蜂屋 弘之, 今田 直樹, 大槻 茂雄, 田中 元直

Hiroyuki HACHIYA, Naoki IMADA, Shigeo OHTSUKI, Motonao TANAKA

東京工業大学精密工学研究所

Precision and Intelligence Laboratory, Tokyo Institute of Technology

キーワード : Tissue characterization, Non-deformable measurement, Sound speed, Rat liver, Frequency-time analysis

Sound speed is an important acoustic parameter for quantitative characterization of living tissues. In this paper, relation between measuring sound speed and density of rat liver tissues are presented. Male Wister rats weighting 200-600 g were used in this experiments. The sound speed was measured by the non-deformable technique based on frequency-time analysis of the pulse response. This method does not require physical contact of ultrasonic probes with living or freshly excised tissue specimens and travel times are estimated using frequency-time analysis of the pulse response to avoid sensitivity to waveform distortion due to tissue inhomogeneity and surface roughness. The rats were divided into a group with 13 normal rats and another group with 6 rats given CCl₄ (0.1 ml/kg)twice a week for 6∼8 weeks by intramuscular injection. In the group given CCl₄, tap water in which phenobarbitone was dissolved at a concentration of 0.5 g/l was the only drinking water available to the rats. The sound speed was measured for 25 points by scanning a 2×2 mm area 0.5 mm intervals. Measurement was performed in 0.9% saline at 37.0±0.2°C of the bath (coupling) medium. The sound speed and the density in 13 normal livers were 1608.3±2.1 m/s and 1.082±0.002 g/cm³. The sound speed and the density in normal livers are very stable and had no relation to body weight and age. In liver tissues of rats given CCl₄ for 6 and 7 weeks, the sound speeds (the density)were 1592.7±2.0 m/s(1.072 g/cm³) and 1584.3±1.9 m/s (1.068 g/cm³) respectively. In liver tissues of 4 rats given CCl₄ for 8 weeks, the values were 1573.3±4.3 m/s and 1.064±0.002 g/cm³, respectively. From the microscopic image of HE stained liver tissues, these rat livers were considered to be fatty liver. It was found that the sound speed and the density in rat liver tissues decrease with the progress of fatty liver.