<title>Quantitative image quality of spatially filtered x-ray fluoroscopy</title>

Abstract

One potential method to lower x-ray fluoroscopy dose without compromising image quality is to acquire images at a decreased exposure rate and digitally filter to reduce noise. In both single image frames and image sequences, we investigated the effect of noise-reduction spatial filtering on the detection of stationary cylinders that mimicked arteries, catheters, and guide wires in x-ray imaging. We simulated ideal edge- preserving spatial filters by filtering the noise only and then adding targets for detection. Fitters used were three different center-weighted averagers that reduce pixel noise variance by factors of 0.75, 0.5, and 0.25. Detection performance in unfiltered and spatially filtered noisy image sequences and single frames was measured using a reference/test, 9-alternative, adaptive forced-choice method. Performance level was fixed and results were obtained in the form of signal contrast sensitivity. In single images, the effect of filtering on detection was insignificant at all filtering levels. On the other hand, filtering in image sequences improved detectability by as much as 23%, yielding a potential x-ray dose savings of 34%. Comparing results with the prewhitening matched filter model indicated that human observers have improved detection efficiency in spatially filtered image sequences, as compared to white-noise sequences. We conclude that edge-preserving spatial filtering is more effective in sequences than in single frames. Such filtering can potentially improve image quality in noisy image sequences such as x-ray fluoroscopy.