Abstract
PurposeScatter is a very important artifact causing factor in dental cone-beam CT (CBCT), which has a major influence on the detectability of details within images. This work aimed to improve the image quality of dental CBCT through scatter correction.MethodsScatter was estimated in the projection domain from the low frequency component of the difference between the raw CBCT projection and the projection obtained by extrapolating the model fitted to the raw projections acquired with 2 different sizes of axial field-of-view (FOV). The function for curve fitting was optimized by using Monte Carlo simulation. To validate the proposed method, an anthropomorphic phantom and a water-filled cylindrical phantom with rod inserts simulating different tissue materials were scanned using 120 kVp, 5 mA and 9-second scanning time covering an axial FOV of 4 cm and 13 cm. The detectability of the CT image was evaluated by calculating the contrast-to-noise ratio (CNR).ResultsBeam hardening and cupping artifacts were observed in CBCT images without scatter correction, especially in those acquired with 13 cm FOV. These artifacts were reduced in CBCT images corrected by the proposed method, demonstrating its efficacy on scatter correction. After scatter correction, the image quality of CBCT was improved in terms of target detectability which was quantified as the CNR for rod inserts in the cylindrical phantom.ConclusionsHopefully the calculations performed in this work can provide a route to reach a high level of diagnostic image quality for CBCT imaging used in oral and maxillofacial structures whilst ensuring patient dose as low as reasonably achievable, which may ultimately make CBCT scan a reliable and safe tool in clinical practice.
Highlights
Cross-sectional radiography and computed tomography methods with multiplanar cross sections and 3D reconstructions are important diagnostic means in current dental and craniomaxillofacial medicine
Beam hardening and cupping artifacts were observed in cone-beam CT (CBCT) images without scatter correction, especially in those acquired with 13 cm FOV
These artifacts were reduced in CBCT images corrected by the proposed method, demonstrating its efficacy on scatter correction
Summary
Cross-sectional radiography and computed tomography methods with multiplanar cross sections and 3D reconstructions are important diagnostic means in current dental and craniomaxillofacial medicine. Dental cone-beam CT (CBCT) is an alternative to a MDCT scan that is appropriate for a wide range for craniomaxillofacial indications [4,5,6]. The radiation dose required is lower compared with conventional MDCT in most indications. MDCT produces relatively good image equality and stable CT numbers, mainly due to smaller inherent scatter signals as well as more linear detectors and sophisticated correction algorithms that have been developed over the past several decades. This work aimed to improve the image quality of dental CBCT through scatter correction. To reach this goal, a Monte Carlo simulator was built to characterize the scattered x-ray photons in dental CBCT. According to the research findings from the simulation results, a scatter correction strategy was proposed and validated using experimental measurements
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