Review of the ultrashort echo time magnetic resonance imaging of cortical bone

The evaluation of bone quality, especially cortical bone, is very important for diagnosing and treating the bone diseases. Because of the rapidly aging population of the global society, noninvasively, precisely and feasibly evaluating the bone quality has become a hot topic in the contemporary medical physics studies. Among the several available methods of evaluation, the bone mineral density (B MD) measured with dual-energy X-ray absorptiometry is currently considered to be the gold standard in clinical applications. However, the BMD is limited by its incapability of assessing the organic matrix, microstructure, porosity and perfusion of bone. In addition, the BMD can neither provide a definite diagnose of osteoporosis nor predict fractures precisely. Cortical bone shows near zero signal with all conventional clinical magnetic resonance imaging (MRI) sequences, because of the rapid decay of the magnetic resonance signal in the bone. Due to the recently developed theories, methods and hardware, ultrashort time echo (UTE) sequences with nominal TE of less than 100 is have aroused the increasing research interest. In this paper an introduction to the basic physics of UTE MRI of cortical bone is presented. The newly proposed qualitative and quantitative UTE MRI methods are reviewed with an introduction to the research work in the authors' laboratory. The features, application scopes and limitations of those methods are also summarized. Finally, the authors point out the directions and steps of further studies. The paper will be helpful for understanding theoretical research and the clinical applications of UTE imaging of cortical bone.