Measurement of phosphorus content in normal and osteomalacic rabbit bone by solid‐state 3D radial imaging

Abstract

In osteomalacia decreased mineralization reduces the stiffness and static strength of bone. We hypothesized that hypomineralization in osteomalacic bone could be quantified by solidstate 31 Osteomalacia (rickets) is a disease characterized by hypomineralization of bone (1). Among the various causes of hypomineralization is a deficiency of vitamin D, calcium, and phosphorus resulting from inadequate nutrition, renal failure, or interference of certain drugs with calcium and vitamin D metabolism (2). Hypomineralization implies a reduced mineral mass per unit volume of bone tissue (also referred to as the degree of mineralization of bone (DMB) (3)). Both the stiffness and compressive strength of bone are largely determined by its mineral content, which in the normal skeleton is very tightly regulated. Currey (4) showed that even small variations in mineral content can have a disproportionately large influence on breaking strength, and noted that the latter decreased threefold for a decrease in ash content (mineral content) from 70% to 63%. Hypomineralization thus results in impaired mechanical competence of the skeleton and therefore increased fracture risk. Evaluation of the DMB requires knowledge about both bone mass and bone volume. The most common modalities used in the diagnosis of bone disease-dual-energy X-ray absorptiometry (DEXA) and X-ray computed tomography (CT)-cannot distinguish between osteoporosis (i.e., a reduced amount of normally mineralized bone) and osteomalacia (a normal amount of undermineralized bone) because these techniques measure only the apparent density as the amount of mineral mass per unit area (or volume, respectively) of tissue. While several destructive methods for measuring true mineral density (gravimetric analysis, microradiography, chemical analysis, etc.) are available, there is currently no noninvasive modality for measuring the DMB.Magnetic resonance imaging (MRI) offers a unique opportunity for noninvasive quantification of bone mineral whose major constituent is a poorly crystalline nonstoichiometric calcium phosphate similar in composition to low-crystalline hydroxyapatite, Ca 10 (OH) 2 (PO 4 ) 6 . The feasibility of imaging 31 P by solid-state MRI (SS-MRI) was recently demonstrated in bone specimens (5,6) as well as in vivo (7,8). However, there has been no demonstration so far that differences in mineralization density can be detected in bone disease. Quantification of phosphorus by MRI is complicated by the lower magnetic moment and unfavorable relaxation properties of the 31 P nucleus. The absence of rapid molecular motions in solids results in extremely short transverse relaxation times (8) and long spin-lattice relaxation times (9), both of which adversely affect the SNR.The purpose of the present work was to explore the feasibility of using 31 P solid-state MRI to quantify phosphorus with sufficient precision to distinguish between osteomalacic and normally mineralized bone in a rabbit model of osteomalacia. Toward this objective we designed and implemented a 3D ...

Direct magnetic resonance detection of myelin and prospects for quantitative imaging of myelin density

“…S4): SW = 200 kHz, TE = 20/1,200 μs, TI = 500 ms, TR = 1 s, field of view = 15 mm, matrix size = 128 × 128 × 128, number of views = 5,342, pulse duration = 20 μs. The sequence was based on that used by Anumula et al (38). TI was determined empirically as the duration yielding optimal GM suppression (because GM is expected to have negligible myelin concentration) in a complex difference image.…”

Methods for Assessing Bone Quality: A Review

“…Furthermore, this technique can be used quantitatively to determine the mass of bone mineral in the tissue [85], enabling detection of hypomineralization in osteomalacic rabbit tissue at an isotropic spatial resolution of approximately 280 lm [1]. Quantitative NMR analyses of bone mineral chemistry have also been performed in vivo, but such studies typically require long acquisition times in specialized scanners and are currently limited to the fingers, wrist, and hand [13,22,86].…”

“…The following key questions are addressed: (1) What are the techniques currently available for assessment of the mechanical, geometric, and material components of bone quality? (2) What are the main outcomes of each method?…”

NMR studies of biomineralisation

“…The role of structural water molecules in bones has been studied by 1 H MAS NMR as well as 31 P{ 1 H} and 13 C{ 1 H} LG-CP MAS NMR spectroscopy [161,162]. Finally, magnetic resonance imaging (MRI) investigations of bones, implants, related materials are gaining increasing interest [163][164][165][166][167].…”