高强度聚焦超声“切除”组织的剂量学研究

Study on Therapeutic Dosimetry of HIFU Ablation Tissue

运用高强度聚焦超声（High intensity focused ultrasound．HIFU）技术完整切除组织块并确立相应的能效关系，从而进行HIFU剂量学研究。按照由生物学焦域（Biological focal region，BFR）→束损伤→片损伤→块损伤的治疗原则，使用ISATA为0～27700W／cm^2，扫描速度1～4mm／s，束损伤的空间间距5～10mm，片损伤的空间间距10～20mm，在离体牛肝组织中形成不同治疗深度的束损伤、片损伤和块损伤，从而实现完整切除组织块。并把形成单位体积凝固性坏死所需的HIFU超声能量叫做HIFU治疗的能效因子（Energy—efficiency factor．EEF），用EEF量化HIFU在组织内的能量存积。研究结果表明，在不同治疗深度处形成的束损伤的EEF随治疗深度的增加而增大。形成片损伤、块损伤的EEF远远小于在不同治疗深度处形成束损伤的EEF，且形成块损伤的EEF小于形成片损伤的EEF。形成片损伤、块损伤的EEF并不是不同治疗深度的束损伤的EEF、不同治疗层面的片损伤的EEF的简单叠加，它与一个已存在的损伤改变了组织声环境有关，提示可通过改变组织声环境来改变EEF。因此，用EEF来进行HIFU的剂量学研究是一个新思路。对一个固定的聚焦超声换能器，EEF除了与声功率、辐照时间、治疗深度、组织结构和功能状态有关外，另一个重要的影响因素是H1FU治疗过程中组织声环境的改变。

It is a difficult problem in high intensity focused uhrasound（HIFU） therapeutic dosimetry that how to use a BFR to ablate a mass in tissue and to determine the energy-efficiency relation, that is, the scale of biological effects of HIFU. A mass lesion was realized in this study according to a treatment principle of damaging tissue from BFRs to fascicle lesions, slice lesions and a mass lesion. A 1.6 MHz transducer, 150 mm in diameter and with a focal length of 120 mm, was used. The focal intensities （ISATA） were 0-27 000 W/cm^2 and the scanning speeds were 1-4 mm/s. The distance between every fascide lesion was 5-10 mm and the distance between two slice lesions was 10-20 mm. Different irradiation depths of fasicle slice and mass lesion were observed after HIFU procedures in this study. The dosage of HIFU required for tissue coagulated necrosis was evaluated with energy of HIFU （J） per cubic millimeter （mm3）, i.e. , J/mm^3 which was defined as energy-efficiency factor （EEF）. Results showed that EEF needed for producing fascicle lesions increased with the increase of irradiation depth. EEF required for inducing various lesions in biological tissue was different. Generally, it followed the law： EEFmaac〈 EEFalice〈EEFfacicle. EEF for slice lesion was not simply a summation of EEFs for fascicle lesions at different irradiation depths, although the slice lesion was assembled with fascicle lesions at different irradiation depths in the same treatment slice. In the same way, EEF for a mass lesion was not simple summation of EEFs for slice lesions at different layers. So HIFU therapeutic dosimetry can be carried on investigation by using EEF, Factors of affecting EEF of HIFU include acoustic power, exposure time, irradiation depth, tissue structure, and tissue functional status. Besides, another important factor is the change of the acoustic environment in tissue during the HIFU procedure.