Flow dependence of 2-D temperature distributions induced in the perfused canine kidney by ultrasound.
The influence of perfusate flow rate on the two-dimensional (2-D) temperature distributions induced by hyperthermia in the canine kidney was evaluated. Localized hyperthermia was induced by ultrasound (frequency 2.040 MHz, transducer diameter 6.7 cm) in the ex-vivo perfused kidney. Temperatures were mapped using shielded copper/constantan thermocouple sensors. The 2-D temperature distribution of the kidney was obtained by pulling these sensors through a planar array of eight stainless-steel trocars inserted along its longitudinal axis. The perfusion system allowed for the control of internal/external organ temperature and type of perfusate, and it simulated vasodilation and vasoconstriction by changing the arterial volume flow rate. The temperature data obtained at flow rates ranging from 0 to 570 ml/min and power levels from 0 to 150 W showed that acoustic power densities in excess of 1.5 W/cm2 were required to maintain therapeutic temperatures in this system. Contour maps for characterizing the 2-D temperature distributions induced in this system were analysed with the introduction of a quantitative measure based on the area within a given isotherm. They show the effects of tissue heterogeneity, flow rate, and non-uniform power deposition. Time constants computed from the exponentially decaying temperatures measured following power off ranged from 5 to 555 s. These findings provide a basis for comparison with temperature measurements being acquired in the in-vivo kidney system. Information acquired from this system may facilitate the process of developing tissue-equivalent dynamic phantoms for ultrasound-induced hyperthermia. The ex-vivo model presented in this paper might be used to study the performance of alternative heating applicators, the effect of haematocrit, blood viscosity, and the use of vasoactive drugs.
Prionas
S D
SD
Department of Radiation Oncology, Stanford University School of Medicine, CA 94305.
Raftery
K A
KA
Edmonds
P D
PD
Constantinou
C E
CE
D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D001831:Body Temperature; D003198:Computer Simulation; D004285:Dogs; D005069:Evaluation Studies as Topic; D066298:In Vitro Techniques; D007668:Kidney / Q000502:physiology*; D010477:Perfusion; D012079:Renal Circulation; D014464:Ultrasonic Therapy / Q000295:instrumentation / Q000379:methods