title: 31P NMR relaxation of cortical bone mineral at multiple magnetic field strengths and levels of demineralization.
abstract: Recent work has shown that solid-state (1) H and (31) P MRI can provide detailed insight into bone matrix and mineral properties, thereby potentially enabling differentiation of osteoporosis from osteomalacia. However, (31) P MRI of bone mineral is hampered by unfavorable relaxation properties. Hence, accurate knowledge of these properties is critical to optimizing MRI of bone phosphorus. In this work, (31) P MRI signal-to-noise ratio (SNR) was predicted on the basis of T1 and T2 * (effective transverse relaxation time) measured in lamb bone at six field strengths (1.5-11.7 T) and subsequently verified by 3D ultra-short echo-time and zero echo-time imaging. Further, T1 was measured in deuterium-exchanged bone and partially demineralized bone. (31) P T2 * was found to decrease from 220.3 ± 4.3 µs to 98.0 ± 1.4 µs from 1.5 to 11.7 T, and T1 to increase from 12.8 ± 0.5 s to 97.3 ± 6.4 s. Deuteron substitution of exchangeable water showed that 76% of the (31) P longitudinal relaxation rate is due to (1) H-(31) P dipolar interactions. Lastly, hypomineralization was found to decrease T1, which may have implications for (31) P MRI based mineralization density quantification. Despite the steep decrease in the T2 */T1 ratio, SNR should increase with field strength as B0 (0.4) for sample-dominated noise and as B0 (1.1) for coil-dominated noise. This was confirmed by imaging experiments.
authors.affiliation: Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Alan C
authors.initials: AC
authors.lastname: Seifert
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Wright
authors.forename: Suzanne L
authors.initials: SL
authors.lastname: Wehrli
authors.forename: Henry H
authors.initials: HH
authors.lastname: Ong
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000502:physiology*; D002113:Calcification, Physiologic; D003903:Deuterium / Q000378:metabolism; D060526:Magnetic Fields; D009682:Magnetic Resonance Spectroscopy; D008903:Minerals / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*; D011846:Radio Waves; D012756:Sheep; D059629:Signal-To-Noise Ratio; D013997:Time Factors
chemical_list: D008903:Minerals; D010758:Phosphorus; D003903:Deuterium
keywords: 31P MRI; bone mineral; mineralization; relaxation; signal-to-noise ratio