Dual-frequency irradiation CEST-MRI of endogenous bulk mobile proteins

化学交换饱和转移(CEST)磁共振成像(MRI)已成为检测低浓度有机化合物(如代谢物或蛋白质)的一种重要的对比机制。CEST-MRI的主要优势是它可以在分子水平上获得信息，而不需要应用造影剂，并且具有与传统MRI相当的空间分辨率。然而，在活体组织中，许多不同溶质的CEST信号在光谱上重叠，阻碍了体内对一种感兴趣的特定化合物的选择性检测。提高特异度已成为CEST-MRI研究领域最重要的问题之一。最近，我们开发了一种基于CEST的新技术-DualCEST-克服了这一限制，并能够选择性地在体内检测内源性大宗可移动蛋白(即主要是胞浆蛋白)。这种非侵入性成像技术可能对与蛋白质表达深刻变化相关的疾病的诊断特别感兴趣，如癌症和阿尔茨海默氏症。与传统的CEST相比，排除来自其他细胞化合物的成分有望提高图像对比度在描绘健康和病变组织方面的特异性。对于人体检查，双重CEST技术可以很容易地在3T磁共振扫描仪上实施，使其在临床环境中得到广泛应用。我们已经通过对一名3T脑肿瘤患者的原则证明检查验证了双重CEST技术在人类中的适用性。然而，目前双重CEST检查仍然需要大约20分钟，而且只允许采集2D图像。此外，需要通过先导研究明确确认其作为诊断工具的重要性，才能将其纳入常规临床检查。因此，本提案的中心目标是建立双重CEST-MRI作为一种诊断工具来检测人类内源性大宗移动蛋白的变化。首先，将进一步开发双CEST脉冲序列，以实现快速和稳健的成像，从而在大约5分钟内对人脑进行高分辨率3D检查。双重CEST方法的诊断意义将在两个单独的针对脑瘤和阿尔茨海默氏症患者的试点研究中进行评估。双重CEST图像对比度有望为在分子水平上识别肿瘤组织提供补充信息，从而改进治疗方法。对于阿尔茨海默病，避免辐射暴露的诊断工具将允许定期和频繁的检查，从而提高患者护理水平。同时，将对先前利用的具有基因修改的细胞模型进行研究，以验证在生理相关规模上蛋白质组变化的可检测性。

Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) has emerged as an important contrast mechanism for the detection of organic compounds in low concentration such as metabolites or proteins. The major advantage of CEST-MRI is that it allows information to be obtained at the molecular level without the application of contrast media and with a spatial resolution comparable to conventional MRI. However, in living tissue the CEST signals of many diverse solutes are spectrally overlapping preventing the selective detection of one specific compound of interest in vivo. The improvement of specificity has become one of the most important issues in the research field of CEST-MRI. Recently, we developed a novel CEST-based technique – dualCEST – which overcomes this limitation and enables the selective detection of endogenous bulk mobile proteins in vivo (i.e. mainly cytosolic proteins). Such a noninvasive imaging technique may be of particular interest for the diagnosis of diseases associated with profound alterations of protein expression, like cancer and Alzheimer’s. In comparison to conventional CEST, the exclusion of contributions from other cellular compounds is expected to improve the specificity of the image contrast in terms of delineating healthy and diseased tissue.With regards to examinations in humans, the dualCEST technique can be readily implemented on 3T MR scanners making it widely applicable for practical applications in clinical settings. We have already verified the applicability of the dualCEST technique in humans by a proof-of-principle examination of a brain tumor patient at 3 T. However, currently a dualCEST examination still takes about 20 min, and moreover only allows acquisition of 2D images. In addition, an unequivocal validation of its significance as a diagnostic tool by a pilot study is required to allow its incorporation into routine clinical examinations.Thus, the central aim of this proposal is to establish the novel technique of dualCEST-MRI as a diagnostic tool to detect changes of endogenous bulk mobile proteins in humans. Firstly, the dualCEST pulse sequence will be further developed to enable a fast and robust imaging permitting a high-resolution 3D examination of the human brain in approximately 5 min. The diagnostic significance of the dualCEST approach will then be evaluated in two separate pilot studies with brain tumor and Alzheimer’s patients. The dualCEST image contrast is expected to provide complementary information for the identification of tumorous tissue at a molecular level, thus leading to improved treatments. For Alzheimer's disease, a diagnostic tool avoiding radiation exposure would allow regular and frequent examinations, and thus an improved level of patient care. In parallel, a previously utilized cell model with a genetic modification will be investigated to verify the detectability of proteomic changes on a physiologically relevant scale.