Dynamic Bowtie for Fan-beam CT

TL;DR

This paper introduces a dynamic bowtie filter for fan-beam CT that adapts in real-time to optimize x-ray flux distribution, improving photon count uniformity and reducing signal dynamic range, with potential for patient-specific customization.

Contribution

It presents a novel mathematical model and design methodology for a dynamic bowtie filter that adjusts during scanning, tailored to patient anatomy, enhancing spectral CT performance.

Findings

Dynamic bowtie equalizes photon counts in ideal cases.

Reduces dynamic range of detected signals in practical scenarios.

Applicable to elliptical cross-sections and adaptable to real patient geometries.

Abstract

A bowtie is a filter used to shape an x-ray beam and equalize its flux reaching different detector channels. For development of spectral CT with energy-discriminative photon-counting (EDPC) detectors, here we propose and evaluate a dynamic bowtie for performance optimization based on a patient model or a scout scan. Our dynamic bowtie modifies an x-ray beam intensity profile by mechanical rotation and adaptive adjustment of the x-ray source flux. First, a mathematical model for dynamic bowtie filtering is established for an elliptical section in fan-beam geometry, and the contour of the optimal bowtie is derived. Then, numerical simulation is performed to compare the performance of the dynamic bowtie in the cases of an ideal phantom and a realistic cross-section relative to the counterparts without any bowtie and with a fixed bowtie respectively. Our dynamic bowtie can equalize the expected numbers of photons in the case of an ideal phantom. In practical cases, our dynamic bowtie can effectively reduce the dynamic range of detected signals inside the field of view. Although our design is optimized for an elliptical phantom, the resultant dynamic bowtie can be applied to a real fan-beam scan if the underlying cross-section can be approximated as an ellipse. Furthermore, our design methodology can be applied to specify an optimized dynamic bowtie for any cross-section of a patient, preferably using rapid prototyping technology. This fan-beam dynamic bowtie work could be extended to the cone-beam geometry in a follow-up study.