OPTIMIZATION OF ENCODING GRADIENTS FOR MR-ARFI

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目及 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 研究中心，而研究中心不一定是研究者所在的机构。 对于无显著加热的高强度聚焦超声（HIFU）治疗，可以通过声辐射力成像（MR-ARFI）进行MR监测。MR-ARFI测量由HIFU引起的小位移，这可能对许多新的HIFU应用有用，例如暂时性血脑屏障破坏和细胞内分子递送。目前，MR-ARFI使用大的单瓣梯度来编码位移，这可能使图像对运动敏感，大b值导致SNR低，并且容易受到相位图中伪影的影响。在这项研究中，MR-ARFI编码梯度的开发，以解决上述问题。 重复双极梯度集和反向双极梯度集（由重聚焦脉冲周围的两个相同或相反极性的双极梯度组成）与具有相同TE/TR和运动编码脉冲宽度的传统两个单叶梯度集进行了比较。HIFU系统由MR序列触发，以发射与编码梯度同步的超声，占空比小于5%。

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. For high intensity focused ultrasound (HIFU) treatments without significant heating, MR monitoring could be done by acoustic radiation force imaging (MR-ARFI). MR-ARFI measures small displacement induced by HIFU, which might be useful for many novel HIFU applications, e.g. temporary blood-brain barrier disruption and intracellular molecular delivery. Currently, MR-ARFI uses large single-lobe gradients to encode the displacement, which may render the image sensitive to motion, low SNR from the large b-value, and susceptible to artifacts in the phase map. In this study, MR-ARFI encoding gradients are developed to account for the above problems. A repeated bipolars gradient set and an inverted bipolars gradient set, which consisted of two identical or opposite-polarity bipolar gradients around the refocusing pulse, were compared to the conventional two single lobes gradient set with the same TE/TR and motion encoding pulse width. The HIFU system was triggered by the MR sequence to emit ultrasound synchronized with the encoding gradients with a duty cycle less than 5%.