Ultrasonic volume backscatter by postmortem human liver was investigated in the 1 to 5 MHz frequency range. Representative values of the backscatter coefficient, its range, and frequency dependence were determined. The backscatter level correlated significantly with protein content in normal livers and with lipid content in abnormal fatty livers. The latter suggests the possible development of a simple, noninvasive, quantitative test for fatty infiltration of the liver.
Various ultrasonic properties of whitefish (Coregonus dupeaformis) tissues have been determined. The sound velocity, impedance, and absorption were measured at 22°C with pulse echo techniques for the frequencies of 1, 2, 3, 7, and 11 MHz. The average impedance and absorption of fresh whitefish myomere with a fat content of approximately 8% were 1.634 × 105 cgs units and 0.7 dB/cm/MHz, respectively. No significant velocity or absorption anisotropy was observed for the muscle tissues. The effects of freezing on velocity and absorption were investigated. The mean velocity in thawed flesh was only 0.8% higher than in fresh flesh, but increases up to 100% or more were noted in the absorption. This increase depended on the rate at which freezing proceeded; a longer freezing period generally resulted in greater absorption.
The three-dimensional distribution of Triaenophorus infection in the whitefish (Coregonus clupeaformis) body and the ultrasonic echos received from the parasite cysts are studied in relation to the problem of detecting the parasites with ultrasound. It is shown that ultrasonic scanning of only 15% of the total surface area of a whitefish is required to illuminate (on the average) 70% of the total number of cysts in the body. As a result the search effort required for effective ultrasonic parasite detection can be greatly reduced. A considerably larger ratio of infection (3:2) for the right and left sides of the body is observed than has been previously reported. It is also shown that in the epaxial muscles a parasite is much more likely to be encysted near the surface than deep inside the flesh. Measurements of the ultrasonic cyst-echo durations yielded a distribution with two peaks of different amplitudes indicating a preponderance of spindle-shaped cysts as is actually observed. A negligible percentage of the echos in the distribution are less than 2 μsec in duration; the median width is 6.4 μsec. An outline is given of how these findings can be used to reduce the error rate in an automatic detection system. The paper concludes with a brief discussion of the effects of the transducer aperture on the latter distribution.
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