Quantitative micro-computed tomography:​ a non-invasive method to assess equivalent bone mineral density

Nazarian, Ara; Snyder, Brian D.; Zurakowski, David; Müller, Ralph

Affiliations

¹Orthopedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, 02215, USA

²Institute for Biomedical Engineering, University and ETH Zürich, 8044 Zürich, Switzerland

³Department of Orthopaedic Surgery, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA

⁴Institute for Biomechanics, ETH Zürich, 8093 Zürich, Switzerland

Abstract and keywords

One of the many applications of micro computed tomography (µCT) is to accurately visualize and quantify cancellous bone microstructure. However, µCT based assessment of bone mineral density has yet to be thoroughly investigated. Specifically, the effects of varying imaging parameters, such as tube voltage (kVp), current (μA), integration time (ms), object to X-ray source distance (mm), projection number, detector array size and imaging media (surrounding the specimen), on the relationship between equivalent tissue density (ρEQ) and its linear attenuation coefficient (μ) have received little attention. In this study, in house manufactured, hydrogen dipotassium phosphate liquid calibration phantoms (K₂HPO₄) were employed in addition to a resin embedded hydroxyapatite solid calibration phantoms supplied by Scanco Medical AG Company. Variations in current, integration time and projection number had no effect on the conversion relationship between µ and ρEQ for the K₂HPO₄ and Scanco calibration phantoms [p > 0.05 for all cases]. However, as expected, variations in scanning tube voltage, object to X-ray source distance, detector array size and imaging media (referring to the solution that surrounds the specimen in the imaging vial) significantly affected the conversion relationship between μ and ρEQ for K₂HPO₄ and Scanco calibration phantoms [p < 0.05 for all cases]. A multivariate linear regression approach was used to estimate ρEQ based on attenuation coefficient, tube voltage, object to X-ray source distance, detector array size and imaging media for K₂HPO₄ liquid calibration phantoms, explaining 90% of the variation in ρEQ. Furthermore, equivalent density values of bovine cortical bone (converted from attenuation coefficient to equivalent density using the K₂HPO₄ liquid calibration phantoms) samples highly correlated [R² = 0.92] with the ash densities of the samples.

In conclusion, Scanco calibration phantoms can be used to assess equivalent bone mineral density; however, they cannot be scanned with a specimen or submerged in a different imaging media. The K₂HPO₄ liquid calibration phantoms provide a cost effective, easy to prepare and convenient means to perform quantitative µCT analysis using any µCT system, with the ability to choose different imaging media according to study needs. However, as with any liquid calibration phantom, they are susceptible to degradation over time.

Keywords: Micro-computed tomography; Calibration phantom; Calibration; Bone density; Bone mineralization

Links

DOI: 10.1016/j.bone.2008.04.009

PubMed: 18539557

WoS: 000257928300010

History

Received: 2007-05-23

Revised: 2008-04-10

Accepted: 2008-04-14

Online: 2008-04-30

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