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）的重要对比机制。CEST-MRI的主要优点是，它允许在分子水平上获得信息，而无需应用造影剂，并且空间分辨率与传统MRI相当。然而，在活组织中，许多不同溶质的CEST信号在光谱上重叠，从而阻止了在体内选择性检测一种特定的感兴趣化合物。提高CEST-MRI的特异性已成为CEST-MRI研究领域的重要课题之一。最近，我们开发了一种新的CEST为基础的技术- dualCEST -它克服了这一限制，使内源性散装移动的蛋白质在体内（即主要是胞质蛋白）的选择性检测。这种非侵入性成像技术可能对诊断与蛋白质表达的深刻改变相关的疾病（如癌症和阿尔茨海默氏症）特别感兴趣。与传统的CEST相比，排除其他细胞化合物的贡献有望提高图像对比度在描绘健康和患病组织方面的特异性。关于人体检查，dualCEST技术可以很容易地在3 T MR扫描仪上实现，使其广泛适用于临床环境中的实际应用。我们已经通过在3 T下对脑肿瘤患者进行的原理验证检查验证了dualCEST技术在人类中的适用性。然而，目前双CEST检查仍然需要大约20分钟，而且仅允许采集2D图像。此外，明确验证其作为一种诊断工具的重要性的试点研究是必要的，以允许其纳入常规的临床examinations.Thus，本提案的中心目的是建立新的技术dualCEST-MRI作为一种诊断工具，以检测内源性散装移动的蛋白在人类的变化。首先，将进一步开发dualCEST脉冲序列，以实现快速和稳健的成像，允许在大约5分钟内对人脑进行高分辨率3D检查。然后将在两项单独的试点研究中对脑肿瘤和阿尔茨海默病患者进行评估。dualCEST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，从而改善治疗。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，将研究先前使用的具有遗传修饰的细胞模型，以验证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.