ABSTRACTS, ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION SYHPOSIUM

ABSTRACTS

MONDAY, JUNE 11

1. TISSUE PARAMETERS

1.1 DETECTION OF STRUCTURAL CHANGES IN KIDNEY PARENCHYMA IN PATIENTS WITH DIFFUSE RENAL DISEASE USING QUANTITATIVE ULTRASOUND, Brian S. Garra,l Michael F. Insana,2 Robert F. Wagner,' Haryann Russell,. Kelly A. Thomas,= Steven C. Horii,= Robert K. Zeman,% and Paul M. Silverman,= XDept. of Radiology, Georgetown Univ. Hospital, 3800 Reservoir Rd. NW, Washington, DC 20007, =Dept. of Radiology, University of Kansas Medical Center, Kansas City, KS 66103, 'Center for Devices and Radiologic Health (FDA), Rockville, MD 20857, 'Diagnostic Radiology Dept., Clinical Center, National Institutes of Health, Bethesda, MD 20892.

Diffuse kidney disease is an important clinical problem in which one must frequently resort to renal biopsy for diagnosis. Because of this, we have extended the tissue characterization methods we used in the liver to the evaluation of the renal cortex. So far, 16 normals, 33 patients with various renal diseases, and 17 patients with renal transplants have been studied. Five tissue characterization features (mean scatterer spacing (MSS), specular- diffuse backscatter intensity ratio, specular backscatter intensity variation, frequency dependent attenuation coefficient, avg. backscatter amplitude) were calculated from digitized radiofrequency signals obtained from renal cortex. Avg. correlation length (D), scattering strength, and the integrated backscatter coefficient (IBC) were also computed. The value D, which is a measure of scatterer size, averaged 215 Hm (S.D.= 37 Hm) for normal kidneys and 213 Hm (S.D.= 59) for normally functioning transplants. This agrees well with published values for the size of the glomerulus (avg. 200 pm). The average value of D for patients with decreased renal function was significantly (p < 0.01) higher (D = 253 pm). A similar increase in D was noted for the group of patients with proteinuria whether or not renal function was decreased. The MSS for normal kidneys was 1.31 mm while that for patients with decreased renal function was significantly (p < 0.03) lower at 1.18 mm (S.D. = 0.15). This inverse relation between scatterer size (D) and MSS was also noted for the patients with proteinuria, diabetes mellitus, and abnormally functioning renal transplants. Using D and MSS to detect disease, an area under the ROC curve of 0.80 was achieved. Adding IBC and the specular-diffuse backscatter ratio results in some further improvement in disease detection (Hotelling trace increases from 0.64 to 0.96). The above findings are being correlated with histologic measurements from biopsy samples.

1.2 CORRELATION OF ACOUSTIC PARAMETER ESTIMATES WITH HISTOLOGY, Timothy Hall,= Michael Insana,= Glendon Coxa and James Fishback=, Departments of 'Diagnostic Radiology and aPathology, University of Kansas Medical Center, Kansas City, KS 66103.

Experiments are being performed to determine if changes in histological structures correlate with changes in acoustic parameters. Variations in tissue microstructure are measured using parametric imaging techniques and by analysis of histological slides.

We have previously reported techniques for estimating acoustic parameters which describe the microstructure of a scattering

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ABSTRACTS, ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION SYMPOSIUM

medium. Acoustic parameters such as the scatterer size (or correlation length), the product of their number density times their impedance difference, and the integrated backscatter coefficient were estimated over small volumes and displayed in an image format. When these techniques are used on in vitro tissue samples, we believe we may be obtaining information about the amount and spatial organization of collagen and fat.

We are currently studying the correlation between our parameter estimates for in vitro tissue samples and histological observations from the same regions of interest. For this study, freshly excised surgical and autopsy tissue samples are scanned in normal saline. Several adjacent tissue slices were processed by the pathologist; half of these were stained for collagen, the other half for fat. The size of structures within histological samples and their number density were estimated. Several methods for making this estimation and performing the correlation will be discussed.

This work was supported in part by the West Trust and the Whitaker Foundation.

1.3 IN VIVO TISSUE CHARACTERIZATION FOR ABDOMINAL PARENCHYMAL ORGANS; COMPARISON OF ATTENUATION AND BACKSCATTER ANALYSIS WITH B- SCAN IMAGE ANALYSIS, M. Fein, I. Zuna, U. RBth, G. Layer, G. van Kaick and W.J. Lorenz, Institute of Radiology and Pathophysiology, German Cancer Research Center, Im Neuenheimer Feld 280, D-6900 Heidelberg, FRG.

The advantages and limitations of rf signal analysis versus B- scan image analysis were studied for different examination modalities with in vivo imaging of the liver, spleen, right and left kidney and the psoas muscle. Forty six healthy volunteers were examined. The averaging of at least three images of one patient for each task minimizes the variance due to intra- and interindividual differences, guarantees examination conditions similar to phantom measurements and a close relation to the clinical practice. Our online ultrasonic system with a 3.5 MHZ phased array sector scanner provides the rf signal sampled with 16 MHz and B-scan lines with 2 MHz. For preprocessing, an axial and lateral diffraction correction and the detection of nonergodic structure was done. Eight different methods are used for calculating the attenuation in time and frequency domain. A high sampled envelope was reconstructed by a Hilbert transform and several backscatter characteristics, e.g., the average scatterer spacing were examined. New developed procedures that describe the scatterer contributions were tested. The result for rf signal analysis were compared with our standard calculation of texture parameters. The texture parameters are much more stable than the rf parameters except for 'central frequency' and 'bandwidth', that describe transducer characteristics. Although particularly the first order texture parameters show significant differences between the organs and no difference with one organ, there is no significant difference for, e.g., the average scatterer spacing and most of the rf parameters. The size of the region of interest imitates the in vivo calculation of attenuation to the liver and the spleen. It is remarkable that the attenuation coefficient is not correlated with the mean grey level or other B-scan parameters. The results indicate that B-scan lmage analysis led to reprodicable results in clinical examination and describes the differences of image quality in different organs better than rf signal parameters.

1.4 IN VIVO STUDY OF QUASI REAL-TIME LIVER TISSUE CLASSIFICATION BASED ON POWER SPECTRUM ANALYSIS, M. Lang,l H. Ermert' and L. Heuser=, =Institut far Hoch-und HBchstfrequenztechnik, Ruhr- Universitat Bochum, P.O. Box 10 21 40, D-4630 Bochum 1, FRG and

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