A photodiode array x-ray imaging system for digital angiography

A line scanning imaging system that can be used to make low-noise x-ray images to detect low-contrast structure is described. The system makes use of a 1024-element, self-scanning, photodiode array (Reticon RL 1024S) optically coupled to an x-ray image intensifier tube. Low-noise images are obtained by imaging only small areas of interest at a time to reduce the noise resulting from the detection of scattered radiation, and by making use of the very large dynamic range (8000:1) solid-state photodetector. Some performance characteristics of the diode array system are discussed. It was found that while sensitivities of individual elements differed by up to +/- 15% from the average, they could be corrected with a precision of 0.02% to 0.04% of the maximum signal. The limiting spatial resolution of the system in the direction of the diode array was 2.0 cycles/mm, limited by the image intensifier. The system linearity was studied by measuring the attenuation of a monoenergetic x-ray beam by Plexiglas. The measured attenuation agreed with the expected exponential decrease over a range of approximately 1000 to within experimental error. The imaging capabilities of the system were demonstrated by imaging an angiographic phantom consisting of an iodine-filled tube with an asymmetric 20% stenosis. The stenosis was oriented on the tube surface furthermost from the detector resulting in an image with a 2% radiographic contrast change but no decrease of the tube width. The stenosis was clearly imaged using a temporal subtraction technique.