Department of Biomedical Engineering, Duke University, Durham, North Carolina 27708, USA.
Int J Hyperthermia. 2009;25(6):422-33. doi: 10.1080/02656730903133762.
MR thermometry using the proton resonance frequency shift (PRFS) method has been used to measure temperature changes during clinical hyperthermia treatment. However, frequency drift of the MRI system can add large errors to the measured temperature change. These drifts can be measured and corrected using oil references placed around the treatment region. In this study, the number and position of four or more oil references were investigated to obtain a practical approach to correct frequency drift during PRFS thermometry in phantoms and in vivo.
Experiments were performed in a 140 MHz four antenna mini-annular phased array (MAPA) heat applicator (for treatment of extremity tumours) and an applicator for heating of the breast, with symmetric and asymmetric positioning of the oil references, respectively. Temperature change PRFS images were obtained during an hour or more of measurement with no application of heat. Afterwards, errors in calculating temperature change due to system drift were quantified with and without various oil reference correction arrangements.
Results showed good temperature correction in phantoms and in a human leg, with average errors of 0.28 degrees C and 0.94 degrees C respectively. There was further improvement in the leg when using eight or more oil references, reducing the average error to 0.44 degrees C, while the phantoms showed no significant improvement.
These results indicate that oil reference correction performs well in vivo, and that eight references can improve the correction by up to 0.5 degrees C compared to four references.
使用质子共振频率偏移（PRFS）方法的磁共振测温已用于测量临床热疗过程中的温度变化。然而，MRI 系统的频率漂移会给测量的温度变化带来很大的误差。这些漂移可以通过在治疗区域周围放置油参考物来测量和校正。在这项研究中，研究了四个或更多油参考物的数量和位置，以找到一种实用的方法来校正 PRFS 测温中在体模和体内的频率漂移。
在 140 MHz 四天线迷你环形相控阵（MAPA）热施加器（用于治疗四肢肿瘤）和用于加热乳房的施加器中进行了实验，分别对油参考物进行了对称和不对称定位。在没有施加热量的情况下，进行了长达一个小时或更长时间的测量，获得了温度变化 PRFS 图像。然后，量化了由于系统漂移而导致的温度变化计算误差，包括使用不同数量的油参考物校正的情况。
结果表明，在体模和人体腿部中均实现了较好的温度校正，平均误差分别为 0.28°C 和 0.94°C。当使用八个或更多油参考物时，腿部的平均误差进一步降低至 0.44°C，而体模则没有显著改善。
这些结果表明，油参考物校正方法在体内效果良好，与四个参考物相比，八个参考物可以将校正误差降低多达 0.5°C。
