Quantification of Chemical Exchange with Low Field T1rho Dispersion MRI

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.