Richards Nicholas, Malmberg Michael, Odéen Henrik, Johnson Sara, Kline Michelle, Merrill Robb, Hadley Rock, Parker Dennis L, Payne Allison
Department of Biomedical Engineering, University of Utah, Salt Lake City, Utah, USA.
Department of Radiology and Imaging Sciences, University of Utah Health, Salt Lake City, Utah, USA.
Magn Reson Med. 2025 May;93(5):2070-2085. doi: 10.1002/mrm.30413. Epub 2025 Jan 20.
The single reference variable flip angle sequence with a multi-echo stack of stars acquisition (SR-VFA-SoS) simultaneously measures temperature change using proton resonance frequency (PRF) shift and T-based thermometry methods. This work evaluates SR-VFA-SoS thermometry in MR-guided focused ultrasound in an in vivo rabbit model.
Simultaneous PRF shift thermometry and T-based thermometry were obtained in a New Zealand white rabbit model (n = 7) during MR-guided focused ultrasound surgery using the SR-VFA-SoS sequence at 3 T. Distinct locations in muscle (n = 16), fat (n = 12), or the interface of both tissues (n = 23) were heated. The T-temperature coefficient of fat was determined using least-squares fitting of inversion recovery-based T maps of untreated fat harvested from the animal and was applied to the in vivo measured heat-induced T changes to create temperature maps.
Using k-space weighted image contrast reconstruction, temporal resolution of 1.71 s was achieved for simultaneous thermometry at 1.5 × 1.5 × 2 mm voxel resolution. PRF shift thermometry was not sensitive to heating in fat. T changes were observed in fat at the ultrasound focus. The mean T-temperature coefficient for fat was determined to be 1.9%/°C ± 0.2%/°C. Precision was 0.76°C ± 0.18°C for PRF shift thermometry in muscle and 1.93°C ± 0.60°C for T-based thermometry in fat. Sonications in muscle showed an increase in T of 2.4%/°C ± 0.9%/°C.
The SR-VFA-SoS sequence was shown to simultaneously measure temperature change using PRF shift and T-based methods in an in vivo model, providing thermometry for both aqueous and fat tissues.
具有多回波星状采集的单参考变量翻转角序列（SR-VFA-SoS）利用质子共振频率（PRF）偏移和基于T的测温方法同时测量温度变化。本研究在体内兔模型中评估SR-VFA-SoS测温技术在磁共振引导聚焦超声中的应用。
在3T磁共振引导聚焦超声手术过程中，使用SR-VFA-SoS序列在新西兰白兔模型（n = 7）中同时获得PRF偏移测温法和基于T的测温法。对肌肉（n = 16）、脂肪（n = 12）或两种组织的界面（n = 23）中的不同位置进行加热。使用从动物身上采集的未处理脂肪的基于反转恢复的T图进行最小二乘拟合来确定脂肪的T温度系数，并将其应用于体内测量的热诱导T变化以创建温度图。
使用k空间加权图像对比度重建，在1.5×1.5×2mm体素分辨率下实现了同时测温的1.71秒时间分辨率。PRF偏移测温法对脂肪加热不敏感。在超声焦点处的脂肪中观察到T变化。脂肪的平均T温度系数确定为1.9%/°C±0.2%/°C。肌肉中PRF偏移测温法的精度为0.76°C±0.18°C，脂肪中基于T的测温法的精度为1.93°C±0.60°C。肌肉中的超声处理显示T升高2.4%/°C±0.9%/°C。
SR-VFA-SoS序列在体内模型中被证明可以使用PRF偏移和基于T的方法同时测量温度变化，为水性和脂肪组织提供测温。
