Zhang Xiaoliang
Department of Radiology and Biomedical Imaging, School of Medicine, University of California, San Francisco, CA, USA.
UC Berkeley/UCSF Joint Graduate Group in Bioengineering, University of California, San Francisco, CA, USA.
Quant Imaging Med Surg. 2017 Apr;7(2):170-176. doi: 10.21037/qims.2017.02.10.
Traveling wave MR uses the far fields in signal excitation and reception, therefore its acquisition efficiency is low in contrast to the conventional near field magnetic resonance (MR). Here we show a simple and efficient method based on the local resonator to improving sensitivity of traveling wave MR technique. The proposed method utilizes a standalone or free local resonator to amplify the radio frequency magnetic fields in the interested target. The resonators have no wire connections to the MR system and thus can be conveniently placed to any place around imaging simples.
A rectangular loop L/C resonator to be used as the free local resonator was tuned to the proton Larmor frequency at 7T. Traveling wave MR experiments with and without the wireless free local resonator were performed on a living rat using a 7T whole body MR scanner. The signal-to-noise ratio (SNR) or sensitivity of the images acquired was compared and evaluated.
7T imaging results show that traveling wave MR with a wireless free local resonator placed near the head of a living rat achieves at least 10-fold SNR gain over the images acquired on the same rat using conventional traveling wave MR method, i.e. imaging with no free local resonators.
The proposed free local resonator technique is able to enhance the MR sensitivity and acquisition efficiency of traveling wave MR at ultrahigh fields . This method can be a simple solution to alleviating low sensitivity problem of traveling wave MRI.
行波磁共振成像在信号激发和接收过程中使用远场，因此与传统的近场磁共振成像相比，其采集效率较低。在此，我们展示了一种基于局部谐振器的简单高效方法，以提高行波磁共振成像技术的灵敏度。所提出的方法利用独立或自由的局部谐振器来放大感兴趣目标区域内的射频磁场。这些谐振器与磁共振系统没有电线连接，因此可以方便地放置在成像样本周围的任何位置。
将用作自由局部谐振器的矩形环形L/C谐振器调谐到7T场强下的质子拉莫尔频率。使用7T全身磁共振扫描仪，在一只活体大鼠上进行了有无无线自由局部谐振器的行波磁共振成像实验。对采集图像的信噪比（SNR）或灵敏度进行了比较和评估。
7T场强下的成像结果表明，在活体大鼠头部附近放置无线自由局部谐振器的行波磁共振成像，与使用传统行波磁共振成像方法（即不使用自由局部谐振器成像）在同一只大鼠上采集的图像相比，信噪比至少提高了10倍。
所提出的自由局部谐振器技术能够提高超高场下行波磁共振成像的灵敏度和采集效率。该方法可能是缓解行波磁共振成像低灵敏度问题的一种简单解决方案。
