[Micro MRI of trabecular bone]

Recent progress in noninvasive imaging techniques--notably magnetic resonance imaging (MRI) and computed tomography (CT)--in terms of improvements in achievable signal-to-noise ratio (SNR) and spatial resolution, has led to specialized modalities (often referred to micro-CT and micro-MRI) that now enable visualization and quantitative analysis of trabecular bone architecture in vivo in animals and humans. We have during the past decade been dedicated to the development of acquisition and processing methods permitting quantitative characterization of the complex architecture of trabecular and cortical bone from micro-MRI data obtained in the limited spatial resolution regime inherent to measurements performed in vivo. Fundamental to achieving such a goal is an image acquisition strategy that ensures faithful retrieval of the structural features, which includes appropriate imaging pulse sequences and control of and correction for involuntary subject motion. Preprocessing of the raw images results in noise-free grayscale images representing maps of bone volume fraction, which are subvoxel-processed (a method for reducing partial volume blurring with application) to yield images in higher spatial resolution. From the binarized and skeletonized images the three-dimensional topology of the network can be retrieved allowing each voxel to be characterized as belonging to a surface, curve or junction between the fundamental topological types. Surfaces and curves are the lower-dimensionality counterparts of plates and rods for better differentiation of bone quality.