Analysis Of Influencing Factors On Ultrasonic Ablation Of Uterine Fibroids And Effects Of Fat And Muscle Tissue On High-intensity Focused Ultrasound (HIFU) Ablation Energy

Background:Hysteromyoma, originated from smooth muscle cell and pathogenesisof which still not clear, is a common and frequently-occurring disease.Uterine fibroids can cause many clinical symptoms such as abnormal uterinebleeding, pelvic compression symptoms, abortion and infertility.Uterine fibroids can be managed by many kind of treatment methods,and the current most common treatment for symptomatic fibroids is surgery.High-Intensity Focused Ultrasound (HIFU) is a non-invasive thermalablation technique that developed rapidly in the clinical application in recentdecade. Ultrasonic energy will be focused on the targeted fibroid and thencauses coagulative necrosis. Tumors can be removed in situ. It is confirmedthat HIFU, which has wide application prospects, is safe and effective.With the advancement of clinical protocols and study of dosimetry onHIFU treatment of hysteromyoma, the ablation rate is improved and treatment time shortened. Especially part of the myomas with high signalson T2WI and/or enhanced-T1WI can be ablated satisfactorily. Therefore, it’sworthy of finding out the influencing factors on HIFU ablation results.Objective：1. To exploring the influencing factors of ablation rate and efficiency ofHIFU treatment for uterine fibroids through single factor correlationanalysis.2. To compare the acoustic attenuation of high-intensity focusedultrasound energy within the pork when through different thickness of fatand muscle tissue.Methods：1. A total of63patients (76fibroids) accepted one session of HIFUtreatment. Pelvic enhanced-MRI was performed before and within3daysafter the treatment. All of the myomas were divided into groups according totype, location, tumor size, target-skin distance, signals on T2WI, signals onenhanced-T1WI and intensity of therapy. Ablation rate and efficiency wasrespectively compared between different levels within every group.2. The pork with different thickness of fat (0mm,20mm,28mm) wereselected. The focus of HIFU was placed at the same distance from thesuperficial and sonicated with the same power of200W for10seconds. Thenecrosis regions were compared. Then, the pork with25mm thickness of fatwas selected, the focus was placed at20mm,30mm away from the muscle surface and sonicated with200W of power for10seconds; then select skinand fat-free pork, place the focus at20mm,30mm away from the musclesurface and sonicated the target point with the same power for10seconds.Results:1. Percentage of uterine fibroids of which ablation rate was≥70%wasover65%, and that of ablation efficiency≥50mm3/s was over56%.Ablation rate of myomas on the anterior wall, those on the fundus of anterialuterus, and those on the side wall of uterus that ultrasonic energy didn’t gothrough the normal uterine wall when being treated, exceeded the ablationrate of myomas on the posterior wall, those on the fundus of posterial uterus,and those on the side wall of uterus that ultrasonic energy went through thenormal uterine wall when being treated (P＜0.05). Difference of ablationrate among myomas with low, equal and high signals of enhanced-T1WIwas statistically significant (P＜0.05), while type, size, target-skin distance,signals on T2WI and treatment intensity of myomas did not affect the HIFUablation rate significantly (P＞0.05). Difference of ablation efficiencybetween tumor size of＜5cm and≥5cm, and that among myomas with low,equal and high signals of enhanced-T1WI were both statistically significant(P＜0.05), while type, location, target-skin distance, signals on T2WI andtreatment intensity of myomas did not affect the HIFU ablation efficiencysignificantly (P＞0.05).2. With the increase in fat thickness under the same sonication condition, the volume of coagulation necrosis region gradually reduced;simultaneously with the increase of the thickness of the fat, the long axis ofcoagulation necrosis area has gradually increased, while the minor axis hasgradually narrowed. When treat fat free pork with under the same sonicationcondition, with the increase of the thickness of the muscle, the damagevolume reduced. The fat tissue has more acoustic attenuation effects onHIFU than the muscle tissue.Conclusions:1. Location and signal on enhanced-T1WI both affect the HIFUtreatment ablation rate of uterine fibroids. Size and signal onenhanced-T1WI both affect the HIFU treatment ablation efficiency ofuterine fibroids.2. The acoustic attenuation effects occur when high intensity focusedultrasound pass the fat tissue or the muscle tissue; fat tissue has moreattenuation effects than the muscle tissue.