MRI of Bio-Magnetism
Human body can be weakly (on the order of 0.01ppm) magnetized by the strong magnetic field inside MRI scanners. This magnetization originates from the magnetic susceptibility of biomolecules and certain trace metals; it is further influenced by the cellular architecture of tissue. Until very recently, the spatial distribution of the magnetization and the corresponding magnetic susceptibility inside our body could not be measured, as traditional magnetometers only measure the magnetic field outside the body. Recent developments in MRI have overcome this limitation and begun to allow the mapping of magnetic susceptibility in 3D space. Magnetic susceptibility mapping not only provides a means to produce high-resolution MR images, but also offers quantitative information of the molecular contents and cellular architectures of both healthy and diseased tissues. For example, it allows the quantification of tissue iron stores, calcification in tumors, myelination in white matter, aggregation of b-amyloid in Alzheimer’s disease and the dynamic conversion between oxy- and deoxyhemoglobin. Magnetic susceptibility is also orientation dependent and is a tensor quantity. Quantifying magnetic susceptibility anisotropy allows the mapping of the orientations of axonal fibers, myofibers and collagens. In NMR spectroscopy, studying magnetic susceptibility anisotropy of biomolecules have greatly enhanced the ability to determine protein structures. Similarly, studying magnetic susceptibility of biological tissue will help us assess its molecular and cellular architecture on a larger scale. These techniques have now found applications in many tissues and organs including the brain, heart, liver, kidney and knee joints.
Chunlei Liu is an Associate Professor at the University of California, Berkeley, with the Department of Electrical Engineering and Computer Sciences, and the Helen Wills Neuroscience Institute. He received a B.S. in Physics from Peking University, an M.S. in Physics from the University of North Carolina, Chapel Hill, and a Ph.D. in Electrical Engineering from Stanford University. He was previously Associate Professor of Radiology and Biomedical Engineering at Duke University. Dr. Liu’s research is in the area of magnetic resonance imaging and remote cell modulation. Dr. Liu pioneered higher-order tensor diffusion MRI which utilizes higher-order tensor statistics (variance, sknewness, kurtosis etc.) to measure the diffusion processes in biological tissues. Dr. Liu is also credited for developing susceptibility tensor imaging for mapping bio-magnetism. He received NIH Pathway to Independence Award (K99) in 2006, ISMRM Young Investigator Award finalist in 2007 and RSNA Margulis Award in 2015.