M.J. McAllister

University of Virginia, Charlottesville, Virginia, United States

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Publications (9)0.4 Total impact

  • D.A. Guenther · K. Ranganathan · M.J. McAllister · W.F. Walker · K.W. Rigby
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    ABSTRACT: Conventional coherent imaging systems map the energy which is reflected directly back towards the transducer. While extremely useful, these systems fail to utilize information in the energy field which has been scattered at other angles. Angular scatter imaging attempts to form images from the scattered energy field at angles other than the 180° backscattered path. We propose a synthetic aperture based imaging scheme for acquiring angular scatter data in medical ultrasound. We describe this technique in k-space and provide an intuitive explanation of the imaging system's behavior. This method, which we term Synthetic Aperture Angular Scatter (SAAS) imaging effectively uses single element geometries to acquire data at a range of scattering angles. In this paper, we present experimental results implementing SAAS on a GE Logiq 700MR system. We applied the SAAS method to form angular scatter images of a 5-wire depth of field (DOF) phantom and a tissue mimicking 3-wire phantom (steel, nylon and cotton). We present results from this data and discuss the degree of uniformity necessary in element response for successful SAAS imaging. Results from these experiments show new image information previously unavailable in conventional B-mode images and suggest that angular scatter imaging may have applications in the breast, thyroid and peripheral vasculature.
    No preview · Conference Paper · Dec 2004
  • D.A. Guenther · K. Ranganathan · M.J. McAllister · W.F. Walker · K.W. Rigby
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    ABSTRACT: Angular scatter imaging has been proposed as a new source of image contrast in medical ultrasound and as a parameter for tissue characterization. We describe a new method that combines the translating apertures algorithm (TAA) with synthetic aperture methods to coherently obtain angular scatter information with high resolution in both space and scattering angle. This method, which we term synthetic aperture angular scatter (SAAS) imaging effectively applies the TAA to single array elements and then focuses the data synthetically to form high resolution images at precisely defined scattering angles. In this paper, we present experimental results implementing SAAS to form angular scatter images of a 5-wire depth of field phantom, a tissue mimicking 3-wire phantom, and in vivo human thyroid. We discuss the degree of uniformity necessary in element response for successful SAAS imaging. These experiments show new image information previously unavailable in conventional B-mode images and suggest that angular scatter imaging may have applications in the breast, thyroid, and peripheral vasculature.
    No preview · Conference Paper · Sep 2004
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    ABSTRACT: A method for coherently acquiring backscatter and angular scatter information was described using a synthetic aperture based approach on a 1D linear array. The method of angular scatter imaging uses a single element synthetic aperture approach to acquire reflected acoustic data at multiple scattering angles. The SAAS imaging approach using the translating apertures algorithm (TAA) half element step samples K-space in between the backscatter and full element TAA K-space samples. It was found that by using a K-space motivated algorithm, lateral spatial frequency sampling was increased on an otherwise undersampled linear array. The results show that the beamplots for the backscattered case, the grating lobes rise to a level around -23 dB.
    No preview · Article · Apr 2004 · Proceedings of SPIE - The International Society for Optical Engineering
  • W.F. Walker · M.J. McAllister
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    ABSTRACT: Human tissues exhibit variation in scattering magnitude as the angle between transmission and reception is changed. These angular scatter variations result from intrinsic acoustic properties and sub-resolution structure. We have developed a clinical imaging system that uses the translating apertures algorithm to obtain statistically reliable, local angular scatter measurements. The obtained data can be processed to yield novel images. A significant problem with angular scatter imaging is limited depth of field (DOF). We describe a new method to improve DOF by applying shift variant filters to the data obtained at each angle. We show that this approach is optimal in a minimum sum squared error sense. The filter coefficients used in the technique can be determined via experiment or simulation. Unlike prior methods, this approach does not assume a model for the source of decorrelation, rather it includes all sources of decorrelation implicitly. We present simulation results showing the improvements in DOF obtained using this technique. We present experimental angular scatter data from phantoms and human subjects. In one phantom, designed to mimic microcalcifications in soft tissue, experimental data shows the angular scatter from 500 um glass spheres falling off by 50% over a 20 degree range of interrogation angles. In the same phantom the angular scatter from 50 um sephadex spheres fell off by only 10% over the same range. In the human calf muscle, brightness fell off by 60% over 20 degrees, while tendon brightness dropped by only 20%. Interestingly, the brightest target in the phantom (glass spheres) exhibited the greatest angular scatter variation, while the brightest target in the calf (tendon) exhibited the least angular scatter variation. These results provide compelling evidence that angular scatter properties are uncorrelated to b-mode image brightness.
    No preview · Conference Paper · Nov 2002
  • W.F. Walker · M.J. McAllister
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    ABSTRACT: Ultrasonic imaging plays a critical diagnostic role in a broad range of medical specialties; however, there continue to be areas of clinical medicine where the advantages of ultrasound cannot be brought to bear because the targets of most interest do not exhibit sufficient image contrast. We have investigated a novel imaging method that utilizes modified ultrasonic imaging equipment to interrogate a previously unexploited source of image contrast, namely ultrasonic angular scatter variations. This technique takes advantage of the fact that the ultrasonic scattering from tissue changes with the angle between the incident (transmitted) ultrasonic wave and the observed (received) ultrasonic wave. Angular scatter variations result from spatial variations in the intrinsic material properties of density and compressibility, as well as the geometry of the tissue microstructure. We present experimental results from tissue mimicking and in vivo human tissues indicating that angular scatter differentiates targets that are indistinguishable in conventional ultrasound images. We also present cases where angular scatter images improve the contrast of interesting targets relative to conventional images. Early in vivo results from the myotendinous junction of the human gastrocnemius muscle indicate that different soft tissues have different angular scatter profiles and that these profiles can be used to discern between tissues.
    No preview · Conference Paper · Jan 2002
  • M.J. McAllister · K.W. Rigby · W.F. Walker
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    ABSTRACT: Traditional ultrasound systems measure backscatter in B-mode, capturing only the acoustic energy that is reflected directly from the target region to the transducer face. These systems fail to utilize the information in the echo field that is scattered in other directions and therefore cannot characterize the angular scattering behavior of the targets being observed. Since target-specific angular scattering has great potential as a source of increased contrast in biological tissues, it is desirable to modify the method of acquisition in order to obtain reliable information about this behavior. However, prior systems used to investigate this information have been clinically unwieldy and statistically inaccurate over small regions. We have implemented a method of acquisition that utilizes the translating apertures algorithm: (TAA) to reliably separate target-specific angular scatter information from the effects of changing acquisition geometry. This acquisition method has been implemented in real-time on a clinical linear array system. Seven interrogation angles are acquired for each imaging line, and the TAA is implemented repeatedly across the array to yield per-pixel maps of angular scatter behavior
    No preview · Conference Paper · Feb 2001
  • Michael J. McAllister · William F. Walker
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    ABSTRACT: A new method of acquiring and processing angular scatter data in ultrasonic imaging is presented. This method, based on the translating apertures algorithm, eliminates system-dependent changes in the received point spread function (psf) that are associated with more conventional methods of angular scatter measurement. This ensures that changes in the received echo are dominated by changes in the angular scattering behavior of insonified targets, and allows for the development of a variety of new imaging methods. Comparison of received echoes acquired at multiple interrogation angles serves to enhance the contrast of targets exhibiting variations in angular scattering behavior relative to the surrounding medium. Emphasis is placed on the improved ability to highlight biological targets that exhibit significant variations in compressibility or density relative to background tissue (e.g. breast microcalcifications, calcified atherosclerotic plaques). Simulation indicates the enhancement of breast microcalcification contrast by 10 - 30 dB over standard b-mode acquisition at 10 MHz. More sophisticated imaging methods involving the frequency dependence of angular scatter and angular speckle coherence are also discussed. Practical implementation and evaluation of this method on a modern imaging system is discussed, and expectations for the performance and utility of this algorithm in clinical diagnosis are investigated.
    No preview · Article · Apr 2000 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Tissue elasticity estimation is a major topic of ultrasound research. While most research focuses on cancer detection, the authors have concentrated on the detection of mechanical changes in the vitreous body of the eye. These changes are believed to contribute to retinal detachment. Thus, an accurate method of imaging vitreous mechanical properties might enable identification of patients at high risk before the presentation of symptoms. The authors are developing a new method of vitreous imaging which attempts to image tissue stiffness by applying acoustic radiation force. Force is applied at either a single location or along a line, with resultant target displacements estimated from returned echoes. This approach yields the dynamic response of targets to the applied forces. Images can be formed of the maximum induced displacement, or the relative elasticity and relative viscosity found by fitting experimental data to the Voigt model. The authors present B-Mode, maximum displacement, relative elasticity, and relative viscosity images of tissue mimicking phantoms and an enzymatically modified porcine eye. Images show the expected correlation between material stiffness and measured displacement. The potential of radiation force imaging was further explored by using a clinical ultrasound system to interrogate a phantom. At 84 mW/cm<sup>2</sup> small displacements were visible in the B-Mode image, suggesting that measurable displacements may be generated at 50 mW/cm<sup>2</sup>, the historical FDA ophthalmic power limit
    No preview · Conference Paper · Feb 1999
  • W.F. Walker · M.J. McAllister
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    ABSTRACT: Conventional ultrasound systems depict tissue backscatter; that is, the energy reflected directly back to the transmitter. While diagnostically useful, these systems fail to exploit information available in the echoes scattered in other directions (angular scatter). This paper describes a new method of angular scatter imaging. It applies the translating apertures algorithm to maintain a nearly uniform psf over a range of interrogation angles. Data from two angles is processed to form images of the constant scatter with angle and the differential scatter with angle. The authors refer to these images as c-weighted (constant) and d-weighted (difference) images. Since psf uniformity is maintained and speckle variation avoided, these images depict local angular scatter without spatial averaging. The authors present an algorithm and accompanying equations for formation of c- and d-weighted images. They present simulations showing that c- and d-weighted images may offer improved contrast in soft tissues, and that they will significantly improve the detectability of microcalcifications (MCs), important indicators of breast cancer
    No preview · Conference Paper · Jan 1999

Publication Stats

8 Citations
0.40 Total Impact Points

Institutions

  • 2002-2004
    • University of Virginia
      • Department of Biomedical Engineering
      Charlottesville, Virginia, United States