Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA.
Mayo Clinic Graduate School of Biomedical Sciences, Mayo Clinic, Rochester, Minnesota, USA.
Magn Reson Med. 2024 Oct;92(4):1714-1727. doi: 10.1002/mrm.30145. Epub 2024 May 31.
To study implant lead tip heating because of the RF power deposition by developing mathematical models and comparing them with measurements acquired at 1.5 T and 3 T, especially to predict resonant length.
A simple exponential model and an adapted transmission line model for the electric field transfer function were developed. A set of wavenumbers, including that calculated from insulated antenna theory (King wavenumber) and that of the embedding medium were considered. Experiments on insulated, capped wires of varying lengths were performed to determine maximum temperature rise under RF exposure. The results are compared with model predictions from analytical expressions derived under the assumption of a constant electric field, and with those numerically calculated from spatially varying, simulated electric fields from body coil transmission. Simple expressions for the resonant length bounded between one-quarter and one-half wavelength are developed based on the roots of transcendental equations.
The King wavenumber for both models more closely matched the experimental data with a maximum root mean square error of 9.81°C at 1.5 T and 5.71°C at 3 T compared to other wavenumbers with a maximum root mean square error of 27.52°C at 1.5 T and 22.01°C for 3 T. Resonant length was more accurately predicted compared to values solely based on the embedding medium.
Analytical expressions were developed for implanted lead heating and resonant lengths under specific assumptions. The value of the wavenumber has a strong effect on the model predictions. Our work could be used to better manage implanted device lead tip heating.
通过开发数学模型并将其与在 1.5T 和 3T 下获得的测量结果进行比较，研究由于射频功率沉积导致的植入式导线尖端加热问题，尤其是预测谐振长度。
开发了用于电场传递函数的简单指数模型和改进的传输线模型。考虑了一组波数，包括绝缘天线理论（King 波数）和嵌入介质的波数。对不同长度的绝缘、带帽导线进行了实验，以确定在射频暴露下的最大温升。将结果与假设恒定电场条件下从解析表达式推导出的模型预测值进行比较，并与从体线圈传输的空间变化、模拟电场进行数值计算的结果进行比较。基于超越方程的根，开发了介于四分之一波长和半波长之间的谐振长度的简单表达式。
对于这两种模型，King 波数与实验数据更为匹配，在 1.5T 时最大均方根误差为 9.81°C，在 3T 时最大均方根误差为 5.71°C，而其他波数在 1.5T 时最大均方根误差为 27.52°C，在 3T 时最大均方根误差为 22.01°C。与仅基于嵌入介质的情况相比，谐振长度的预测更为准确。
在特定假设下，针对植入式导线加热和谐振长度开发了解析表达式。波数的值对模型预测有很大影响。我们的工作可用于更好地管理植入式设备导线尖端加热问题。
