Ferumoxytol Enhanced Hyperfine Low Field Strength MRI

Ferumoxytol is a superparamagnetic iron oxide nanoparticle (SPION) preparation that was originally designed as an MRI contrast agent, but later received FDA approval as a treatment for iron deficiency anemia. Contrast agents alter MR images by changing tissue magnetic relaxation constants such as T1 and T2 (or T2*). Gadolinium-based contrast agents decrease T1 values, causing increased signal on T1-weighted images. At low field strength, T1 values are already very short so a further decrease may provide little contrast. At typical field strengths, Ferumoxytol strongly decreases T1 and also T2 (and T2*) values, increasing signal on T1-weighted images and (conversely) decreasing signal on T2-weighted images. This T2-based contrast mechanism may be maintained at lower field strength.

Patients with iron deficiency anemia are commonly prescribed Ferumoxytol periodically as part of their standard clinical care. Multiple studies have characterized the efficacy and safety of Ferumoxytol in the treatment of iron deficiency anemia. Patients prescribed Ferumoxytol for iron-deficiency anemia typically include otherwise healthy women with heavy menstrual periods, patients with inflammatory bowel disease, and patients with chronic kidney disease. Such patients make ideal candidates for characterizing the effects of Ferumoxytol on novel imaging devices by obviating a medically unnecessary injection of the contrast agent.

Contrast agents play a key role in diagnosing and managing numerous diseases. Ferumoxytol has been used to image a variety of pathologies and organs, including tumors and inflammation in the brain, liver, pancreas, and prostate. In addition to the different magnetic relaxation properties described above, Ferumoxytol has a higher molecular weight and prolonged blood pool period compared to typical gadolinium-based agents, facilitating imaging vasculature prior to the contrast agent leaking into the extravascular tissue. This has been exploited at higher field strengths and may be particularly advantageous for low field imaging that requires longer scan times. Ferumoxytol iron particles are taken up through the reticuloendothelial system and added to physiologic iron stores, rather than being excreted through the kidneys, resulting in increased plasma half-life while also avoiding concerns related to impaired renal function that sometimes arise with other contrast agents.

The Hyperfine device is a newly developed MRI unit that has multiple potential advantages over standard CT or MRI including portability, easier upkeep, open design, and ease of use. Unlike CT, the Hyperfine device does not use moving parts or X-rays to generate images. Unlike routine MRI, the Hyperfine device uses two permanent magnets with open space between and around them, rather than a super-cooled superconducting magnetic tube. In contrast to CT and routine MRI, the device can be wheeled from place to place and moved into position with the patient remaining on a gurney or hospital bed. Relative to routine MRI, the device uses a very low magnetic field strength of 64 mT compared to 1.5 T or 3 T, making it safer for patients or environments with medical devices having metallic components.

Standard images of different types are obtained on the Hyperfine device at the push of a button on an attached touch pad. Imaging protocols include those for anatomical depiction such as balance steady-state free precession (bSFFP), T1-weighted (T1W) gradient echo (GRE), and fast low-angle shot (FLASH) as well as imaging methods focused on the detection of pathology and tissue damage such as diffusion-weighted imaging (DWI), fluid attenuated inversion recovery (FLAIR), and T2-weighted (T2W) fast spin echo (FSE). However, it is not known if existing contrast agents can provide effective contrast in the Hyperfine low-field MRI.

Thus, the primary purpose of this study is to evaluate the efficacy of Ferumoxytol as a contrast agent in low-field MRI scanners. Patients who are already receiving Ferumoxytol as a treatment for iron deficiency anemia will be scanned before and after Ferumoxytol infusion. Degree of contrast enhancement in intravascular and extravascular compartments including the cerebral vasculature and the brain parenchyma will be the primary end-point for the study.