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Ultrasonic Imaging    [3 followers]  Follow    
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 0161-7346 - ISSN (Online) 1096-0910
     Published by Sage Publications Homepage  [718 journals]   [SJR: 0.651]   [H-I: 33]
  • Mean Scatterer Spacing Estimation in Normal and Thermally Coagulated Ex
           Vivo Bovine Liver
    • Authors: Rubert, N; Varghese, T.
      Pages: 79 - 97
      Abstract: The liver has been hypothesized to have a unique arrangement of microvasculature that presents as an arrangement of quasiperiodic scatterers to an interrogating ultrasound pulse. The mean scatterer spacing (MSS) of these quasiperiodic scatterers has been proposed as a useful quantitative ultrasound biomarker for characterizing liver tissue. Thermal ablation is an increasingly popular method for treating hepatic tumors, and ultrasonic imaging approaches for delineating the extent of thermal ablation are in high demand. In this work, we examine the distribution of estimated MSS in thermally coagulated bovine liver and normal untreated bovine liver ex vivo. We estimate MSS by detecting local maxima in the spectral coherence function of radio frequency echoes from a clinical transducer, the Siemens VFX 9L4 transducer operating on an S2000 scanner. We find that normal untreated bovine liver was characterized by an MSS of approximately 1.3 mm. We examined regions of interest 12 mm wide laterally, and ranging from 12 mm to 18 mm axially, in 2 mm increments. Over these parameters, the mode of the MSS estimates was between 1.25 and 1.37 mm. On the other hand, estimation of MSS in thermally coagulated liver tissue yields a distribution of MSS estimates whose mode varied between 0.45 and 1.0 mm when examining regions of interest over the same sizes. We demonstrate that the estimated MSS in thermally coagulated liver favors small spacings because the randomly positioned scatterers in this tissue are better modeled as aperiodic scatterers. The submillimeter spacings result from the fact that this was the most probable spacing to be estimated if the discretely sampled spectral coherence function was a uniformly random two-dimensional function.
      PubDate: 2014-02-18T20:34:33-08:00
      DOI: 10.1177/0161734613511232|hwp:resource-id:spuix;36/2/79
      Issue No: Vol. 36, No. 2 (2014)
  • Acoustic Radiation Force Impulse Imaging (ARFI) on an IVUS Circular Array
    • Authors: Patel, V; Dahl, J. J, Bradway, D. P, Doherty, J. R, Lee, S. Y, Smith, S. W.
      Pages: 98 - 111
      Abstract: Our long-term goal is the detection and characterization of vulnerable plaque in the coronary arteries of the heart using intravascular ultrasound (IVUS) catheters. Vulnerable plaque, characterized by a thin fibrous cap and a soft, lipid-rich necrotic core is a precursor to heart attack and stroke. Early detection of such plaques may potentially alter the course of treatment of the patient to prevent ischemic events. We have previously described the characterization of carotid plaques using external linear arrays operating at 9 MHz. In addition, we previously modified circular array IVUS catheters by short-circuiting several neighboring elements to produce fixed beamwidths for intravascular hyperthermia applications. In this paper, we modified Volcano Visions 8.2 French, 9 MHz catheters and Volcano Platinum 3.5 French, 20 MHz catheters by short-circuiting portions of the array for acoustic radiation force impulse imaging (ARFI) applications. The catheters had an effective transmit aperture size of 2 mm and 1.5 mm, respectively. The catheters were connected to a Verasonics scanner and driven with pushing pulses of 180 V p-p to acquire ARFI data from a soft gel phantom with a Young’s modulus of 2.9 kPa. The dynamic response of the tissue-mimicking material demonstrates a typical ARFI motion of 1 to 2 microns as the gel phantom displaces away and recovers back to its normal position. The hardware modifications applied to our IVUS catheters mimic potential beamforming modifications that could be implemented on IVUS scanners. Our results demonstrate that the generation of radiation force from IVUS catheters and the development of intravascular ARFI may be feasible.
      PubDate: 2014-02-18T20:34:33-08:00
      DOI: 10.1177/0161734613511595|hwp:resource-id:spuix;36/2/98
      Issue No: Vol. 36, No. 2 (2014)
  • Speckle Suppressing Anisotropic Diffusion Filter for Medical Ultrasound
    • Authors: Ovireddy, S; Muthusamy, E.
      Pages: 112 - 132
      Abstract: Ultrasonography is often preferred over the other medical imaging modalities due to its noninvasive nature, cost-effectiveness, and portability. However, the resolution of the ultrasound image greatly depends upon the presence of speckle noise. Speckle noise generally tends to reduce the image resolution and contrast, thereby reducing the diagnostic resolution of this imaging modality. In this paper, we propose a speckle suppressing anisotropic diffusion (SSAD) filter, to remove the speckle noise from B-Mode Ultrasound images. The performance of the SSAD filter is compared with the existing diffusion filters. The evaluation is based on their application to images simulated by Field II (developed by Jensen et al.). The algorithms were also tested for clinical ultrasound images of polycystic ovaries obtained from HDI 5000 Ultrasound Scanner. Performance evaluation was done by both numerical and functional parameters. The proposed filter yields better results in terms of greatest structural similarity index map (SSIM) of 0.95 and accuracy of 99.5.
      PubDate: 2014-02-18T20:34:33-08:00
      DOI: 10.1177/0161734613512200|hwp:resource-id:spuix;36/2/112
      Issue No: Vol. 36, No. 2 (2014)
  • Contrast in Intracardiac Acoustic Radiation Force Impulse Images of
           Radiofrequency Ablation Lesions
    • Authors: Eyerly, S. A; Bahnson, T. D, Koontz, J. I, Bradway, D. P, Dumont, D. M, Trahey, G. E, Wolf, P. D.
      Pages: 133 - 148
      Abstract: We have previously shown that intracardiac acoustic radiation force impulse (ARFI) imaging visualizes tissue stiffness changes caused by radiofrequency ablation (RFA). The objectives of this in vivo study were to (1) quantify measured ARFI-induced displacements in RFA lesion and unablated myocardium and (2) calculate the lesion contrast (C) and contrast-to-noise ratio (CNR) in two-dimensional ARFI and conventional intracardiac echo images. In eight canine subjects, an ARFI imaging-electroanatomical mapping system was used to map right atrial ablation lesion sites and guide the acquisition of ARFI images at these sites before and after ablation. Readers of the ARFI images identified lesion sites with high sensitivity (90.2%) and specificity (94.3%) and the average measured ARFI-induced displacements were higher at unablated sites (11.23 ± 1.71 µm) than at ablated sites (6.06 ± 0.94 µm). The average lesion C (0.29 ± 0.33) and CNR (1.83 ± 1.75) were significantly higher for ARFI images than for spatially registered conventional B-mode images (C = –0.03 ± 0.28, CNR = 0.74 ± 0.68).
      PubDate: 2014-02-18T20:34:33-08:00
      DOI: 10.1177/0161734613519602|hwp:resource-id:spuix;36/2/133
      Issue No: Vol. 36, No. 2 (2014)
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