An Analysis of Scatter Characteristics in X-ray CT Spectral Correction

TL;DR

This paper analyzes how spectral correction in X-ray CT affects scatter characteristics, providing an analytical framework for scatter compensation and demonstrating its practical application with phantom studies and spectral modulator technology.

Contribution

It offers a novel analytical characterization of scatter behavior during spectral correction, enabling improved scatter compensation methods in spectral CT imaging.

Findings

Scatter impact scales with the derivative of the spectral mapping function.

Scatter distribution in transmission is scaled by the derivative and exponential of projection differences.

Validated scatter compensation approach on phantom studies and applied in spectral modulator CT imaging.

Abstract

X-ray scatter remains a major physics challenge in volumetric computed tomography (CT), whose physical and statistical behaviors have been commonly leveraged in order to eliminate its impact on CT image quality. In this work, we conduct an in-depth derivation of how the scatter distribution and scatter to primary ratio (SPR) will change during the spectral correction, leading to an interesting finding on the property of scatter: when applying the spectral correction before scatter is removed, the impact of SPR on a CT projection will be scaled by the first derivative of the mapping function; while the scatter distribution in the transmission domain will be scaled by the product of the first derivative of the mapping function and a natural exponential of the projection difference before and after the mapping. Such a characterization of scatter's behavior provides an analytic approach of compensating for the SPR as well as approximating the change of scatter distribution after spectral correction, even though both of them might be significantly distorted as the linearization mapping function in spectral correction could vary a lot from one detector pixel to another. We conduct an evaluation of SPR compensations on a Catphan phantom and an anthropomorphic chest phantom to validate the characteristics of scatter. In addition, this scatter property is also directly adopted into CT imaging using a spectral modulator with flying focal spot technology (SMFFS) as an example to demonstrate its potential in practical applications.