Magnetic resonance imaging of the Amine-Proton EXchange (APEX) dependent contrast.
Magnetic resonance imaging of the Amine-Proton EXchange (APEX) dependent contrast.
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DOI：
10.1016/j.neuroimage.2011.08.014
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发表时间：
2012-01-16
期刊：
影响因子：
5.7
通讯作者：
Kim, Seong-Gi
中科院分区：
文献类型：
--
作者：
Jin, Tao;Wang, Ping;Zong, Xiaopeng;Kim, Seong-Gi
关键词：
水与来自氨基酸、蛋白质和其他分子的不稳定质子之间的化学交换可以利用磁共振成像（MRI）技术来提供组织对比。使用非共振自旋锁定（SL）方案进行信号准备是有利的，因为可以通过调整SL脉冲参数将图像对比度调谐到特定的交换速率。虽然酰胺质子转移（APT）的对比度最佳地获得与稳态准备，使用低功率和长的照射脉冲，图像对比度从更快的胺-水质子交换（APEX）在瞬态优化与更高的功率和更短的SL脉冲。我们的体模实验表明，APEX对比度对蛋白质和氨基酸浓度以及pH值敏感。在体内9.4-T SL MRI数据的大鼠大脑与辐射参数优化，以减缓交换率有一个尖锐的峰值在3.5 ppm，也宽峰在-2至-5 ppm，诱导负对比度的APT加权图像，而APEX图像具有由许多不同胺基团的加权总和产生的大正信号。由心脏骤停诱导的脑缺血使纯APT信号从~1.7%降低至~ 0%，并使APEX信号从~8%增加至~ 16%。在大脑中动脉闭塞（MCAO）模型中，APEX信号显示出不同的空间和时间模式，与APT和水扩散图相比，动物间差异较大。由于化学交换饱和转移（CEST）和SL技术之间的相似性，APEX对比度也可以通过CEST方法使用类似的辐照参数来获得。APEX可以为许多涉及蛋白质、肽、氨基酸或pH水平变化的疾病提供有用的信息，并且可以作为敏感的神经成像生物标志物。
Chemical exchange between water and labile protons from amino-acids, proteins and other molecules can be exploited to provide tissue contrast with magnetic resonance imaging (MRI) techniques. Using an off-resonance Spin-Locking (SL) scheme for signal preparation is advantageous because the image contrast can be tuned to specific exchange rates by adjusting SL pulse parameters. While the amide-proton transfer (APT) contrast is obtained optimally with steady-state preparation, using a low power and long irradiation pulse, image contrast from the faster amine-water proton exchange (APEX) is optimized in the transient state with a higher power and a shorter SL pulse. Our phantom experiments show that the APEX contrast is sensitive to protein and amino acid concentration, as well as pH. In vivo 9.4-T SL MRI data of rat brains with irradiation parameters optimized to slow exchange rates have a sharp peak at 3.5 ppm and also broad peak at −2 to −5 ppm, inducing negative contrast in APT-weighted images, while the APEX image has large positive signal resulting from a weighted summation of many different amine-groups. Brain ischemia induced by cardiac arrest decreases pure APT signal from ~1.7% to ~0%, and increases the APEX signal from ~8% to ~16%. In the middle cerebral artery occlusion (MCAO) model, the APEX signal shows different spatial and temporal patterns with large inter-animal variations compared to APT and water diffusion maps. Because of the similarity between the chemical exchange saturation transfer (CEST) and SL techniques, APEX contrast can also be obtained by a CEST approach using similar irradiation parameters. APEX may provide useful information for many diseases involving a change in levels of proteins, peptides, amino-acids, or pH, and may serve as a sensitive neuroimaging biomarker.
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