Invasive "body-opening" autopsy represents the traditional means of postmortem investigation in humans. However, modern cross-sectional imaging techniques can supplement and may even partially replace traditional autopsy. Computed tomography (CT) is the imaging modality of choice for two- and three-dimensional documentation and analysis of autopsy findings including fracture systems, pathologic gas collections (eg, air embolism, subcutaneous emphysema after trauma, hyperbaric trauma, decomposition effects), and gross tissue injury. Various postprocessing techniques can provide strong forensic evidence for use in legal proceedings. Magnetic resonance (MR) imaging has had a greater impact in demonstrating soft-tissue injury, organ trauma, and nontraumatic conditions. However, the differences in morphologic features and signal intensity characteristics seen at antemortem versus postmortem MR imaging have not yet been studied systematically. The documentation and analysis of postmortem findings with CT and MR imaging and postprocessing techniques ("virtopsy") is investigator independent, objective, and noninvasive and will lead to qualitative improvements in forensic pathologic investigation. Future applications of this approach include the assessment of morbidity and mortality in the general population and, perhaps, routine screening of bodies prior to burial.
Objective To test the hypothesis that Fourier transform infrared (FTIR) spectral imaging, coupled with multivariate data processing techniques, can image the spatial distribution of matrix constituents in native and engineered cartilage samples. Methods Tissue sections from native and trypsin‐digested bovine nasal cartilage (BNC) and from engineered cartilage, generated by chick sternal chondrocytes grown in a hollow fiber bioreactor, were placed either on calcium fluoride windows for FTIR analysis or gelatinized microscope slides for histologic analysis. Based on the assumption that cartilage is predominantly chondroitin sulfate (CS) and type II collagen, chemical images were extracted from FTIR spectral imaging data sets using 2 multivariate methods: the Euclidean distance algorithm and a least‐squares approach. Results Least‐squares analysis of the FTIR data of native BNC yielded a collagen content of 54 ± 13% and a CS content of 37 ± 16% (mean ± SD). Euclidean distance analysis of measurements made on trypsin‐digested BNC demonstrated only trace amounts of CS. For engineered cartilage, the CS content was significantly lower (15 ± 5%), while the collagen content (73 ± 6%) was significantly higher than biochemically determined values (CS 34%, collagen 5%, protein 61%). These differences are due to the fact that the dimethylmethylene blue assay overestimated the CS content of the tissue because it is not specific for CS, while the FTIR spectral imaging technique overestimated the collagen content because it lacks specificity for different proteins. Conclusion FTIR spectral imaging combines histology‐like spatial localization with the quantitative capability of bulk chemical analysis. For molecules with a unique spectral signature, such as CS, the FTIR technique coupled with multivariate analysis can define a unique spatial distribution. However, for some applications, the lack of specificity of this technique for different types of proteins may be a limitation.
Objective. To test the hypothesis that magnetic resonance imaging (MRI) results correlate with the biochemical composition of cartilage matrix and can therefore be used to evaluate natural tissue development and the effects of biologic interventions.Methods. Chondrocytes harvested from day-16 chick embryo sterna were inoculated into an MRIcompatible hollow-fiber bioreactor. The tissue that formed over a period of 2-4 weeks was studied biochemically, histologically, and with MRI. Besides natural development, the response of the tissue to administration of retinoic acid, interleukin-1 (IL-1), and daily dosing with ascorbic acid was studied.Results. Tissue wet and dry weight, glycosaminoglycan (GAG) content, and collagen content all increased with development time, while tissue hydration decreased. The administration of retinoic acid resulted in a significant reduction in tissue wet weight, proteoglycan content, and cell number and an increase in hydration as compared with controls. Daily dosing with ascorbic acid increased tissue collagen content significantly compared with controls, while the administration of IL-1 resulted in increased proteoglycan content. The water proton longitudinal and transverse relaxation rates correlated well with GAG and collagen concentrations of the matrix as well as with tissue hydration. In contrast, the magnetization transfer value for the tissue correlated only with total collagen. Finally, the selfdiffusion coefficient of water correlated with tissue hydration.Conclusion. Parameters derived from MR images obtained noninvasively can be used to quantitatively assess the composition of cartilage tissue generated in a bioreactor. We conclude that MRI is a promising modality for the assessment of certain biochemical properties of cartilage in a wide variety of settings.
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