Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee.
Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee.
Magn Reson Med. 2019 Apr;81(4):2385-2398. doi: 10.1002/mrm.27567. Epub 2018 Nov 5.
To perform multi-echo water/fat separated proton resonance frequency (PRF)-shift temperature mapping.
State-of-the-art, iterative multi-echo water/fat separation algorithms produce high-quality water and fat images in the absence of heating but are not suitable for real-time imaging due to their long compute times and potential errors in heated regions. Existing fat-referenced PRF-shift temperature reconstruction methods partially address these limitations but do not address motion or large time-varying and spatially inhomogeneous B shifts. We describe a model-based temperature reconstruction method that overcomes these limitations by fitting a library of separated water and fat images measured before heating directly to multi-echo data measured during heating, while accounting for the PRF shift with temperature.
Simulations in a mixed water/fat phantom with focal heating showed that the proposed algorithm reconstructed more accurate temperature maps in mixed tissues compared to a fat-referenced thermometry method. In a porcine phantom experiment with focused ultrasound heating at 1.5 Tesla, temperature maps were accurate to within 1 C of fiber optic probe temperature measurements and were calculated in 0.47 s per time point. Free-breathing breast and liver imaging experiments demonstrated motion and off-resonance compensation. The algorithm can also accurately reconstruct water/fat separated temperature maps from a single echo during heating.
The proposed model-based water/fat separated algorithm produces accurate PRF-shift temperature maps in mixed water and fat tissues in the presence of spatiotemporally varying off-resonance and motion.
进行多回波水/脂分离质子共振频率（PRF）位移温度测绘。
最先进的迭代多回波水/脂分离算法在没有加热的情况下产生高质量的水和脂肪图像，但由于计算时间长且在加热区域可能存在误差，不适合实时成像。现有的基于脂肪参考的 PRF 位移温度重建方法部分解决了这些限制，但没有解决运动或大的时变和空间不均匀 B 位移问题。我们描述了一种基于模型的温度重建方法，通过在加热过程中直接将加热前测量的分离水和脂肪图像库拟合到多回波数据，同时考虑温度的 PRF 位移，克服了这些限制。
在具有焦点加热的混合水/脂体模中的模拟表明，与基于脂肪参考的测温方法相比，所提出的算法在混合组织中重建了更准确的温度图。在 1.5T 聚焦超声加热的猪体模实验中，温度图与光纤探头温度测量值的误差在 1°C 以内，每个时间点的计算时间为 0.47 秒。自由呼吸的乳房和肝脏成像实验证明了运动和离共振补偿。该算法还可以从加热过程中的单个回波准确重建水/脂分离的温度图。
所提出的基于模型的水/脂分离算法在存在时空变化的离共振和运动的情况下，在混合水和脂肪组织中产生准确的 PRF 位移温度图。
