MRI-guided High Intensity Focused Ultrasound Ablation of Uterine Fibroids

子宫肌瘤（平滑肌瘤）是育龄妇女子宫出血和疼痛的常见原因，也是美国子宫切除术的最常见原因。 妇女正在寻求新的方法来治疗症状性子宫肌瘤，使他们能够避免手术。 这项研究是这一探索的第一步。 我们将研究磁共振成像（MRI）在提高FDA批准的高强度聚焦超声（HIFU）治疗子宫肌瘤的安全性方面的新用途。 术语高强度聚焦超声意味着使用超声来加热和热破坏组织，在这种情况下，是子宫肌瘤。MRI系统将允许我们在治疗过程中观察超声路径，并监测手术过程中肌瘤组织的温度升高。 与现有的HIFU系统相似，Philips系统能够在MR图像引导下消融子宫肌瘤。然而，Philips系统为现有MR引导HIFU治疗增加了两个独特功能，与现有MR引导HIFU系统相比，这两个功能有可能减少治疗时间并提高安全性。这些是体积消融和自动热反馈的使用。 体积加热是指使用旋转焦点，该焦点以电子方式在具有固定半径的圆形路径中高速移动。与现有HIFU系统使用的逐点超声处理相比，这使得能够在一次超声处理中加热更大的区域或细胞。逐点超声处理使用固定焦斑递送HIFU，所述固定焦斑在以行和列布置的治疗单元的预定光栅或网格布局中移动。在体积超声处理期间，换能器以连续循环的方式向治疗单元内的相邻点施加热量。这些直径为4、8或12 mm的治疗单元被放置在目标治疗区域内，以构成计划的治疗体积（PTV）。治疗是通过逐步通过几个治疗细胞消融与每次超声处理之间的冷却时间。每次HIFU体积细胞消融均采用超声功率水平进行，以实现50 - 70 ℃的组织加热。曝光的持续时间与细胞大小有关，并由系统固定。体积治疗允许完整和均匀的细胞覆盖，与现有的MR引导HIFU系统相比，有可能减少治疗时间。在将体积消融的使用与光栅化或逐点超声处理进行比较的动物实验中，已经显示体积超声处理在使用12 mm体积单元的情况下比使用相同尺寸的单点消融的情况下具有快达7倍的治疗速度。 Philips HIFU系统还允许使用自动热反馈进行体积加热。当启用自动热反馈时，超声处理的持续时间将受到单元中测量的热剂量的限制，如通过MR温度测量所检测的。例如，如果在4 mm治疗单元的情况下在20秒之前达到由MR测量的最佳热剂量，则系统软件停止超声处理，防止组织过热。现有的MR引导的HIFU系统完全依赖于操作者对升高的热剂量的检测，以便停止治疗。自动热反馈的使用具有额外的好处，即通过最小化过热和过度治疗的风险来确保输送最佳热剂量并提高安全性。 在这项初步研究中，患有症状性肌瘤的女性将接受MRI引导的HIFU，然后进行子宫切除术。 这将使我们能够确认在动物身上进行的研究，这些研究表明，有可能破坏特定组织，而不伤害目标区域周围的正常组织。 所有研究受试者均已入组。该器械似乎是安全的，未观察到显著不良事件。 计划的治疗区域与治疗后的影像学表现和子宫标本的组织病理学表现高度相关。

Uterine fibroids (leiomyomas) are a common cause of heavy uterine bleeding and pain in reproductive aged women and are the most common cause of hysterectomy in the United States. Women are seeking new ways to treat symptomatic uterine fibroids that allow them to avoid surgery. This study is the first step in this quest. We will study the novel use of magnetic resonance imaging (MRI) in enhancing the safety of the FDA approved technique to treat fibroids called High Intensity Focused Ultrasound (HIFU). The term high intensity focused ultrasound means using ultrasound to heat and to thermally destroy tissue, in this case, uterine fibroids. The MRI system will allow us to watch the ultrasound path during treatment and monitor the temperature increase in the fibroid tissue that comes during the procedure. Similar to existing HIFU systems, the Philips system enables ablation of uterine fibroids under MR image guidance. However, the Philips system adds two unique features to existing MR guided HIFU therapy, which have the potential to reduce treatment times and improve safety compared to existing MR guided HIFU systems. These are the use of volumetric ablation and automated thermal feedback. Volumetric heating refers to the use of a rotating focal spot, which is moved electronically in a circular path with a fixed radius at high speed. This enables heating of larger zones or cells in one sonication compared with point by point sonication used by existing HIFU systems. Point by point sonication delivers HIFU using a fixed focal spot that moves in a pre-determined raster or grid layout of treatment cells arranged in rows and columns. During volumetric sonication, the transducer applies heat in a continuous circular manner to adjacent points within the treatment cell. These treatment cells, with diameters of 4, 8, or 12 mm, are placed within a target treatment area to make up the planned treatment volume (PTV). Treatment is performed by stepping through several treatment cell ablations with cooling times between each sonication. Each HIFU volumetric cell ablation is performed with an ultrasound power level set to achieve a tissue heating of 50 70C. The duration of the exposures are linked with the cell size, and are fixed by the system. Volumetric treatment allows for complete and uniform cell coverage, with the potential to reduce treatment time compared to existing MR guided HIFU systems. In animal experiments comparing the use of volumetric ablation to rastered, or point by point sonication, volumetric sonication has been shown to have treatment speeds up to 7 times faster with the use of the 12 mm volumetric cell than with the use of a single point ablation of the same size. The Philips HIFU system also allows volumetric heating to be performed with automated thermal feedback. When automated thermal feedback is enabled, the duration of sonication will be limited by the measured thermal dose in the cell, as detected by MR thermometry. For example, if optimal thermal dose as measured by MR is reached prior to 20 seconds in the case of a 4-mm treatment cell, the sonication is stopped by the system software, preventing tissue overheating. Existing MR guided HIFU systems rely entirely on the operators detection of elevated thermal doses in order to stop the treatment. The use of automated thermal feedback has the added benefit of ensuring delivery of optimal thermal dose and improving safety by minimizing the risk of overheating and thus overtreatment. In this pilot study, women with symptomatic fibroids will undergo MRI guided HIFU and then have a hysterectomy. This will allow us to confirm studies done in animals which show that it is possible to destroy specific tissue without harming normal tissue surrounding the targeted area. All study subjects have been accrued. The device appears to be safe and no significant adverse events were observed. The planned treated area correlates highly with both the imaging findings after treatment and the histopathologic findings of the uterine specimen.