Xiangtao Yin - Academia.edu (original) (raw)
Papers by Xiangtao Yin
Journal of Ultrasound in Medicine, 2010
Objective. Transcranial images are affected by a "stripe artifact" (also known as a "streak artif... more Objective. Transcranial images are affected by a "stripe artifact" (also known as a "streak artifact"): two dark stripes stem radially from the apex to the base of the scan. The stripes limit the effective field of view even on patients with good temporal windows. This study investigated the angle dependency of ultrasound transmission through the skull to elucidate this artifact. Methods. In vivo transcranial images were obtained to illustrate the artifact. In vitro hydrophone measurements were performed in water to evaluate transcranial wavefronts at different incidence angles of the ultrasound beam. Both a thin acrylic plate, as a simple bone model, and a human temporal bone sample were used. Results. The imaging wavefront splits into two after crossing the solid layer (acrylic model or skull sample) at an oblique angle. An early-arrival wavefront originates from the direct longitudinal wave transmission through water-bone interfaces, while a late-arrival wavefront results from longitudinal-to-transverse mode conversion at the water-bone interface, propagation of the transverse wave through the skull, and transverse-to-longitudinal conversion at the bone-water interface. At normal incidence, only the direct wavefront (without mode conversion) is observed. As the incidence angle increases, the additional "mode conversion" wavefront appears. The amplitude of the transcranial wavefront decreases and reaches a minimum at an incidence angle of about 27°. Beyond that critical angle, only the mode conversion wavefront is transmitted. Conclusions. The stripes are a consequence of the angle-dependent ultrasound transmission and mode conversion at fluid-solid interfaces such as between the skull and the surrounding fluidlike soft tissues.
2007 IEEE Ultrasonics Symposium Proceedings, 2007
Abstract Transcranial ultrasound sector images are affected by a streak artifact: two dark str... more Abstract Transcranial ultrasound sector images are affected by a streak artifact: two dark streaks stem radially from the apex to the maximal depth of the scan at particular angles, limiting the effective field of view and diagnostic confidence. The aim of this paper is to investigate ...
The Journal of the Acoustical Society of America, 2005
The objective of our research during the past few years has been to develop multichannel ultrasou... more The objective of our research during the past few years has been to develop multichannel ultrasound phased arrays for noninvasive brain interventions. We have been successful in developing methods for correcting the skull induced beam distortions and thus, are able to produce sharp focusing through human skulls. This method is now being tested for thermal ablation of tumors, with results from animal studies demonstrating feasibility. In addition, the ability of ultrasound to open the blood-brain barrier (BBB) locally has been explored in animal models. The results suggest that the transcranial ultrasound exposures can induce BBB opening such that therapeutic agents can be localized in the brain. This tool is especially powerful since the beam can be guided by MR images, thus providing anatomical or functional targeting. This talk will review our current status in this research, which ultimately aims for the clinical use of this methodology.
Physics in Medicine and Biology, 2005
The feasibility of transcranial ultrasound focusing with a non-moving phased array and without sk... more The feasibility of transcranial ultrasound focusing with a non-moving phased array and without skull-specific aberration correction was investigated using computer simulations. Three cadaver skull CT image data sets were incorporated into an acoustic wave transmission model to simulate transskull ultrasound wave propagation. Using a 0.25 MHz hemispherical array (125 mm radius of curvature, 250 mm diameter, 24 255 elements), the simulated beams could be focused and steered with transducer element driving phases and amplitude adjusted for focal beam steering in water (water-path). A total of 82 foci, spanning wide ranges of distance in the three orthogonal dimensions, were simulated to test the focal beam steering capability inside the three skulls. The acoustic pressure distribution in a volume of 20 x 20 x 20 mm(3) centred at each focus was calculated with a 0.5 mm spacing in each axis. Clearly defined foci were retained through the skulls (skull-path) in most cases. The skull-path foci were on average 1.6 +/- 0.8 mm shifted from their intended locations. The -3 dB skull-path beam width and length were on average 4.3 +/- 1.0 mm and 7.7 +/- 1.8 mm, respectively. The skull-path sidelobe levels ranged from 25% to 55% of the peak pressure values. The skull-path peak pressure levels were about 10%-40% of their water-path counterparts. Focusing low-frequency beam through skull without skull-specific aberration correction is possible. This method may be useful for applying ultrasound to disrupt the blood-brain barrier for targeted delivery of therapeutic or diagnostic agents, or to induce microbubbles, or for other uses of ultrasound in brain where the required power levels are low and the sharp focusing is not needed.
ABSTRACT Currently, most phased array systems intended for therapy are 1-dimensional and employ b... more ABSTRACT Currently, most phased array systems intended for therapy are 1-dimensional and employ between 5 and 200 elements, with a few 2-dimensional systems using several hundred elements. The move towards lambda/2 inter-element spacing, which provides complete 3D beam steering, would require a large number of closely spaced elements (0.15 mm to 3 mm). The solution to the resulting problem of cost and cable assembly size, which this study examines, is to quantize the phases available at the array input. By connecting elements with similar phases to a single wire, a significant reduction in the number of incoming lines can be achieved, while maintaining focusing and beam steering capability. This study has explored the feasibility of such an approach using computer simulations and experiments with a test circuit driving a 100-element linear array. The simulation results demonstrated that adequate focusing can be obtained with only four phase signals, without large increases in the grating lobes or the dimensions of the focus. The experiments showed that the method can be implemented in practice and adequate focusing can be achieved with four phase signals with a reduction of 20% in the peak pressure amplitude squared when compared with the infinite phase resolution case. The results indicate that the use of this technique would make it possible to drive more than 10000 elements with 33 input lines. The implementation of this method could have a large impact on ultrasound therapy and diagnostic devices
AIP Conference Proceedings
ABSTRACT A sparse large-element hemispherical phased array scheme was investigated for low freque... more ABSTRACT A sparse large-element hemispherical phased array scheme was investigated for low frequency transcranial focused ultrasound applications without skull-specific phase aberration correction. The simulated transcranial focused beams in brain from the randomly distributed sparse array elements (0.25 MHz, 125 mm radius of curvature, 250 mm diameter, 50% sparsity of 953 square elements of 10 mm spacing) could be steered without skull specific aberration correction at 0.25 MHz. The 28 foci were on average 1.7±1.2 mm shifted from their intended locations. The average −3 dB beam width and length were 3.3±1.2 mm and 6.3±2.2 mm, respectively. The sidelobe levels ranged from 28% to 62% of the peak pressure values. The focal beam was steerable 35 mm laterally away from the transducer center axis and 30 mm axially in the transducer center axis when the sidelobe pressure values were 50% of or less than the peak pressure values. This allows the array to be mechanically aimed to one quarter of the brain and then electronically steered. The sparse array design offers a tradeoff between the best beam steering range and the manageable number of elements for a practical clinical system.
2002 IEEE Ultrasonics Symposium, 2002. Proceedings., 2002
The ultrasonic pulse-echo Backscattered Amplitude Integral (BAI)-mode imaging technique [UFFC Tra... more The ultrasonic pulse-echo Backscattered Amplitude Integral (BAI)-mode imaging technique [UFFC Trans, 45:30, 1998] has been developed to detect small channel defects in flexible food package seals. This technique detects 38-Ñ-diameter channels reliably and 6-Ñ-diameter channels occasionally using a 17.3-MHz focused transducer in water (20 o C, 86 Ñ, total sample thickness 220 Ñ). However, interaction between ultrasound and sample microstructure-the underlying detection mechanismis poorly understood. Experimental evidence showed that the subwavelength channel was fused inside the two binding trilaminate plastic package films. Each trilaminate film had three sublayers. Package sample impedance profiles along the ultrasound beam axis were examined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. A generalized impedance profile model was proposed. The defect detection behavior of the echo signal was investigated by solving the 2D linear acoustic wave equations in fluid with finite-difference time-domain method and the perfectly matched layer absorbing boundary. The normalized correlation coefficients between the simulated and the measured RF echo waveforms were greater than 95% for this generalized model.
IEEE Ultrasonics Symposium, 2005., 2005
Non-uniform thermal deposition in skull during transcranial focused ultrasound thermal ablation o... more Non-uniform thermal deposition in skull during transcranial focused ultrasound thermal ablation of brain tumors may cause undesired temperature elevation and produce adverse effects in scalp, skull and the adjacent normal brain tissues. Instead of using continuous wave (CW) sonication scheme, a pulsed wave (PW) sonication scheme was proposed, intending to allow extra cooling between sonicating pulses so that the accumulated
2001 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.01CH37263), 2001
Hermetically-sealed flexible food packages require effective seal integrity tests for quality ass... more Hermetically-sealed flexible food packages require effective seal integrity tests for quality assurance purpose. 10-pmdiameter channel defects can propagate microorganisms into food. The channel diameter limits of human inspection are about 50 pm in transparent food packages. A reliable methodology is thus needed to detect 50-pmdiameter and smaller channels. The pulseecho Backscattered Amplitude Integral (BAI)mode imaging technique W C Trans, 4530, 19981 has been developed and demonstrated by us to 100% reliably detect 38-pmdiameter and larger channels in plastic films tested using a static stop-and-go transducer scanning pattern. In this study, we examined experimentally the spatial sampling issue of the BAImode imaging technique with a new real-time transducer scanning protocol to simulate continuous package production line motion. A focused transducer (17.3 MHz,-6 d B pulseecho focal beam diameter of 173 pm) acquired RF data in a zigzag raster scanning pattern from plastic film samples bearing point reflectors arranged in a rectangular grid of varying spacings. The contrast-to-noise ratio (CNR) and the average BAI value difference (ABAI) between defected and background regions were assessed to quantitatively study image quality versus the varying grid size and the changing spatial scanning step sizes. For any given spatial grid size, the CNR and ABAI values degraded as scanning step size in each spatial dimension increased. When the CrBAI dropped below 5% of the maximum BAT value, the point targets could not be separated in the image.
International Journal of Environment and Pollution, 2000
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2007
Currently, most phased-array systems intended for therapy are one-dimensional (1-D) and use betwe... more Currently, most phased-array systems intended for therapy are one-dimensional (1-D) and use between 5 and 200 elements, with a few two-dimensional (2-D) systems using several hundred elements. The move toward lambda/2 interelement spacing, which provides complete 3-D beam steering, would require a large number of closely spaced elements (0.15 mm to 3 mm). A solution to the resulting problem of cost and cable assembly size, which this study examines, is to quantize the phases available at the array input. By connecting elements with similar phases to a single wire, a significant reduction in the number of incoming lines can be achieved while maintaining focusing and beam steering capability. This study has explored the feasibility of such an approach using computer simulations and experiments with a test circuit driving a 100-element linear array. Simulation results demonstrated that adequate focusing can be obtained with only four phase signals without large increases in the grating...
Ultrasonics, IEEE Symposium, 2007
A fast Rayleigh-Sommerfeld integral-based method was presented in this paper to speed up acoustic... more A fast Rayleigh-Sommerfeld integral-based method was presented in this paper to speed up acoustic field simulation using a modified summation scheme. Partitioning source aperture with uniform large patches instead of simple sources, the modified summation scheme outperformed the conventional simple source based approach by both reducing the number of source-field interaction pairs and reusing the beam directivity of a single
Ultrasonics, IEEE Symposium, 2007
The work presented in this paper is to investigate High Intensity Focused Ultrasound (HIFU) techn... more The work presented in this paper is to investigate High Intensity Focused Ultrasound (HIFU) technology for acoustic hemostasis to stop internal bleeding in the human limbs, especially those caused by injuries on the battlefield. A ID 64-element cylindrical HIFU array has been used for the feasibility study. Both simulation and experiment results are presented, including acoustic field characterization in a
The Journal of the Acoustical Society of America, 2001
ABSTRACT The principal concern with regard to defect detection in hermetically sealed flexible fo... more ABSTRACT The principal concern with regard to defect detection in hermetically sealed flexible food packages is the safety and shelf life of the food. The spatial sampling issue of the pulse echo backscattered amplitude integral (BAI) mode imaging technique for defect detection is investigated. In our previous spatial sampling study, it has been shown that for channel defects, the contrast to noise ratio (CNR) degrades as a function of scanning step size on each dimension of the image. To further understand spatial sampling resolution of this method, BAI imaging technique is applied to rectilinear grided dot samples with different grid sizes (distance between adjacent dots). Data is collected with the transducer scanned in a zigzag raster pattern. Quantitatively, the CNR and ΔBAI values are assessed to evaluate the image quality versus the changing spatial interval between dots. At a given operating frequency and a fixed spatial grid size, the CNR and ΔBAI value degrade as a function of the scanning step size on each dimension. Not only the scanning step size, but also the ultrasound beam spot size affect the spatial sampling resolution in the BAI imaging technique for defect detection. [Work supported by the C‐FAR program, University of Illinois.]
Journal of Nondestructive Evaluation, 2000
The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Tra... more The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Trans. UFFC, 45:30 (1998)] has demonstrated sensitive detection of subwavelength channel defects (38-m diameter reliably and 6-m diameter occasionally) in flexible 220-m-thick food package seals (17.3 MHz, Ϸ 86 m). However, the underlying subwavelength defect detection mechanism is poorly understood. In this contribution, a theoretical modeling study was undertaken to elucidate the mechanism. The subwavelength diameter channel was fused in-between two plastic package films by applying heat from one side of the films. The sample cross-section microstructure was characterized from both optical and acoustic images. The cross-section impedance profiles along sample thickness dimension were determined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. Transient finite-element heat conduction analysis and impedance profiles of multiple-sealed package samples showed that the single-sided heating process caused an asymmetric impedance profile. A generalized impedance model was proposed based on these observations. An efficient two-dimensional simulation tool using a finite-difference time-domain method and the perfectly matched layer numerically evaluated the defect detection behavior of the radio-frequency (rf) echo waveforms. The normalized correlation coefficients between the simulated and the measured rf echo waveforms were greater than 95% for this generalized model, which suggested the validity of the proposed impedance model.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000
The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique has been ... more The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique has been developed to inspect the seal integrity of hermetically sealed, flexible food packages. With a focused 17.3-MHz transducer acquiring radio frequency (RF) echo data in a static rectilinear stop-and-go pattern, this technique was able to reliably detect channel defects as small as 38 m in diameter and occasionally detect 6-m-diameter channels. This contribution presents our experimental spatial sampling study of the BAI-mode imaging technique with a continuous zigzag scanning protocol that simulates a real-time production line inspection method in continuous motion. Two transducers (f/2 17.3 MHz and f/3 20.3 MHz) were used to acquire RF echo data in a zigzag raster pattern from plastic film samples bearing rectilinear point reflector arrays of varying grid spacings. The average BAI-value difference (∆BAI) between defective and intact regions and the contrast-to-noise ratio (CNR) were used to assess image quality as a function of three spatial sampling variables: transducer spatial scanning step size, array sample grid spacing, and transducer ;6-dB pulse-echo focal beam spot size. For a given grid size, the ∆BAI and CNR degraded as scanning step size in each spatial dimension increased. There is an engineering trade-off between the BAImode image quality and the transducer spatial sampling. The optimal spatial sampling step size has been identified to be between one and two times the ;6-dB pulse-echo focal beam lateral diameter.
This animal study addresses the treatment efficacy of the MR-guided thermal ablation technique an... more This animal study addresses the treatment efficacy of the MR-guided thermal ablation technique and temperature monitoring in rabbit tumors. Specifically, the relationship between the thermal dose coverage in the tumors and the rabbit survival rate was investigated. Two groups of rabbits (14 in back tumor group and 12 in thigh tumor group) were treated with the ExAblate-2000 MR-guided focused ultrasound
ABSTRACT Current, minimally invasive, treatments for cardiac arrhythmia use a transvenous radio-f... more ABSTRACT Current, minimally invasive, treatments for cardiac arrhythmia use a transvenous radio-frequency (RF) catheter to ablate the malfunctioning cardiac muscle regions. The paper proposes a noninvasive transesophageal cardiac thermal ablation using focused ultrasound. A planar phased array (1 MHz, 60×10 mm2, 0.525 mm element center-to-center distance, 2280 elements) was put in the esophagus. Using electronic beam steering, a matrix of 5×3×5 foci in the cardiac muscle was defined in three planes parallel to the transducer surface at short, medium and long (20, 40 and 60 mm) radial ranges and different steering angles. The transmitted ultrasound pressure distribution in a volume of 20×20×20 mm3 centered at each focus was calculated using a multilayer acoustic wave transmission model. The thermal lesions due to the acoustic energy absorption in cardiac muscle were simulated using the bioheat transfer equation. For short, medium and long (1-, 10- and 20-second) sonications, the acoustic powers needed to achieve 60°C and 70°C peak temperatures in the cardiac muscle were 89-725, 25-125, 20-86 W and 128-1040, 36-179, 28-123 W, respectively. The simulated tissue lesion (thermal dose >240 min at 43°C) lengths at these foci were 2-10, 5-12, 6-14 mm and 3-13, 7-15, 9-17 mm, respectively. The lesion widths were 2-8, 3-10, 4-11 mm and 3-11, 4-12, 5-13 mm, respectively. The simulations show that noninvasive transesophageal cardiac ablation with a planar phased ultrasound array is feasible.
Journal of Ultrasound in Medicine, 2010
Objective. Transcranial images are affected by a "stripe artifact" (also known as a "streak artif... more Objective. Transcranial images are affected by a "stripe artifact" (also known as a "streak artifact"): two dark stripes stem radially from the apex to the base of the scan. The stripes limit the effective field of view even on patients with good temporal windows. This study investigated the angle dependency of ultrasound transmission through the skull to elucidate this artifact. Methods. In vivo transcranial images were obtained to illustrate the artifact. In vitro hydrophone measurements were performed in water to evaluate transcranial wavefronts at different incidence angles of the ultrasound beam. Both a thin acrylic plate, as a simple bone model, and a human temporal bone sample were used. Results. The imaging wavefront splits into two after crossing the solid layer (acrylic model or skull sample) at an oblique angle. An early-arrival wavefront originates from the direct longitudinal wave transmission through water-bone interfaces, while a late-arrival wavefront results from longitudinal-to-transverse mode conversion at the water-bone interface, propagation of the transverse wave through the skull, and transverse-to-longitudinal conversion at the bone-water interface. At normal incidence, only the direct wavefront (without mode conversion) is observed. As the incidence angle increases, the additional "mode conversion" wavefront appears. The amplitude of the transcranial wavefront decreases and reaches a minimum at an incidence angle of about 27°. Beyond that critical angle, only the mode conversion wavefront is transmitted. Conclusions. The stripes are a consequence of the angle-dependent ultrasound transmission and mode conversion at fluid-solid interfaces such as between the skull and the surrounding fluidlike soft tissues.
2007 IEEE Ultrasonics Symposium Proceedings, 2007
Abstract Transcranial ultrasound sector images are affected by a streak artifact: two dark str... more Abstract Transcranial ultrasound sector images are affected by a streak artifact: two dark streaks stem radially from the apex to the maximal depth of the scan at particular angles, limiting the effective field of view and diagnostic confidence. The aim of this paper is to investigate ...
The Journal of the Acoustical Society of America, 2005
The objective of our research during the past few years has been to develop multichannel ultrasou... more The objective of our research during the past few years has been to develop multichannel ultrasound phased arrays for noninvasive brain interventions. We have been successful in developing methods for correcting the skull induced beam distortions and thus, are able to produce sharp focusing through human skulls. This method is now being tested for thermal ablation of tumors, with results from animal studies demonstrating feasibility. In addition, the ability of ultrasound to open the blood-brain barrier (BBB) locally has been explored in animal models. The results suggest that the transcranial ultrasound exposures can induce BBB opening such that therapeutic agents can be localized in the brain. This tool is especially powerful since the beam can be guided by MR images, thus providing anatomical or functional targeting. This talk will review our current status in this research, which ultimately aims for the clinical use of this methodology.
Physics in Medicine and Biology, 2005
The feasibility of transcranial ultrasound focusing with a non-moving phased array and without sk... more The feasibility of transcranial ultrasound focusing with a non-moving phased array and without skull-specific aberration correction was investigated using computer simulations. Three cadaver skull CT image data sets were incorporated into an acoustic wave transmission model to simulate transskull ultrasound wave propagation. Using a 0.25 MHz hemispherical array (125 mm radius of curvature, 250 mm diameter, 24 255 elements), the simulated beams could be focused and steered with transducer element driving phases and amplitude adjusted for focal beam steering in water (water-path). A total of 82 foci, spanning wide ranges of distance in the three orthogonal dimensions, were simulated to test the focal beam steering capability inside the three skulls. The acoustic pressure distribution in a volume of 20 x 20 x 20 mm(3) centred at each focus was calculated with a 0.5 mm spacing in each axis. Clearly defined foci were retained through the skulls (skull-path) in most cases. The skull-path foci were on average 1.6 +/- 0.8 mm shifted from their intended locations. The -3 dB skull-path beam width and length were on average 4.3 +/- 1.0 mm and 7.7 +/- 1.8 mm, respectively. The skull-path sidelobe levels ranged from 25% to 55% of the peak pressure values. The skull-path peak pressure levels were about 10%-40% of their water-path counterparts. Focusing low-frequency beam through skull without skull-specific aberration correction is possible. This method may be useful for applying ultrasound to disrupt the blood-brain barrier for targeted delivery of therapeutic or diagnostic agents, or to induce microbubbles, or for other uses of ultrasound in brain where the required power levels are low and the sharp focusing is not needed.
ABSTRACT Currently, most phased array systems intended for therapy are 1-dimensional and employ b... more ABSTRACT Currently, most phased array systems intended for therapy are 1-dimensional and employ between 5 and 200 elements, with a few 2-dimensional systems using several hundred elements. The move towards lambda/2 inter-element spacing, which provides complete 3D beam steering, would require a large number of closely spaced elements (0.15 mm to 3 mm). The solution to the resulting problem of cost and cable assembly size, which this study examines, is to quantize the phases available at the array input. By connecting elements with similar phases to a single wire, a significant reduction in the number of incoming lines can be achieved, while maintaining focusing and beam steering capability. This study has explored the feasibility of such an approach using computer simulations and experiments with a test circuit driving a 100-element linear array. The simulation results demonstrated that adequate focusing can be obtained with only four phase signals, without large increases in the grating lobes or the dimensions of the focus. The experiments showed that the method can be implemented in practice and adequate focusing can be achieved with four phase signals with a reduction of 20% in the peak pressure amplitude squared when compared with the infinite phase resolution case. The results indicate that the use of this technique would make it possible to drive more than 10000 elements with 33 input lines. The implementation of this method could have a large impact on ultrasound therapy and diagnostic devices
AIP Conference Proceedings
ABSTRACT A sparse large-element hemispherical phased array scheme was investigated for low freque... more ABSTRACT A sparse large-element hemispherical phased array scheme was investigated for low frequency transcranial focused ultrasound applications without skull-specific phase aberration correction. The simulated transcranial focused beams in brain from the randomly distributed sparse array elements (0.25 MHz, 125 mm radius of curvature, 250 mm diameter, 50% sparsity of 953 square elements of 10 mm spacing) could be steered without skull specific aberration correction at 0.25 MHz. The 28 foci were on average 1.7±1.2 mm shifted from their intended locations. The average −3 dB beam width and length were 3.3±1.2 mm and 6.3±2.2 mm, respectively. The sidelobe levels ranged from 28% to 62% of the peak pressure values. The focal beam was steerable 35 mm laterally away from the transducer center axis and 30 mm axially in the transducer center axis when the sidelobe pressure values were 50% of or less than the peak pressure values. This allows the array to be mechanically aimed to one quarter of the brain and then electronically steered. The sparse array design offers a tradeoff between the best beam steering range and the manageable number of elements for a practical clinical system.
2002 IEEE Ultrasonics Symposium, 2002. Proceedings., 2002
The ultrasonic pulse-echo Backscattered Amplitude Integral (BAI)-mode imaging technique [UFFC Tra... more The ultrasonic pulse-echo Backscattered Amplitude Integral (BAI)-mode imaging technique [UFFC Trans, 45:30, 1998] has been developed to detect small channel defects in flexible food package seals. This technique detects 38-Ñ-diameter channels reliably and 6-Ñ-diameter channels occasionally using a 17.3-MHz focused transducer in water (20 o C, 86 Ñ, total sample thickness 220 Ñ). However, interaction between ultrasound and sample microstructure-the underlying detection mechanismis poorly understood. Experimental evidence showed that the subwavelength channel was fused inside the two binding trilaminate plastic package films. Each trilaminate film had three sublayers. Package sample impedance profiles along the ultrasound beam axis were examined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. A generalized impedance profile model was proposed. The defect detection behavior of the echo signal was investigated by solving the 2D linear acoustic wave equations in fluid with finite-difference time-domain method and the perfectly matched layer absorbing boundary. The normalized correlation coefficients between the simulated and the measured RF echo waveforms were greater than 95% for this generalized model.
IEEE Ultrasonics Symposium, 2005., 2005
Non-uniform thermal deposition in skull during transcranial focused ultrasound thermal ablation o... more Non-uniform thermal deposition in skull during transcranial focused ultrasound thermal ablation of brain tumors may cause undesired temperature elevation and produce adverse effects in scalp, skull and the adjacent normal brain tissues. Instead of using continuous wave (CW) sonication scheme, a pulsed wave (PW) sonication scheme was proposed, intending to allow extra cooling between sonicating pulses so that the accumulated
2001 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.01CH37263), 2001
Hermetically-sealed flexible food packages require effective seal integrity tests for quality ass... more Hermetically-sealed flexible food packages require effective seal integrity tests for quality assurance purpose. 10-pmdiameter channel defects can propagate microorganisms into food. The channel diameter limits of human inspection are about 50 pm in transparent food packages. A reliable methodology is thus needed to detect 50-pmdiameter and smaller channels. The pulseecho Backscattered Amplitude Integral (BAI)mode imaging technique W C Trans, 4530, 19981 has been developed and demonstrated by us to 100% reliably detect 38-pmdiameter and larger channels in plastic films tested using a static stop-and-go transducer scanning pattern. In this study, we examined experimentally the spatial sampling issue of the BAImode imaging technique with a new real-time transducer scanning protocol to simulate continuous package production line motion. A focused transducer (17.3 MHz,-6 d B pulseecho focal beam diameter of 173 pm) acquired RF data in a zigzag raster scanning pattern from plastic film samples bearing point reflectors arranged in a rectangular grid of varying spacings. The contrast-to-noise ratio (CNR) and the average BAI value difference (ABAI) between defected and background regions were assessed to quantitatively study image quality versus the varying grid size and the changing spatial scanning step sizes. For any given spatial grid size, the CNR and ABAI values degraded as scanning step size in each spatial dimension increased. When the CrBAI dropped below 5% of the maximum BAT value, the point targets could not be separated in the image.
International Journal of Environment and Pollution, 2000
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2007
Currently, most phased-array systems intended for therapy are one-dimensional (1-D) and use betwe... more Currently, most phased-array systems intended for therapy are one-dimensional (1-D) and use between 5 and 200 elements, with a few two-dimensional (2-D) systems using several hundred elements. The move toward lambda/2 interelement spacing, which provides complete 3-D beam steering, would require a large number of closely spaced elements (0.15 mm to 3 mm). A solution to the resulting problem of cost and cable assembly size, which this study examines, is to quantize the phases available at the array input. By connecting elements with similar phases to a single wire, a significant reduction in the number of incoming lines can be achieved while maintaining focusing and beam steering capability. This study has explored the feasibility of such an approach using computer simulations and experiments with a test circuit driving a 100-element linear array. Simulation results demonstrated that adequate focusing can be obtained with only four phase signals without large increases in the grating...
Ultrasonics, IEEE Symposium, 2007
A fast Rayleigh-Sommerfeld integral-based method was presented in this paper to speed up acoustic... more A fast Rayleigh-Sommerfeld integral-based method was presented in this paper to speed up acoustic field simulation using a modified summation scheme. Partitioning source aperture with uniform large patches instead of simple sources, the modified summation scheme outperformed the conventional simple source based approach by both reducing the number of source-field interaction pairs and reusing the beam directivity of a single
Ultrasonics, IEEE Symposium, 2007
The work presented in this paper is to investigate High Intensity Focused Ultrasound (HIFU) techn... more The work presented in this paper is to investigate High Intensity Focused Ultrasound (HIFU) technology for acoustic hemostasis to stop internal bleeding in the human limbs, especially those caused by injuries on the battlefield. A ID 64-element cylindrical HIFU array has been used for the feasibility study. Both simulation and experiment results are presented, including acoustic field characterization in a
The Journal of the Acoustical Society of America, 2001
ABSTRACT The principal concern with regard to defect detection in hermetically sealed flexible fo... more ABSTRACT The principal concern with regard to defect detection in hermetically sealed flexible food packages is the safety and shelf life of the food. The spatial sampling issue of the pulse echo backscattered amplitude integral (BAI) mode imaging technique for defect detection is investigated. In our previous spatial sampling study, it has been shown that for channel defects, the contrast to noise ratio (CNR) degrades as a function of scanning step size on each dimension of the image. To further understand spatial sampling resolution of this method, BAI imaging technique is applied to rectilinear grided dot samples with different grid sizes (distance between adjacent dots). Data is collected with the transducer scanned in a zigzag raster pattern. Quantitatively, the CNR and ΔBAI values are assessed to evaluate the image quality versus the changing spatial interval between dots. At a given operating frequency and a fixed spatial grid size, the CNR and ΔBAI value degrade as a function of the scanning step size on each dimension. Not only the scanning step size, but also the ultrasound beam spot size affect the spatial sampling resolution in the BAI imaging technique for defect detection. [Work supported by the C‐FAR program, University of Illinois.]
Journal of Nondestructive Evaluation, 2000
The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Tra... more The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Trans. UFFC, 45:30 (1998)] has demonstrated sensitive detection of subwavelength channel defects (38-m diameter reliably and 6-m diameter occasionally) in flexible 220-m-thick food package seals (17.3 MHz, Ϸ 86 m). However, the underlying subwavelength defect detection mechanism is poorly understood. In this contribution, a theoretical modeling study was undertaken to elucidate the mechanism. The subwavelength diameter channel was fused in-between two plastic package films by applying heat from one side of the films. The sample cross-section microstructure was characterized from both optical and acoustic images. The cross-section impedance profiles along sample thickness dimension were determined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. Transient finite-element heat conduction analysis and impedance profiles of multiple-sealed package samples showed that the single-sided heating process caused an asymmetric impedance profile. A generalized impedance model was proposed based on these observations. An efficient two-dimensional simulation tool using a finite-difference time-domain method and the perfectly matched layer numerically evaluated the defect detection behavior of the radio-frequency (rf) echo waveforms. The normalized correlation coefficients between the simulated and the measured rf echo waveforms were greater than 95% for this generalized model, which suggested the validity of the proposed impedance model.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000
The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique has been ... more The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique has been developed to inspect the seal integrity of hermetically sealed, flexible food packages. With a focused 17.3-MHz transducer acquiring radio frequency (RF) echo data in a static rectilinear stop-and-go pattern, this technique was able to reliably detect channel defects as small as 38 m in diameter and occasionally detect 6-m-diameter channels. This contribution presents our experimental spatial sampling study of the BAI-mode imaging technique with a continuous zigzag scanning protocol that simulates a real-time production line inspection method in continuous motion. Two transducers (f/2 17.3 MHz and f/3 20.3 MHz) were used to acquire RF echo data in a zigzag raster pattern from plastic film samples bearing rectilinear point reflector arrays of varying grid spacings. The average BAI-value difference (∆BAI) between defective and intact regions and the contrast-to-noise ratio (CNR) were used to assess image quality as a function of three spatial sampling variables: transducer spatial scanning step size, array sample grid spacing, and transducer ;6-dB pulse-echo focal beam spot size. For a given grid size, the ∆BAI and CNR degraded as scanning step size in each spatial dimension increased. There is an engineering trade-off between the BAImode image quality and the transducer spatial sampling. The optimal spatial sampling step size has been identified to be between one and two times the ;6-dB pulse-echo focal beam lateral diameter.
This animal study addresses the treatment efficacy of the MR-guided thermal ablation technique an... more This animal study addresses the treatment efficacy of the MR-guided thermal ablation technique and temperature monitoring in rabbit tumors. Specifically, the relationship between the thermal dose coverage in the tumors and the rabbit survival rate was investigated. Two groups of rabbits (14 in back tumor group and 12 in thigh tumor group) were treated with the ExAblate-2000 MR-guided focused ultrasound
ABSTRACT Current, minimally invasive, treatments for cardiac arrhythmia use a transvenous radio-f... more ABSTRACT Current, minimally invasive, treatments for cardiac arrhythmia use a transvenous radio-frequency (RF) catheter to ablate the malfunctioning cardiac muscle regions. The paper proposes a noninvasive transesophageal cardiac thermal ablation using focused ultrasound. A planar phased array (1 MHz, 60×10 mm2, 0.525 mm element center-to-center distance, 2280 elements) was put in the esophagus. Using electronic beam steering, a matrix of 5×3×5 foci in the cardiac muscle was defined in three planes parallel to the transducer surface at short, medium and long (20, 40 and 60 mm) radial ranges and different steering angles. The transmitted ultrasound pressure distribution in a volume of 20×20×20 mm3 centered at each focus was calculated using a multilayer acoustic wave transmission model. The thermal lesions due to the acoustic energy absorption in cardiac muscle were simulated using the bioheat transfer equation. For short, medium and long (1-, 10- and 20-second) sonications, the acoustic powers needed to achieve 60°C and 70°C peak temperatures in the cardiac muscle were 89-725, 25-125, 20-86 W and 128-1040, 36-179, 28-123 W, respectively. The simulated tissue lesion (thermal dose >240 min at 43°C) lengths at these foci were 2-10, 5-12, 6-14 mm and 3-13, 7-15, 9-17 mm, respectively. The lesion widths were 2-8, 3-10, 4-11 mm and 3-11, 4-12, 5-13 mm, respectively. The simulations show that noninvasive transesophageal cardiac ablation with a planar phased ultrasound array is feasible.