Single-scan energy-selective imaging on cone-beam CT: a preliminary study

Abstract

On an onboard cone-beam CT (CBCT) system, the poly-energetic beam generated by current commercial x-ray tubes hardens as it penetrates the object. The beam-hardening effect results in CT image artifacts of up to 100 HU, especially around dense objects (e.g. bones). We propose to insert a half-blocked beam filter between x-ray source and object, such that any ray passing through the object is filtered once from one of the opposite directions in a single full scan. The conventional data processing of dual energy imaging is then applied to obtain material decomposition as well as CT images with no beam-hardening artifacts. In this preliminary study, we demonstrate the method feasibility using computer simulations. The beam filter thickness is optimized to balance the CT number accuracy and the noise level on the reconstructed images via both analytical calculation and measurement of image noise. A calibration phantom is designed to obtain the decomposition function for energy selective imaging by projection measurements without the knowledge of x-ray spectrum and detector response. Using the optimized beam blocker and the calibration phantom, we simulate the data acquisition using scan settings of a commercial CBCT system. Our proposed approach significantly suppresses beam-hardening artifacts and reduces the image error from 65 HU to 9 HU in the selected regions of interest on a head phantom. The method also successfully decomposes bone and soft tissue, with 95% accuracy.

Iterative image‐domain decomposition for dual‐energy CT

“…21,22 Projection-domain decomposition numerically converts the measured projections into line integrals of basis materials (e.g., soft tissue and bone) using a nonlinear model. 8,20,23 The decomposed CT images are then reconstructed using conventional CT reconstruction algorithms on the integrals of basis materials. 8,20 Image-domain decomposition directly operates on conventional CT images of two or more energy levels using linear matrix inversion.…”

A general framework of noise suppression in material decomposition for dual‐energy CT

“…The raw projections are converted into line integrals of basis materials (e.g., soft tissue and bone) using an analytical or numerical decomposition function, which is typically measured during system calibration. 10 For DECT in the diagnostic energy range, the decomposition function is theoretically nonlinear, but with a dominant linear component. 11 The decomposed CT images are reconstructed from line integrals of basis materials using CT reconstruction.…”