In:
The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 86, No. S1 ( 1989-11-01), p. S28-S28
Abstract:
Estimates of temperature increase in soft fetal tissues exposed to medical ultrasound can be made with existing knowledge. However, little knowledge is available to make a resonable estimate of the temperature increase in fetal bone and surrounding tissues during in vivo exposures. An experimental study of the temperature increase measured in vitro in human fetal femurs exposed to 1-MHz, continuous wave ultrasound at 37°C has been conducted. The temperature increase in the femur specimens is measured with a small implanted thermocouple probe. Specimens range in gestational age from 59 to 150 days. The temperature increase measured in a 59-day gestational age specimen at 20 s following the initiation of exposure at 1 W/cm2, for example, was 0.10°C, while the temperature increase for a 108-day specimen with the same exposure conditions was 2.9°C. A temperature increase of 4.0°C was measured in the 108-day specimen for a 60 s exposure at 1 W/cm2. The temperature rise is found to increase linearly with intensity over the range of 0.5 to 10 W/cm2. The initial rate of the temperature increase, evaluated at 0.2 s following initiation of exposure, has also been measured and is found to increase rapidly with gestational age. For example, I−1 dT/dt at 0.2 s measured for the 59-day specimen is 0.06°C/s/(W/cm2), while for the 108-day specimen 0.81°C/s/(W/cm2) was measured. The values of initial temperature increase measured in the fetal femur specimens can be compared to that obtained for soft tissue using the quantity I−1 dT/dt = 2α/ρCρ. For α = 0.05 cm−1, and ρCρ = 3.78 J/°C/cm3, I−1 dT/dt = 0.026°C/s/(W/cm2). The values of I−1 dT/dt measured for the 59- and 108-day gestational age specimens are approximately 2 and 30 times greater than that for soft tissue.
Type of Medium:
Online Resource
ISSN:
0001-4966
,
1520-8524
Language:
English
Publisher:
Acoustical Society of America (ASA)
Publication Date:
1989
detail.hit.zdb_id:
1461063-2
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