Abstract：
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.
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.
摘要：
目的：这项工作的目的是开发一种测温方法，以测量体内温度的升高，具有足以验证热模拟的精度和准确性。这种MR测温模型将是获得关于MR成像中的主要安全问题之一的指示的有价值的工具:由于射频(RF)暴露而发生的组织加热。为了防止温度过度升高，射频功率沉积,表示为比吸收率，不能超过预定义的阈值。使用这些阈值，MRI已经证明了安全使用的广泛历史。然而，MR测温将是解决射频安全评估领域一些未满足需求的宝贵工具。例如比吸收率和热模拟的验证，在扫描过程中调查局部峰值温度，或基于温度的安全指南。
方法：提出了基于谐波初始化模型的多回波方法。该方法将先前发布的基于模型的多回波水/脂肪分离方法与先前发布的近谐波2D重建方法相结合。该方法在7T的多发射阵列下在人体大腿上进行了测试，在三名志愿者中，和几个RF垫片。
结果：与以前的脂肪参考方法相比，精度和准确性大大提高（精度：0.09vs.0.19°C)。测量的温升分布与特定对象的模拟对应物的比较显示了多个RF垫片设置的良好相对一致性。
结论：高精度显示了用于验证目的和其他RF安全性应用的潜力。
方法：提出了基于谐波初始化模型的多回波方法。该方法将先前发布的基于模型的多回波水/脂肪分离方法与先前发布的近谐波2D重建方法相结合。该方法在7T的多发射阵列下在人体大腿上进行了测试，在三名志愿者中，和几个RF垫片。
结果：与以前的脂肪参考方法相比，精度和准确性大大提高（精度：0.09vs.0.19°C)。测量的温升分布与特定对象的模拟对应物的比较显示了多个RF垫片设置的良好相对一致性。
结论：高精度显示了用于验证目的和其他RF安全性应用的潜力。
