Kikken Mathijs W I, Steensma Bart R, van den Berg Cornelis A T, Raaijmakers Alexander J E
Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
Magn Reson Med. 2023 Jun;89(6):2347-2360. doi: 10.1002/mrm.29591. Epub 2023 Jan 23.
The aim of this work is the development of a thermometry method to measure temperature increases in vivo, with a precision and accuracy sufficient for validation against thermal simulations. Such an MR thermometry model would be a valuable tool to get an indication on one of the major safety concerns in MR imaging: the tissue heating occurring due to radiofrequency (RF) exposure. To prevent excessive temperature rise, RF power deposition, expressed as specific absorption rate, cannot exceed predefined thresholds. Using these thresholds, MRI has demonstrated an extensive history of safe usage. Nevertheless, MR thermometry would be a valuable tool to address some of the unmet needs in the area of RF safety assessment, such as validation of specific absorption rate and thermal simulations, investigation of local peak temperatures during scanning, or temperature-based safety guidelines.
The harmonic initialized model-based multi-echo approach is proposed. The method combines a previously published model-based multi-echo water/fat separated approach with an also previously published near-harmonic 2D reconstruction method. The method is tested on the human thigh with a multi-transmit array at 7 T, in three volunteers, and for several RF shims.
Precision and accuracy are improved considerably compared to a previous fat-referenced method (precision: 0.09 vs. 0.19°C). Comparison of measured temperature rise distributions to subject-specific simulated counterparts show good relative agreement for multiple RF shim settings.
The high precision shows promising potential for validation purposes and other RF safety applications.
本研究的目的是开发一种测温方法，用于测量体内温度升高，其精度和准确性足以与热模拟进行验证。这样的磁共振测温模型将是一个有价值的工具，可用于了解磁共振成像中的一个主要安全问题：由于射频（RF）暴露而导致的组织加热。为防止温度过度升高，以比吸收率表示的射频功率沉积不能超过预定义的阈值。基于这些阈值，磁共振成像已证明具有广泛的安全使用历史。然而，磁共振测温将是一个有价值的工具，可用于解决射频安全评估领域中一些未满足的需求，例如比吸收率和热模拟的验证、扫描期间局部峰值温度的研究或基于温度的安全指南。
提出了基于谐波初始化模型的多回波方法。该方法将先前发表的基于模型的多回波水/脂分离方法与同样先前发表的近谐波二维重建方法相结合。该方法在三名志愿者的人体大腿上使用7T的多发射阵列以及几种射频匀场进行了测试。
与先前的脂肪参考方法相比，精度和准确性有了显著提高（精度：0.09对0.19°C）。将测量的温度升高分布与特定受试者的模拟对应物进行比较，结果表明在多种射频匀场设置下具有良好的相对一致性。
高精度显示出在验证目的和其他射频安全应用方面具有广阔的潜力。
