Song Xiaolei, Xu Jiadi, Xia Shuli, Yadav Nirbhay N, Lal Bachchu, Laterra John, Bulte Jeff W M, van Zijl Peter C M, McMahon Michael T
Division of MR Research, The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, USA; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
Magn Reson Med. 2015 Feb;73(2):488-96. doi: 10.1002/mrm.25567. Epub 2014 Dec 16.
The aim of this study was to develop a technique for rapid collection of chemical exchange saturation transfer images with the saturation varied to modulate signal loss transfer and enhance contrast.
Multi-echo Length and Offset VARied Saturation (MeLOVARS) divides the saturation pulse of length Tsat into N = 3-8 submodules, each consisting of a saturation pulse with length of Tsat /N (∼0.3-1 s), one or more low flip-angle gradient-echo readout(s) and a flip back pulse. This results in N readouts with increasing saturation time from Tsat /N to Tsat without extra scan time.
For phantoms, eight images with Tsat incremented every 0.5 s from 0.5-4 s were collected simultaneously using MeLOVARS, which allows rapid determination of exchange rates for agent protons. For live mice bearing glioblastomas, the Z-spectra for five different Tsat values from 0.5 to 2.5 s were acquired in a time normally used for one Tsat . With the additional Tsat -dependence information, LOVARS phase maps were produced with a more clearly defined tumor boundary and an estimated 4.3-fold enhanced contrast-to-noise ratio (CNR). We also show that enhancing CNR is achievable by simply averaging the collected images or transforming them using the principal component analysis.
MeLOVARS enables collection of multiple saturation-time-weighted images without extra time, producing a LOVARS phase map with increased CNR.
本研究的目的是开发一种技术，用于快速采集化学交换饱和转移图像，通过改变饱和度来调节信号损失转移并增强对比度。
多回波长度和偏移可变饱和度（MeLOVARS）将长度为Tsat的饱和脉冲划分为N = 3 - 8个子模块，每个子模块由一个长度为Tsat /N（约0.3 - 1秒）的饱和脉冲、一个或多个低翻转角梯度回波读出以及一个翻转回脉冲组成。这使得在不增加额外扫描时间的情况下，能够获得N个饱和度时间从Tsat /N增加到Tsat的读出结果。
对于体模，使用MeLOVARS同时采集了八幅图像，Tsat从0.5秒到4秒每隔0.5秒增加一次，这使得能够快速确定试剂质子的交换率。对于患有胶质母细胞瘤的活体小鼠，在通常用于一个Tsat的时间内获取了五个不同Tsat值（从0.5到2.5秒）的Z谱。利用额外的Tsat依赖性信息，生成的LOVARS相位图具有更清晰定义的肿瘤边界，估计对比度噪声比（CNR）提高了4.3倍。我们还表明，通过简单地对采集的图像进行平均或使用主成分分析对其进行变换，就可以提高CNR。
MeLOVARS能够在不增加额外时间的情况下采集多个饱和时间加权图像，生成具有更高CNR的LOVARS相位图。
