THE INFLUENCE OF IMAGE-ENHANCEMENT AND RECONSTRUCTION ON QUANTITATIVECORONARY ARTERIOGRAPHY

In the coming years, cinefilm will gradually be replaced by some digit al medium for the archiving of angiographic images. However, not only the question which digital archiving medium will be used in the future is important, but also wich images are to be stored. Options are to e ither archive the raw, unprocessed images, or the enhanced images as t hey are displayed on the viewing monitor in the catheterization labora tory. In the first case, an off-line workstation will need additional hardware to display the images with the same image quality as they wer e acquired; in the second case, the question remains whether quantitat ive analysis programs still provide reliable results. Goal of this stu dy was to investigate the possible effects of image enhancement and re construction on the results from quantitative coronary arteriographic (QCA) measurements with the Philips ACA-package (Automated Coronary An alysis). Image enhancement was achieved by an unsharp masking approach ; the reconstruction of the original image from the enhanced image was attempted by an iterative deconvolution approach. The evaluation stud y consisted of two parts; a technical evaluation on eleven phantom tub es with known dimensions, and a clinical evaluation study on 48 corona ry lesions. The results of the technical evaluation demonstrate that t he measurement errors increase for the smaller vessel sizes (< 1.2 mm) when QCA is applied to reconstructed images. The systematic differenc e on the smallest phantom tube (0.687 mm) on unprocessed images was li mited to 0.050 mm, while it increased to 0.089 mm for the reconstructe d images. Moreover, the random differences for the smaller vessel size s increased for all processed images: for 0.159 mm for the unprocessed image to 0.189 mm far the enhanced and 0.204 mm for the reconstructed image (p < 0.01). For the larger vessels, in general, no significant differences could be observed between the results of the unprocessed a nd processed images. The results of the clinical evaluation study demo nstrate that especially the obstruction diameter is overestimated when QCA is applied to reconstructed images (0.113 mm). Although the measu rements on the enhanced images did not show a significant overestimati on of the obstruction diameter, the intra-observer random difference w as much higher (0.199 mm for the enhanced images versus 0.140 mm for t he unprocessed images, p < 0.01). In more general terms, applying QCA on enhanced images increases the random difference values, while recon structing the original image from the enhanced images increases the sy stematic errors in the measured diameters. This study has clearly demo nstrated that especially the smaller diameter values (< 1.2 mm) are in fluenced by image enhancement. Therefore, to obtain quantitative resul ts with the desired small values for systematic and random differences , requires that the raw, unprocessed image data be archived.