title: In vivo MRI of submillisecond T(2) species with two-dimensional and three-dimensional radial sequences and applications to the measurement of cortical bone water.
abstract: Water in dense collagenous tissues such as tendons and ligaments, as well as water in cortical bone that occupies the spaces of the lacuno-canicular system or is tightly bound to collagen, is not ordinarily detectable by MRI. Water proton T(2) in these structures is generally less than 1 ms. Recent advances in instrumentation in conjunction with non-Cartesian imaging strategies now allow center of k-space to be scanned 100 micros or less after excitation. We examined the performance of two radial pulse sequences, a 2D sequence with half-pulse excitation and a new 3D hybrid sequence with variable-echo Cartesian encoding in the third dimension, on a whole-body 3 T scanner. Both pulse sequences used long-T(2) soft-tissue suppression pulses. The half-pulse slice profiles observed experimentally agreed well with those computed on the basis of a numerical solution of Bloch equations. The techniques yielded a signal-to-noise ratio of the order of 25 in 9 min scan time at a nominal voxel size of 0.58 x 0.58 x 8 mm(3) and 50-90 micros 'echo time' in the cortex of the tibial mid-shaft. With the use of an external reference, the water volume fraction of cortical bone in four subjects (mean +/- SD age 32.25 +/- 5.3 years) was found to be 22.5 +/- 2.7%, in good agreement with literature values.
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA 19104, USA.
authors.forename: Aranee
authors.initials: A
authors.lastname: Techawiboonwong
authors.forename: Hee Kwon
authors.initials: HK
authors.lastname: Song
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000328:Adult; D001842:Bone and Bones / Q000378:metabolism*; D003198:Computer Simulation; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water