Image Sciences Institute/Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Magn Reson Med. 2010 Jul;64(1):239-48. doi: 10.1002/mrm.22429.
MRI allows for absolute temperature measurements in substances containing two spectral resonances of which the frequency difference Delta f(T) is related to absolute temperature. This frequency difference can be extracted from spectroscopic data. An image-based MR technique that allows for the acquisition of spectroscopic data at high temporal and spatial resolution is the multi-gradient-echo sequence. In this work, the application of the multi-gradient-echo sequence for MR thermometry purposes was further developed. We investigated the possibility of postprocessing the multi-gradient-echo data into absolute temperature maps, using time-domain analysis of the magnitude of the multi-gradient-echo signals. In this approach, instead of an indirect computation of Delta f(T) from separately found frequencies, Delta f(T) is a direct output parameter. In vitro experiments were performed to provide proof of concept for retrieving absolute temperature maps from the time-domain analysis of multi-gradient-echo magnitude images. It is shown that this technique is insensitive to both field drift and local field disturbances. Furthermore, ex vivo bone marrow experiments were performed, using the fat resonance as a reference for absolute temperature mapping. It is shown that the postprocessing based on the magnitude signal in the time domain allows for the determination of Delta f(T) in bone marrow.
MRI 允许在含有两个光谱共振的物质中进行绝对温度测量，其中频率差 Δf(T) 与绝对温度有关。这个频率差可以从光谱数据中提取出来。一种基于图像的 MR 技术，可以在高时间和空间分辨率下获取光谱数据，这就是多梯度回波序列。在这项工作中，进一步开发了多梯度回波序列在 MR 测温中的应用。我们研究了通过对多梯度回波信号的幅度进行时域分析，将多梯度回波数据处理成绝对温度图的可能性。在这种方法中，不是从单独找到的频率间接计算 Δf(T)，而是将 Δf(T) 作为直接输出参数。进行了体外实验，以提供从多梯度回波幅度图像的时域分析中检索绝对温度图的概念验证。结果表明，该技术对磁场漂移和局部磁场干扰都不敏感。此外，还进行了骨髓的离体实验，使用脂肪共振作为绝对温度映射的参考。结果表明，基于时域幅度信号的后处理可以确定骨髓中的 Δf(T)。
