RESUMO
Objective To evaluate the influence of Circle of Willis on intravascular hypothermia. Methods A patient-specific model of the Circle of Willis was constructed based on the CT images and the in vitro perfusion experiment with cold water for 20 ℃ was performed. The water was injected from right intracarotid artery (ICA) to the area of middle cerebral artery (MCA) at the flow rate of 30 mL/min and made the cooling period last 15 min. The cooling and rewarming characteristics in the phantom and fluid around MCA were investigated using thermocouples arranged at 27 and 1 spatial locations. The areas distributed with cold water were further visualized using the dyed solution. Results The cold water from right ICA was mainly distributed to right anterior cerebral artery (ACA), MCA, and posterior communicating artery (PCoA), while only a little part of the water could possibly pass through anterior communicating artery (ACoA) to the left ACA. The nearer the locations to the area with cold water, the faster cooling down and also faster temperature recovery rate would be obtained. Moreover, the phantom temperature distributions were asymmetric around MCA due to the complicated bifurcation structures in this area. Conclusions This physical model is useful for investigating the influence of vasculature on endovascular hypothermia and applicable in designing patient-specific hypothermia therapy.
RESUMO
Objective To investigate the cooling effect of blood flow on living tissue heating. MethodThe ultrasonic tissue phantom with a U-tube was used to simulate the living tissue with counter-current vessels. The distilled water with constant temperature (37.5 °C) was pumped into the phantom through the U-tube. The phantom was then immersed in another water bath and heated from 37.5 °C to 43.5 °C with a constant heating rate in order to simulate the environment of hyperthermia. Meanwhile, 46 thermocouples were employed to measure the temperatures of liquid flow, tube wall and the phantom. Finally, the experimental results of the temperature distribution were visualized by AVS (Advanced Visual System) software. ResultsWith the increase of flow velocity, the temperature of tissue was reduced, especially in the area surrounded by the U-tube. Moreover, the temperatures in the U tube bounded area reduced more significantly when the Reynolds number varied from 50 to 130. ConclusionsThis perfusion phantom experiment was successful to simulate the influences of the counter-current flow on the characteristics of the heat transfer. It showed that because of the existence of the counter-current vessels, the cooling effect of internal tissue surrounded by U-shaped tube was more evident.