Article

Accuracy of Peripheral Quantitative Computed Tomography (pQCT) for Assessing Area and Density of Mouse Cortical Bone

Department of Orthopaedic Surgery Barnes-Jewish Hospital at Washington University, Orthopaedic Research Laboratories, St. Louis, MO 63110, USA.
Calcified Tissue International (Impact Factor: 2.75). 11/2003; 73(4):411-8. DOI: 10.1007/s00223-002-0006-0
Source: PubMed

ABSTRACT Peripheral quantitative computed tomography (pQCT) is increasingly used for measurement of cortical bone geometry and density in mice. We evaluated the accuracy of pQCT for area and density measurements of thin-walled aluminum phantoms and mouse femora. Aluminum tubes with varying wall thicknesses and femora from 1- to 6-month-old C3H/HeJ (C3H) and C57B1/6J (B6) mice (average cortical thickness 0.14-0.29 mm) were scanned at 70- or 90-microm resolution. pQCT values of area were compared to optical values determined after sectioning, while pQCT density (vBMD) was compared to solid aluminum density or correlated to bone ash content. For the aluminum phantoms, the error in pQCT area and density depended strongly on wall thickness, and density was consistently underestimated. For mouse femora, threshold values were found that produced zero error in bone area for each strain and age group, although the optimal threshold differed between groups. pQCT vBMD correlated strongly with ash content (r2=0.7), although the regression equations differed between strains and the magnitude of the inter-strain difference in vBMD was fourfold greater than the difference in ash content. This finding suggests that pQCT can overestimate the differences in volumetric mineral density between inbred mouse strains whose bones are of different thickness (e.g., C3H vs. B6). In conclusion, both area and density values obtained by pQCT depend strongly on specimen thickness, consistent with a partial volume averaging artifact. Investigators using pQCT to assess cortical bones in mice should be aware of the potential for cortical thickness-dependent errors.

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    • "[2] DXA measurements have been a valuable screening tool for bone diseases, but the accuracy of DXA measurements has been questioned and DXA cannot account for the three-dimensional architectural properties of bone.[2] [3] To overcome the challenges of DXA, peripheral quantitative computed tomography (pQCT) has been used to separate trabecular bone from cortical bone and estimate mechanical strength.[4] [5] While pQCT can assess both mineral content and structural properties in three dimensions from the same scan, its relatively low resolution can lead to errors when scanning small specimens [6] [7]. The resolution of microcomputed tomography (μCT) images is superior to clinical pQCT and, as a result, μCT has become the standard for accurate morphological and mineral density measurements in many pre-clinical studies [7]. "
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    ABSTRACT: Bone mineral density (BMD) measurements are critical in many research studies investigating skeletal integrity. For pre-clinical research, micro-computed tomography (microCT) has become an essential tool in these studies. However, the ability to measure the BMD directly from microCT images can be biased by artifacts, such as beam hardening, in the image. This three-part study was designed to understand how the image acquisition process can affect the resulting BMD measurements and to verify that the BMD measurements are accurate. In the first part of this study, the effect of beam hardening-induced cupping artifacts on BMD measurements was examined. In the second part of this study, the number of bones in the X-ray path and the sampling process during scanning was examined. In the third part of this study, microCT-based BMD measurements were compared with ash weights to verify the accuracy of the measurements. The results indicate that beam hardening artifacts of up to 32.6% can occur in sample sizes of interest in studies investigating mineralized tissue and affect mineral density measurements. Beam filtration can be used to minimize these artifacts. The results also indicate that, for murine femora, the scan setup can impact densitometry measurements for both cortical and trabecular bone and morphologic measurements of trabecular bone. Last, when a scan setup that minimized all of these artifacts was used, the microCT-based measurements correlated well with ash weight measurements (R(2)=0.983 when air was excluded), indicating that microCT can be an accurate tool for murine bone densitometry.
    Bone 08/2009; 45(6):1104-16. DOI:10.1016/j.bone.2009.07.078 · 4.46 Impact Factor
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    • "However, in contrast to the commonly reported volumetric mineral density (vBMD) values [2] [6] [30] the DMB we report here is not affected by structural properties. The differences in DMB of approximately 4% in cortical bone of B6 and C3H male mice are almost four-fold lower than the difference measured by pQCT in the same 6- month-old mice strains of these strains reported by Brodt et al. [30]. This difference in SR-μCT and pQCT values likely results from the difference in spatial resolution of the two techniques. "
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    • "Two hundred-MHz SAM reveals the bone architecture with a resolution comparable to lCT [10] [14] and accurate morphological measurements can be performed on the impedance images. Our geometrical measurements of bone diameter and cortical width of the mid-diaphyseal femur fell in the range of previously reported values for these strains measured by means of lCT, pCT and histomorphometry [3] [15] [16]. In contrast to many previous studies on mice and, to the best of our knowledge, all ultrasound studies on small animal skeleton the high spatial resolution used here allowed an exclusion of small cavities and canals in the cortical layer. "
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