| BackgroundThe traditional complete ablation method of High-intensity focused ultrasound(HIFU)for tumors,with the large energy delivery and the long treatment time especially for the larger tumors,treatment,which have increased the risk of treatment complications incidence or adverse reactions.At the margin of the malignant tumors growing with rich blood supply and proliferate actively.If they can be completely ablated on the edge,they are expected to reduce the complications.Some scholars conducted a preliminary discussion on this issue,named “peripheral ablation”,and verified its feasibility in vitro experiments.But these studies all applied continuous wave HIFU.Pulse high-intensity focused ultrasound(PHIFU)uses intermittent energy delivery methods.If it can achieve the same ablation effect as CHIFU,it will further reduce energy delivery and complications incidence.The blood vessels in the target area will shift the focus around the blood vessel or the focal region will be deformed,which will lead to tissue remnants and make the surface ablation edge necrosis incomplete.This study investigated the effect of the angle,position,and diameter of the blood vessel in the target area on the sealing of the marginal necrosis isolation zone when PHIFU was ablated.Provides a reference for the methodology of HIFU therapy.purposeTo explore the effect of the angel between blood vessels and acoustic axis in the target area,position and diameter of the tumor vessels on the sealing of necrosis zones after PHIFU peripheral ablation.method1.Subject: A tissue-like egg white phantom was used.The size(length× width × height)of the phantom was: 13.5 cm × 8 cm × 6 cm.The target size of the PHIFU ablation target was 30 mm × 30 mm × 30 mm.A blood vessel about 30 mm in length was embedded in the edge of the ablation target area.The blood vessels were selected from the thoracic and abdominal aorta of 100 New Zealand white rabbits(Chongqing Medical University Experimental Animal Center).2.Grouping methods: 1)The different angle between blood vessel and acoustic axis groups: Select a rabbit thoracic aorta with a blood vesseldiameter of about 3mm,and angle it to 0°,45°,and 90° according to its angle to the acoustic axis.grouped into B,C and D groups respectively,group A is set as the blank control(each group of ten).2)Groups of different locations of blood vessels in the target : The angle between the blood vessel and acoustic axis is 90°,according the blood vessels distance the ablation top surface are 5mm,15 mm,and 25 mm respectively,and divided into group D1,group D2,and group D3(n=10).3)Different vascular diameter groups in the target area: the angle between vascular and acoustic axes are 90°,and the distance from the ablation top surface is15 mm.According to the diameters of the buried blood vessels were 1mm,2mm,3mm and 4mm,divided into group C1,group C2,group C3,and group C4(n=10).3.Peripheral ablation method: Under the B-ultrasound monitoring,the surface ablation was performed with PHIFU,and the treatment parameters of each group were set the same.The entire target area is divided into 16 treatment depths parallel to each other in the z-axis direction.The interval between the layers is 2mm.The treatment power is 300 W(top layer),250W(middle),and 200 W(bottom layer).Through the B-ultrasound monitoring,The treatment head moved in the three directions of X,Y and Z,Firstly,ablating the top layer,from shallow to deep layer by layer until to the bottom layer.The top layer and the bottom layer were completely covered and ablated,the line spacing was 2 mm,and the middle layer onlyablated the edge,u the edge region was completely irradiated and stopped irradiation.The pulse repetition frequency is 100 Hz,the duty cycle is 50%,and the head movement speed is 3 mm/s.4.Evaluation index: In the course of ablation,the temperature of the target area of the vascular surface is measured and recorded,and the ultrasound image is collected and saved.After the ablation,the phantom was cut step by step for visually observed and photographed for preservation.The diameters of the coagulation necrosis zones were measured for each group and the total volume(V)of each group was calculated and compared.Take irradiated blood vessels for pathological examinationResult1.Effects of the target blood vessels angled with acoustic axis on the peripheral mode scanning with PHIFU ablation: 1)Visual observation:White coagulative necrosis can be formed around groups A and B.Incomplete necrosis can be seen on the deep blood vessels in groups C and D.No necrosis is formed in the central non-irradiated areas of each group;2)Ultrasound observation: A strong echogenic zone can be seen on the edges of the irradiated areas in groups A and B.The echoes in the deep part of the C and D groups showed hypoechoic appearance,while the unirradiated area in the center showed low echo.3)The maximaltemperatures in control group,B,C and D group was(98.60±5.76)?,(98.90±7.09)?,(71.10±13.85)? and(70.20±9.14)?,respectively.Statistical difference was found between control group and C and D group(all P<0.05).4)The total volume in control group,B,C and D group was(40709.70±3193.31)mm3,(40029.02±3580.17)mm3,(34562.59±3883.26)mm3 and(36737.01±3278.68)mm3,respectively,and no statistical difference was found between control group and B group(P>0.05).5)Patological examination showed that the elastic fibers fractured partly and disruption of cell nucleus was seen in C and D group.2.Effects of the target blood vessels,different position on the PHIFU peripheral ablation: 1)At each group center of the unablation area and the area that behind the blood vessels showed no coagulative necrosis formed.Corresponding section on ultrasound image showed low echo while strong echo in the rest peripheral areas.The non-necrotic formation areas behind the blood vessels in group A,group D1,and group D2,be defined as the thermal ablation blind zone.And the maximum longitudinal diameters of the blind zone was(3.34±0.30)mm,(3.2±0.52)mm,(2.94±0.36)mm,respectively.There was no significant difference compared between groups(P>0.05).3.Effects of the target blood vessel,s different diameter on the peripheral mode scanning with PHIFU ablation: 1)Visual observation andultrasound image: Thermal ablation blind spots are visible behind the blood vessels in each group,and the corresponding sectional acoustic image shows low echo.2)The effect of blood vessel,s diameter on the size of the thermal ablation blind zone: The transverse diameters of the blood vessels in the C1,C2,C3,and C4 groups was(1.16±0.3)mm,(1.99±0.35)mm,(3.10±0.3)mm,(3.67±0.14)mm respectively.the maximum longitudinal dimension of the blind zone behind the corresponding blood vessel was(1.11±0.37)mm,(2.39±1.08)mm,(3.32±0.2)mm,(4.18±2.38)mm respectively.The ratio of the diameter of blood vessels in each group to the corresponding length of the largest longitudinal diameter of the ablation blind zone was approximately 1:1.3)The effect of the vertical diameter of the blood vessels on the size of the thermal ablation blind area behind the blood vessels.When the blood vessel transverse diameters was(2.39±1.08)mm,And the vertical diameters of the vessels was(1.93±0.38)mm,(2.62±0.27)mm,(2.90±0.23)mm,(2.28±0.69)mm,(1.44±0.37)mm.And the corresponding thermal ablation blind area behind the blood vessels was(2.31±0.49)mm,(2.79±0.39)mm,(3.15±0.56)mm,(2.68±0.42)mm,(2.28±0.44)mm respectively.The ratio of the vertical diameter of the blood vessel to the length of the corresponding thermal ablation blind zone is approximately 1:1.Conclusion1.In the surface ablation mode,PHIFU can also achieve the complete ablation around the organization,when the angle between blood vessel and the acoustic axis is 0°,the impact on energy deposition in the target area is minimal;When the angle is 45°and 90°,there is an area of incomplete ablation behind the blood vessels,and the damage to the vessel wall is stronger.2.The size and shape of the incompletely ablated area behind the blood vessel are similar to the size of the blood vessel diameter,but not to the position of the blood vessel. |
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