Ultrasound-induced heating in a foetal skull bone phantom and its dependence on beam width and perfusion.
The cooling effect of single and multiple perfusing channels has been measured in a model of human foetal skull bone heated by wide and narrow beams of simulated pulsed spectral Doppler ultrasound (US). A focussed transducer operating with a centre frequency of 3.5 MHz, that emitted pulses of 5.7 micros duration with a repetition frequency of 8 kHz, was used. This produced a beam of power 100 +/- 2 mW with -6 dB diameters of 3.1 mm and 7.8 mm at 9 cm and 6 cm, respectively, from the transducer face. Arterial perfusion was simulated by allowing distilled water to flow in a large single channel or a grid of fine channels near the heated bone target. This study has established that: 1. perfusion-induced cooling is significantly enhanced when the bone phantom is heated by a wide rather than a narrow beam; 2. irrespective of the US beam width, a grid of small channels is more effective in cooling a heated bone target than a single larger diameter channel with the same volume flow rate; 3. the measured temperature rise and rate of temperature rise support the prediction of inverse proportionality to the US beam width; and 4. the perfusion time constants determined in our phantom model are 2 to 30 times larger than that assumed for the thermal index (TIB) algorithm.
Vella
Gilbert J
GJ
School of Biomedical Sciences, The University of Sydney, Sydney, Lidcombe NSW, Australia. G.Vella@fhs.usyd.edu.au
Humphrey
Victor F
VF
Duck
Francis A
FA
Barnett
Stanley B
SB
D000465:Algorithms; D001833:Body Temperature Regulation; D001921:Brain / Q000196:embryology; D002560:Cerebrovascular Circulation; D006358:Hot Temperature; D006801:Humans; D019047:Phantoms, Imaging; D012886:Skull / Q000000981:diagnostic imaging* / Q000196:embryology; D013696:Temperature; D014159:Transducers; D018617:Ultrasonography, Doppler, Pulsed / Q000379:methods; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods*; D016216:Ultrasonography, Prenatal / Q000379:methods*