PubMed · 13351692
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P Santy, P Marion, J Garvier, P Charney. 1956-05-30. [13351692].. https://pubmed.ncbi.nlm.nih.gov/13351692/
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Segmentation of time series of 3D cardiac images is clinically used for the assessment of the mechanical function of the left ventricle. To take into account the 4D (3D+T) nature of those images, we propose to extend the deformable surface framework by introducing time-dependent constraints. Thus, in addition to computing an internal force for enforcing the regularity of the deformable model, prior motion knowledge is introduced in the deformation process through either temporal smoothing or trajectory constraints. In this paper, deformable surfaces are represented as simplex meshes owing to their generality and their ability to compute mean curvature at each vertex. The segmentation accuracy of this 4D deformable model is estimated on synthetic SPECT image sequences for which a ground truth about the LV volume is known. Segmentation of non-synthetic SPECT and other modalities 4D images is also discussed.
OBJECTIVES: In myocardial perfusion imaging, the type of orbit that provides the best image quality is still the subject of debate. This study correlates the effects of angular rotation (180 degrees vs. 360 degrees), type of orbit (circular vs. body contouring) and location of the heart within the orbit, with changes in spatial resolution and consequential changes in the uniformity of short axis slices of a normal myocardial phantom. METHODS: All studies were performed on a dual-head gamma camera equipped with low energy all-purpose collimators. A myocardium was suspended in air with no scattering or attenuating material present. SPECT acquisitions were performed using circular and body-contouring orbits of various radii and with the myocardium at the maximum off-axis position. RESULTS: The average uniformity of myocardial short axis slices was approximately 4% for 360 degrees circular orbits and for 180 degrees circular orbits where the myocardium was close to the centre of rotation. With body-contouring orbits, the average uniformity increased to 8% and 18% when the myocardium was located on the long and short axes of rotation, respectively. Changes in system resolution with a rotation of >3 mm increased non-uniformities in the myocardial images. CONCLUSIONS: Changes in resolution associated with the angular rotation, type of orbit and myocardial location affect the apparent distribution of activity in short axis slices of the heart. The most uniform images were obtained with a 360 degrees circular orbit. Results with a 180 degrees circular orbit and both 360 degrees and 180 degrees body-contouring orbits were highly dependent on the location of the myocardium.
The identification of protein kinase C isozymes in distinct localities within the cell has led to the suggestion that each isozyme mediates a unique function. This has necessitated the development of methodologies that are capable of assigning specific function to an isozyme. For many years the location of individual isozymes in a particulate fraction was used to correlate specific isozymes with cellular function. More recently over-expression of selective isozymes and genetic knockouts have provided tissue-specific and developmentally regulated information on function. It is now known that specific proteins act as isozyme selective receptors for activated C kinase (RACKs) which determine subcellular localization of specific isozymes. As a result, peptides have been designed from the interaction site between the isozyme and its RACK that prevent the binding of isozymes to their respective RACKs. This has allowed the modulation of function of individual isozymes. This review will examine the development of the peptides as isozyme selective inhibitors or activators of PKC and its impact on understanding the role of isozymes in cellular function in the healthy and diseased heart. The possible development of isozyme-specific drugs for therapeutic use will be discussed.