We have conducted an in-depth analysis of the use of calibration phantoms to measure equivalent bone mineral density in high resolution µCT imaging. Particularly, we investigated three calibration phantoms, one available commercially with the scanner, the other available commercially, and the third manufactured at the lab, and modeled the effects of varying imaging parameters on measurement of equivalent bone mineral density in hopes of offering the scientific community basic guidelines in the rapidly growing yet understudied use of µCT imaging to assess bone mineral density. 

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The importance of this work is to highlight the factors that affect the assessment of bone tissue density from micro-computed tomography in general, and not to provide a comparative assessment of bone tissue density assessment from different manufacturers, as they all use very similar sources and detectors. The manufacturer provided solid and the in house made liquid calibration phantoms proved to be useful each with specific positive and negative characteristics. As µCT based assessment of bone mineral density is and will be on the rise in future, it is recommended to establish guidelines and standards in order to accurately compare these density measures across laboratories and scanner makes and models worldwide. For now, the best way to obtain accurate attenuation values from µCT imaging is to include appropriately sized calibration phantoms with each specimen to be imaged. The presence of calibration phantoms in each specimen cross-sectional image can provide a direct conversion to known density values. 

In a follow-up study, we have generated a family of correction curves which can be readily used to improve density measurement outputs. Finally, some concerns regarding the spatial configuration and positioning of objects within the reconstruction space have been addressed in this study. The current project in tandem with the recent publications in the field open the possibility of designing a universal calibration phantom which takes into account the homogeneity of the material, density range, size and the location of the densities which will allow the researchers to compare density values generated by different μCT systems using different imaging settings.

Relevant Publications: 11, 12 , 13 , 30