Specimen size and porosity can introduce error into μCT-based tissue mineral density measurements. Trans 53rd Orthop Res Soc

The accurate measurement of tissue mineral density, ρ m , in specimens of unequal size or quantities of bone mineral using polychromatic μCT systems is important, since studies often compare samples with a range of sizes and bone densities. We assessed the influence of object size on μCT measurements of ρ m using (1) hydroxyapatite rods (HA), (2) precision-manufactured aluminum foams (AL) simulating trabecular bone structure, and (3) bovine cortical bone cubes (BCt). Two beam-hardening correction (BHC) algorithms, determined using a 200 and 1200 mg/cm 3 HA wedge phantom, were used to calculate ρ m of the HA and BCt. Introduction Measurement of equivalent bone tissue mineral density (ρ m ) using polychromatic planar radiography and computed tomography are established techniques whose precision, accuracy, and potential sources of error have been well studied [e.g., 1,2-6]. Polychromatic micro-computed (μCT) tomographic analyses of bone were originally focused only on structural assessments of trabecular and cortical bone tissue [7,8] and not measurements of ρ m . Recently, methods for the measurement of ρ m have been developed for polychromatic μCT and several studies have incorporated these techniques [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. However, only a few published studies of the precision and accuracy of μCT-based equivalent ρ m have been performed to date [23][24][25][26], in contrast to the numerous studies completed for clinical [27][28][29][30][31][32][33][34][35][36][37][38]. The accuracy and precision of μCT-based measurements of ρ m can be affected by factors related to the scan settings, tissue samples, and scan artifacts. Recent studies have examined the influence of factors such as the X-ray tube voltage, current intensity, and sample dimensions [24,25,39,40]. Beam-hardening related artifacts such as streaking [41], dark banding [low attenuation spots between two higher density objects; [42][43][44]], cupping [26,45], as well as ring artifacts [41,46] can introduce errors in measured attenuation values. One topic of specific interest is the effect of sample dimensions or bone mass differences on the accurate measurement of ρ m since (1) object thickness (size) is known to impact linear X-ray attenuation independent of ρ m [1,42,44] and (2) a wide range of orthopedic and bone biology studies incorporate specimens of varying size or quantities of bone including animal models of osteoporosis (disease), bone biomechanics, bone tissue engineering, aging, and interspecies studies of bone structure and function [21,22,[47][48][49][50][51][52][53][54][55][56][57]. For polychromatic computed tomography X-ray systems, the measure