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Sonographic characterization of fetal lung maturation
ABSTRACTS,
ULTRASONIC
IMAGING
AND TISSUE
CHARACTERIZATION
SYMPOSIUM
obtained using a commercial phased array scanner and a 2.25 MHz transducer. In 6 subjects, images were digitized from stop-frame photographs and in 10 subjects images were obtained directly in digital format from the scanner. Average gray level was measured in a portion of the left ventricular posterior wall in parasternal long-axis images obtained at end-diastole and end-systole. Using anatomical landmarks, similar portions of the posterior wall were analyzed at the two points in the cardiac cycle. RESULTS Acquisition Method Photographic (N=6) Direct Digital (N=lO)
(average
gray
End-Diastole 175 2 5.8 71 + 3.4
We conclude that average gray level dimensional echo images decreases from This confirms previous observations, control in studies of ultrasonic tissue
level
f SEM) End-Systole 167 f 5.1 59 * 2.5
p c.05 c.005
in the posterior left ventricular wall in twoend-diastole to end-systole in normal subjects. and is an important factor to consider and to characterization.
CHARACTERIZATION OF OPHTHALMIC TUMOR TYPE AND ASSESSMENT OF THERAPY EFFECTIVENESS, E. .I. Feleppa', D. J. Coleman2, R. Silverman2, and J. Torpey2, lRiverF. L. Lizzi', side Research Institute, New York, NY 10036, and 2Cornell University Medical College, New York, NY 10021. The type and nature of ophthalmic tumors can be assessed by applying digital signal-processing methods to acquired rf echo signals. These methods have been used to characterize such lesions as malignant melanoma of the choriod or ciliary body, Furthermore, metastatic carcinoma, and hemangioma. these methods can distinguish between melanoma classes such a mixed-epitheloid and spindle-cell tumors. In addition, melanomas monitored using these methods before and during cobalt-plaque therapy show marked changes in parameters; these changes may have value as a means of monitoring the effectiveness of therapy. The parameters used to date are derived primarily from digitally-generated normalized power spectra of rf signals obtained from the focal region of the transducer. Examples of spectrally-derived parameters are: spectral slope (i.e., slope of the best straight-line fit to the spectrum); spectral amplitude (i.e., the amplitude of best straight-line fit) extrapolated to zero freattenuation; various shape-related factors; and the variability of each of quency; In addition, these parameters over the tumor volume. tumor dimensions, particularly tumor height, also appear to be useful when used in conjunction with spectrally-derived parameters for predicting efficacy of therapy. This research is supported by NIH Research Grants EY-01212 and EY-03183. RELIABILITY OF THE IN VIVO DETERMINATION OF TWO ULTRASONIC PARAMETERS OF HUMAN LIVER TISSUE, F. G. SommerT, ??%. Gregory*, L. L. Fellingham', R. A. SternI, M. Nassi3, and Departments of Radiology' and Medicine', Stanford University School A. J. Rossetti3, of Medicine, Stanford, CA 94305, and 3Diasonics Corporation, Milpitas, CA 95035. A study of the reliability and validity of the --in vivo ultrasonic characterizaThree of the subjects were tion of liver tissue was performed for ten subjects. normals, while seven had biopsy-proved diffuse liver disease of varying severity. At fifty rf backscattered waveforms from each of several each data acquisition session, regions of interest in each liver were recorded employing a prototype Diasonics RA-1 scanner. The scanner allowed the acquisition of rf waveforms from tissue regions Of This data interest selected interactively with the aid of realtime ultrasonic images. was then analyzed using a DEC LSI 11/23 computer system; for each session, values of mean scatterer spacing and attenuation were determined for the liver tissue examined. The calculation of mean scatterer spacing was performed via a technique employing and attenuation was computed by means of a auto-correlations of frequency spectra, technique of short-time Fourier analysis. Data acquisition and analysis for each subject were performed a total of eight Two data acquisition sessions per day were performed for each subject on four times. The parameters calculated in the separate days, at approximately weekly intervals. to assess the variabistudy were then subjected to a components of variance analysis, lity of the measurements within days and between days. In general, the results showed a good degree of reliability of measurement of the two ultrasonic parameters. This research made possible by funding from the American Cancer Society, Grant and the Diasonics Corporation. #PDT-188, SONOGRAPHIC CHARACTERIZATION OF FETAL LUNG MATURATION, G. W. Silvers4, and C. R. Meyers3, M. L. Johnson*,
184
G. A. Thiemei, P. L. Carson3,
R. A. Banjavic2, 'Department
of
ABSTRACTS,
ULTRASONIC
IMAGING
AND TISSUE
CHARACTERIZATION
SYMPOSIUM
Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN 37232, 2Departments of Radiology and 4Medicine, University of Colorado Health Sciences Center Denver, CO, and 3Department of Radiology, University of Michigan Hospital, Ann Arbor, MI 48109. Ultrasound evaluation of fetal lung development could be a noninvasive --in utero method for frequent monitoring of the state of pulmonary maturity and predicting when parturition could occur with minimum or no risk of respiratory distress syndrome (RDS) of the newborn. In cases of high-risk obstetrical management in premature labor, this ability may be a particularly useful tool. To pursue this possibility, the lungs and livers of thirteen living fetal lambs were successfully imaged with a modified clinical B-scanner under carefully-controlled conditions; physiologic function tests on the excised lungs determined the state of pulmonary maturity. In eight cases, maturity or immaturity was correctly identified by sonographic criteria. The results were ambiguous in four cases. One case of immature lung was incorrectly identified as mature. In addition, preliminary clinical results will be presented. Mature fetal lung was established by obtaining a mature lecithin/sphingomyelin ratio (LSR) from amniotic fluid or by observing that a newborn did not develop RDS. Immature fetal lung was determined by obtaining an immature LSR or by the development of RDS in the newborn. Ultrasound criteria correctly predicted 15 of 18 mature states and 2 of 2 immature states. Ultrasound criteria predicted immature lungs in two cases where lungs were mature; one ultrasound result was ambigious. SESSION
8:
ATTENUATION
MEASUREMENTS
IN REFLFXTION
II
OPTIMAL ESTIMATION OF CENTER FREQUENCY LOCATION OF A GAUSSIAN SPECTRUM, Roman Kuc, Departments of Electrical Engineering and Diagnostic Radiology, Yale University, New Haven, CT 06520. One currently popular technique for estimating the attenuation characteristics of soft tissue is to observe the downward shift in a Gaussian-shaped power spectrum as a the pulse propagates through tissue [l]. This technique is suitable for both transmission and reflection experiments. The downward shift is usually determined empirically from estimates of the center-frequency locations of spectra calculated from near and far region reflections. In this presentation, five different estimators for the center-frequency location of a distorted Gaussian spectrum are considered: the mean frequency, the inverse of the zero-crossing count, the location of the spectral and two correlation detectors. maximum, Simulation results will be used to compare the accuracy of the different estimators. It is found that the estimator with the minimum variance is obtained from one of the correlation detectors, having a variance four times smaller than the mean frequency estimator. An evaluation of the accuracy vs. complexity for the different estimators will be made. The results described here were made possible through the support of the National Science Foundation, Grant ECS-7919601, and an equipment grant from the Picker Corporation. [l] Kuc, R., Schwartz, M., and Von Micsky, L., in --1976 IEEE Ultrasonic Symposium Proceedings, pp. 44-47 (IEEE cat. no.76 /CH. 1120-SSU). OPTIMIZATION OF SHORT-TIME FOURIER ANALYSIS OF BACKSCATTERED ULTRASOUND SIGNALS FOR ATTENUATION MEASUREMENT, R. A. Stern', F. G. Sommerl, M. Nassi2, 'Department of RadioStanford University School of Medicine, Stanford, CA 94305, and 2Diasonics, l%Y, Inc., Milpitas, CA 95035. It has been shown that when a pulse with Gaussian spectrum propagates in a medium with attenuation proportional to frequency, the propagating pulse remains exactly Gaussian with reduced amplitude, a mean frequency that decreases linearly with depth, and constant variance [l]. It will be shown that when a Gaussian pulse is reflected from a random distribution of scatterers embedded in an attenuating medium, the backscattered signal is not Gaussian. However, by assuming that the propagating pulse is locally stationary, the signal backscattered from a spatially uncorrelated distribution of scatterers will be approximately Gaussian. Theory is presented detailing an optimum method for using short-time Fourier analysis to estimate the attenuation coefficient, optimum in the sense of minimizing the variance of the estimate. The theory predicts optimum values for data segment length, the amount of overlap between segments, and the overall length of data required for a given variance of the estimate. Rf data from phantoms are analyzed and the statistics of the estimates are compared to those predicted by the theory presented. A suggested analysis algorithm involving nonlinear estimation of the parameters of the Gaussian spectrum, correction
185
ULTRASONIC
IMAGING
AND TISSUE
CHARACTERIZATION
SYMPOSIUM
obtained using a commercial phased array scanner and a 2.25 MHz transducer. In 6 subjects, images were digitized from stop-frame photographs and in 10 subjects images were obtained directly in digital format from the scanner. Average gray level was measured in a portion of the left ventricular posterior wall in parasternal long-axis images obtained at end-diastole and end-systole. Using anatomical landmarks, similar portions of the posterior wall were analyzed at the two points in the cardiac cycle. RESULTS Acquisition Method Photographic (N=6) Direct Digital (N=lO)
(average
gray
End-Diastole 175 2 5.8 71 + 3.4
We conclude that average gray level dimensional echo images decreases from This confirms previous observations, control in studies of ultrasonic tissue
level
f SEM) End-Systole 167 f 5.1 59 * 2.5
p c.05 c.005
in the posterior left ventricular wall in twoend-diastole to end-systole in normal subjects. and is an important factor to consider and to characterization.
CHARACTERIZATION OF OPHTHALMIC TUMOR TYPE AND ASSESSMENT OF THERAPY EFFECTIVENESS, E. .I. Feleppa', D. J. Coleman2, R. Silverman2, and J. Torpey2, lRiverF. L. Lizzi', side Research Institute, New York, NY 10036, and 2Cornell University Medical College, New York, NY 10021. The type and nature of ophthalmic tumors can be assessed by applying digital signal-processing methods to acquired rf echo signals. These methods have been used to characterize such lesions as malignant melanoma of the choriod or ciliary body, Furthermore, metastatic carcinoma, and hemangioma. these methods can distinguish between melanoma classes such a mixed-epitheloid and spindle-cell tumors. In addition, melanomas monitored using these methods before and during cobalt-plaque therapy show marked changes in parameters; these changes may have value as a means of monitoring the effectiveness of therapy. The parameters used to date are derived primarily from digitally-generated normalized power spectra of rf signals obtained from the focal region of the transducer. Examples of spectrally-derived parameters are: spectral slope (i.e., slope of the best straight-line fit to the spectrum); spectral amplitude (i.e., the amplitude of best straight-line fit) extrapolated to zero freattenuation; various shape-related factors; and the variability of each of quency; In addition, these parameters over the tumor volume. tumor dimensions, particularly tumor height, also appear to be useful when used in conjunction with spectrally-derived parameters for predicting efficacy of therapy. This research is supported by NIH Research Grants EY-01212 and EY-03183. RELIABILITY OF THE IN VIVO DETERMINATION OF TWO ULTRASONIC PARAMETERS OF HUMAN LIVER TISSUE, F. G. SommerT, ??%. Gregory*, L. L. Fellingham', R. A. SternI, M. Nassi3, and Departments of Radiology' and Medicine', Stanford University School A. J. Rossetti3, of Medicine, Stanford, CA 94305, and 3Diasonics Corporation, Milpitas, CA 95035. A study of the reliability and validity of the --in vivo ultrasonic characterizaThree of the subjects were tion of liver tissue was performed for ten subjects. normals, while seven had biopsy-proved diffuse liver disease of varying severity. At fifty rf backscattered waveforms from each of several each data acquisition session, regions of interest in each liver were recorded employing a prototype Diasonics RA-1 scanner. The scanner allowed the acquisition of rf waveforms from tissue regions Of This data interest selected interactively with the aid of realtime ultrasonic images. was then analyzed using a DEC LSI 11/23 computer system; for each session, values of mean scatterer spacing and attenuation were determined for the liver tissue examined. The calculation of mean scatterer spacing was performed via a technique employing and attenuation was computed by means of a auto-correlations of frequency spectra, technique of short-time Fourier analysis. Data acquisition and analysis for each subject were performed a total of eight Two data acquisition sessions per day were performed for each subject on four times. The parameters calculated in the separate days, at approximately weekly intervals. to assess the variabistudy were then subjected to a components of variance analysis, lity of the measurements within days and between days. In general, the results showed a good degree of reliability of measurement of the two ultrasonic parameters. This research made possible by funding from the American Cancer Society, Grant and the Diasonics Corporation. #PDT-188, SONOGRAPHIC CHARACTERIZATION OF FETAL LUNG MATURATION, G. W. Silvers4, and C. R. Meyers3, M. L. Johnson*,
184
G. A. Thiemei, P. L. Carson3,
R. A. Banjavic2, 'Department
of
ABSTRACTS,
ULTRASONIC
IMAGING
AND TISSUE
CHARACTERIZATION
SYMPOSIUM
Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN 37232, 2Departments of Radiology and 4Medicine, University of Colorado Health Sciences Center Denver, CO, and 3Department of Radiology, University of Michigan Hospital, Ann Arbor, MI 48109. Ultrasound evaluation of fetal lung development could be a noninvasive --in utero method for frequent monitoring of the state of pulmonary maturity and predicting when parturition could occur with minimum or no risk of respiratory distress syndrome (RDS) of the newborn. In cases of high-risk obstetrical management in premature labor, this ability may be a particularly useful tool. To pursue this possibility, the lungs and livers of thirteen living fetal lambs were successfully imaged with a modified clinical B-scanner under carefully-controlled conditions; physiologic function tests on the excised lungs determined the state of pulmonary maturity. In eight cases, maturity or immaturity was correctly identified by sonographic criteria. The results were ambiguous in four cases. One case of immature lung was incorrectly identified as mature. In addition, preliminary clinical results will be presented. Mature fetal lung was established by obtaining a mature lecithin/sphingomyelin ratio (LSR) from amniotic fluid or by observing that a newborn did not develop RDS. Immature fetal lung was determined by obtaining an immature LSR or by the development of RDS in the newborn. Ultrasound criteria correctly predicted 15 of 18 mature states and 2 of 2 immature states. Ultrasound criteria predicted immature lungs in two cases where lungs were mature; one ultrasound result was ambigious. SESSION
8:
ATTENUATION
MEASUREMENTS
IN REFLFXTION
II
OPTIMAL ESTIMATION OF CENTER FREQUENCY LOCATION OF A GAUSSIAN SPECTRUM, Roman Kuc, Departments of Electrical Engineering and Diagnostic Radiology, Yale University, New Haven, CT 06520. One currently popular technique for estimating the attenuation characteristics of soft tissue is to observe the downward shift in a Gaussian-shaped power spectrum as a the pulse propagates through tissue [l]. This technique is suitable for both transmission and reflection experiments. The downward shift is usually determined empirically from estimates of the center-frequency locations of spectra calculated from near and far region reflections. In this presentation, five different estimators for the center-frequency location of a distorted Gaussian spectrum are considered: the mean frequency, the inverse of the zero-crossing count, the location of the spectral and two correlation detectors. maximum, Simulation results will be used to compare the accuracy of the different estimators. It is found that the estimator with the minimum variance is obtained from one of the correlation detectors, having a variance four times smaller than the mean frequency estimator. An evaluation of the accuracy vs. complexity for the different estimators will be made. The results described here were made possible through the support of the National Science Foundation, Grant ECS-7919601, and an equipment grant from the Picker Corporation. [l] Kuc, R., Schwartz, M., and Von Micsky, L., in --1976 IEEE Ultrasonic Symposium Proceedings, pp. 44-47 (IEEE cat. no.76 /CH. 1120-SSU). OPTIMIZATION OF SHORT-TIME FOURIER ANALYSIS OF BACKSCATTERED ULTRASOUND SIGNALS FOR ATTENUATION MEASUREMENT, R. A. Stern', F. G. Sommerl, M. Nassi2, 'Department of RadioStanford University School of Medicine, Stanford, CA 94305, and 2Diasonics, l%Y, Inc., Milpitas, CA 95035. It has been shown that when a pulse with Gaussian spectrum propagates in a medium with attenuation proportional to frequency, the propagating pulse remains exactly Gaussian with reduced amplitude, a mean frequency that decreases linearly with depth, and constant variance [l]. It will be shown that when a Gaussian pulse is reflected from a random distribution of scatterers embedded in an attenuating medium, the backscattered signal is not Gaussian. However, by assuming that the propagating pulse is locally stationary, the signal backscattered from a spatially uncorrelated distribution of scatterers will be approximately Gaussian. Theory is presented detailing an optimum method for using short-time Fourier analysis to estimate the attenuation coefficient, optimum in the sense of minimizing the variance of the estimate. The theory predicts optimum values for data segment length, the amount of overlap between segments, and the overall length of data required for a given variance of the estimate. Rf data from phantoms are analyzed and the statistics of the estimates are compared to those predicted by the theory presented. A suggested analysis algorithm involving nonlinear estimation of the parameters of the Gaussian spectrum, correction
185