ECHO COMBINATION TO REDUCE TEMPERATURE MEASUREMENT ERRORS IN THE PRESENCE OF FAT

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。引言：脂质在质子共振频率（PRF）偏移方法的温度估计中产生误差。正常的肝组织可以含有超过6%的脂质，而患病的肝可以由大约20%或更多的脂质信号组成。通常使用脂肪抑制，但增加成像时间，并且在低场强下很困难。在这项研究中，我们研究了一种简单的方法，通过重新聚焦几个梯度回波并结合相应的温度图来大大减少这些误差。这种回波组合技术消除了对肝脏等组织中脂肪抑制的需要。 方法和讨论：仿真了温度误差随回波时间（TE）和脂肪百分比的变化，并提出了回波合成方案。为了验证模拟结果，在纯水、纯脂肪以及约80%水和20%脂肪的均匀混合物中进行实验，将其加热至90 ℃并在冷却至室温期间成像。对于回波组合，在三个回波时间（TE 1/TE 2/TE 3 = 14.3、21.4、28.6 ms）采集数据，对应于2？，三个？4？脂肪和水之间的相位角所有回波均在单次重聚焦梯度回波采集中采集。其他成像参数为TR = 60 ms，翻转角= 60，FOV = 16 cm，BW = 15.6 kHz，层厚= 8 mm，矩阵大小128 <$128。为了进行比较，使用相同的成像参数采集GRE序列的温度图，但使用TE = 25 ms和BW = 6.9 kHz的单次回波。在室温下在参考体模中测量相位漂移，并在所有温度图中进行校正。此外，用光纤温度传感器测量试管中的温度。比较了不同采集的SNR、温度不确定度和温度误差。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Introduction: Lipids create errors in temperature estimation with the proton resonant frequency (PRF) shift method. Normal liver tissue can contain more than 6% lipid while diseased liver may consist of lipid signal on the order of 20% or more. Fat suppression is commonly used, but increases imaging time and is difficult at low field strengths. In this study, we investigate a simple method to substantially reduce these errors by refocusing several gradient echoes and combining the corresponding temperature maps. This echo combination technique eliminates the need for fat suppression in tissues such as the liver. Methods and Discussion: Simulation of temperature errors were made as a function of echo time (TE) and fat percentage, and an echo combination scheme was developed. To verify the simulation results, experiments were performed in pure water, pure fat and a homogeneous mixture of approximately 80% water and 20% fat that were heated to 90¿C and imaged during cooling to room temperature. For the echo combination, data was acquired at three echo times (TE1/TE2/TE3= 14.3, 21.4, 28.6 ms) corresponding to 2?, 3?, and 4? phase angles between fat and water. All echoes were acquired in a single refocused gradient echo acquisition. Additional imaging parameters were TR = 60 ms, flip angle = 60, FOV = 16 cm, BW = 15.6 kHz, slice thickness = 8 mm, matrix size 128¿128. For comparison, temperature maps of a GRE sequence were acquired with the same imaging parameters but with a single echo at TE = 25 ms and BW = 6.9 kHz. Phase drift was measured in a reference phantom at room temperature and corrected in all temperature maps. In addition, temperature in the test tubes was measured with a fiber optic temperature sensor. SNR, temperature uncertainty, and temperature errors were compared for the different acquisitions.