Université de Strasbourg, CNRS, ICube, UMR7357, Strasbourg, France.
Image Guided Therapy, Pessac, France.
Phys Med Biol. 2023 Jan 24;68(3). doi: 10.1088/1361-6560/acac5e.
The aim of the paper is to propose an all-in-one method based on magnetic resonance-supersonic shear wave imaging (MR-SSI) and proton resonance frequency shift (PRFS) to monitor high intensity focused ultrasound (HIFU) thermal ablations.Mechanical properties have been shown to be related to tissue damage induced by thermal ablations. Monitoring elasticity in addition to temperature changes may help in ensuring the efficacy and the accuracy of HIFU therapies. For this purpose, an MR-SSI method has been developed where the ultrasonic transducer is used for both mechanical wave generation and thermal ablation. Transient quasi-planar shear waves are generated using the acoustic radiation force, and their propagation is monitored in motion-sensitized phase MR images. Using a single-shot gradient-echo echo-planar-imaging sequence, MR images can be acquired at a sufficiently high temporal resolution to provide an update of PRFS thermometry and MR-SSI elastography maps in real time.The proposed method was first validated on a calibrated elasticity phantom, in which both the possibility to detect inclusions with different stiffness and repeatability were demonstrated. The standard deviation between the 8 performed measurements was 2% on the background of the phantom and 11%, at most, on the inclusions. A second experiment consisted in performing a HIFU heating in a gelatin phantom. The temperature increase was estimated to be 9 °C and the shear modulus was found to decrease from 2.9 to 1.8 kPa, reflecting the gel softening around the HIFU focus, whereas it remained steady in non-heated areas.The proposed MR-SSI technique allows monitoring HIFU ablations using thermometry and elastography simultaneously, without the need for an additional external mechanical exciter such as those used in MR elastography.
本文旨在提出一种基于磁共振-超声剪切波成像（MR-SSI）和质子共振频率偏移（PRFS）的一体化方法，以监测高强度聚焦超声（HIFU）热消融。已有研究表明，力学特性与热消融引起的组织损伤有关。除了温度变化之外，监测弹性可能有助于确保 HIFU 治疗的疗效和准确性。为此，开发了一种 MR-SSI 方法，其中超声换能器既用于产生机械波，也用于进行热消融。利用声辐射力产生瞬态准平面剪切波，并在运动敏感的相位 MR 图像中监测其传播。使用单次激发梯度回波平面回波成像序列，可以以足够高的时间分辨率采集 MR 图像，以实时提供 PRFS 测温和 MR-SSI 弹性成像图的更新。该方法首先在经过校准的弹性体模型上进行了验证，结果表明该方法能够检测到具有不同刚度的包含物，且具有可重复性。在模型背景下，8 次测量的标准偏差为 2%，在包含物中最大为 11%。第二项实验是在明胶模型中进行 HIFU 加热。估计温度升高了 9°C，剪切模量从 2.9kPa 降低到 1.8kPa，反映了 HIFU 焦点周围凝胶的软化，而在未加热区域则保持稳定。该方法允许使用测温法和弹性成像法同时监测 HIFU 消融，无需使用如磁共振弹性成像中使用的外部机械激励器等附加的机械激励器。
