Optimization of detector pixel size for stent visualization in x-ray fluoroscopy

Abstract

Pixel size is of great interest in flat-panel detector design. To visualize small interventional devices such as a stent in angiographic x-ray fluoroscopy, pixels should be small to limit contrast dilution from partial-area and large to collect sufficient x-rays for an adequate signal-to-noise ratio (SNR). Using quantitative experimental and modeling techniques, we investigated the optimal pixel sizes for visualization of a stent created from 50 μm diameter wires. Image quality was evaluated by the ability of subjects to perform two tasks: detect the presence of a stent and discriminate a partially deployed stent from a fully deployed one. With regard to detection, for the idealized direct detector, the 100 μm pixel size resulted in maximum measured contrast sensitivity. For an idealized indirect detector, with a scintillating layer, the maximal measured contrast sensitivity was obtained at 200 μm pixel size. The channelized human observer model predicted a peak at 150 and 170 μm, for idealized direct and indirect detectors, respectively. Stent deployment is more sensitive to pixel size than stent detection, resulting in a steeper drop in performance with large pixels. With regard to stent deployment detection, smaller even pixel sizes are favored for both detector types. With increasing exposures, the model predicts a smaller optimal pixel size because the noise penalty is reduced.