A generalizable new figure of merit for dose optimization in dual energy cone beam CT scanning protocols

Abstract

Objective: This study proposes and evaluates a new figure of merit (FOMn) for dose¬ optimization of Dual-energy CBCT (DE-CBCT) scanning protocols based on size-dependent modeling of radiation dose and multi-scale image quality.
Approach: FOMn was defined using Z-score normalization and was proportional to the dose efficiency providing better multi-scale image quality, including comprehensive contrast-to-noise ratio (CCNR) and electron density (CED) for CatPhan604 inserts of various materials. Acrylic annuluses were combined with CatPhan604 to create four phantom sizes (diameters of the long axis are 200 mm, 270 mm, 350 mm, and 380 mm, respectively). DE-CBCT was decomposed using image-domain iterative methods based on Varian kV-CBCT images acquired using 25 protocols (100 kVp and 140 kVp combined with 5 tube currents).
Main results: The accuracy of CED was approximately 1% for all protocols, but degraded monotonically with the increased phantom sizes. Combinations of lower voltage + higher current and higher voltage + lower current were optimal protocols balancing CCNR and dose. The most dose-efficient protocols for CED and CCNR were inconsistent, underlining the necessity of including multi-scale image quality in the evaluation and optimization of DE-CBCT. Pediatric and adult anthropomorphic phantom tests confirmed dose-efficiency of FOMn-recommended protocols.
Significance: FOMn is a comprehensive metric that collectively evaluates radiation dose and multi-scale image quality for DE-CBCT. The models and data can also serve as lookup tables, suggesting personalized dose-efficient protocols for specific clinical imaging purposes.

Technical note: TIGRE‐DE for the creation of virtual monoenergetic images from dual‐energy cone‐beam CT

“…Optimizing the VM image creation process with respect to imaging dose and mAs settings remains a significant avenue for exploration. 33…”

Low-cost dual-energy CBCT by spectral filtration of a dual focal spot X-ray source

“…Phantom imaging studies were performed using the same x-ray exposure (mAs) for the two beams. Due to the differences in x-ray attenuation from the filters and the object, the post-object dose rate of the HE beam was about 70% of that of the LE beam, resulting in a higher noise level for the HE images, which may not be ideal for the overall image quality 35 . With two independently controlled cathodes and focal spots, the X-ray exposure and the dose rate of the two beams from the dual-focus x-ray source can be readily modulated in this system, as demonstrated in Fig.…”