Laboratory for Molecular and Functional Imaging, UMR5231, CNRS, University Victor Segalen Bordeaux 2, 33076 Bordeaux, France.
Med Phys. 2010 Jun;37(6):2533-40. doi: 10.1118/1.3413996.
High intensity focused ultrasound (HIFU) is a promising method for the noninvasive treatment of liver tumors. However, the presence of ribs in the HIFU beam path remains problematic since it may lead to adverse effects (skin burns) by absorption and reflection of the incident beam at or near the bone surface. This article presents a method based on magnetic resonance (MR) imaging for identification of the ribs in the HIFU beam, and for selection of the transducer elements to deactivate.
The ribs are visualized on anatomical images acquired prior to heating and manually segmented. The resulting regions of interest surrounding the ribs are projected onto the transducer surface by ray tracing from the focal point. The transducer elements in the "shadow" of the ribs are then deactivated. The method was validated ex vivo and in vivo in pig liver during breathing under multislice real-time MR thermometry, using the proton resonance frequency shift method.
Ex vivo and in vivo temperature data showed that the temperature increase near the ribs was substantial when HIFU sonications were performed with all elements active, whereas the temperature was reduced with deactivation of the transducer elements located in front of the ribs. The temperature at the focal point was similar with and without deactivation of the transducer elements, indicative of no loss of heat efficiency with the proposed technique.
This method is simple, rapid, and reliable, and enables intercostal HIFU ablation while sparing ribs and their surrounding tissues.
高强度聚焦超声（HIFU）是一种有前途的非侵入性治疗肝脏肿瘤的方法。然而，肋骨在 HIFU 射束路径中的存在仍然是一个问题，因为它可能会导致不良影响（皮肤灼伤），这是由于入射射束在骨表面或附近的吸收和反射。本文提出了一种基于磁共振（MR）成像的方法，用于识别 HIFU 射束中的肋骨，并选择要停用的换能器元件。
在加热之前获取解剖图像，并手动对肋骨进行分割，以可视化肋骨。通过从焦点进行光线追踪，将围绕肋骨的感兴趣区域投影到换能器表面上。然后停用肋骨“阴影”中的换能器元件。该方法在多切片实时 MR 测温下，使用质子共振频率偏移法，在猪肝的离体和体内进行了验证。
离体和体内温度数据表明，当所有元件都处于活跃状态时，HIFU 超声治疗时肋骨附近的温度升高很大，而当停用位于肋骨前面的换能器元件时，温度降低。焦点处的温度与停用或不停用换能器元件时相似，表明该技术没有降低热效率。
该方法简单、快速、可靠，能够实现肋间 HIFU 消融，同时保护肋骨及其周围组织。
