title: Ultrasonic heating of the brain of the fetal sheep in utero.
abstract: The fetal sheep was used as a model to determine the extent of ultrasound-induced heating of brain tissue in procedures involving pulsed Doppler examination of fetal intracranial arteries. Temperature measurements were recorded in late-gestation fetuses insonated in utero. The centre frequency was 3.5 MHz and a pulse repetition rate of 6 to 10 kHz produced a power output of 0.6 or 2 W. The brain was insonated in the near field of a focussed beam where the -6-dB beam width was 1.7 cm for the 0.6-W transducers and 1.2 cm for the 2-W transducers. Mean (standard error) maximal temperature increases of 3.0 degrees C (0.3) and 12.5 degrees C (1.3), respectively, were recorded in dead fetuses. The mean values obtained in normally perfused living fetuses were lower by 43% and 30%, respectively, showing that vascular perfusion substantially limited ultrasonic heating in sheep fetal brain tissue. There were no changes in blood flow to the heated brain tissue as measured using radiolabelled microspheres.
authors.affiliation: Department of Obstetrics and Gynaecology, National Women's Hospital, Auckland, New Zealand.
authors.forename: P M
authors.initials: PM
authors.lastname: Duggan
authors.forename: G C
authors.initials: GC
authors.lastname: Liggins
authors.forename: S B
authors.initials: SB
authors.lastname: Barnett
mesh_terms: D000818:Animals; D001158:Arteries / Q000000981:diagnostic imaging; D001831:Body Temperature; D001921:Brain / Q000098:blood supply / Q000196:embryology*; D002540:Cerebral Cortex / Q000098:blood supply / Q000000981:diagnostic imaging / Q000196:embryology; D002560:Cerebrovascular Circulation; D003037:Cobalt Radioisotopes; D004453:Echoencephalography / Q000295:instrumentation; D005260:Female; D005313:Fetal Death; D005865:Gestational Age; D006358:Hot Temperature; D008863:Microspheres; D011247:Pregnancy; D012756:Sheep; D012886:Skull / Q000098:blood supply / Q000000981:diagnostic imaging / Q000196:embryology; D013821:Thermometers; D014159:Transducers; D018617:Ultrasonography, Doppler, Pulsed / Q000295:instrumentation; D016216:Ultrasonography, Prenatal / Q000295:instrumentation
chemical_list: D003037:Cobalt Radioisotopes