MRI of Short and Ultrashort-T_2 Tissues: Making the Invisible Visible

This book comprehensively covers ultrashort echo time (UTE), zero echo time (ZTE), and other magnetic resonance imaging (MRI) acquisition techniques for imaging of short and ultrashort-T2 tissues. MRI uses a large magnet and radio waves to generate images of tissues in the body. The MRI signal is characterized by two time constants, spin-lattice relaxation time (T1) which describes how fast the longitudinal magnetization recovers to its initial value after tipping to the transverse plane, and spin-spin relaxation time (T2) which describes how fast the transverse magnetization decays. Conventional MRI techniques have been developed to image and quantify tissues with relatively long T2s. However, the body also contains many tissues and tissue components such as cortical bone, menisci, ligaments, tendons, the osteochondral junction, calcified tissues, lung parenchyma, iron containing tissues, and myelin, which have short or ultrashort-T2s. These tissues are “invisible” with conventional MRI, and their MR and tissue properties are not measurable. UTE and ZTE type sequences resolve these challenges and make these tissues visible and quantifiable.

This book first introduces the basic physics of conventional MRI as well as UTE and ZTE type MRI, including radiofrequency excitation, data acquisition, and image reconstruction. A series of contrast mechanisms are then introduced and these provide high resolution, high contrast imaging of short and ultrashort-T2 tissues. A series of quantitative UTE imaging techniques are described for measurement of MR tissue properties (proton density, T1, T2, T2*, T1p,magnetization transfer, susceptibility, perfusion and diffusion). Finally, clinical applications in the musculoskeletal, neurological, pulmonary and cardiovascular systems are described.

This is an ideal guide for physicists and radiologists interested in learning more about the use of UTE and ZTE type techniques for MRI of short and ultrashort-T2 tissues.

Dr Jiang Du is a physicist who is Professor of Radiology and Director of the Ultrashort Echo Time (UTE) Imaging Lab at the University of California, San Diego (UCSD). His research focuses on the development of magnetic resonance imaging (MRI), especially UTE MRI of short and ultrashort-T2 tissues such as cortical bone, tendons, ligaments, menisci, iron containing tissues and myelin. He has published over 200 papers and mentored more than 100 trainees. Currently,he is a principal investigator for three NIH RO1 grants and one VA merit grant to study osteoarthritis (OA), osteoporosis (OP), Alzheimer’s disease (AD), and traumatic brain injury (TBI). He has served on many academic organizations and review committees, including study sections for the National Institute of Health (NIH), Department of Defense (DOD), and Radiological Society of North America (RSNA). He has won numerous awards including the RSNA Research Scholarship, the American Heart Association (AHA) Young Investigator Award, the International Society of Magnetic Resonance in Medicine (ISMRM) Outstanding Teacher Award, the International Skeletal Society (ISS) Excellence Award, and the Academy for Radiology & Biomedical Imaging Research (ARBIR) Distinguished Investigator Award. Dr Du is Fellow of the ISMRM and American Institute for Medical and Biological Engineering (AIMBE).

Dr Graeme Bydder is a radiologist who began clinical MRI in 1981 and has continued to the present day. He was a joint author of the first paper on the use of MRI in multiple sclerosis in 1981 and the first comprehensive paper on MRI of the brain in 1982. He was also a joint author of many of the first papers describing techniques now commonly used in clinical imaging. These include: inversion recovery and heavily T2-weighted spin echo sequences, Gd based contrast agents, STIR, susceptibility weighted imaging and FLAIR. He has worked at UCSD since 2003 on UTE development which uses radial imaging and high performancegradients to detect signals from bone, tendon, ligaments and other short and ultrashort-T2 tissues. He is also working on multiplied, added, subtracted and divided inversion recovery (MASDIR) sequences which provide improved lesion contrast in clinical MRI. He is a past president of the ISMRM, gold medalist of the ISMRM and Royal College of Radiologists, as well as an honorary member of the American and British Societies of Neuroradiology.