Quantification of Chemical Exchange with Low Field T1rho Dispersion MRI

除了提供详细的解剖图像外，磁共振成像（MRI）还可以制作定量图，更深入地了解组织组成，包括损伤或疾病的迹象。一种可以用核磁共振成像成像的物理现象是水和蛋白质等分子之间的化学交换，这种交换可能在中风后或癌症、阿尔茨海默氏症、多发性硬化症和其他神经系统疾病的发展过程中受到影响。能够可靠地成像这些分子和细胞的变化可以帮助我们更好地理解这些疾病是如何随着时间的推移而出现或恶化的。一种公认的测量化学交换的方法被称为化学交换饱和转移（CEST）。CEST可以检测体内已经存在的分子（如蛋白质）的交换过程，也可以检测在扫描前注射的特殊设计的造影剂。CEST数据的质量通常随着磁场强度的增加而提高，这意味着高场（高于3特斯拉）系统比低场系统（1.5T及以下）更适合CEST。然而，这种系统既昂贵又罕见；大多数商用核磁共振扫描仪的工作温度为1.5T，这使得像CEST这样的方法无法在大多数最有效的地方使用。拟议的研究计划将探索另一种MRI对比机制，称为T1？色散，以确定它在低磁场强度下的表现，以及它是否可以作为CEST的替代品。已知T1？分散测量对化学交换很敏感，但在低场还没有广泛应用，在低场它们可能与CEST相匹配甚至优于CEST。我们会实现T1吗？分散方法在三种不同的MRI扫描仪上-一种3T临床系统，一种3T临床前系统，以及一种由加拿大Synaptive Medical公司开发的新型0.5T扫描仪。然后，我们将评估哪种方法能够提供关于化学交换的最可靠的信息，以及哪种方法可以在合理的时间内获得以允许实际应用。通过这项研究所取得的技术进步，将使化学交换对比成像更广泛地获得，从而使加拿大乃至全世界的基础科学受益。目前，只有那些拥有超高场MRI扫描仪或专用造影剂的设施才能进行实际的CEST成像。如果T1 ?分散可以有效地提供与CEST相同的信息，但在低场更可行，这项技术可以部署到全国各地已经使用的数百台低场扫描仪上，以及像Synaptive 0.5T这样的新系统。这将为恶性神经过程的生物分子和细胞基础研究开辟新的途径，这将不仅仅局限于少数学术研究中心，而是可以在市场上的任何MRI扫描仪上进行。

In addition to providing detailed images of anatomy, Magnetic Resonance Imaging (MRI) can also make quantitative maps which provide a more in-depth look at tissue composition, including signs of damage or disease. One physical phenomenon that can be imaged with MRI is chemical exchange between water and molecules such as proteins, which can be affected after a stroke, or during the development process of cancer, Alzheimer's, multiple sclerosis and other neurological disorders. Being able to reliably image such molecular and cellular changes could help improve our understanding of how these diseases appear or worsen over time. One well-established method for measuring chemical exchange is called Chemical Exchange Saturation Transfer, or CEST. CEST can examine exchange processes involving molecules such as proteins that are already in the body, or it can detect specially designed contrast agents that are injected before a scan. The quality of CEST data generally improves as the magnetic field strength increases, meaning that high field (above 3 Tesla) systems are much better suited to CEST than lower field systems (1.5T and below). However, such systems are expensive and rare; most commercial MRI scanners operate at 1.5T, making methods like CEST inaccessible to the majority of sites where it would be the most impactful. The proposed research program will explore an alternate MRI contrast mechanism known as T1? dispersion, to determine how it performs at low magnetic field strength and whether it might serve as a surrogate for CEST. It is already known that T1? dispersion measurements are sensitive to chemical exchange, but they have not been widely used at low field, where they may match or even outperform CEST. We will implement T1? dispersion methods on three different MRI scanners - a 3T clinical system, a 3T preclinical system, and a novel 0.5T scanner developed by Synaptive Medical, a Canadian company. We will then assess which method gives the most reliable information regarding chemical exchange, and which can be acquired in a reasonable amount of time to allow practical applications. The technological advances made possible through this research will benefit basic science throughout Canada and beyond by making chemical exchange contrast imaging more widely accessible. Currently, only those facilities with ultra-high field MRI scanners or access to specialized contrast agents can perform practical CEST imaging. If T1? dispersion can effectively provide the same information as CEST but is more feasible at lower field, this technique can then be deployed onto the hundreds of low-field scanners already in use across the country, as well as novel systems such as the Synaptive 0.5T. This would open up new avenues of research into the biomolecular and cellular underpinnings of malignant neurological processes that would not be limited to a handful of academic research centers but could be carried out on virtually any MRI scanner on the market.