Ultrasound in Med. & BioL Vol. 17, No. 7, pp. 709-714, 1991 0301-5629/91 $3.00 + .00 Printed in the U.S.A. ~e> 1991 Pergamon Press plc OOriginal Contribution THE ULTRASONIC PROPERTIES OF GASTRIC CANCER TISSUES OBTAINED WITH A SCANNING ACOUSTIC MICROSCOPE SYSTEM YOSHIFUMI SAIJO, MOTONAO TANAKA, HIROAKI OKAWAI and FLOYD DUNN* Department of Medical Engineering and Cardiology, Research Institute for Chest Diseases and Cancer, Tohoku University, Sendai 980, Japan and *Bioacoustics Research Laboratory, University of Illinois, Urbana, IL 61801, USA (Received 31 August 1990; in final form 15 March 1991) Abstract--A newly developed scanning acoustic microscope (SAM) system operating in the frequency range of 100-200 MHz has been employed to measure the attenuation and the sound speed of formalin-fixed specimens of five different types of gastric cancer. Signet-ring cell carcinoma specimens exhibit attenuation constant and sound speed values significantly lower than other types of gastric cancer tissues. Tubular adenocarcinoma specimens exhibit a trend toward higher attenuation and sound speed values as the cell type become differentiated. Our measurements and observations suggest that the ultrasonic properties are influenced by cellular arrangement, intercellular junction and intracellular chemical components. Key Words: Scanning acoustic microscope, Gastric cancer, Attenuation constant, Sound speed, Ultrasonic tissue characterization. INTRODUCTION A specially developed scanning acoustic microscope (SAM) system has been employed to determine quan- titatively the ultrasonic properties of biological tissues (Okawai et al. 1987, 1988). Endoscopic ultrasonogra- phy (EUS), which is also undergoing development (DiMango et al. 1980), has observed a five-layered structure of the alimentary tract and submucosal in- vasions of cancerous tissue not detected by standard endoscopic biopsy. However, EUS cannot be used as yet for the classification of gastric cancer. We report measurements of ultrasonic attenuation and sound speed of five different types of gastric cancer tissues by using the SAM system. We include a discussion of the acoustical properties of gastric cancer tissues. METHODS Twenty surgically excised gastric cancer tissue specimens from twenty patients were studied. The specimens were formalin-fixed, paraffin-embedded and sliced in sections approximately 10 ~m in thick- ness by a microtome. The specimens were mounted on glass slides, but were not covered by cover slips for measurement by the SAM system. The paraffin was removed just before the ultrasonic measurement by graded alcohol methods. 709 The classification of the gastric cancer specimens was done pathologically and found to be papillary ade- nocarcinoma, well-differentiated tubular adenocarci- noma, moderately-differentiated tubular adenocarci- noma, poorly-differentiated adenocarcinoma and sig- net-ring cell carcinoma. The SAM system can display two-dimensional distributions of the attenuation constant and the sound speed at the microscopic level. Figure 1 is a block diagram of the SAM system. The ultrasonic fre- quency is variable over the range of 100-200 MHz and the beam width is 5 ~m (at 200 MHz) to 10 ~m (at 100 MHz) at the focal volume. The ultrasonic beam is transmitted for every 4 #m interval over a 2 mm width with the mechanical scanner. The number of sampling points are 480 in one scanning line, and 480 × 480 points make one frame in 4 s. Figure 2 is a schematic illustration of the rela- tionship between the ultrasonic beam components and the tissue sample. The detected wave amplitude and phase shift are described by the following rela- tions: L = -(10 logy 2 - 10 log y~) d~ = arg( y/y3) Y= yl + Y2710 Ultrasound in Medicine and Biology Volume 17, Number 7, 1991 ULTRASONIC TRANSDUCERS ix I S NER I (3) REFLECTION • , [ TRANSMITTER OSCILLATOR + IJ RF RECEIVER i~ 4 LOCAL OSCILLATOR I r "11 r DETECTOR ~ TM I u J ~r~ PHASE I I ~ : ANPLITUDE ( LINEAR ) A/D CONVERTER I ANPLITUDE ( LOG ) (5) TRAN~ISCION "I I I FREQUENCY ADJUSTER GAIN{I) GAIN (2) J OFFSET xl 4 SGAN CONTROLLERI PULSE GENERATOR I ADDRESS CONTROLLER Ii, ~_~ I_, __ INTERFACE FRANE MBWORY ( B ) i ~, - - (4) F- "1 FP~E MEMORY ( A ) ~ DISPLAY CONTROLLER(A) I I I I I [ OG~PUTER q [DISPLAY CONTROLLER(B) ] I ] I [ ORT COLOR 1 I ORT MONOCHROME I I J U J Fig. 1. Block diagram of the scanning acoustic microscope system. (l) Ultrasonic transducers; (2) mechanical scanner; (3) analogue signal processor; (4) display unit; (5) image processor. where L is the amplitude, @ is the phase shift and y~, Y2, Y3 are the ultrasonic beam components illustrated in Fig. 2. The original image produced in the analogue sig- nal processor can be displayed in the display unit di- rectly. However, these original data do not have val- ues of attenuation constant or sound speed. Figure 3 is the flow chart showing the processing steps for de- termining the attenuation constant and the sound speed. The image processor stores the 16 original images; 11 amplitude images in the range 100-200 JY~ C. I°/ COUPLING y2 MEDIUM J TISSUE GLASS SURFACE Fig. 2. Schematic illustration of the relationship between the ultrasonic components and the tissue sample. (y~, Y2, Y3: ultrasonic beam components; C: specimen sound speed; Cw: sound speed of coupling medium; d: thickness of speci- men). MHz and five phase images in the range 100-140 MHz. The thickness of the specimen is determined from the frequency characteristics of the amplitude and the phase images (Okawai et al. 1987). The attenu- ation constant and the sound speed are calculated by the computer using the equations: Taking original images ] I Storing images Extraction of frequency characteristics of amplitude and phase Comparison of characteristic Patterns I Determination of specimen thickness J Calculation of the images of sound speed and attenuation constant Display in color scales Fig. 3. Flow chart of processing actual values of attenuation constant and sound speed.The ultrasonic properties of gastric Table I. Relationship between color bar scale and values of attenuation constant and sound speed. Color bar Attenuation constant Sound speed scale (dB/mm/MHz) (m/s) Red Magenta Orange Brown Yellow Green Olive green Cyan Royal blue Blue Black