Feasibility of dual-energy CBCT by spectral filtration of a dual-focus CNT x-ray source

Abstract

Cone beam computed tomography (CBCT) is now widely used in dentistry and growing areas of medical imaging. The presence of strong metal artifacts is however a major concern of using CBCT especially in dentistry due to the presence of highly attenuating dental restorations, fixed appliances, and implants. Virtual monoenergetic images (VMIs) synthesized from dual energy CT (DECT) datasets are known to reduce metal artifacts. Although several techniques exist for DECT imaging, they in general come with significantly increased equipment cost and not available in dental clinics. The objectives of this study were to investigate the feasibility of developing a low-cost dual energy CBCT (DE-CBCT) by retrofitting a regular CBCT scanner with a carbon nanotube (CNT) x-ray source with dual focal spots and corresponding low-energy (LE) and high-energy (HE) spectral filters. A testbed with a CNT field emission x-ray source (NuRay Technology, Chang Zhou, China), a flat panel detector (Teledyne, Waterloo, Canada), and a rotating object stage was used for this feasibility study. Two distinct polychromatic x-ray spectra with the mean photon energies of 66.7keV and 86.3keV were produced at a fixed 120kVp x-ray tube voltage by using Al+Au and Al+Sn foils as the respective LE and HE filters attached to the exist window of the x-ray source. The HE filter attenuated the x-ray photons more than the LE filter. The calculated post-object air kerma rate of the HE beam was 31.7% of the LE beam. An anthropomorphic head phantom (RANDO, Nuclear Associates, Hicksville, NY) with metal beads was imaged using the testbed and the images were reconstructed using an iterative volumetric CT reconstruction algorithm. The VMIs were synthesized using an image-domain basis materials decomposition method with energy ranging from 30 to 150keV. The results were compared to the reconstructed images from a single energy clinical dental CBCT scanner (CS9300, Carestream Dental, Atlanta, GA). A significant reduction of the metal artifacts was observed in the VMI images synthesized at high energies compared to those from the same object imaged by the clinical dental CBCT scanner. The ability of the CNT x-ray source to generate the output needed to compensate the reduction of photon flux due to attenuation from the spectral filters and to maintain the CT imaging time was evaluated. The results demonstrated the feasibility of DE-CBCT imaging using the proposed approach. Metal artifact reduction was achieved in VMIs synthesized. The x-ray output needed for the proposed DE-CBCT can be generated by a fixed-anode CNT x-ray source.

The Impact of AI on Metal Artifacts in CBCT Oral Cavity Imaging

“…The use of high-photonenergy virtual monoenergetic images (VMIs) has proven effective in various applications [31][32][33]. There are initial, positive reports showing the application of these techniques in CBCT imaging [29,34]. Other approaches, such as iterative deblurring methods and segmentation-based approaches, offer significant improvements in image quality [35,36].…”

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

“…This work aimed to optimize scanning protocols for DE-CBCT by balancing radiation dose and multi-scale image quality, which complements previous low-dose attempts using novel algorithms (Zbijewski et al 2013) or hardware innovations such as multi-slit beam-filter (Lee et al 2017), carbon nanotube (CNT) x-ray source (Li et al 2022), filters of various materials (Iramina et al 2018), and dual-layer detector (Shi et al 2020b), etc. The protocol optimization might be used in combination with the new algorithm and hardware to further improve the dose efficiency of DE-CBCT, which is worthy of more studies in the future.…”

Multisource cone beam computed tomography using a carbon nanotube x-ray source array

“…It consists of eight gated CNT field emission cathodes and eight corresponding focal spots on an extended W anode with an inter-source spacing of 12 mm, as shown in Figure 3a. A collimator was used to confine the radiation from each source to a rectangular field with a measured cone beam angle of 2.4 ° [24], significantly smaller than the ~10 ° cone angle needed to cover the same FOV in the conventional CBCT configuration (N1 ms-CBCT configuration). Figure 3b demonstrates the radiation fields formed by the individual X-ray beams of the CNT X-ray source array after collimation at 200 mm away from the focal line.…”