Hidehiko Sasaki

Ultrasonic tissue characterization of infarcted myocardium by scanning acoustic microscopy

The purpose of this study was to ultrasonically characterize infarcted human myocardial tissue at the microscopic level by scanning acoustic microscopy. Infarcted myocardial specimens from ten cases with acute myocardial infarction were studied. Specimens were formalin fixed, paraffin embedded and sectioned to 10-micron thickness. A specially developed scanning acoustic microscope system, operating in the 100- to 200-MHz ultrasound frequency range, was used for the measurements. The values of the attenuation constant were 0.94 +/- 0.04 dB/mm/MHz in normal myocardium, 0.71 +/- 0.12 dB/mm/MHz in degenerated myocardium, 0.88 +/- 0.47 dB/mm/MHz in granulation tissue and 1.75 +/- 0.11 dB/mm/MHz in fibrosis. The values of sound speed were 1620.2 +/- 8.2 m/s in normal myocardium, 1572.4 +/- 10.6 m/s in degenerated myocardium, 1590.2 +/- 32.5 m/s in granulation tissue and 1690.3 +/- 9.1 m/s in fibrosis. The ultrasonic properties of the diseased myocardium at the microscopic level will provide important information for ultrasonic tissue characterization at the macroscopic level.

ACOUSTIC PROPERTIES OF ATHEROSCLEROSIS OF HUMAN AORTA OBTAINED WITH HIGH-FREQUENCY ULTRASOUND

The ultrasonic properties of the tissue elements in the aorta were measured using a scanning acoustic microscope (SAM). Twelve autopsied aortas were formalin-fixed, frozen and sectioned at 10 microm thickness and mounted on glass slides for SAM investigation. A specially developed SAM system operating in the frequency range of 100-200 MHz was employed, and color-coded images of the two-dimensional (2-D) distributions of attenuation and sound speed were displayed. The region-of-interest (ROI) for attenuation and sound speed measurements was determined by comparison of optical and acoustic images. The average value of the slope of attenuation was 0.61 dB/mm/MHz and the sound speed was 1568 m/s in the normal intima; 2.5 dB/mm/MHz, 1760 m/s in the calcificated lesion; 1.7 dB/mm/MHz and 1677 m/s in the fibrosis; and 0.34 dB/mm/MHz, 1526 m/s in the fatty material, respectively. Acoustic microscopy provides the basic data for understanding the IVUS imaging of atherosclerosis, as well as on the pathological features of atherosclerosis.

Ultrasonic Tissue Characterization of Atherosclerosis by a Speed-of-Sound Microscanning System

We have been developing a scanning acoustic microscope (SAM) system for medicine and biology featuring quantitative measurement of ultrasonic parameters of soft tissues. In the present study, we propose a new concept sound speed microscopy that can measure the thickness and speed of sound in the tissue using fast Fourier transform of a single pulsed wave instead of burst waves used in conventional SAM systems. Two coronary arteries were frozen and sectioned approximately 10 mum in thickness. They were mounted on glass slides without cover slips. The scanning time of a frame with 300 X 300 pixels was 90 s and two- dimensional distribution of speed of sound was obtained. The speed of sound was 1680 plusmn 30 m/s in the thickened intima with collagen fiber, 1520 plusmn 8 m/s in the lipid deposition underlying the fibrous cap, and 1810 plusmn 25 m/s in a calcified lesion in the intima. These basic measurements will help in the understanding of echo intensity and pattern in intravascular ultrasound images.

Application of scanning acoustic microscopy for assessing stress distribution in atherosclerotic plaque.

AbstractScanning acoustic microscopy (SAM) was equipped to assess the acoustic properties of normal and atherosclerotic coronary arteries. The SAM image in the atherosclerotic lesion clearly demonstrated that the sound speed was higher than that in the normal intima, and that the variation of elasticity was found within the fibrous cap of the plaque. Youngs elastic modulus of each region was calculated and the finite element analysis was applied to derive the stress distribution in these arterial walls. In a case of normal coronary artery, the stress was dominant in the intima and the distribution was rather homogeneous and in a case of atherosclerosis, high stress was concentrated to the relatively soft lesion in the fibrous cap overlying lipid pool. SAM provides information on the physical properties, which cannot be obtained by the optical microscope. The results would help in understanding the pathological features of atherosclerosis.

Influence of tissue preparation on the high-frequency acoustic properties of normal kidney tissue

The influence of various tissue preparations on the acoustic properties of normal kidney tissue at high frequencies was investigated. Eight surgically excised normal kidney tissue specimens were classified into three groups: (i) fresh, frozen section, (ii) formalin-fixed, frozen section and (iii) formalin-fixed, paraffin section. Scanning acoustic microscopy operating in the frequency range of 100-200 MHz was used to display the two-dimensional distribution of attenuation constant and sound speed. Our results indicate that (i) there is no significant variation in both acoustic parameters between the three tissue groups, (ii) fixation by 10% formalin produces no significant change in the acoustic parameters, (iii) in fat-free tissue regions, the acoustic parameters are independent of preparation method and (iv) frozen sections must be used to assess the acoustic parameters in fat-rich tissues.

Visualization of human umbilical vein endothelial cells by acoustic microscopy

The morphology and acoustic properties of the human umbilical vein endothelial cells (HUVECs) were evaluated using a scanning acoustic microscope system. HUVECs were cultured for 4 days and exposed to the endotoxin for 4 h. The frequency of the scanning acoustic microscope was variable between 100 and 210 MHz. By changing the measuring frequency, ultrasonic amplitude and phase were measured and the quantitative value of attenuation was calculated. Before and after endotoxin stimuli, HUVECs were observed by scanning acoustic microscopy and the attenuation was measured. The acoustic images were successfully obtained to identify the outer shape of the HUVEC and the location of the nucleus in the cell. The attenuation of the nucleus is higher than that of the cytoplasm. The attenuation of the cytoplasm was increased and became inhomogeneous after endotoxin exposure. This finding would be related to the change of F-actin filaments, which is the main component of the cytoskeleton. Scanning acoustic microscopy is useful for assessing the cellular viscoelastic properties since it can detect both the morphological and acoustic changes without contacting the cellular surface.

Ultrasonic Tissue Characterization of Renal Cell Carcinoma Tissue

The purpose of this study was to characterize renal cell carcinoma tissue by the measurement of microacoustic properties. A scanning acoustic microscope system operating in the frequency range of 100-200 MHz was employed and the attenuation constant and sound speed were measured on the two-dimensional distribution. The values of attenuation constant and sound speed were lower in both kinds of cancer cells than those in normal kidney, although a significant difference was not found between the clear cell and granular cell. Also, both acoustic parameters of cancer cells were significantly lower than those in hemorrhage and fibrosis. These data suggest that the elasticity of renal cell carcinoma tissue may be lower than that of normal kidney. Moreover, the high intensity echo in clinical echography may be related to the heterogeneity of the microacoustic field in the carcinoma tissue.

Influence of tissue preparation on the acoustic properties of tissue sections at high frequencies

The purpose of the present study was to clarify the influence of tissue preparation on the high-frequency acoustic properties by comparing the acoustic properties of the formalin-fixed, paraffin-embedded, deparaffinized sections and formalin-fixed, frozen sections for two types of fat-containing renal cancer and fat-free renal oncocytoma using a SAM. There was no significant difference for the sound speed among the clear cell, granular cell renal cancer and oncocytoma in either groups, but the attenuation constant was significantly higher for the frozen than for that of the paraffin section in fat-containing renal cancer. In fat-free oncocytoma, there was no significant difference for the attenuation constant in either group. The data suggest that the fat component, which had been eluted by paraffinization, is stored and the true acoustic properties of the tissue can be measured in frozen section.

High Frequency Acoustic Properties of Tumor Tissue

Ultrasonic tissue characterization of tumor tissue is important for two reasons; first that the acoustic parameters provide the physical mechanical properties not determinable by for example, optical microscopy, and second that such data provides information for understanding echographic imaging.

CHARACTERIZATION OF RENAL ANGIOMYOLIPOMA BY SCANNING ACOUSTIC MICROSCOPY

A scanning acoustic microscope system was used to differentiate renal angiomyolipoma from renal cell carcinoma. The ultrasonic frequency used ranged from 100 to 200 MHz, and the attenuation constant and sound speed were measured on a two‐dimensional distribution. The sound speed was significantly lower for lipoma cells than for vessels, smooth muscle fibres, clear cell renal cancer or granular cell renal cancer. The attenuation constant was significantly lower for lipoma cells than for vessels or clear cells. Both acoustic parameters for smooth muscle fibres were significantly lower than for vessels. The heterogeneity of the microacoustic field in renal angiomyolipoma is closely related to the high intensity echo observed on clinical echography. Renal angiomyolipoma and renal cell carcinoma can thus be distinguished by acoustic examination.