title: The cooling effect of liquid flow on the focussed ultrasound-induced heating in a simulated foetal brain.
abstract: There is a need to investigate the thermal effects of diagnostic ultrasound (US) to assist the development of appropriate safety guidelines for obstetric use. The cooling effect of a single liquid flow channel was measured in a model of human foetal brain and skull bone heated by a focussed beam of simulated pulsed spectral Doppler US. Insonation conditions were 5.7 micros pulses, repeated at 8 kHz from a focussed transducer operating with a centre frequency of 3.5 MHz, producing a beam of -6 dB diameter of 3.1 mm at the focus and power outputs of up to 255 +/- 5 mW. Brain perfusion was simulated by allowing distilled water to flow at various rates in a 2 mm diameter wall-less channel in the brain soft tissue phantom material. This study established that the cooling effect of the flowing water; 1. was independent of the acoustic source power, 2. was more effective close to the flow channel, for example, there was a marked cooling at a distance of 1 mm and negligible cooling at a distance of 3 mm from the channel; and 3. initially increased at low flow rates, but further increase above normal perfusion had very little effect.
authors.affiliation: School of Biomedical Sciences, The University of Sydney, Sydney, Australia. G.Vella@fhs.usyd.edu.au
authors.forename: Gilbert J
authors.initials: GJ
authors.lastname: Vella
authors.forename: Victor F
authors.initials: VF
authors.lastname: Humphrey
authors.forename: Francis A
authors.initials: FA
authors.lastname: Duck
authors.forename: Stanley B
authors.initials: SB
authors.lastname: Barnett
mesh_terms: D001921:Brain / Q000196:embryology*; D002560:Cerebrovascular Circulation; D004453:Echoencephalography / Q000009:adverse effects*; D005260:Female; D005315:Fetal Diseases / Q000209:etiology / Q000503:physiopathology; D005334:Fever / Q000209:etiology* / Q000503:physiopathology; D006358:Hot Temperature; D006801:Humans; D019047:Phantoms, Imaging; D011247:Pregnancy; D012886:Skull / Q000000981:diagnostic imaging / Q000196:embryology; D013696:Temperature; D016216:Ultrasonography, Prenatal / Q000009:adverse effects*