Variable-Field Nuclear Magnetic Relaxometer

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Project Summary/ Abstract The MGH Institute for Innovation in Imaging (i3) requests nuclear magnetic relaxometry instrumentation with field cycling capabilities between 0.00023T and 3.0T. A relaxometer is a device that measures the nuclear magnetic relaxation times (T1, T2) of samples as a function of applied magnetic field. Relaxometry measurements performed at a given field strength are used to screen the efficacy small molecule and macromolecule probes that are used in magnetic resonance imaging (MRI). Relaxometry measurements performed as a function of varied field and/ or temperature us to characterize the molecular mechanisms that underpin nuclear magnetic relaxation enhancement and thus guide molecular strategies to probe optimization. Relaxometry can also be used to interrogate interactions between biomolecules and paramagnetic ions, to characterize and quantify molecular level pathologic changes in tissue, or to better understand how physiological fluctuations in blood or tissue may influence signal in an MRI scan. There is currently no functioning relaxometer at MGH. Until recently, MGH researchers screened the efficacy of newly developed relaxation agents using one of two fixed-field relaxometers functioning at 0.47T and 1.4T. However, both instruments are over 20 years old and are no longer operational. Relaxometry measurements can occasionally be performed using MRI scanners at the MGH Martinos Center, but the scanners are heavily booked for imaging studies, researchers are billed $655 and $300 per hour for the use of clinical and non-clinical scanners, and current experimental configuration provide poor control over sample temperature. Measurements can also occasionally be performed using the 11.7T or 14.1T vertical bore magnets used for NMR spectroscopy in the Charlestown Navy Yard. These spectrometers enable variable temperature recordings but these spectrometers operate at very high field compared to clinical MR scanners and the vast majority of non-clinical MR scanners, thus diminishing the relevance of measurements performed to screen MR imaging probe efficacy. The requested instrumentation will (1) replace the 0.47T and 1.4T relaxometers that have been heavily relied upon to screen new MR imaging probes, and (2) provide a unique and extremely powerful experimental resource that can be applied to interrogate molecular mechanisms that govern nuclear magnetic relaxation, guide imaging probe optimization, interrogate structure, dynamics, and speciation of biomolecules in biological systems, to facilitate engineering of phantoms to test on new MRI scanner technology being developed in parallel, to develop quantitative models of how physiologic changes (pO2, hematocrit) and MR imaging probes impact human fMRI signals, and to guide identification of imaging biomarkers.