Prism-array lenses for energy filtering in medical x-ray imaging

TL;DR

This paper introduces prism-array lenses (PALs) for energy filtering in medical x-ray imaging, demonstrating their potential to improve dose efficiency over traditional filters through experimental and theoretical analysis.

Contribution

The study presents the first experimental and theoretical evaluation of silicon PALs for energy filtering in medical x-ray imaging using a standard x-ray tube.

Findings

PALs effectively shape the x-ray spectrum.

PALs increase dose efficiency compared to standard filters.

Experimental results validate the theoretical predictions.

Abstract

Conventional energy filters for x-ray imaging are based on absorbing materials which attenuate low energy photons, sometimes combined with an absorption edge, thus also discriminating towards photons of higher energies. These filters are fairly inefficient, in particular for photons of higher energies, and other methods for achieving a narrower bandwidth have been proposed. Such methods include various types of monochromators, based on for instance mosaic crystals or refractive multi-prism x-ray lenses (MPL's). Prism-array lenses (PAL's) are similar to MPL's, but are shorter, have larger apertures, and higher transmission. A PAL consists of a number of small prisms arranged in columns perpendicular to the optical axis. The column height decreases along the optical axis so that the projection of lens material is approximately linear with a Fresnel phase-plate pattern superimposed on it. The focusing effect is one dimensional, and the lens is chromatic. Hence, unwanted energies can be blocked by placing a slit in the image plane of a desired energy. We present the first experimental and theoretical results on an energy filter based on a silicon PAL. The study includes an evaluation of the spectral shaping properties of the filter as well as a quantification of the achievable increase in dose efficiency compared to standard methods. Previously, PAL's have been investigated with synchrotron radiation, but in this study a medical imaging setup, based on a regular x-ray tube, is considered.