In vivo MRI of submillisecond T₂ 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.

In Vivo Quantitative MR Imaging of Bound and Pore Water in Cortical Bone

“…The use of dedicated or specialized RF coils for signal reception offers the best opportunity to improve resolution and imaging time, albeit with a smaller field of view. Beyond hardware improvements, reduced (35) or anisotropic (36,37) field of view methods might be effective in increasing resolution or in enabling access to regions such as the femoral neck that would otherwise require a relatively large three-dimensional field of view and long imaging time. Similarly, another possible approach is to use two-dimensional rather than threedimensional UTE acquisitions.…”

Can MRI Replace CT in Evaluating Semicircular Canal Dehiscence?

“…11 As a result, fluid in the membranous labyrinth has high signal, whereas cortical bone has null signal because of low proton density and very short T1 and T2. 15 These features result in very high contrast between the membranous labyrinth and the surrounding petrous bone. FIESTA is theoretically wellsuited for the evaluation of SC dehiscence by enabling discrimination of very thin bone coverage between the membranous labyrinth and CSF, which is essential in the diagnosis of SC dehiscence.…”

Measurements of mobile and bound water by nuclear magnetic resonance correlate with mechanical properties of bone

“…One previous study investigated connections between architectural indices of trabecular bone (as determined by MRI) and bone strength [54], while another related water content (as determined by NMR-derived diffusion characteristics of exchangeable water) to bone density and strength in an animal model of hypomineralization [49]. MRI studies of bone have been focused on assessing the structure or architecture of trabecular and cortical bone (see review by Wehrli for details [57]), but recently, water volume fraction in the mid-shaft of human tibiae was quantified by analyzing T 2 protons with a 3 Tesla, clinical MRI scanner [58]. The effect of aging or water distribution however was not a focus in either of these studies, as it was here.…”