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Bi‐component T 2 * analysis of bound and pore bone water fractions fails at high field strengths
Author(s) -
Seifert Alan C.,
Wehrli Suzanne L.,
Wehrli Felix W.
Publication year - 2015
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.3305
Subject(s) - porosity , cortical bone , materials science , bound water , matrix (chemical analysis) , mineralogy , osteoporosis , chemistry , analytical chemistry (journal) , nuclear magnetic resonance , composite material , physics , chromatography , anatomy , molecule , medicine , organic chemistry , endocrinology
Osteoporosis involves the degradation of the bone's trabecular architecture, cortical thinning and enlargement of cortical pores. Increased cortical porosity is a major cause of the decreased strength of osteoporotic bone. The majority of cortical pores, however, are below the resolution limit of MRI. Recent work has shown that porosity can be evaluated by MRI‐based quantification of bone water. Bi‐exponential T 2 * fitting and adiabatic inversion preparation are the two most common methods purported to distinguish bound and pore water in order to quantify matrix density and porosity. To assess the viability of T 2 * bi‐component analysis as a method for the quantification of bound and pore water fractions, we applied this method to human cortical bone at 1.5, 3, 7 and 9.4 T, and validated the resulting pool fractions against micro‐computed tomography‐derived porosity and gravimetrically determined bone densities. We also investigated alternative methods: two‐dimensional T 1 – T 2 * bi‐component fitting by incorporation of saturation recovery, one‐ and two‐dimensional fitting of Carr–Purcell–Meiboom–Gill (CPMG) echo amplitudes, and deuterium inversion recovery. The short‐ T 2 * pool fraction was moderately correlated with porosity ( R 2 = 0.70) and matrix density ( R 2 = 0.63) at 1.5 T, but the strengths of these associations were found to diminish rapidly as the field strength increased, falling below R 2 = 0.5 at 3 T. The addition of the T 1 dimension to bi‐component analysis only slightly improved the strengths of these correlations. T 2 *‐based bi‐component analysis should therefore be used with caution. The performance of deuterium inversion recovery at 9.4 T was also poor ( R 2 = 0.50 vs porosity and R 2 = 0.46 vs matrix density). The CPMG‐derived short‐ T 2 fraction at 9.4 T, however, was highly correlated with porosity ( R 2 = 0.87) and matrix density ( R 2 = 0.88), confirming the utility of this method for independent validation of bone water pools. Copyright © 2015 John Wiley & Sons, Ltd.