| Background and objective: High-intensity focused ultrasound (HIFU) consists of focused ultrasound waves emitted from a transducer that are capable of inducing tissue damage. As a non-invasive, repeatable, feasible, and organ-preserving therapeutic method, it has been investigated for its potential as a therapeutic tool in many fields such as masses of abdominal solid organs, benign prostate hyperplasia, refractory glaucoma, etc. Studies showed that controllable damage could be induced with these organs, and the successful clinical application of HIFU in the treatment of them also has been reported. Nearly assumption of cardiac use with HIFU has been proposed and some elementary steps showed the optimal damages with proper depth and dimension in myocardium, but the exact dose-response relation was not given. Our objective is to determine the dimension and shape of the damage area of myocardium according to different dosage, and the temperature alteration in the focus was also analyzed in this study in order to provide experimental data for further steps.Methods: The HIFU therapeutic apparatus was separately used to selectively destroy the different parts of myocardial tissue of 30 fresh normal swine in-vitro hearts. The myocardium was exposed to different HIFU dosages composed of different acoustic intensity and exposure time. The dissectionwas applied and then the lesion volumes were measured by PC software, and pathologic changes in border between normal and lesion area under each HIFU dosage were observed with a microscope. The temperature alteration in the focus was detected and recorded by a thermocouple probe that is just located in the focal field under the B-mode ultrasound monitoring. And each condition of this experiment was repeated five times.Results: The lesion volume varied from (11. 2 ?1. 9) mm3 to ( 283. 2 ?4. 5) mm3 with the change of exposed time between Is ~8s and acoustic intensity varied between 11000 W/cm2 -22200W/cm2, and significant difference was found among different levels of both acoustic intensity and exposure time (F=3. 387, 7.108, p=0.043, 0.002), and they effected each other ( F=4.430, p=Q. 031) .The lesion shapes enlarged from ellipse with relatively clear borderlines to irregular triangles with sharp borders. Marked pathologic changes in regional myocardial tissue showed that the border between viable and necrotic tissue was extremely sharp comprising only 1-3 cell-layers. And it was observed that the highest temperature in focal field varied from (66.4 ?11.2)癈 to (85. 8?. 4)癈 when HIFU dose changed between 11000 W/cm2 ~22200W/cm2 and Is ~15s. And significant difference was also found among different levels of acoustic intensity (F=5. 639, p=0. 019), but there was no significant difference among different levels of exposure times (F=2. 627, p=Q. 073), and interaction was also found between acoustic intensity and exposure time. After HIFU irradiation was stopped, the tendency of the temperature-descending curve went down slowly about 30 seconds later. Conclusions: The technique of HIFU is effective to obtain controllable ablation of myocardial tissue. The temperature in focal field can reach to the degree that lead to irreversible change in cells under the different HIFU dose used in this study. This investigation may suggest the potential use of HIFU asa non-invasive or micro-invasive method in treatment of heart diseases. |
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