谷口 信行, 伊東 紘一, 森 博昭

Nobuyuki TANIGUCHI, Kouichi ITOH, Hiroaki MORI

自治医科大学臨床病理学教室

Department of Clinical Pathology, Jichi Medical School

キーワード : Diagnostic ultrasound Frequency dependent attenuation (FDA), Skeletal muscle Acoustic intensity histogram

Frequency dependent attenuation (FDA) of ultrasound in the normal human rectus femoris muscle, and gastrocnemius muscle in vivo were measured by spectral-shift zero-crossing method in axial and sagittal section using annular array 7.5 MHz transducer. This method had been previously developed in our laboratory, and the application to the liver, spleen, breast, and thyroid had been reported as one of the new tools in diagnostic ultrasound for tissue characterization.
FDAs of the rectus femoris muscle at rest (n=30) were mean value of 0.42 with standard deviation of ±0.15 dB/cm/MHz in axial section, and 0.41±0.15 dB/cm/MHz in sagittal section. FDAs of the gastrocnemius muscle at rest (n=40) were 0.42±0.13 dB/cm/MHz in axial section, and 0.39±0.15 dB/cm/MHz in sagittal section. There were no difference in FDAs between the rectus femoris and gastrocnemius muscle in given sections, or axial and sagittal sections in given two muscles. There is no significant difference between FDAs measured by 3.5 MHz transducer and by 7.5 MHz transducer in rectus femoris muscle.
FDAs of the gastrocnemius muscle at contraction were 0.86±0.32 dB/cm/MHz in axial section (n=25), and 0.89±0.36 dB/cm/MHz in sagittal section (n=16). FDAs of the gastrocnemius muscle at stretch were 0.30±0.14 dB/cm/MHz in axial section (n=26), and 0.22±0.13 dB/cm/MHz in sagittal section (n=13). FDA of the gastrocnemius muscle at contraction is significantly higher than FDA at rest, and FDA at stretch is significantly lower than FDA at rest.
Peak histogram levels of the gastrocnemius muscle at contraction were lower than the level at rest in acoustic-intensity histogram. The muscle fibers are thicker at contraction than at rest. Results suggest that reflection counts at the margin between muscle fibers and the perimisium were decreased at contraction.
Attenuation of ultrasound in muscle occurs by scatter, reflection, and absorption. Elevation of FDA probably due to increased absorption in relation to increased muscular denasity at contraction. Because there is no suggestive data of increase in reflection or scatter of ultrasound by histogram analysis.
Measurement of FDA may develop the new application in ultrasonic clinical diagnosis and evaluation of the disease of the skeletal muscles.