Image-Processing Techniques Applied to the Study of the Musculoskeletal System and Its Interactions with Biomaterials
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Advancement in Histomorphometry of Bone Tissue Image processing speeds up routine analysis procedures by evaluating, in a less tedious and quicker way, a greater
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number of images, parameters, or both. Semiautomated computerized imageprocessing Systems have been in use for a long time, based on computer-assisted analysis of objects whose contours were tracked manually by a digitizing Cursor. Histological images were, generally, projected from the microscope over a digi tizing tablet, with the Operator visually recognizing the structure of interest and picking up its contours. The critical advance brought to histomorphometry by semiautomated techniques has been the practical measurement of surface-related parameters. The particular application of comput erized morphometry to trabecular bone histomorphometry has been strongly favored because the spongy nature of tra becular bone tissue allows imaging in a fairly automated fashion by this tech nique. In particular, it is reasonably easy to distinguish between the structure of the trabeculae and the background Signal (sometimes with just a simple thresholding procedure). Image processing is also well suited for the study of bone structures because the principal mechanical f unction of the structure can be adequately described in terms of morphology. In biomaterials research, it is effective to apply image-processing procedures in
the quantitative evaluation of the longterm performance of bioactive coatings (e.g., hydroxyapatite and bioactive glasses) on metals. We found that because the electron density of the coating (as observed on backscattering electron microscopic images) is in a ränge between that of metal and bone, there is no "edge effect" affecting the quantitative measure ment of the surface of the coating in the histological plane. 4 The "edge effect" is the phenomenon by which the optoelectronic sensor of the CCD camera erroneously assigns extra pixels to one of two contiguous objects presenting a high contrast. Within the funding of the European Union's Brite-EuRam Project on Surface Coatings for Biomaterials, 5,6 an imageprocessing System for this specific appli cation has been developed to integrate Standard histological procedures (Figure 1). It operates in an MS-DOS environment using Microsoft C 5.0 language. Images are acquired by a Hitachi KP-116 CCD camera mounted on the microscope. Optical-disk storage and ASCII coding allow the capture of many images and their exchange across Computer platforms. The system also offers high interactivity and surface measurements of up to four classes of objects. In measuring the long-term Perfor mance of the coatings, the System has advantages compared with the other two most common ways to analyze these kinds of samples: ■ In contrast with Systems that measure just the thickness of the coating at one or more sites, the measurement of the total surface is far more precise and reproducible. ■ In contrast with Systems that measure the total surface by manual or semiauto mated contouring of the inner and
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