Biomedical subjects

Jonathan B Moody

Publications and source records attributed to Jonathan B Moody.

4 recordsLinked to original sources

PubMed2005

High-throughput magnetic resonance imaging in mice for phenotyping and therapeutic evaluation.

High-throughput mouse magnetic resonance imaging (MRI) is seeing rapidly increasing demand in development of therapeutics. Recent advances including higher-field systems, new gradient and radio frequency coils and new pulse sequences, coupled with efficient animal preparation and data handling, allow high-throughput MRI under certain protocols. However, with current shifts from anatomic to functional and molecular imaging, innovative technology is required to meet new throughput demands. The first multiple mouse imaging strategies have provided a glimpse of the future state-of-the-art. However, the successful translation of standard clinical MRI technology to preclinical MRI is required to facilitate next-generation high-throughput MRI.

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PubMed2004

Analysis of multi-exponential relaxation data with very short components using linear regularization.

Linear regularization is a common and robust technique for fitting multi-exponential relaxation decay data to obtain a distribution of relaxation times. The regularization algorithms employed by the Uniform-Penalty inversion (UPEN) and CONTIN computer programs have been compared using simulated transverse (T2) relaxation data derived from a typical bimodal distribution observed in cartilage tissue which contain a component shorter than t(0), the time of the first decay sample. We examined the reliability of detecting sub-t(0) relaxation components and the accuracy of statistical estimates of T2 distribution parameters. When the integrated area of the sub-t(0) component relative to that of the total distribution was greater than 0.25, our results indicated a signal-to-noise threshold of about 300 for detecting the presence of the sub-t(0) component with a probability of 0.9 or greater. This threshold was obtained using both the UPEN and CONTIN algorithms. In addition, when using the second-derivative-squared regularizer, UPEN solutions provided statistical estimates of T2 distribution parameters which were substantially free of the biasing effect of the regularizer observed in analagous CONTIN solutions.

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PubMed2003

Imaging the physical and morphological properties of a multi-zone young articular cartilage at microscopic resolution.

PURPOSE: To characterize a number of physical and morphologic properties of young articular cartilage. These properties include the anisotropy of T(2) relaxation, optical retardation, orientation of the collagen fibrils, total thickness of the tissue, number of histologic sub-zones in the tissue, width of individual sub-zones, and correlation between the depths of the local T(2) maxima and the local retardation minima. MATERIALS AND METHODS: Microscopic magnetic resonance imaging (mciro MRI) and polarized light microscopy (PLM) were used to examine three side-by-side specimens from a humeral head of a three-month-old beagle that exhibited a unique topographic heterogeneity from three-zones centrally to multi-zone peripherally. RESULTS: The centrally located specimen showed that the collagen fibrils across the tissue depth have a pattern of the classic three histologic sub-zones (tangential, transitional, and radial). A much more complicated multi-zone structure was found in the specimen located peripherally, with a second transitional zone and a second tangential zone located at the deep part of the tissue. We also showed that the orientation of the collagen fibrils that form the cocoon-shaped territorial matrix surrounding the clusters of chondrocytes can be imaged by our PLM technique. CONCLUSION: The results from the young animal in this report, together with our observations from older animals, demonstrate that MRI and PLM can be used to study the epiphyseal expansion of cartilage in young animals during its growth and subsequent loss in older animals. An illustrative model for the structure of collagen fibrils in a humeral head is suggested as an extension to the classic three-zone model for young articular cartilage.

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PubMed2002

Orientational dependence of T2 relaxation in articular cartilage: A microscopic MRI (microMRI) study.

The experiments reported herein are the first MRI investigations of the orientational dependence of T(2) relaxation in articular cartilage at microscopic resolution over the 360 degrees angular space. For each of six canine cartilage specimens, 48 independent T(2)-weighted proton images were acquired for 12 different specimen orientations. Pixel-wise monoexponential fits of these proton images produced 12 T(2) relaxation images, each with an in-plane pixel resolution of 13.7 microm. Cartilage T(2) as a function of specimen orientation was shown to follow approximately the angular dependence of the nuclear dipole-dipole interaction, with local maxima at approximately 55 degrees, 125 degrees, 235 degrees, and 305 degrees. However, the relative amplitudes of the T(2) maxima deviated somewhat from those expected from the dipolar interaction. The amplitudes of these maxima also varied with tissue depth: the largest amplitudes were found in the radial zone, intermediate amplitudes were found in the superficial zone, and there was a continuous decrease in amplitude approaching the transitional zone from the superficial zone above and the radial zone below. We explain the discrepancy between the observed T(2) anisotropy and the angular dependence of the dipolar interaction by means of a simple model which considers the average of one isotropic and two anisotropic spin populations-the first being associated with "free" water, and the latter two arising from collagen-associated waters. We show that even for the "long" T(2) components, which arise in multiple-compartment studies of collagen-water systems, there appears to be two subpopulations. Each has the same peak value of T(2), but the angular dependence of one is shifted in phase by 90 degrees relative to the other by virtue of the fact that each is associated with groups of mutually perpendicular fibrils.

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