The changes in acoustic attenuation due to in vitro heating.
The effects of heat-generated changes on the attenuation of ultrasound (US) by porcine liver tissue have been studied over a frequency range of 2.0 to 5.0 MHz. Samples of fresh tissue, 4- to 5-mm thick, were pressurized and cooled before measurement. The insertion loss was measured at room temperature, using a broadband 3.5-MHz transducer of focal length 10 cm, employing a pulse-reflection technique. Fourier analysis of the results gave the frequency-dependence of the insertion loss. Samples were then heated in a water bath to a temperature in the range of 40 to 80 degrees C, for between 30 and 500 s. The insertion loss was then re-measured at room temperature. The frequency-dependence of the change in insertion loss, expressed as a coefficient, in dB/cm, was fitted by linear regression, from which the attenuation change at 3.5 MHz was determined. This change was attributed to protein coagulation. Increases of up to 2.4 dB/cm, (80 degrees C, 300 s) were found. The averaged data were fitted to a single step exponential model, resulting in a time constant on the order of 118 +/- 5 s, and an asymptotic limit to the increase of attenuation coefficient of 2.67 +/- 0.5 dB/cm.
Clarke
R L
RL
Physics Department, College of Natural Sciences, Carleton University, Ottawa, Ontario, Canada. clarke@physics.carleton.ca
Bush
N L
NL
Ter Haar
G R
GR
D000818:Animals; D006358:Hot Temperature; D066298:In Vitro Techniques; D008099:Liver / Q000000981:diagnostic imaging*; D019060:Minimally Invasive Surgical Procedures; D011506:Proteins / Q000378:metabolism; D013048:Specimen Handling; D013552:Swine; D013997:Time Factors; D014464:Ultrasonic Therapy / Q000009:adverse effects*; D014463:Ultrasonography
D011506:Proteins