43. AN AUTOMATED MICRO-CT BASED QUANTITATIVE ANALYSIS OF HEALTHY AND METASTATICALLY INVOLVED VERTEBRAL ARCHITECTURE

Abstract

Purpose: The objective of this study is to develop and utilize a highly automated microCT based analysis tool to quantify microstructural differences in bone due to metastatic involvement in whole rat vertebrae.

Method: First and Third lumbar vertebrae from healthy (n=4) and metastatically involved (n=4) rnu/rnu rats were excised for analysis (total of 8 vertebrae). Lytic metastases were developed via intracardiac injection of MT1 human breast cancer cells. The specimens were scanned using microCT at 17.5 microns isotropic resolution. A highly automated algorithm was developed for whole vertebral segmentation based on the microCT data, including the posterior elements (AmiraDev3.1). This was accomplished using an atlas-based method incorporating demons deformable registration followed by refinement through level set curvature evolution. Volumetric concurrency was used to compare segmentations generated by the automated algorithm to manually refined segmentations. The segmentations were up-sampled by 4 and edge-enhanced and further segmented using a thresholding technique to have a clear segmentation of the individual trabeculae without advancing into the bone marrow(AmiraDev3.1). The cortical shell was removed automatically before analyzing the trabecular structure. Cortical bone volume(CBV) was calculated by subtracting the volume of the full segmentation from the segmentation with no cortical shell. The interior segmentation was then used to calculate Trabecular Bone Volume(TBV), Trabecular Thickness(TbTh), Trabecular Separation(TbSp), Trabecular Number(TbN) based on the expressions described by Parfitt, et al(1983). Finally mean intercept length(MIL) was used to calculate the anisotropy of the trabecular tissue. Analysis were carried out on both the healthy and metastatically involved vertebrae.

Results: The automated algorithm including the level set method refinement produced good tracking of the boundaries of entire rat vertebrae. Consistent results yielded significant reduction in TBV, slight reduction in TbN and TbTh, and significant increase in TbS in metastatic vertebrae compared to healthy. no significant differences were observed in CBV. The metastatic vertebrae was also found to be significantly more anisotropic than the healthy group.

Conclusion: The accuracy of the highly automated algorithm developed in this study to analyze microstructure in whole rat vertebrae make it a suitable tool for further analyzing the effects of existing and new treatments for spinal metastases at a preclinical level.