Algorithm‐enabled partial‐angular‐scan configurations for dual‐energy CT
Authors: Chen Buxin , Zhang Zheng , Xia Dan , Sidky Emil Y. , Pan Xiaochuan 
Published: March 2018

Purpose

We seek to investigate an optimization‐based one‐step method for image reconstruction that explicitly compensates for nonlinear spectral response (i.e., the beam‐hardening effect) in dual‐energy CT, to investigate the feasibility of the one‐step method for enabling two dual‐energy partial‐angular‐scan configurations, referred to as the short‐ and half‐scan configurations, on standard CT scanners without involving additional hardware, and to investigate the potential of the short‐ and half‐scan configurations in reducing imaging dose and scan time in a single‐kVp‐switch full‐scan configuration in which two full rotations are made for collection of dual‐energy data.

Methods

We use the one‐step method to reconstruct images directly from dual‐energy data through solving a nonconvex optimization program that specifies the images to be reconstructed in dual‐energy CT. Dual‐energy full‐scan data are generated from numerical phantoms and collected from physical phantoms with the standard single‐kVp‐switch full‐scan configuration, whereas dual‐energy short‐ and half‐scan data are extracted from the corresponding full‐scan data. Besides visual inspection and profile‐plot comparison, the reconstructed images are analyzed also in quantitative studies based upon tasks of linear‐attenuation‐coefficient and material‐concentration estimation and of material differentiation.

Results

Following the performance of a computer‐simulation study to verify that the one‐step method can reconstruct numerically accurately basis and monochromatic images of numerical phantoms, we reconstruct basis and monochromatic images by using the one‐step method from real data of physical phantoms collected with the full‐, short‐, and half‐scan configurations. Subjective inspection based upon visualization and profile‐plot comparison reveals that monochromatic images, which are used often in practical applications, reconstructed from the full‐, short‐, and half‐scan data are largely visually comparable except for some differences in texture details. Moreover, quantitative studies based upon tasks of linear‐attenuation‐coefficient and material‐concentration estimation and of material differentiation indicate that the short‐ and half‐scan configurations yield results in close agreement with the ground‐truth information and that of the full‐scan configuration.

Conclusions

The one‐step method considered can compensate effectively for the nonlinear spectral response in full‐ and partial‐angular‐scan dual‐energy CT. It can be exploited for enabling partial‐angular‐scan configurations on standard CT scanner without involving additional hardware. Visual inspection and quantitative studies reveal that, with the one‐step method, partial‐angular‐scan configurations considered can perform at a level comparable to that of the full‐scan configuration, thus suggesting the potential of the two partial‐angular‐scan configurations in reducing imaging dose and scan time in the standard single‐kVp‐switch full‐scan CT in which two full rotations are performed. The work also yields insights into the investigation and design of other nonstandard scan configurations of potential practical significance in dual‐energy CT.