Relationship between resolution and partial volume effect among μCT, MDCT and SDCT

Partial volume effect is defined as the loss of accuracy for small objects caused by the low resolution of an imaging system. With low resolution computed tomography (CT), the trabecular bone and cavity are mixed and the brightness representing each of the spaces is averaged. Therefore, information regarding bony microstructure is absent. In this study, the partial volume effect was evaluated for multi-detector row CT (MDCT) and single-detector row CT (SDCT) in comparison with micro CT (µCT). Obvious and typical geometric patterns of healthy and osteoporotic bones were used to create virtual sectional images of various resolutions. Six parameters were evaluated: areal bone mineral density (aBMD), volumetric BMD (vBMD), bone volume (BV), bone mineral content (BMC), frequency distribution density of BMD (FDD) in the image, and the orientation angle of the bone. vBMD and BV values were dependent on the CT resolution, whereas aBMD and BMC values showed constant values independent of the resolution. Therefore, aBMD and BMC do not require high resolution CT and could be useful for clinically evaluating trabecular bone volume. Regarding FDD, the number of pixels with intermediate brightness increased as CT resolution decreased, and FDD converged on specific brightness representing aBMD. In addition, µCT estimated the bone orientation angle correctly, MDCT estimated the correct angle only for osteoporotic images, and SDCT was unable to estimate the angle. Many more cavities were present in the osteoporotic model than the Healthy model and the distribution of bone was sparse, which could have decreased the partial volume effect and enabled the major orientation angle of the bone to be distinguished. These findings suggest that MDCT could be useful for the clinical evaluation of osteoporotic bone structure.