| BackgroundThe peripheral ablation mode is a new therapy method which is based on the growth character of tumors.It differs from the traditional way of HIFU therapy as its basic concept is using HIFU to form a closed shell-like barrier around the target,thus cutting down the nutrition supply and transition pathway of a tumor.So far,the feasibility of this hypothesis has been approved,and it is more efficiency than the traditional ablation mode.HIFU treatment exist two kinds of irradiation methods: continuous and pulsed wave,the current routine clinical way is CHIFU(Continuous High Intensity Focused Ultrasound)irradiation for its recognized efficacy,while the problem is that when using it to ablate large tumor,long irradiation time and large irradiation dose are easily lead to the emergence of complications.Previous studies on peripheral ablation mode were all carried out with CHIFU for irradiation,and there was no report on the use of PHIFU(Pulsed High Intensity Focused Ultrasound)for peripheral ablation mode.The current foundation research on PHIFU is rare,and its efficacy is affected by multiple treatment parameters,but studies have shown that in vivo animal experiments,when using PHIFU and CHIFU to ablate the same volume of tumors,under the premise of the same ablation effect,using PHIFU is more safety for causing fewer complications.Under the peripheral ablation mode,what about the effect of PHIFU and CHIFU ablation,and what kind of irradiation method is more conducive to the desired ablation effect,which is related to the choice of irradiation mode when peripheral ablation mode is applied.Moreover,ultrasound is one of the conventional guidance in HIFU therapy.Its key role is evaluating treatment effect and real time monitoring.Whether ultrasound can effectively evaluate the ablation effect of HIFU peripheral ablation is Important to the promotion and application of this new method.ObjectiveTo investigate the advantages and disadvantages of PHIFU and CHIFU peripheral ablation mode,this research compared the peripheral ablation mode with PHIFU and CHIFU in aspects of ablation effect and efficiency,as well as ultrasonic monitoring.MethodsFresh bovine livers were harvested within 5 hours after slaughtered,select areas with fewer blood vessels and with a thickness at least 50 mm,and then cut the livers into pieces.Forty sample liver tissues were randomly divided into group A(n=30)and group B(n=10)according to irradiation method.Group A were performed with PHIFU peripheral ablation and group B were performed with CHIFU peripheral ablation.According to the duty cycles,the samples in group A were randomly divided into 3 equal subgroups: group A1(DC=10%,n=10),group A2(DC=30%,n=10),and group A3(DC=50%,n=10).The preset ablation zones are the same both in group A and group B,the size of the ROI is 30mm×30mm×15mm.The top layer of the cube zone is located at depth of 35 mm,and the bottom is located at depth of 20 mm.Before irradiation,set the temperature probe in the geometry center of the cube target.During ablation: with ultrasound guidance,the target areas in all groups were applied with liner scanning and peripheral ablation from deep to shallow level.Meanwhile,the temperature changes in the geometric center were recorded.Each time the single lesion is formed,a sonogram is captured.After ablation: capture the ultrasound image layer by layer,and calculate tissue damage size.Slice the target and observe the damaged situation of irradiation and non-irradiation areas.Use TTC staining to define the necrosis area,and calculate the actual damaged size of the target,then compare it to the size measured on ultrasound image.At the same time,calculate the total damaged volume and the energy efficiency factor(EEF).Above all,to figure out the pathological changes of cells in irradiation and non-irradiation areas,specimens were performed with HE staining and light microscope observation.Results1.Ablation effect: 1)common: complete closed necrosis barrier around the target were formed both in group A and group B.The necrosis type of group A2 and group A3 were the same as those in group B,and all of them were coagulation necrosis,tissue damage were also observed in group A2,group A3 and group B;2)difference: the edge of barrier in group A is more regular and clear than that in group B.The type of irradiation areas in group A were different from that in group B.The irradiation areas in group A1 was manifested by liquid necrosis.While coagulation necrosis were seen in group A2,group A3 and group B.In addition,the internally non-irradiation areas in group A1 was different from other groups for it showed no obvious tissue damage.2.Ablation efficiency: EEF in group A was less than that of group B(P<0.05).The EEF of group A1,group A2 and group A3 were(0.81±0.05)J/mm3,(1.34±0.02)J/mm3,(1.36±0.05)J/mm3,respectively.That is,the EEF of PHIFU group increased with the increase of duty cycles.3.Temperature:1)common: during ablation,when the focus is moving on the top surface(depth 35mm)and the bottom(depth 20mm)of the target,the core temperature of the target increased significantly,while irradiating other surfaces,no significant changes were observed;2)difference: the highest central temperature of the target in all subgroups from group A1 were lower than that in group B,the difference was statistically significant(P< 0.05).Compared with the other groups,the highest central temperature of the target in group A1 was lower than 60?.while temperature in group A2,group A3 and group B were all above the 60 ?.4.Sonogram during ablation: 1)common: immediately echo changes were seen after liner scanning both in group A and group B;2)difference: the intensity,distribution range of the immediately echo changes in group A were different from those in group B.In group A1,echo decreased immediately after irradiation.In group A2 and group A3,the echo of the tissue was hyperechogenicity with an incompletely clear edge(edge closed to transducer was clear).The echo of the group B was increased immediately after irradiation,but the echo enhancement area was irregular and the edge was blurred.In all subgroups in,mediate echo changes were all in the preset scan range.While in group B,echo change areas were beyond the preset scan range,specimens of bovine liver showed thermal damage.5.Sonogram after ablation: 1)common: the general morphology and ultrasound image has a good correlation both in group A and group B;2)difference: the internal non-irradiation and irradiation areas were not totally the same in group A and group B.Echoes of necrosis areas in group A1 were hypoechoic,and the echo of non-irradiation internal zone was similar to the normal liver tissues.Necrosis area in group A2,group A3 and group B appeared hyperechoic,internal echo was slightly higher than that of non-irradiated target areas outside.Target size of ultrasound image and specimen in group A has no statistically significant difference(P>0.05),target size of general image is larger than that in the ultrasound image,the difference was statistically significant(P<0.05).Conclusion1.PHIFU peripheral ablation mode can achieve the same treatment goal as CHIFU peripheral ablation mode.That is to form a complete closed necrosis barrier around the target.Compared with the CHIFU peripheral ablation mode,the ablation efficiency of PHIFU ablation mode is higher;2.Under the peripheral ablation mode,use PHIFU with a higher duty cycle and CHIFU to irradiate the tissues are more effective for the damage of the non-irradiated area in the center;3.During CHIFU peripheral ablation and PHIFU peripheral ablation with different duty cycles,the characteristics of instantaneous echo change in irradiated area were different,which was related to the actual damaged status of the target tissue.PHIFU ablation mode is more advantageous than CHIFU ablation mode in evaluating size of damaged tissue. |
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