title: Characterization of trabecular bone density with ultra-short echo-time MRI at 1.5, 3.0 and 7.0 T--comparison with micro-computed tomography.
abstract: The goal of this study was to test the potential of ultra-short echo-time (UTE) MRI at 1.5, 3.0 and 7.0 T for depiction of trabecular bone structure (of the wrist bones), to evaluate whether T2* relaxation times of bone water and parametric maps of T2* of trabecular bone could be obtained at all three field strengths, and to compare the T2* relaxation times with structural parameters obtained from micro-computed tomography (micro-CT) as a reference standard. Ex vivo carpal bones of six wrists were excised en bloc and underwent MRI at 1.5, 3.0 and 7.0 T in a whole-body MR imager using the head coil. A three-dimensional radial fat-suppressed UTE sequence was applied with subsequent acquisitions, with six different echo times TE of 150, 300, 600, 1200, 3500 and 7000 µs. The T2* relaxation time and pixel-wise computed T2* parametric maps were compared with a micro-computed-tomography reference standard providing trabecular bone structural parameters including porosity (defined as the bone-free fraction within a region of interest), trabecular thickness, trabecular separation, trabecular number and fractal dimension (Dk). T2* relaxation curves and parametric maps could be computed from datasets acquired at all field strengths. Mean T2* relaxation times of trabecular bone were 4580 ± 1040 µs at 1.5 T, 2420 ± 560 µs at 3.0 T and 1220 ± 300 µs at 7.0 T, when averaged over all carpal bones. A positive correlation of T2* with trabecular bone porosity and trabecular separation, and a negative correlation of T2* relaxation time with trabecular thickness, trabecular number and fractal dimension, was detected (p < 0.01 for all field strengths and micro-CT parameters). We conclude that UTE MRI may be useful to characterize the structure of trabecular bone, comparable to micro-CT.
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
authors.forename: Moritz C
authors.initials: MC
authors.lastname: Wurnig
authors.forename: Maurizio
authors.initials: M
authors.lastname: Calcagni
authors.forename: David
authors.initials: D
authors.lastname: Kenkel
authors.forename: Magdalena
authors.initials: M
authors.lastname: Vich
authors.forename: Markus
authors.initials: M
authors.lastname: Weiger
authors.forename: Gustav
authors.initials: G
authors.lastname: Andreisek
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
authors.forename: Andreas
authors.initials: A
authors.lastname: Boss
mesh_terms: D000368:Aged; D001834:Body Water / Q000737:chemistry; D015519:Bone Density; D001853:Bone Marrow / Q000737:chemistry / Q000000981:diagnostic imaging; D002348:Carpal Bones / Q000737:chemistry* / Q000000981:diagnostic imaging / Q000648:ultrastructure; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D016062:Porosity; D011522:Protons; D055114:X-Ray Microtomography
chemical_list: D011522:Protons
keywords: applications; endogenous contrast methods; methods and engineering, bone; methods and engineering, quantitation; musculoskeletal; post-acquisition processing; relaxometry
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