Quantitative bone matrix density measurement by water‐ and fat‐suppressed proton projection MRI (WASPI) with polymer calibration phantoms

Abstract

The density of the organic matrix of bone substance is a critical parameter necessary to clinically evaluate and distinguish structural and metabolic pathological conditions such as osteomalacia in adults and rickets in growing children. Water-and fat-suppressed proton projection MRI (WASPI) was developed as a noninvasive means to obtain this information. In this study, a density calibration phantom was developed to convert WASPI intensity to true bone matrix density. The phantom contained a specifically designed poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blend, whose MRI properties (T 1 , T 2 , and resonance linewidth) were similar to those of solid bone matrix (collagen, tightly bound water, and other immobile molecules), minimizing the need to correct for differences in T 1 and/or T 2 relaxation between the phantom and the subject. Cortical and trabecular porcine bone specimens were imaged using WASPI with the calibration phantom in the field of view (FOV) as a stable intensity reference. Gravimetric and amino acid analyses were carried out on the same specimens after WASPI, and the chemical results were found to be highly correlated (r 2 ‫؍‬ 0.98 and 0.95, respectively) to the WASPI intensity. By this procedure the WASPI intensity can be used to obtain the true bone matrix mass density in g cm -3 .

Qualitative and quantitative ultrashort echo time (UTE) imaging of cortical bone

“…For example, Techawiboonwong et al have compared the signal from bone and a water phantom to quantify bone water concentration as a new metric of bone quality in human cortical bone in vivo [6,12]. Cao et al have also compared the signal from bone with a polymer calibration phantom, and found that the MR signal could be used to obtain true bone matrix mass density [23].…”

Ultra-short echo-time MRI detects changes in bone mineralization and water content in OVX rat bone in response to alendronate treatment

“…Notably, there is currently no technique other than magnetic resonance to quantify changes of the bone’s hydration state in situ . Recent work indicates that the majority of the proton signal observed in cortical bone is due to exchangeable water (as opposed to organic matrix) (1, 30) even though matrix constituents can also contribute to the solid-state MRI signal (9). …”

Quantitative 31P NMR spectroscopy and 1H MRI measurements of bone mineral and matrix density differentiate metabolic bone diseases in rat models

“…Our group has been engaged in developing 31 P solid-state magnetic resonance imaging (SMRI) to visualize bone mineral [21–23], and quantitative water- and fat-suppressed proton projection MRI (WASPI) to visualize solid bone matrix [24–26]. With these new methods, MRI measurements of bone mineral and matrix density have become available.…”