The intersubject variations in bone phosphorus-31 (31 P) T1 and T 2 * , as well as the implications on in vivo 31 P MRI-based bone mineral quantification, were investigated at 3T field strength. ⋯ Neither 31 P T1 nor T 2 * varies significantly in healthy adults across a 50-year age range, therefore obviating the need for subject-specific measurements.
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Magn Reson Med. 2018 Dec 1; 80 (6): 2514-2524.
Purpose The intersubject variations in bone phosphorus-31 (31 P) T1 and http://www.w3.org/1998/Math/MathML"> T 2 * , as well as the implications on in vivo 31 P MRI-based bone mineral quantification, were investigated at 3T field strength.Methods A technique that isolates the bone signal from the composite in vivo 31 P spectrum was first evaluated via simulation and experiments ex vivo and subsequently applied to measure the T1 of bone 31 P collectively with a spectroscopic saturation recovery sequence in a group of healthy subjects aged 26 to 76 years. http://www.w3.org/1998/Math/MathML"> T 2 * was derived from the bone signal linewidth. The density of bone 31 P was derived for all subjects from 31 P zero TE images acquired in the same scan session using the measured relaxation times. Test-retest experiments were also performed to evaluate repeatability of this in vivo MRI-based bone mineral quantification protocol.Results The T1 obtained in vivo using the proposed spectral separation method combined with saturation recovery sequence is 38.4 ± 1.5 s for the subjects studied. Average 31 P density found was 6.40 ± 0.58 mol/L (corresponding to 1072 ± 98 mg/cm3 mineral density), in good agreement with an earlier study in specimens from donors of similar age range. Neither the relaxation times (P = 0.18 for T1 , P = 0.99 for http://www.w3.org/1998/Math/MathML"> T 2 * ) nor 31 P density (P = 0.55) were found to correlate with subject age. Average coefficients of variation for the repeat study were 1.5%, 2.6%, and 4.4% for bone 31 P T1 , http://www.w3.org/1998/Math/MathML"> T 2 * , and density, respectively.Conclusion Neither 31 P T1 nor http://www.w3.org/1998/Math/MathML"> T 2 * varies significantly in healthy adults across a 50-year age range, therefore obviating the need for subject-specific measurements.© 2018 International Society for Magnetic Resonance in Medicine.
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