背景:监管机构和其他机构要求测试MRI梯度诱导的植入医疗设备的加热。被动髋关节植入物的这项研究采用了ISO10974技术规范(TS)的梯度加热测试。除了一项先前的髋部植入物研究外,所有研究都在临床扫描仪中使用了不均匀的梯度曝光场,并报告了低于5°C的加热。本研究采用了TS的方法,解决了通过暴露于均匀梯度场来识别最坏情况加热的未满足需求。
目的:确定影响髋部植入物和圆柱形钛盘体外最大加热的梯度场参数。
方法:诱导加热的计算模拟和实验验证。
■组织模拟凝胶。
■42T/sRMS,正弦,具有高空间均匀性的连续B场评估:1-10kHz的髋关节植入物加热,通过计算建模,通过有限的点测量验证。4、6和9kHz的植入物在42T/s下暴露的实验测量,在50、100和150秒时分析。
方法:一个样本学生t检验,以评估计算和实验结果之间的差异。实验性与计算结果无显著性差异(p<0.05)。
结果:最大模拟温升(暴露10分钟)在1kHz时为10°C,在10kHz时为0.66°C。21T/s的上升率与在50秒时(dB/dt比率的平方)稳定后,42T/s的RMS为4。
结论:植入物的加热与B场的频率和植入物的横截面积成正比,并且对于其趋肤深度量级的厚度更大。使用较低的dB/dtRMS值和较低成本的放大器进行测试,可以预测具有相同频率分量和波形的dB/dt平方(根据ISOTS)的较高值的加热。一旦热平衡发生。
方法:1技术效果:第一阶段。
BACKGROUND: Testing MRI gradient-induced heating of implanted medical devices is required by regulatory organizations and others. A gradient heating test of the ISO 10974 Technical Specification (TS) for active implants was adopted for this study of passive hip implants. All but one previous study of hip implants used nonuniform gradient exposure fields in clinical scanners and reported heating of less than 5 °C. This present study adapted methods of the TS, addressing the unmet need for identifying worst-
case heating via exposures to uniform gradient fields.
OBJECTIVE: To identify gradient-field parameters affecting maximum heating in vitro for a hip implant and a cylindrical titanium disk.
METHODS: Computational simulations and experimental validation of induced heating.
UNASSIGNED: Tissue-simulating gel.
UNASSIGNED: 42 T/s RMS, sinusoidal, continuous B fields with high spatial uniformity ASSESSMENT: Hip implant heating at 1-10 kHz, via computational modeling, validated by limited point measurements. Experimental measurements of exposures of an implant at 42 T/s for 4, 6, and 9 kHz, analyzed at 50, 100, and 150 seconds.
METHODS: One sample student\'s t-test to assess difference between computational and experimental results. Experimental vs. computational results were not significantly different (p < 0.05).
RESULTS: Maximum simulated temperature rise (10-minute exposure) was 10 °C at 1 kHz and 0.66 °C at 10 kHz. The ratio of the rise for 21 T/s vs. 42 T/s RMS was 4, after stabilizing at 50 seconds (dB/dt ratio squared).
CONCLUSIONS: Heating of an implant is proportional to the frequency of the B field and the implant\'s cross-sectional area and is greater for a thickness on the order of its skin depth. Testing with lower values of dB/dt RMS with lower cost amplifiers enables prediction of heating at higher values for dB/dt squared (per ISO TS) with identical frequency components and waveforms, once thermal equilibrium occurs.
METHODS: 1 TECHNICAL EFFICACY: Stage 1.