Structural analysis of high resolution in vitro MR images compared to stained grindings

The recent advancement of high resolution magnetic resonance imaging has op ened up new avenues for the determination of structural characteristics of the trabecular network, which may significantly improve the diagnosis of os teoporosis. An analysis of the calcaneus in healthy women has shown similar age-related changes when comparing structural parameters in high resolutio n MR images and BMD as measured by DXA [1]. Here we undertook an in vitro s tudy to further compare structural measurements in MR images with those fro m stained grindings. A 3D gradient echo sequence on a 1.5 T scanner was use d to obtain four contiguous sagittal MR images with a slice thickness of mm and an in plane pixel size of 195 mum. Twenty-one stained grindings with a slice thickness of 1 mum each were obtained from a 3 mm thick; slab of the same volume investigated by MR. The stack of stained grindings was also us ed to simulate the influence of variations in slice thickness and in plane resolution. Results for structural parameters derived from the high resolut ion MR images differed considerably from those derived from the stained gri ndings because the MR images are heavily influenced by partial volume artif acts. This finding was supported by simulations which also revealed that ev en at a slice thickness of 500 mum and an in plane pixel size of 13 mum. ac curate results could not be obtained when a histomorphometric type analysis was applied. Results also depended strongly on the segmentation method. Ho wever, contrary to the stained grindings, images averaged over several slic es reveal the three-dimensional network character of the trabecular structu re, New efforts should be undertaken to develop analysis strategies that ar e more adequate for in vivo high resolution images instead of using analysi s techniques applied in classical histomorphometry.