Curved-slit collimation for fan-beam-based virtual fluoroscopy

Objective.Interventional radiology procedures can expose patients and physicians to high doses of radiation. Virtual fluoroscopy based on fan-beams helps to reduce this level of irradiation. Here, we demonstrate the benefits of using fan-beams obtained by curved-slit collimation rather than the straight-slit collimation previously proposed.Approach.We study spiral-slits that allow for a localization procedure identical to that with straight-slits. We show that the localization error depends on the shape of the slit and we bound this error. This bound can be used to optimize the slit geometry according to different performance criteria.Main results.Several curved-slit geometries are studied, and their relative performance is evaluated through numerical experiments and preliminary tests on x-ray equipment. These experiments show a systematic improvement in performance with the proposed curved-slit geometries compared with the straight-slit. In particular, a curved-slit geometry with a linear spiral part and an exponential part reduces localization error and solves the problem of the blind central zone with the straight-slit geometry.Significance.We have developed a framework for analyzing the amplification of localization errors in a rotating collimator with symmetrical spiral-slits, as well as criteria for measuring this amplification and bounds indicating their optimality. This framework can be reused to identify or compare slits under conditions of use different from those in our study.