Ultralow-Field Magnetic Resonance Imaging

Ultralow-field magnetic resonance imaging (ULF MRI) is performed in fields of typically 130 microtesla, four orders of magnitude lower than in conventional MRI. Imaging at such low fields is made possible first, by prepolarizing the protons with a much higher magnetic field and second, by detecting the signal from the precessing protons with a SQUID (Superconducting QUantum Interference Device). The high longitudinal relaxation time T1-contrast intrinsic to ULF can be enhanced using a combination of inversion recovery and multiple echo sequences, as illustrated by in vivo images of the human brain showing brain tissue, blood, cerebrospinal fluid (CSF) and scalp fat. Furthermore a study of 35 patients reveals a significant T1-contrast between ex vivo normal prostate tissue and tumor tissue. Methods to enhance the signal-to-noise ratio of ULF-MRI signals and thus improve the spatial resolution and reduce the imaging time are discussed. In addition to ongoing studies, other potential clinical applications of ULF MRI include imaging cancer without the need for a contrast agent and imaging traumatic brain injury (TBI) caused by, for example, stroke, traffic accidents, high impact sports and combat-related explosions.