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Bone‐composition imaging using coherent‐scatter computed tomography: Assessing bone health beyond bone mineral density
Author(s) -
Batchelar Deidre L.,
Davidson Melanie T. M.,
Dabrowski Waldemar,
Cunningham Ian A.
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2179151
Subject(s) - soft tissue , bone mineral , materials science , biomedical engineering , tomography , imaging phantom , bone tissue , quantitative computed tomography , cadaveric spasm , bone density , medical imaging , nuclear medicine , radiology , osteoporosis , medicine , pathology , anatomy
Quantitative analysis of bone composition is necessary for the accurate diagnosis and monitoring of metabolic bone diseases. Accurate assessment of the bone mineralization state is the first requirement for a comprehensive analysis. In diagnostic imaging, x‐ray coherent scatter depends upon the molecular structure of tissues. Coherent‐scatter computed tomography (CSCT) exploits this feature to identify tissue types in composite biological specimens. We have used CSCT to map the distributions of tissues relevant to bone disease (fat, soft tissue, collagen, and mineral) within bone‐tissue phantoms and an excised cadaveric bone sample. Using a purpose‐built scanner, we have measured hydroxyapatite (bone mineral) concentrations based on coherent‐scatter patterns from a series of samples with varying hydroxyapatite content. The measured scatter intensity is proportional to mineral density in true g ∕ cm 3 . Repeated measurements of the hydroxyapatite concentration in each sample were within, at most, 2% of each other, revealing an excellent precision in determining hydroxyapatite concentration. All measurements were also found to be accurate to within 3% of the known values. Phantoms simulating normal, over‐, and under‐mineralized bone were created by mixing known masses of pure collagen and hydroxyapatite. An analysis of the composite scatter patterns gave the density of each material. For each composite, the densities were within 2% of the known values. Collagen and hydroxyapatite concentrations were also examined in a bone‐mimicking phantom, incorporating other bone constituents (fat, soft tissue). Tomographic maps of the coherent‐scatter properties of each specimen were reconstructed, from which material‐specific images were generated. Each tissue was clearly distinguished and the collagen‐mineral ratio determined from this phantom was also within 2% of the known value. Existing bone analysis techniques cannot determine the collagen‐mineral ratio in intact specimens. Finally, to demonstrate the in situ potential of this technique, the mineralization state of an excised normal cadaveric radius was examined. The average collagen‐mineral ratio of the cortical bone derived from material‐specific images of the radius was 0.53 ± 0.04 , which is in agreement with the expected value of 0.55 for healthy bones.