Fast-switching dual energy cone beam computed tomography using the on-board imager of a commercial linear accelerator

Abstract

Purpose: To evaluate fast-kV switching (FS) dual energy (DE) cone beam computed tomography (CBCT) using the on-board imager (OBI) of a commercial linear accelerator to produce virtual monoenergetic (VM) and relative electron density (RED) images. Methods:Using an polynomial attenuation mapping model, CBCT phantom projections obtained at 80 and 140 kVp with FS imaging, were decomposed into equivalent thicknesses of aluminum (Al) and polymethyl methacrylate (PMMA). All projections were obtained with the titanium foil and bowtie filter in place. Basis material projections were then recombined to create VM images by using the linear attenuation coefficients at the specified energy for each material. Similarly, RED images were produced by replacing the linear attenuation values of Al and PMMA by their respective relative electron density (RED) values in the projection space. VM and RED images were reconstructed using Feldkamp-Davis-Kress (FDK) and an iterative algorithm (iCBCT, Varian Medical Systems). Hounsfield units (HU), contrast-to-noise ratio (CNR) and RED values were compared against known values. Results:The results after VM-CBCT production showed good material decomposition and consistent HU VM values, with measured root mean square errors (RMSE) from theoretical values, after FDK reconstruction, of 20.5, 5.7, 12.8 and 21.7 HU for 50, 80, 100 and 150 keV, respectively. The largest CNR improvements, when compared to polychromatic images, were observed for the 50 keV VM images. Image noise was reduced up to 28% in the VM-CBCT images after iterative image reconstruction. Relative electron density values measured for our method resulted in a mean percentage error of 0.0 ± 1.8%. Conclusions:This study describes a method to generate VM-CBCT and RED images using FS-DE scans obtained using the OBI of a linac, including the effects of the bowtie filter. The creation of VM and RED images increases the dynamic range of CBCT images, and provides additional

Fast and effective single‐scan dual‐energy cone‐beam CT reconstruction and decomposition denoising based on dual‐energy vectorization

“…It is worthy to note that the proposed method is a general method for DECT reconstruction and material decomposition, rather than only restricted to rfDE‐CBCT. The generality is mainly indicated on three aspects: (1) Some dual‐energy techniques present quite different noise levels in dual‐energy images 34,35 . The proposed method could tackle this issue via dual‐energy vectorization, and the designed filter adjusts the dual‐energy images to a similar noise level; (2) The addressing of SNR degradation starts from the reconstructed images and is not dependent on specific CT scan modes, thus the proposed noise suppression strategy could be used in any image‐domain decomposition tasks, even on diagnostic DECT; (3) The joint bilateral filtering is based solely on low‐ and high‐energy image pair other than the material images, thus, the proposed method could be directly used for image‐domain multi‐material decomposition, 45 regardless of the number of basis materials used.…”

“…The demand of fast acquisition and the concern of patient dose have motivated the development of sophisticated hardware techniques, 17‐19 enabling dual‐energy scan with time and dose comparable to the standard CT scan. These techniques recently have also been investigated and evaluated on DE‐CBCT 34,35 . Besides, researchers are investigating low‐cost single‐scan DE‐CBCT techniques 31,36 via adding extra hardware on current CBCT machine.…”

“…These techniques recently have also been investigated and evaluated on DE-CBCT. 34,35 Besides, researchers are investigating low-cost single-scan DE-CBCT techniques 31,36 via adding extra hardware on current CBCT machine. Lee et al, designed a multi-slit filter and acquired DE-CBCT data via linear reciprocation motion of the filter.…”

Densely sampled spectral modulation for x‐ray CT using a stationary modulator with flying focal spot: a conceptual and feasibility study of scatter and spectral correction

“…17,18 However, more cost-effective alternatives through hardware or algorithm innovations nowadays are also being extensively investigated in both academia and industry, in particular for low-cost systems. 3,4 Taking flatpanel detector based cone-beam CT as an example, its spectral imaging capability is an active research area in the field, [19][20][21] but so far there is a lack of mature solutions for clinical applications. A major challenge for cone-beam CT spectral imaging is that CT projections can be badly contaminated by x-ray scatter if not handled well.…”

Effect of computed tomography value error on dose calculation in adaptive radiotherapy with Elekta X‐ray volume imaging cone beam computed tomography

“…5 , 6 However, CBCTs are more affected by scattered radiation and the heel effect than is computed tomography (CT), making it difficult to obtain accurate 3D CT values. 7 , 8 , 9 , 10 Therefore, various methods have been developed to improve the accuracy of CT values and maintain image uniformity, such as deformable image registration‐based dose verification for CBCT images, 11 , 12 a dual‐energy CBCT to improve image quality and dose calculation accuracy, 13 , 14 deep neural networks to improve the image quality of CBCT images while preserving anatomical structures, 15 , 16 and scattered radiation correction. 17 These technologies have not yet been added to common commercial linear accelerator (linac).…”