We developed prototype Digital Subtraction Angiography (DSA) System with a new large area FPD. Dynamic range, MTF, Contrast ratio and line noise were much improved. The improved FPD is a scintillator-type detector, and has a 40 x 30 cm active area, 2048 x 1536 matrix with 194um pixel pitch. The Prototype DSA system has two x-ray detectors, the FPD and the I.I.-CCD camera, and we can choose them on demand. All images captured from both detectors at 3 frames/sec in DSA mode and 30 frames/sec in Fluoroscopy mode are forwarded to our image-processing unit. We applied the new DSA system to more than 150 studies and compared the results with images from the I.I.-CCD. In DSA mode, FPD System, which has a wide dynamic range, large detecting area, and good contrast ratio yielded superior angiographic images compared with the I.I-CCD system. In Fluoroscopy mode, we improved line noise and increased the contrast of catheters and guide wires with a new image processing technique. With these improvements, the image quality of the FPD System is superior to the I.I.-CCD system at the exposure range of over 2uR/frame (17.4 nGy/frame).

SummaryWe have been engaged in clinical work using DSA, the first in the world, under a joint study agreement with Hitachi Medical Corporation on the use of the Flat Panel Detector FPD since 2001. We are now in the stage where a certain evaluation process has been finished, but the FPD performance study in angiography has just begun, and, therefore, its clinical evaluation results are very few. Therefore, we studied the relativity between clinical images and physical characteristics in order to examine the characteristics of FPD by referencing them to clinical images. We did an evaluation of the clinical images to which their physical characteristics such as granularity, resolution, contrast, etc., are reflected by comparing FPD and I.I. images.

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