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Two-dimensional attenuation imaging for in-vivo human liver
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AXIAL BEAM TRANSLATION (ABT) MEASUREMENT OF ATTENUATION: REDUCTION OF DIFFRACTION ERRORS FOR DIFFERENT MEASUREMENT RANGES, Igancio Cespedes and Jonathan Ophir, Department of Radiology, Ultrasonics Laboratory, University of Texas Medical School, Houston, TX 77030. In recent years, the measurement of the attenuation of tissue has been obscured by the effect of the beam profile of the transducer and by range-dependent phase cancellation problems which cause an inconsistent estimate. The use of ABT to compensate for these effects has been studied by Ophir and Metha [l] and has been shown to be effective at least for a particular range in the far field of an unfocused transducer. In this work, we analyze the effectiveness of ABT for extended ranges spanning 0.5 to 1.6 (radius)2/wavelength. A set of experiments were performed on a water-based gelatin block with graphite scattering particles [2]. Additionally, experiments were performed with a computer simulation program in two dimensions. In general, the ABT case gives estimates which are consistent, i.e., the average of the estimates has small variance for ranges from 0.8 to 1.6 (radius)2/wavelength. In the simulations, the average bias in the ABT case was -2% with standard deviation 1% while in the case with ABT the average bias was -15% with standard deviation 6%. In the ABT experiments, the average bias error is less than -5% with a 2% standard deviation. Similar experiments done without ABT resulted in an average bias error of -8% with a 5% standard deviation. We attribute some of the computed bias error in the experiments to the uncertainty in the independent determination of the true attenuation value. In conclusion, ABT was shown to significantly reduce the bias and improve the precision of the estimate over an extended range. This work was supported by NIH grant number ROlCA38515. [l] J. Ophir and D. Metha, Ultrasonic Imaging a, 139-152 (1988). [2] Courtesy of E. Madsen, University of Wisconsin. TWO-DIMENSIONAL ATTENUATION IMAGING FOR IN-VIVO HUMAN LIVER, K. Murakmi, I. Yamada, A. Shiba, Y. Sugiyama and T. Shimura, Medical Electronics Laboratory, Fujitsu Laboratories Ltd., 1015 Kamikodanaka, Nakahara-ku, Kawasaki 211, Japan. At the last Symposium, we introduced an experimental system for clinically evaluating tissue characterization parameters, and presented an example of a two-dimensional attenuation image of a phantom using conventional SD. We have added an algorithm to obtain a twodimensional attenuation image of the in-vivo human liver. The new algorithm [l], which normalizes the inclination of a log-detected signal with its center frequency, estimates attenuation slopes. A standard deviation of 0.1 dB/MHz/cm was obtained for an ROI of 1.2 cm x 1.2 cm. Our application of this algorithm to a number of normal human livers suggests that measurable regions are restricted due to (1) multiple reflection by the abdominal wall, (2) specular reflection from the diaphragm, and (3) low echo reflection from inside vessels. [l] A. Suzuki, S. Yagi and K. Nakayama, Estimation of local ultrasonic attenuation coefficient by short-term spectral moment analysis of reflected echo, Jon. J. Med. Ultrason 12, No. 6 (1985). CLINICAL ASSESSMENT OF OSTEOPOROTIC BONE FRAGILITY WITH ULTRASOUNDTRANSMISSION VELOCITY, G. Brandenburger,’ L. Avioli: C. Chesnut, III,’ R. Heaney: R. Pass: G. Pratt6 and R. Reeker: ‘Osteo-Technology, Inc., Cambridge, MA, 2Washington University, St. Louis, MO, ‘Univeristy of Washington, Seattle, WA, 4Creighton University, Omaha, NE, ‘Harvard Medical School, Boston, MA and 6Massachussetts Institute of Technology, Cambridge, MA. The theoretical basis for using ultrasound velocity as an indicator of bone fragility is Velocity is directly related to multiple components of bone quality: well established. architecture, material properties and mass density. However, technical obstacles have precluded practical clinical application until recently. A novel approach has been developed for achieving accuracy and reproducibility by anisotropy, overlying soft tissue and multipath overcoming difficulties with inhomogeneity, propagation. Key elements of the design include anatomical site selection, propagation path determination, ultrasound generation and detection, digital signal processing, and apparent velocity estimation.
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ULTRASONIC
IMAGING
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TISSUE
CHARACERIZATION
SYMF’OSIUM
AXIAL BEAM TRANSLATION (ABT) MEASUREMENT OF ATTENUATION: REDUCTION OF DIFFRACTION ERRORS FOR DIFFERENT MEASUREMENT RANGES, Igancio Cespedes and Jonathan Ophir, Department of Radiology, Ultrasonics Laboratory, University of Texas Medical School, Houston, TX 77030. In recent years, the measurement of the attenuation of tissue has been obscured by the effect of the beam profile of the transducer and by range-dependent phase cancellation problems which cause an inconsistent estimate. The use of ABT to compensate for these effects has been studied by Ophir and Metha [l] and has been shown to be effective at least for a particular range in the far field of an unfocused transducer. In this work, we analyze the effectiveness of ABT for extended ranges spanning 0.5 to 1.6 (radius)2/wavelength. A set of experiments were performed on a water-based gelatin block with graphite scattering particles [2]. Additionally, experiments were performed with a computer simulation program in two dimensions. In general, the ABT case gives estimates which are consistent, i.e., the average of the estimates has small variance for ranges from 0.8 to 1.6 (radius)2/wavelength. In the simulations, the average bias in the ABT case was -2% with standard deviation 1% while in the case with ABT the average bias was -15% with standard deviation 6%. In the ABT experiments, the average bias error is less than -5% with a 2% standard deviation. Similar experiments done without ABT resulted in an average bias error of -8% with a 5% standard deviation. We attribute some of the computed bias error in the experiments to the uncertainty in the independent determination of the true attenuation value. In conclusion, ABT was shown to significantly reduce the bias and improve the precision of the estimate over an extended range. This work was supported by NIH grant number ROlCA38515. [l] J. Ophir and D. Metha, Ultrasonic Imaging a, 139-152 (1988). [2] Courtesy of E. Madsen, University of Wisconsin. TWO-DIMENSIONAL ATTENUATION IMAGING FOR IN-VIVO HUMAN LIVER, K. Murakmi, I. Yamada, A. Shiba, Y. Sugiyama and T. Shimura, Medical Electronics Laboratory, Fujitsu Laboratories Ltd., 1015 Kamikodanaka, Nakahara-ku, Kawasaki 211, Japan. At the last Symposium, we introduced an experimental system for clinically evaluating tissue characterization parameters, and presented an example of a two-dimensional attenuation image of a phantom using conventional SD. We have added an algorithm to obtain a twodimensional attenuation image of the in-vivo human liver. The new algorithm [l], which normalizes the inclination of a log-detected signal with its center frequency, estimates attenuation slopes. A standard deviation of 0.1 dB/MHz/cm was obtained for an ROI of 1.2 cm x 1.2 cm. Our application of this algorithm to a number of normal human livers suggests that measurable regions are restricted due to (1) multiple reflection by the abdominal wall, (2) specular reflection from the diaphragm, and (3) low echo reflection from inside vessels. [l] A. Suzuki, S. Yagi and K. Nakayama, Estimation of local ultrasonic attenuation coefficient by short-term spectral moment analysis of reflected echo, Jon. J. Med. Ultrason 12, No. 6 (1985). CLINICAL ASSESSMENT OF OSTEOPOROTIC BONE FRAGILITY WITH ULTRASOUNDTRANSMISSION VELOCITY, G. Brandenburger,’ L. Avioli: C. Chesnut, III,’ R. Heaney: R. Pass: G. Pratt6 and R. Reeker: ‘Osteo-Technology, Inc., Cambridge, MA, 2Washington University, St. Louis, MO, ‘Univeristy of Washington, Seattle, WA, 4Creighton University, Omaha, NE, ‘Harvard Medical School, Boston, MA and 6Massachussetts Institute of Technology, Cambridge, MA. The theoretical basis for using ultrasound velocity as an indicator of bone fragility is Velocity is directly related to multiple components of bone quality: well established. architecture, material properties and mass density. However, technical obstacles have precluded practical clinical application until recently. A novel approach has been developed for achieving accuracy and reproducibility by anisotropy, overlying soft tissue and multipath overcoming difficulties with inhomogeneity, propagation. Key elements of the design include anatomical site selection, propagation path determination, ultrasound generation and detection, digital signal processing, and apparent velocity estimation.
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