MRI-guided High Intensity Focused Ultrasound Ablation of Uterine Fibroids

子宫肌瘤(肌瘤)是育龄妇女子宫大出血和疼痛的常见原因，也是美国子宫切除术最常见的原因。女性正在寻找新的方法来治疗有症状的子宫肌瘤，使她们能够避免手术。这项研究是这一探索的第一步。我们将研究磁共振成像(MRI)在增强FDA批准的治疗肌瘤的高强度聚焦超声(HIFU)技术安全性方面的新应用。术语高强度聚焦超声是指使用超声波加热和热破坏组织，在这种情况下，子宫肌瘤。核磁共振系统将使我们能够在治疗过程中观察超声路径，并监测在治疗过程中肌瘤组织的温度升高。 与现有的HIFU系统类似，飞利浦系统能够在磁共振图像引导下消融子宫肌瘤。然而，飞利浦系统为现有的MR引导HIFU治疗增加了两个独特的功能，与现有的MR引导HIFU系统相比，这两个功能具有减少治疗次数和提高安全性的潜力。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，在高速下以电子方式沿固定半径的圆形路径移动。与现有HIFU系统使用的逐点超声相比，这可以在一次超声波作用下加热更大的区域或单元。点对点超声利用一个固定的焦点提供HIFU，该焦点在预定的栅格或网格布局中移动，处理单元以行和列的形式排列。在体积超声期间，换能器以连续循环的方式将热施加到处理单元内的相邻点。这些直径为4 mm、8 mm或12 mm的处理单元被放置在目标处理区域内，以构成计划的处理体积(PTV)。治疗是通过分步通过几次治疗单元消融，每次超声之间的冷却时间。每次HIFU体积细胞消融的超声功率水平被设置为实现50~70C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。与现有的MR引导HIFU系统相比，体积治疗允许完全和均匀的细胞覆盖，有可能减少治疗时间。在动物实验中，将体积消融的使用与栅状或逐点超声进行比较，已经证明使用12 mm的体积单元的体积超声的治疗速度比使用相同大小的单点消融快7倍。 飞利浦HIFU系统还允许使用自动热反馈进行容积式加热。当启用自动热反馈时，超声波的持续时间将受到通过MR温度计检测到的电池中测量的热剂量的限制。例如，如果在4 mm治疗单元的情况下，通过MR测量的最佳热剂量在20秒之前达到，则系统软件停止超声，以防止组织过热。现有的MR引导HIFU系统完全依赖于操作员检测升高的热剂量来停止治疗。使用自动热反馈还有一个额外的好处，即确保提供最佳热剂量，并通过最大限度地减少过热和过度治疗的风险来提高安全性。 在这项初步研究中，患有症状性子宫肌瘤的妇女将接受MRI引导的HIFU，然后进行子宫切除术。这将使我们能够证实在动物身上所做的研究，这些研究表明，在不损害目标区域周围正常组织的情况下，破坏特定组织是可能的。

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.