| High intensity focused ultrasound (HIFU) is a noninvasive therapeutic method which use the thermal effect, cavitation, mechanical effect to coagulate disease tissue, and less damage to surrounding normal tissue, it also could shortly open blood brain barrier to deliver drug,depress ironic neurological pain and nerve conduction, and ablate various kind of solid tumor in clinical application recent years. The solid tumor may appear surround the blood vessels in human organ, and the nutrient vessel would grow in carcinoma. The existence of these vessels would lead to clinical trouble that the tumor cell residue during HIFU therapy, the safety and effective of application can not guarantee.ObjectiveIn this study we took tissue mimicking material (TMM) as the research object which acoustic characteristic is similar to human soft tissue, and established experimental modal simulating blood vessel, in order to study the effect of blood vessels at different blood flow rate, location and vessel diameter on HIFU forming focal region, which will provide the theoretical data and reference basis for making clinical treatment schedule before HIFU therapy.MethodsBased on the focused ultrasound thermal dose in clinical practice, the experimental modal conducting the relative invariant of tumor and surrounding vessel to patients body surface was established. Experiments were performed in a degassed water tank under certain parameter condition. The volumes of the color-changing focal region formed by HIFU were measured and the obtained data were statistically analyzed to discuss the effect of blood vessels at different quantify of blood flow, locations and diameter on HIFU focal region and compare to focal region in integral phantom under same irradiation parametersResults(1) Under the same output power and irradiation time condition, with irradiation depth increased, the volume of HIFU forming region in phantom increases at first then decreases (2) The color changed region in TMM first emerged from the focused point, then expanded along acoustic axis as irradiation time increased. The expansion rate towards transducer is much faster than the expansion along acoustic axis, to a certain time the expansion rate was slow, finally the center of HIFU focal region was closer than the aim focal point, which means focal region center forward shift.(3) With decrease distance between vessel and focal point, the effect on focal region induced by blood vessel became more obvious. The longer the distance between the vessel and the focal point, the less effect.(4) When the blood vessel2mm in diameter that was located on the acoustic axis, the effect of the blood vessel located before the focal point was negligible as the distance between the vessel center and focal point was larger than8mm; the effect of vessel was negligible either when the blood vessel that was located on the acoustic axis had a distance of>3mm (behind the focal point).(5) When the blood vessel2mm in diameter was vertical to the acoustic axis, with offset distance increased, the differences between region near vessel and region in integral phantom was smaller under the same irradiation dose. The effect of the blood vessel was negligible when the vertical distance between the vessel center and the acoustic axis was larger than3mm.(6) No matter the location of vessel was before or after the focal point when it was vertical to and on the acoustic axis, the change in long axis was more obvious than in short axis; when blood vessel was vertical to acoustic axis and offset, the long and short axis of HIFU forming lesion was all changed.(7) The center of blood vessel of2mm in diameter and acoustic axis was coaxial, focal region irradiated by the focused ultrasound was not existence surrounding the vessel, it is supposed that the existence of vessel had great influence on HIFU lesion forming.(8) With increased vessel diameter(2,4,6mm), the volume of focal region near vessel became smaller, when the irradiation parameter was same. The longer distance between focal point and vessel, the less effect of vessel of different diameter, while a certain far distance is reached distance,the difference was no longer significant.(9) When the blood vessel located in the HIFU focal region, the vessel divided lesion into two parts, and there was a undamaged region surrounding the vessel wall.(10) When the blood vessel was coincident with focal point even internal with or without blood flow had a significant influence on the HIFU focal region, the lesion volume formatted with blood flow is smaller than that without flow. The blood flow had cooling effect on HIFU focal region, when the blood flow on the basis of certain volume continues to increase, the volume of HIFU focal region did not change significantly.Conclusions1. The longer the relative distance between the blood vessel and focal point, the less influence that vessel had on HIFU focal region, and the effect can be negligible when a relative far distance is reached.2. When the blood vessel located on and vertical to the acoustic axis, the long axis was effected by blood vessel, and there is no obvious change of the short axis. While the blood vessel was vertical to the acoustic axis, the length of long and short axis of HIFU focal region decreased by the influence of vessel.3.Under the condition that HIFU irradiate dose remain constant, with increased vessel diameter, the volume of focal region near vessel became smaller.4.The volume of focal region with blood flow was larger than that without, the blood flow had a certain cooling effect on HIFU focal region; the influence of vessel position is greater than the effect of blood flow. |
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