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Clinical attenuation measurements: Some results and implications
ABSTRACTS, ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION SYMPOSIUM
A COMPARISONOF IMAGES DERIVED FROM THE ENVELX)PEAND INSTANTANEOUS FREQUENCYOF PULSE ECHO SIGNALS: EXPERIMENTAL RESULTS, L.A. Ferrari*, R. Ranalli2 and G. Gopinathan*, lDepartment of Radiological Sciences, University of California at Irvine, Irvine, CA 92717, and 'Philips Ultrasound, Inc., Santa Ana, CA 92704. The pulse echo signal generated with ultrasound imaging systems can be modelled as a random-modulated signal. Using the analytical signal representation, we can define the signal amplitude envelope and phase. The instantaneous frequency is defined by the time derivative of the phase. Traditional ultrasound images are based on the signal amplitude In this and ignore the information contained in the phase of the signal. paper, we compare images generated from the instantaneous frequency with those generated by conventional envelope detection. The instantaneous frequency of the pulse echo signal is obtained from a hardware FM demodulator. Frequency images are formed using modified medical ultrasound B-scanner and sector scanners. The images are stored The envelope-detected images are in conventional digital scan converters. formed using unmodified scanners. Comparisons of grey-scale test objects, point scatterers, resolution targets and human anatomy indicate that in many instances the frequency-derived images provide a better representation of the test object than images derived from the amplitude of the signal. This appears to be true in images of the liver as well (see companion abstract). A COMPARISONOF IMAGES DERIVED FROM THE ENVELOPE AND INSTANTANEOUS FREQUENCY OF PULSE ECHO SIGNALS: LIVER DISEASES, David Aufrichtig , R. Friedenbergl, John Hoefs2, L. Ferraril, S. Lottenberg' and R. Rannalli3, University of California at Irvine, Departments of 'Radiological Sciences and *Gastroenterology, Irvine, CA 92717, and 3Philips Ultrasound, Inc., Santa Ana, CA 92704. Images derived from the phase of A-scan signals are generated using modified medical ultrasound imaging systems (see companion abstract). A preliminary study of amplitude-derived and instantaneous frequency-derived images is presented utilizing human subjects. Imaged tissue states include chronic active and chronic persistent hepatitis, alcohol cirrhosis and garry infiltration. In addition, a number of confirmed normal livers were included in the study. The images were examined for known anatomical structure, morphologic changes due to pathology, homogeneity, echogenicity, consistency, attenuation and other characteristics. A preliminary evaluation of the diagnostic utility of the frequency-derived images will be presented.
SESSION 8:
CLINICAL ATTENUATION MEASUREMENTS
CLINICAL ATTENUATION MEASUREMENTS: SOME RESULTS AND IMPLICATIONS, K.J. Parker' and R.C. Waag', University of Rochester, Departments of 't2 Electrical Engineering and *Radiology, Rochester, NY 14627. An analysis of backscattered ultrasonic echoes has been developed which produces accurate, reproducible values of the magnitude of tissue attenuation at 15 discrete frequencies between 2 and 3 MHz. The frequency dependence of attenuation within the 1 MHz bandwidth can be inferred from these data. Parasagittal abdominal scans of 10 normal males aged 22-41, and of one 13 old with an abnormal liver condition, were obtained using a commercial B-scan imaging instrument. The analysis of attenuation magnitude and frequency dependence was performed on regions of interest
228
ABSTRACTS, ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION SYMPOSIUM
The results of this the right lobe of the liver in each subject. showed that the frequency dependence of attenuation can deviate significantly from the linear-with-frequency increase commonly assumed in soft tissue such as liver. Also, a power law fit of the frequency dependence of attenuation provides a two-variable characterization of tissue type which can be a powerful discriminator of tissue type. Finally, in addition to attenuation measurements, the first-order statistics of backscattered pressure have been studied, as a function of frequency and anatomical location within the liver. The results of this study and implications for attenuation measurements will be presented. This work was supported by a grant from the Whitaker Foundation.
within study
AN ANALYSIS OF ULTRASOUND TISSUE CHARACTERIZATION ALGORITHMS, Peter H. Arger, Ronald L. Arenson, Philip Bergey, Reuben S. Mezrich, Beverly G. Coleman, Marshall C. Mintz and Menahem Nassi, Hospital of the University of Pennsylvania, Philadelphia, PA 19104. Twenty-five normal volunteers and thirty patients with proven liver abnormalities were analyzed using three algorithms for estimation of the attenuation coefficients of normal and abnormal liver tissue. Utilized were short-time Fourier analysis, zero-crossing counting and normalized spectra analysis. The technical problems inherent in large sample volumes needed for A comparison between large and statistical significance was analyzed. small sample volumes was done. Noted was the long time needed both for acquiring the data and transferring the data to obtain a significant number of large sample volumes. Scanning technical problems in obtaining such a sample were noted. This included difficulty in finding a homogeneous large area of the liver without vessels or other structures such as the gall bladder. Seriously ill patients had difficulty with breath holding. The practical aspects of thediffractioncorrection in depth being different for different probes due to the phantom-based standard model was noted. A clinical evaluation of the value of the procedure was done by comparing an averaged attenuation coefficient of all the sample volumes with the variability of attenuation seen by analyzing the individual sample volumes' attenuation. ULTRASONIC ATTENUATION IN LIVER AND SPLEEN, D.E. Robinson, L.S. Wilson anti B. Doust, Ultrasonics Institute, Millers Points, NSW, Australia. During the last three years, we have evaluated a number of processing techniques for the measurement of rf attenuation and its slope as a function of frequency, including that due to Kuc [l] which selects wave packets for analysis and uses a fixed time window scheme. With the line of sight translated and an ensemble of echo signals acquired, the data set when frequency transformed has three dimensions, depth, line number and frequency. The attenuation slope may be expressed as a linear combination of the logarithms of the three-dimensional array of spectral values. Partial summation may be used to display the variation of attenuation with depth or frequency, to estimate the accuracy of the spectral slope, and check such model assumptions as tissue inhomogeneity and linearity with respect to frequency. The system has been used on liver and spleen using data acquired by the Ultrasonic Institute Octoson water coupling echoscope. The results to date show the attenuation in normal liver to be 0.53 + 0.2 dB cm-l MHz-l. Cirrhotic and metastatic livers have attenuation of around 0.7 dB cm-1 MHz-l., while the highest values (around 0.1 dB cm-l MHz-11 have been
229
A COMPARISONOF IMAGES DERIVED FROM THE ENVELX)PEAND INSTANTANEOUS FREQUENCYOF PULSE ECHO SIGNALS: EXPERIMENTAL RESULTS, L.A. Ferrari*, R. Ranalli2 and G. Gopinathan*, lDepartment of Radiological Sciences, University of California at Irvine, Irvine, CA 92717, and 'Philips Ultrasound, Inc., Santa Ana, CA 92704. The pulse echo signal generated with ultrasound imaging systems can be modelled as a random-modulated signal. Using the analytical signal representation, we can define the signal amplitude envelope and phase. The instantaneous frequency is defined by the time derivative of the phase. Traditional ultrasound images are based on the signal amplitude In this and ignore the information contained in the phase of the signal. paper, we compare images generated from the instantaneous frequency with those generated by conventional envelope detection. The instantaneous frequency of the pulse echo signal is obtained from a hardware FM demodulator. Frequency images are formed using modified medical ultrasound B-scanner and sector scanners. The images are stored The envelope-detected images are in conventional digital scan converters. formed using unmodified scanners. Comparisons of grey-scale test objects, point scatterers, resolution targets and human anatomy indicate that in many instances the frequency-derived images provide a better representation of the test object than images derived from the amplitude of the signal. This appears to be true in images of the liver as well (see companion abstract). A COMPARISONOF IMAGES DERIVED FROM THE ENVELOPE AND INSTANTANEOUS FREQUENCY OF PULSE ECHO SIGNALS: LIVER DISEASES, David Aufrichtig , R. Friedenbergl, John Hoefs2, L. Ferraril, S. Lottenberg' and R. Rannalli3, University of California at Irvine, Departments of 'Radiological Sciences and *Gastroenterology, Irvine, CA 92717, and 3Philips Ultrasound, Inc., Santa Ana, CA 92704. Images derived from the phase of A-scan signals are generated using modified medical ultrasound imaging systems (see companion abstract). A preliminary study of amplitude-derived and instantaneous frequency-derived images is presented utilizing human subjects. Imaged tissue states include chronic active and chronic persistent hepatitis, alcohol cirrhosis and garry infiltration. In addition, a number of confirmed normal livers were included in the study. The images were examined for known anatomical structure, morphologic changes due to pathology, homogeneity, echogenicity, consistency, attenuation and other characteristics. A preliminary evaluation of the diagnostic utility of the frequency-derived images will be presented.
SESSION 8:
CLINICAL ATTENUATION MEASUREMENTS
CLINICAL ATTENUATION MEASUREMENTS: SOME RESULTS AND IMPLICATIONS, K.J. Parker' and R.C. Waag', University of Rochester, Departments of 't2 Electrical Engineering and *Radiology, Rochester, NY 14627. An analysis of backscattered ultrasonic echoes has been developed which produces accurate, reproducible values of the magnitude of tissue attenuation at 15 discrete frequencies between 2 and 3 MHz. The frequency dependence of attenuation within the 1 MHz bandwidth can be inferred from these data. Parasagittal abdominal scans of 10 normal males aged 22-41, and of one 13 old with an abnormal liver condition, were obtained using a commercial B-scan imaging instrument. The analysis of attenuation magnitude and frequency dependence was performed on regions of interest
228
ABSTRACTS, ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION SYMPOSIUM
The results of this the right lobe of the liver in each subject. showed that the frequency dependence of attenuation can deviate significantly from the linear-with-frequency increase commonly assumed in soft tissue such as liver. Also, a power law fit of the frequency dependence of attenuation provides a two-variable characterization of tissue type which can be a powerful discriminator of tissue type. Finally, in addition to attenuation measurements, the first-order statistics of backscattered pressure have been studied, as a function of frequency and anatomical location within the liver. The results of this study and implications for attenuation measurements will be presented. This work was supported by a grant from the Whitaker Foundation.
within study
AN ANALYSIS OF ULTRASOUND TISSUE CHARACTERIZATION ALGORITHMS, Peter H. Arger, Ronald L. Arenson, Philip Bergey, Reuben S. Mezrich, Beverly G. Coleman, Marshall C. Mintz and Menahem Nassi, Hospital of the University of Pennsylvania, Philadelphia, PA 19104. Twenty-five normal volunteers and thirty patients with proven liver abnormalities were analyzed using three algorithms for estimation of the attenuation coefficients of normal and abnormal liver tissue. Utilized were short-time Fourier analysis, zero-crossing counting and normalized spectra analysis. The technical problems inherent in large sample volumes needed for A comparison between large and statistical significance was analyzed. small sample volumes was done. Noted was the long time needed both for acquiring the data and transferring the data to obtain a significant number of large sample volumes. Scanning technical problems in obtaining such a sample were noted. This included difficulty in finding a homogeneous large area of the liver without vessels or other structures such as the gall bladder. Seriously ill patients had difficulty with breath holding. The practical aspects of thediffractioncorrection in depth being different for different probes due to the phantom-based standard model was noted. A clinical evaluation of the value of the procedure was done by comparing an averaged attenuation coefficient of all the sample volumes with the variability of attenuation seen by analyzing the individual sample volumes' attenuation. ULTRASONIC ATTENUATION IN LIVER AND SPLEEN, D.E. Robinson, L.S. Wilson anti B. Doust, Ultrasonics Institute, Millers Points, NSW, Australia. During the last three years, we have evaluated a number of processing techniques for the measurement of rf attenuation and its slope as a function of frequency, including that due to Kuc [l] which selects wave packets for analysis and uses a fixed time window scheme. With the line of sight translated and an ensemble of echo signals acquired, the data set when frequency transformed has three dimensions, depth, line number and frequency. The attenuation slope may be expressed as a linear combination of the logarithms of the three-dimensional array of spectral values. Partial summation may be used to display the variation of attenuation with depth or frequency, to estimate the accuracy of the spectral slope, and check such model assumptions as tissue inhomogeneity and linearity with respect to frequency. The system has been used on liver and spleen using data acquired by the Ultrasonic Institute Octoson water coupling echoscope. The results to date show the attenuation in normal liver to be 0.53 + 0.2 dB cm-l MHz-l. Cirrhotic and metastatic livers have attenuation of around 0.7 dB cm-1 MHz-l., while the highest values (around 0.1 dB cm-l MHz-11 have been
229