb; Pages: 1513 - 1523 Abstract: Objective: The aim of this study was to reconstruct low-quality High-density surface EMG (HDsEMG) signals, recorded with 2-D electrode arrays, using image inpainting and surface reconstruction methods. Methods: It is common that some fraction of the electrodes may provide low-quality signals. We used variety of image inpainting methods, based on partial differential equations (PDEs), and surface reconstruction methods to reconstruct the time-averaged or instantaneous muscle activity maps of those outlier channels. Two novel reconstruction algorithms were also proposed. HDsEMG signals were recorded from the biceps femoris and brachial biceps muscles during low-to-moderate-level isometric contractions, and some of the channels (5–25%) were randomly marked as outliers. The root-mean-square error (RMSE) between the original and reconstructed maps was then calculated. Results: Overall, the proposed Poisson and wave PDE outperformed the other methods (average RMSE$\text{8.7}\,{\mu} \text{V}_{\rm{rms}}\pm \text{6.1}\,\mathrm{\mu} \text{V}_{\rm{rms}}$and$\text{7.5}\,{\mu} \text{V}_{\text{rms}}\pm \text{5.9}\,{\mu} \text{V}_{\text{rms}}$) for the time-averaged single-differential and monopolar map reconstruction, respectively. Biharmonic Spline, the discrete cosine transform, and the Poisson PDE outperformed the other methods for the instantaneous map reconstruction. The running time of the proposed Poisson and wave PDE methods, implemented using a Vectorization package, was$\text{4.6} \pm \text{5.7}\,\text{ms}$and$\rm{0.6\,\pm \,0.5\,ms}$, respectively, for each si-nal epoch or time sample in each channel. Conclusion: The proposed reconstruction algorithms could be promising new tools for reconstructing muscle activity maps in real-time applications. Significance: Proper reconstruction methods could recover the information of low-quality recorded channels in HDsEMG signals. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Estimation of Pulse Transit Time as a Function of Blood Pressure Using a Nonlinear Arterial Tube-Load Model • Authors: Mingwu Gao;Hao-Min Cheng;Shih-Hsien Sung;Chen-Huan Chen;Nicholas Bari Olivier;Ramakrishna Mukkamala; Pages: 1524 - 1534 Abstract: Objective: pulse transit time (PTT) varies with blood pressure (BP) throughout the cardiac cycle, yet, because of wave reflection, only one PTT value at the diastolic BP level is conventionally estimated from proximal and distal BP waveforms. The objective was to establish a technique to estimate multiple PTT values at different BP levels in the cardiac cycle. Methods: a technique was developed for estimating PTT as a function of BP (to indicate the PTT value for every BP level) from proximal and distal BP waveforms. First, a mathematical transformation from one waveform to the other is defined in terms of the parameters of a nonlinear arterial tube-load model accounting for BP-dependent arterial compliance and wave reflection. Then, the parameters are estimated by optimally fitting the waveforms to each other via the model-based transformation. Finally, PTT as a function of BP is specified by the parameters. The technique was assessed in animals and patients in several ways including the ability of its estimated PTT-BP function to serve as a subject-specific curve for calibrating PTT to BP. Results: the calibration curve derived by the technique during a baseline period yielded bias and precision errors in mean BP of 5.1 ± 0.9 and 6.6 ± 1.0 mmHg, respectively, during hemodynamic interventions that varied mean BP widely. Conclusion: the new technique may permit, for the first time, estimation of PTT values throughout the cardiac cycle from proximal and distal waveforms. Significance: the technique could potentially be applied to improve arterial stiffness monitoring and help realize cuff-less BP monitoring. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Automated Compression Device for Viscoelasticity Imaging • Authors: Alireza Nabavizadeh;Randall R. Kinnick;Mahdi Bayat;Carolina Amador;Matthew W. Urban;Azra Alizad;Mostafa Fatemi; Pages: 1535 - 1546 Abstract: Noninvasive measurement of tissue viscoelastic properties is gaining more attention for screening and diagnostic purposes. Recently, measuring dynamic response of tissue under a constant force has been studied for estimation of tissue viscoelastic properties in terms of retardation times. The essential part of such a test is an instrument that is capable of creating a controlled axial force and is suitable for clinical applications. Such a device should be lightweight, portable, and easy to use for patient studies to capture tissue dynamics under external stress. In this paper, we present the design of an automated compression device for studying the creep response of materials with tissue-like behaviors. The device can be used to apply a ramp-and-hold force excitation for a predetermined duration of time and it houses an ultrasound probe for monitoring the creep response of the underlying tissue. To validate the performance of the device, several creep tests were performed on tissue-mimicking phantoms, and the results were compared against those from a commercial mechanical testing instrument. Using a second-order Kelvin–Voigt model and surface measurement of the forces and displacements, retardation times${\boldsymbol{T}_1}$and${\boldsymbol{T}_2}$were estimated from each test. These tests showed strong agreement between our automated compression device and the commercial mechanical testing system, with an average relative error of 2.9% and 12.4%, for${\boldsymbol{T}_1}$and${\boldsymbol{T}_2}$, respectively. Also, we present the application of compression device to measure local retardation times for four different p-antoms with different size and stiffness. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Development and Evaluation of a Wearable Device for Sleep Quality Assessment • Authors: Chih-En Kuo;Yi-Che Liu;Da-Wei Chang;Chung-Ping Young;Fu-Zen Shaw;Sheng-Fu Liang; Pages: 1547 - 1557 Abstract: Objective: In this study, a wearable actigraphy recording device with low sampling rate (1 Hz) for power saving and data reduction and a high accuracy wake-sleep scoring method for the assessment of sleep were developed. Methods: The developed actigraphy recorder was successfully applied to overnight recordings of 81 subjects with simultaneous polysomnography (PSG) measurements. The total length of recording reached 639.8 h. A wake-sleep scoring method based on the concept of movement density evaluation and adaptive windowing was proposed. Data from subjects with good (N = 43) and poor (N = 16) sleep efficiency (SE) in the range of 52.7–97.42% were used for testing. The Bland–Altman technique was used to evaluate the concordance of various sleep measurements between the manual PSG scoring and the proposed actigraphy method. Results: For wake-sleep staging, the average accuracy, sensitivity, specificity, and kappa coefficient of the proposed system were 92.16%, 95.02%, 71.30%, and 0.64, respectively. For the assessment of SE, the accuracy of classifying the subject with good or poor SE reached 91.53%. The mean biases of SE, sleep onset time, wake after sleep onset, and total sleep time were −0.95%, 0.74 min, 2.84 min, and −4.3 min, respectively. Conclusion: These experimental results demonstrate the robustness and reliability of our method using limited activity information to estimate wake-sleep stages during overnight recordings. Significance: The results suggest that the proposed wearable actigraphy system is practical for the in-home screening of objective sleep mea-urements and objective evaluation of sleep improvement after treatment. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Multilevel Contextual 3-D CNNs for False Positive Reduction in Pulmonary Nodule Detection • Authors: Qi Dou;Hao Chen;Lequan Yu;Jing Qin;Pheng-Ann Heng; Pages: 1558 - 1567 Abstract: Objective: False positive reduction is one of the most crucial components in an automated pulmonary nodule detection system, which plays an important role in lung cancer diagnosis and early treatment. The objective of this paper is to effectively address the challenges in this task and therefore to accurately discriminate the true nodules from a large number of candidates. Methods: We propose a novel method employing three-dimensional (3-D) convolutional neural networks (CNNs) for false positive reduction in automated pulmonary nodule detection from volumetric computed tomography (CT) scans. Compared with its 2-D counterparts, the 3-D CNNs can encode richer spatial information and extract more representative features via their hierarchical architecture trained with 3-D samples. More importantly, we further propose a simple yet effective strategy to encode multilevel contextual information to meet the challenges coming with the large variations and hard mimics of pulmonary nodules. Results: The proposed framework has been extensively validated in the LUNA16 challenge held in conjunction with ISBI 2016, where we achieved the highest competition performance metric (CPM) score in the false positive reduction track. Conclusion: Experimental results demonstrated the importance and effectiveness of integrating multilevel contextual information into 3-D CNN framework for automated pulmonary nodule detection in volumetric CT data. Significance: While our method is tailored for pulmonary nodule detection, the proposed framework is general and can be easily extended to many other 3-D object detection tasks from volumetric medical images, where the targeting objects have large variations and are accompanied by a number of hard mimics. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • A Deep Denoising Autoencoder Approach to Improving the Intelligibility of Vocoded Speech in Cochlear Implant Simulation • Authors: Ying-Hui Lai;Fei Chen;Syu-Siang Wang;Xugang Lu;Yu Tsao;Chin-Hui Lee; Pages: 1568 - 1578 Abstract: Objective: In a cochlear implant (CI) speech processor, noise reduction (NR) is a critical component for enabling CI users to attain improved speech perception under noisy conditions. Identifying an effective NR approach has long been a key topic in CI research. Method: Recently, a deep denoising autoencoder (DDAE) based NR approach was proposed and shown to be effective in restoring clean speech from noisy observations. It was also shown that DDAE could provide better performance than several existing NR methods in standardized objective evaluations. Following this success with normal speech, this paper further investigated the performance of DDAE-based NR to improve the intelligibility of envelope-based vocoded speech, which simulates speech signal processing in existing CI devices. Results: We compared the performance of speech intelligibility between DDAE-based NR and conventional single-microphone NR approaches using the noise vocoder simulation. The results of both objective evaluations and listening test showed that, under the conditions of nonstationary noise distortion, DDAE-based NR yielded higher intelligibility scores than conventional NR approaches. Conclusion and significance: This study confirmed that DDAE-based NR could potentially be integrated into a CI processor to provide more benefits to CI users under noisy conditions. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Local Transverse-Slice-Based Level-Set Method for Segmentation of 3-D High-Frequency Ultrasonic Backscatter From Dissected Human Lymph Nodes • Authors: Thanh Minh Bui;Alain Coron;Jonathan Mamou;Emi Saegusa-Beecroft;Tadashi Yamaguchi;Eugene Yanagihara;Junji Machi;S. Lori Bridal;Ernest Joseph Feleppa; Pages: 1579 - 1591 Abstract: Objective: To detect metastases in freshly excised human lymph nodes (LNs) using three-dimensional (3-D), high-frequency, quantitative ultrasound (QUS) methods, the LN parenchyma (LNP) must be segmented to preclude QUS analysis of data in regions outside the LNP and to compensate ultrasound attenuation effects due to overlying layers of LNP and residual perinodal fat (PNF). Methods: After restoring the saturated radio-frequency signals from PNF using an approach based on smoothing cubic splines, the three regions, i.e., LNP, PNF, and normal saline (NS), in the LN envelope data are segmented using a new, automatic, 3-D, three-phase, statistical transverse-slice-based level-set (STS-LS) method that amends Lankton's method. Due to ultrasound attenuation and focusing effects, the speckle statistics of the envelope data vary with imaged depth. Thus, to mitigate depth-related inhomogeneity effects, the STS-LS method employs gamma probability-density functions to locally model the speckle statistics within consecutive transverse slices. Results: Accurate results were obtained on simulated data. On a representative dataset of 54 LNs acquired from colorectal-cancer patients, the Dice similarity coefficient for LNP, PNF, and NS were 0.938$\pm$0.025, 0.832$\pm$0.086, and 0.968$\pm$0.008, respectively, when compared to expert manual segmentation. Conclusion: The STS-LS outperforms the established methods based on global and local statistics in our datasets and is capable of accurately handling the depth-dependent effects due to attenuation and focusing. Significance: This advance permits the automatic QUS-based cancer detection in the LNs. Furthermore, the-STS-LS method could potentially be used in a wide range of ultrasound-imaging applications suffering from depth-dependent effects. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • A Theoretical Analysis of Electrogastrography (EGG) Signatures Associated With Gastric Dysrhythmias • Authors: Stefan Calder;Greg O’Grady;Leo K. Cheng;Peng Du; Pages: 1592 - 1601 Abstract: Routine screening and accurate diagnosis of chronic gastrointestinal motility disorders represent a significant problem in current clinical practice. The electrogastrography (EGG) provides a noninvasive option for assessing gastric slow waves, as a means of diagnosing gastric dysrhythmias, but its uptake in motility practice has been limited partly due to an incomplete sensitivity and specificity. This paper presents the development of a human whole-organ gastric model to enable virtual (in silico) testing of gastric electrophysiological dispersion in order to improve the diagnostic accuracy of EGG. The model was developed to simulate normal gastric slow wave conduction as well as three types of dysrhythmias identified in recent high-resolution gastric mapping studies: conduction block, re-entry, and ectopic pacemaking. The stomach simulations were then applied in a torso model to identify predicted EGG signatures of normal and dysrhythmic slow wave profiles. The resulting EGG data were compared using percentage differences and correlation coefficients. Virtual EGG channels that demonstrated a percentage difference over 100% and a correlation coefficient less than$\pm$0.2 (threshold relaxed to$\pm$0.5 for the ectopic pacemaker case) were further investigated for their specific distinguishing features. In particular, anatomical locations from the epigastric region and specific channel configurations were identified that could be used to clinically diagnose the three classes of human gastric dysrhythmia. These locations and channels predicted by simulations present a promising methodology for improving the clinical reliability and applications of EGG. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Wavelet-Based Sit-To-Stand Detection and Assessment of Fall Risk in Older People Using a Wearable Pendant Device • Authors: Andreas Ejupi;Matthew Brodie;Stephen R. Lord;Janneke Annegarn;Stephen J. Redmond;Kim Delbaere; Pages: 1602 - 1607 Abstract: Goal: Wearable devices provide new ways to identify people who are at risk of falls and track long-term changes of mobility in daily life of older people. The aim of this study was to develop a wavelet-based algorithm to detect and assess quality of sit-to-stand movements with a wearable pendant device. Methods: The algorithm used wavelet transformations of the accelerometer and barometric air pressure sensor data. Detection accuracy was tested in 25 older people performing 30 min of typical daily activities. The ability to differentiate between people who are at risk of falls from people who are not at risk was investigated by assessing group differences of sensor-based sit-to-stand measurements in 34 fallers and 60 nonfallers (based on 12-month fall history) performing sit-to-stand movements as part of a laboratory study. Results: Sit-to-stand movements were detected with 93.1% sensitivity and a false positive rate of 2.9% during activities of daily living. In the laboratory study, fallers had significantly lower maximum acceleration, velocity, and power during the sit-to-stand movement compared to nonfallers. Conclusion: The new wavelet-based algorithm accurately detected sit-to-stand movements in older people and differed significantly between older fallers and nonfallers. Significance: Accurate detection and quantification of sit-to-stand movements may provide objective assessment and monitoring of fall risk during daily life in older people. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • System Integration and In Vivo Testing of a Robot for Ultrasound Guidance and Monitoring During Radiotherapy • Authors: Hasan Tutkun Şen;Muyinatu A. Lediju Bell;Yin Zhang;Kai Ding;Emad Boctor;John Wong;Iulian Iordachita;Peter Kazanzides; Pages: 1608 - 1618 Abstract: We are developing a cooperatively controlled robot system for image-guided radiation therapy (IGRT) in which a clinician and robot share control of a 3-D ultrasound (US) probe. IGRT involves two main steps: 1) planning/simulation and 2) treatment delivery. The goals of the system are to provide guidance for patient setup and real-time target monitoring during fractionated radiotherapy of soft tissue targets, especially in the upper abdomen. To compensate for soft tissue deformations created by the probe, we present a novel workflow where the robot holds the US probe on the patient during acquisition of the planning computerized tomography image, thereby ensuring that planning is performed on the deformed tissue. The robot system introduces constraints (virtual fixtures) to help to produce consistent soft tissue deformation between simulation and treatment days, based on the robot position, contact force, and reference US image recorded during simulation. This paper presents the system integration and the proposed clinical workflow, validated by an in vivo canine study. The results show that the virtual fixtures enable the clinician to deviate from the recorded position to better reproduce the reference US image, which correlates with more consistent soft tissue deformation and the possibility for more accurate patient setup and radiation delivery. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Variability of Ventricular Repolarization Dispersion Quantified by Time-Warping the Morphology of the T-Waves • Authors: Julia Ramírez;Michele Orini;J. Derek Tucker;Esther Pueyo;Pablo Laguna; Pages: 1619 - 1630 Abstract: Objective: We propose two electrocardiogram (ECG)-derived markers of T-wave morphological variability in the temporal,$d_w$, and amplitude,$d_a$, domains. Two additional markers,$d_w^{\mathrm{NL}}$and$d_a^{\mathrm{NL}}$, restricted to measure the nonlinear information present within$d_w$and$d_a$are also proposed. Methods: We evaluated the accuracy of the proposed markers in capturing T-wave time and amplitude variations in 3 situations: 1) In a simulated set up with presence of additive Laplacian noise, 2) when modifying the spatio-temporal distribution of electrical repolarization with an electro-physiological cardiac model, and 3) in ECG records from healthy subjects undergoing a tilt table test. Results: The metrics$d_w$,$d_a$,$d_w^{\mathrm{NL}}$, and$d_a^{\mathrm{NL}}$followed T-wave time- and amplitude-induced variations under different levels of noise, were strongly associated with changes in the spatio-temporal dispersion of repolarization, and showed to provide additional information to differences in the heart rate,$QT$and$T_{\mathrm{pe}}$inte-vals, and in the T-wave width and amplitude. Conclusion: The proposed ECG-derived markers robustly quantify T-wave morphological variability, being strongly associated with changes in the dispersion of repolarization. Significance: The proposed ECG-derived markers can help to quantify the variability in the dispersion of ventricular repolarization, showing a great potential to be used as arrhythmic risk predictors in clinical situations. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • The Development of a Thin-Filmed Noninvasive Tissue Perfusion Sensor to Quantify Capillary Pressure Occlusion of Explanted Organs • Authors: Timothy J. O'Brien;Ali R. Roghanizad;Philip A. Jones;Charles H. Aardema;John L. Robertson;Thomas E. Diller; Pages: 1631 - 1637 Abstract: A new thin-filmed perfusion sensor was developed using a heat flux gauge, thin-film thermocouple, and a heating element. This sensor, termed “CHFT+,” is an enhancement of the previously established combined heat flux–temperature (CHFT) sensor technology predominately used to quantify the severity of burns [1]. The CHFT+ sensor was uniquely designed to measure tissue perfusion on explanted organs destined for transplantation, but could be functionalized and used in a wide variety of other biomedical applications. Exploiting the thin and semiflexible nature of the new CHFT+ sensor assembly, perfusion measurements can be made from the underside of the organ—providing a quantitative indirect measure of capillary pressure occlusion. Results from a live tissue test demonstrated, for the first time, the effects of pressure occlusion on an explanted porcine kidney. CHFT+ sensors were placed on top of and underneath 18 kidneys to measure and compare perfusion at perfusate temperatures of 5 and 20 °C. The data collected show a greater perfusion on the topside than the underside of the specimen for the length of the experiment. This indicates that the pressure occlusion is truly affecting the perfusion, and, thus, the overall preservation of explanted organs. Moreover, the results demonstrate the effect of preservation temperature on the tissue vasculature. Focusing on the topside perfusion only, the 20 °C perfusion was greater than the 5 °C perfusion, likely due to the vasoconstrictive response at the lower perfusion temperatures. PubDate: July 2017 Issue No: Vol. 64, No. 7 (2017) • Automatic Identification of Pathology-Distorted Retinal Layer Boundaries Using SD-OCT Imaging • Authors: Md Akter Hussain;Alauddin Bhuiyan;Andrew Turpin;Chi D. Luu;R. Theodore Smith;Robyn H. Guymer;Ramamohanrao Kotagiri; Pages: 1638 - 1649 Abstract: Objective: We propose an effective automatic method for identification of four retinal layer boundaries from the spectral domain optical coherence tomography images in the presence and absence of pathologies and morphological changes due to disease. Methods: The approach first finds an approximate location of three reference layers and then uses these to bound the search space for the actual layers, which is achieved by modeling the problem as a graph and applying Dijkstra's shortest path algorithm. The edge weight between nodes is determined using pixel distance, slope similarity to a reference, and nonassociativity of the layers, which is designed to overcome the distorting effects that pathology can play in the boundary determination. Results: The accuracy of our method was evaluated on three different datasets. It outperforms the current five state-of-the-art methods. On average, the mean and standard deviation of the root-mean-square error in the form of mean$\pm$standard deviation in pixels for our method is 1.57$\pm$0.69, which is lower than compared to the existing top five methods of 16.17$\pm$22.64, 6.66$\pm$9.11, 5.70$\pm$10.54, 3.69$\pm$2.04, and 2.29$\pm\$ 1.54. Conclusion: Our method is highly accurate, robust, reliable, and consistent. This identification can enable to quantify the biomarkers of the retina in large-scale study for assessing, monitoring di-ease progression, as well as early detection of retinal diseases. Significance: Identification of these boundaries can help to determine the loss of neuroretinal cells or layers and the presence of retinal pathology, which can be used as features for the automatic determination of the stages of retinal diseases.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

• Evaluation of Mobile Phone Performance for Near-Infrared Fluorescence
Imaging
• Authors: Pejhman Ghassemi;Bohan Wang;Jianting Wang;Quanzeng Wang;Yu Chen;T. Joshua Pfefer;
Pages: 1650 - 1653
Abstract: We have investigated the potential for contrast-enhanced near-infrared fluorescence imaging of tissue on a mobile phone platform. Charge-coupled device- and phone-based cameras were used to image molded and three-dimensional-printed tissue phantoms, and an ex vivo animal model. Quantitative and qualitative evaluations of image quality demonstrate the viability of this approach and elucidate variations in performance due to wavelength, pixel color, and image processing.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

• An Electrochemistry Study of Cryoelectrolysis in Frozen Physiological
Saline
• Authors: Thomas J. Manuel;Pujita Munnangi;Boris Rubinsky;
Pages: 1654 - 1659
Abstract: Cryoelectrolysis is a new minimally invasive tissue ablation surgical technique that combines the processes of electrolysis and solid/liquid phase transformation (freezing). This study investigated this new technique by measuring the pH front propagation and the changes in resistance in a tissue simulant made of physiological saline gel with a pH dye as a function of the sample temperature in the high subzero range above the eutectic. Results demonstrated that effective electrolysis can occur in a high subzero freezing milieu and that the propagation of the pH front is only weakly dependent on temperature. These observations are consistent with a mechanism involving ionic movement through the concentrated saline solution channels between ice crystals at subfreezing temperatures above the eutectic. Moreover, results suggest that Joule heating in these microchannels may cause local microscopic melting, the observed weak dependence of pH front propagation on temperature, and the large changes in resistance with time. A final insight provided by the results is that the pH front propagation from the anode is more rapid than from the cathode, a feature indicative of the electro-osmotic flow from the cathode to the anode. The findings in this paper may be critical for designing future cryoelectrolytic ablation surgery protocols.
PubDate: July 2017
Issue No: Vol. 64, No. 7 (2017)

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