Fused micro-computed tomography (µCT) and histological images of bone specimens.

OBJECTIVES: To describe a stepwise process to obtain fused images from micro-computed tomography (µCT) and histological images of bone specimens. MATERIAL AND METHODS: Four surgically resected human femoral heads from four patients who had total hip replacement were imaged at a spatial resolution of 12-microns by using µCT. Histological sections of four focal bone lesions including bone cyst in osteoarthritis (n=2) and subchondral bone plate fracture in osteonecrosis (n=2) were prepared and digitized. µCT images were reformatted and adjusted to match the histological images using a landmark-based visual co-registration. Fused µCT and histological images were displayed in a cine-loop video mode with a gradual transition from one image to the other. RESULTS: µCT images of the four focal bone lesions could be successfully fused with the corresponding histological images with a near perfect match of the bone trabeculae. CONCLUSION: We present a stepwise process to obtain fused images from histological and reformatted µCT images of human femoral heads.

Development of micro-CT protocols for in vivo follow-up of mouse bone architecture without major radiation side effects.

In vivo micro-computed tomography (micro-CT) will offer unique information on the time-related changes in bone mass and structure of living mice, provided that radiation-induced side effects are prevented. Lowering the radiation dose, however, inevitably decreases the image quality. In this study we developed and validated a protocol for in vivo micro-CT imaging of mouse bone architecture that retains high quality images but avoids radiation-induced side effects on bone structure and hematological parameters. The left hindlimb of male C57Bl/6 mice was scanned in vivo at 3 consecutive time points, separated each time by a 2-week interval. Two protocols for in vivo micro-CT imaging were evaluated, with pixel sizes of 9 and 18 µm and administered radiation doses of 434 mGy and 166 mGy per scan, respectively. These radiation doses were found not to influence trabecular or cortical bone architecture in pre-pubertal or adult mice. In addition, there was no evidence for hematological side effects as peripheral blood cell counts and the colony-forming capacity of hematopoietic progenitor cells from bone marrow and spleen were not altered. Although the images obtained with these in vivo micro-CT protocols were more blurred than those obtained with high resolution (5 µm) ex vivo CT imaging, longitudinal follow-up of trabecular bone architecture in an orchidectomy model proved to be feasible using the 9 µm pixel size protocol in combination with a suitable bone segmentation technique (i.e. local thresholding). The image quality of the 18 µm pixel size protocol was too degraded for accurate bone segmentation and the use of this protocol is therefore restricted to monitor marked changes in bone structure such as bone metastatic lesions or fracture healing. In conclusion, we developed two micro-CT protocols which are appropriate for detailed as well as global longitudinal studies of mouse bone architecture and lack noticeable radiation-induced side effects.