INTRODUCTION: High-resolution peripheral quantitative computed tomography (HR-pQCT) is an imaging modality used for in vivo 3D visualization of trabecular microstructure with minimal radiation. The second-generation HR-pQCT has an enhanced resolution of 61 µm compared to the first-generation HR-pQCT with a resolution of 82 µm. Its ability to image peripheral sites such as the distal radius and tibia in patients in vivo has recently been demonstrated [1,2]. Additionally, Individual Trabecula Segmentation (ITS) is a technique used to decompose the trabecula network into individual plates and rods. ITS based on first-generation HR-pQCT images showed strong correlation to gold-standard micro computed tomography (µCT) images [3]. The application of ITS to µCT and first-generation HR-pQCT images has demonstrated how plate-and-rod configurations affect whole bone mechanical properties as well as how trabecular microstructure changes in various musculoskeletal diseases [2,4]. ITS based on second-generation HR-pQCT images has new potentials in musculoskeletal studies but has yet to be validated. The objective of this study was to assess the agreement between ITS-based morphological analysis on second-generation HR-pQCT with gold-standard µCT scans to demonstrate its capability as a clinical tool.

METHODS: Twenty-seven sets of fresh-frozen tibia and radius bones obtained from the Life Legacy Foundation (Tucson, AZ) were scanned in the distal region using second-generation HR-pQCT at 61 µm and µCT at 25 µm. HR-pQCT images were subjected to ITS analysis using a previously developed protocol based on direct voxel-based measurements from the thresholded image obtained automatically [5]. The µCT image of each sample was registered to the corresponding HR-pQCT image to ensure analysis of corresponding regions. A Gaussian filter (sigma 0.8 and support of 1) was applied to the µCT images for noise reduction and a global threshold of 20% of the maximum voxel value was used to binarize the images. ITS analysis was performed on the trabecular region of the registered images. Bone volume fraction (pBV/TV, rBV/TV), number density (pTb.N, rTb.N) and thickness (pTb.Th, rTb.Th) of trabecular plates and rods were obtained. Plate-to-rod ratio (PR ratio), defined as the ratio of plate bone volume vs rod bone volume was obtained to determine plate vs rod characteristics. Difference between these measurements in HR-pQCT and uCT images was also calculated. Paired student t-tests were used to examine the difference between HR-pQCT and µCT measurements. Linear regression was used to determine the correlation coefficient of these parameters between HR-pQCT and µCT images.

RESULTS: Plate and rod decomposition of the trabecular region of the radius and tibia by HR-pQCT and µCT is shown in figure 3, with plates in green and rods in red. Mean and standard deviation of microstructural measurements from the HR-pQCT and µCT images in the distal radius and tibia were calculated. All of the HR-pQCT parameters were statistically different from the µCT measurements. There was a high correlation between BV/TV of HR-pQCT and µCT images in both the radius and tibia (r=0.95 and r=0.94 respectively). Other parameters ranged from fair to strong correlation as well (r=0.24 to r=0.92).

DISCUSSION: The strong correlation of BV/TV, pBV/TV, and rBV/TV between HR-pQCT and µCT microstructural analysis suggests that HR-pQCT can be used to clinically assess changes in plate and rod microstructure. pBV/TV had a stronger correlation than that of rBV/TV, suggesting that rod measurements are susceptible to noise in the lower resolution HR-pQCT images. The PR ratio differed significantly between HR-pQCT and µCT scans but correlated strongly in both the radius and tibia. Significant differences in the HR-pQCT measurements could be due to partial volume effects in the lower resolution images. In order to be used clinically, HR-pQCT measurements could be adjusted by correction values to approach true values measured by gold-standard µCT, though values would be dependent on anatomic site.

SIGNIFICANCE: The validation of ITS-based morphological measurements of HR-pQCT images to gold-standard µCT demonstrates the capability of ITS to be used to clinically assess bone microstructure.

REFERENCES: [1] Nishiyama et al, Curr Osteoporos Res, 2013. [2] Agarwal et al, Osteoporos Int, 2016. [3] Zhou et al, ORS, 2015. [4] Liu et al., JBMR, 2010. [5] Buie et al, Bone, 2007.

1562 - Individual Trabecula Segmentation (ITS)-Based Morphological Analysis of Second-Generation HR-pQCT Compared to Gold-Standard µCT Scans of the Human Distal Radius and Tibia