Tatebe Ken, Ramsay Elizabeth, Mougenot Charles, Kazem Mohammad, Peikari Hamed, Bronskill Michael, Chopra Rajiv
Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390.
Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5, Canada.
Med Phys. 2016 Jan;43(1):241. doi: 10.1118/1.4938099.
Magnetic resonance imaging (MRI) is capable of providing valuable real-time feedback during medical procedures, partly due to the excellent soft-tissue contrast available. Several technical hurdles still exist to seamless integration of medical devices with MRI due to incompatibility of most conventional devices with this imaging modality. In this study, the effect of local perturbations in the magnetic field caused by the magnetization of medical devices was examined using finite element analysis modeling. As an example, the influence of the geometric and material characteristics of a transurethral high-intensity ultrasound applicator on temperature measurements using proton resonance frequency (PRF)-shift thermometry was investigated.
The effect of local perturbations in the magnetic field, caused by the magnetization of medical device components, was examined using finite element analysis modeling. The thermometry artifact generated by a transurethral ultrasound applicator was simulated, and these results were validated against analytic models and scans of an applicator in a phantom. Several parameters were then varied to identify which most strongly impacted the level of simulated thermometry artifact, which varies as the applicator moves over the course of an ablative high-intensity ultrasound treatment.
Key design parameters identified as having a strong influence on the magnitude of thermometry artifact included the susceptibility of materials and their volume. The location of components was also important, particularly when positioned to maximize symmetry of the device. Finally, the location of component edges and the inclination of the device relative to the magnetic field were also found to be important factors.
Previous design strategies to minimize thermometry artifact were validated, and novel design strategies were identified that substantially reduce PRF-shift thermometry artifacts for a variety of device orientations. These new strategies are being incorporated into the next generation of applicators. The general strategy described in this study can be applied to the design of other interventional devices intended for use with MRI.
磁共振成像（MRI）能够在医疗过程中提供有价值的实时反馈，部分原因是其具有出色的软组织对比度。由于大多数传统设备与这种成像方式不兼容，医疗设备与MRI的无缝集成仍然存在一些技术障碍。在本研究中，使用有限元分析模型研究了医疗设备磁化引起的局部磁场扰动的影响。例如，研究了经尿道高强度超声探头的几何和材料特性对使用质子共振频率（PRF）偏移测温法进行温度测量的影响。
使用有限元分析模型研究了医疗设备部件磁化引起的局部磁场扰动的影响。模拟了经尿道超声探头产生的测温伪影，并将这些结果与解析模型以及在体模中对探头的扫描结果进行了验证。然后改变几个参数，以确定哪些参数对模拟测温伪影的水平影响最大，该伪影会随着探头在消融性高强度超声治疗过程中的移动而变化。
被确定对测温伪影大小有强烈影响的关键设计参数包括材料的磁化率及其体积。部件的位置也很重要，特别是当放置位置能使设备对称性最大化时。最后，还发现部件边缘的位置以及设备相对于磁场的倾斜度也是重要因素。
先前用于最小化测温伪影的设计策略得到了验证，并确定了新的设计策略，这些策略可在各种设备方向上大幅减少PRF偏移测温伪影。这些新策略正在被纳入下一代探头的设计中。本研究中描述的一般策略可应用于设计其他打算与MRI一起使用的介入设备。
