Retrospective evaluation of mandibular third molars using simulated low-dose cone-beam computed tomography: A comparative image quality study

Three-dimensional C-arm Cone-beam CT: Applications in the Interventional Suite

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C-arm Cone-beam CT: General Principles and Technical Considerations for Use in Interventional Radiology

To investigate the accuracy and reliability of cone beam computed tomography (CBCT) measurements of buccal alveolar bone height (BBH) and thickness (BBT) using custom acquisition settings. School of Dentistry, Oregon Health & Science University. Twelve embalmed cadavers. Cadaver heads were imaged by CBCT (i-CAT® 17-19, Imaging Sciences International, Hatfield, PA) using a 'long scan' (LS) setting with 619 projection images, 360° revolution, 26.9 s duration, and 0.2 mm voxel size, and using a 'short scan' (SS) setting with 169 projection images, 180° rotation, 4.8 s duration, and 0.3 mm voxel size. BBH and BBT were measured with 65 teeth, indirectly from CBCT images and directly through dissection. Comparisons were assessed using paired t-tests (p≤0.05). Level of agreement was assessed by concordance correlation coefficients, Pearson's correlation coefficients, and Bland-Altman plots. Mean differences in measurements compared to direct measurements were as follows, LS 0.17±0.12 (BBH) and 0.10±0.07 mm (BBT), and SS 0.41±0.32 (BBH) and 0.12±0.11 mm (BBT). No statistical differences were found with any of BBH or BBT measurements. Correlation coefficients and Bland-Altman plots showed agreement was high between direct and indirect measurement methods, although agreement was stronger for measurements of BBH than BBT. Compared to the LS, the similarity in results with the reduced scan times and hence reduced effective radiation dose, favors use of shorter scans, unless other purposes for higher resolution imaging can be defined.

A pilot study evaluating 2D antiscatter grid based scatter suppression for quantitative cone beam CT in radiotherapy.

The present study assessed the quality of images and the presence of marginal gaps on cone-beam computed tomography (CBCT) images of teeth restored with all-ceramic and metal-ceramic crowns and compared the gap sizes observed on CBCT images with those obtained on micro-CT images. Thirty teeth restored with metal-ceramic and all-ceramic crowns, properly adapted and with gaps of 0.30 and 0.50 mm, were submitted to micro-CT and CBCT scans. Linear measurements corresponding to the marginal gap (MG) and the absolute marginal discrepancy (AMD) were obtained. The objective assessment of the quality of CBCT images was performed using the contrast-to-noise ratio (CNR), and the subjective assessment was defined by the diagnoses made by five examiners regarding the presence or absence of gaps. The measurements were always higher for CBCT, with a significant difference regarding AMD. No significant difference in image quality was observed using CNR between the crowns tested. Low accuracy and sensitivity values could be observed for both crowns. Marginal mismatch measures were overestimated in CBCT images. No difference in image quality was observed between the crowns. The correct diagnosis of gaps was considered low, irrespective of crown type and gap size.

Computed gray levels in multislice and cone-beam computed tomography

Improving Hounsfield Unit accuracy in dental CBCT through the integration of 2D anti-scatter grid.

Purpose. Cone beam computed tomography (CBCT) image quality is limited by scattered photons. Monte Carlo (MC) simulations provide the ability of predicting the patient-specific scatter contamination in clinical CBCT imaging. Lengthy simulations prevent MC-based scatter correction from being fully implemented in a clinical setting. This study investigates the combination of using fast MC simulations to predict scatter distributions with a ray tracing algorithm to allow calibration between simulated and clinical CBCT images. Material and methods. An EGSnrc-based user code (egs_cbct), was used to perform MC simulations of an Elekta XVI CBCT imaging system. A 60keV x-ray source was used, and air kerma scored at the detector plane. Several variance reduction techniques (VRTs) were used to increase the scatter calculation efficiency. Three patient phantoms based on CT scans were simulated, namely a brain, a thorax and a pelvis scan. A ray tracing algorithm was used to calculate the detector signal due to primary photons. A total of 288 projections were simulated, one for each thread on the computer cluster used for the investigation. Results. Scatter distributions for the brain, thorax and pelvis scan were simulated within 2% statistical uncertainty in two hours per scan. Within the same time, the ray tracing algorithm provided the primary signal for each of the projections. Thus, all the data needed for MC-based scatter correction in clinical CBCT imaging was obtained within two hours per patient, using a full simulation of the clinical CBCT geometry. Conclusions. This study shows that use of MC-based scatter corrections in CBCT imaging has a great potential to improve CBCT image quality. By use of powerful VRTs to predict scatter distributions and a ray tracing algorithm to calculate the primary signal, it is possible to obtain the necessary data for patient specific MC scatter correction within two hours per patient.

The aim of this study was to evaluate the image quality and dose exposition of different cone-beam computed tomography (CBCT) and low-dose multislice spiral CT (MSCT) scanners. A human cadaver head was examined with three MSCT and five CBCT scanners. The radiation dose was measured using an Alderson RANDO phantom. Standard protocols were used to obtain the CBCT data. For the MSCT devices, the tube voltage and tube current were modified to obtain acceptable image quality while keeping the radiation dose as low as possible. The image quality of MSCT and CBCT devices was determined by examining the enamel-dentin and dentin-pulp interface and the periodontal ligament space of 22 teeth. Inter- and intra-observer agreement was found for the different groups of raters. CBCT systems were rated superior to MSCT devices in terms of image quality for all dental structures. The differences in image quality among the studied CBCT and MSCT scanner groups did not turn out to be significant but were significant between CBCT and MSCT devices. The organ dose varied considerably between the different CBCT and MSCT devices. The differences concerning the organ dose were notably pronounced in the area of the eye lens. The tested devices exhibited significant differences with respect to the organ dose. The variance was particularly pronounced in the CBCT devices. With a dose exposition equal or lower than the CBCT, the image quality in the MSCT devices was judged to be significantly worse.

Evaluation of marginal fit of CAD/CAM restorations fabricated through cone beam computerized tomography and laboratory scanner data

Purpose: Cone Beam CT (CBCT) kilovoltage imaging devices are increasingly available for daily imaging in radiotherapy departments. Flat‐panel based CBCT scanners present a distinctive set of artifacts due mostly to increased scatter, longer data acquisition time and reduced detector quantum efficiency as compared to helical Fan Beam CT (FBCT) systems. Our purpose is to characterize image quality from FBCT and CBCT scanners based on noise, contrast and dose, using FBCT as a benchmark. Method and Materials: we acquired phantom and clinical patient images with a CBCT Varian On‐Board Imager as well as with a FBCT Picker PQ5000 single‐row helical scanner. The CBCT scanner was equipped with antiscatter grid and bowtie filter. By comparing CBCT and FBCT images of a high contrast resolution insert, the CBCT reconstruction voxel size and filter were adjusted until the spatial resolution of the FBCT and CBCT images was approximately matched. Dose was measured with standard CTDI and Farmer chambers. Noise, contrast and SNR were evaluated and compared. Results: CBCT images of both phantom and patient were relatively free of streaking and cupping artifacts, indicating that the grid had successfully attenuated most of the scatter. Low contrast detectability threshold is similar for the two modalities, when CBCT dose is about twice as large as FBCT. Noise and non‐uniformities are more prevalent in patient CBCT images, but pelvic soft tissue structures are well discernible. For patient and phantom images Dose×SNR2 is about 4 times lower for FBCT than in CBCT, which is about 1.5–2 times larger than expected, given the measured grid transmission and detector quantum efficiency. Conclusion: In this study, resolution‐matched CBCT and FBCT images could exhibit similar SNRs and contrast‐to‐noise ratios through a combination of increased imaging dose and reduced spatial resolution.

The added value of a new high-performance ring-gantry CBCT imaging system for prostate cancer patients

Purpose: To evaluate the intrafractional motion errors in patient with prostate cancer received pelvis irradiation during RapidArc radiotherapy.Materials and Methods: A total of eighteen high risk group prostate cancer patients were treated prostate and pelvis lymph nodes by RapidArc radiotherapy then boost dose by Cyberknife. All patients had kV cone beam computerized tomography (CBCT) scans in their first three fractions of treatment. During these treatments, the CBCT scans were registered to planning CT simulation images as reference to perform registration procedure based on soft tissue windows matched with clinical tumor volume (CTV). The errors of isocenter position were corrected by couch shifted. The second and third CBCT images were immediately acquired before and after RapidArc treatment. These errors of isocenter position on the left-right (LR), superior–inferior (SI) and anterior–posterior (AP) directions were analyzed retrospectively.Results: Under RapidArc technique with a shortened treatment delivery time (about 3 min), the residual systemic and random errors in pre and post-radiation treatment revealed limited. Based on the paired 2^(nd) and 3^(rd) CBCT images, the intrafractional errors (mean ± SD) in LR-SI-AP directions were -0.4 ± 0.8, -0.2 ± 1.0, 0.1 ± 0.8 mm. No intrafractional error differences in three axes, except borderline significant in LR direction (p= 0.046). Isotropic planning margins created with the linear addition of internal margin to clinical tumor volume was respectively 3.6, 4.4, 4.5 mm in LR-SI-AP axes and 2.5, 3.2, 3.3 mm if generated with quadrature addition.Conclusion: Use of the faster RapidArc technique with accurate kV CBCT images online verification for prostate cancer pelvis radiotherapy, the intrafractional motion errors were limited. These speculated intrafractional errors could be applied to improve the accuracy of radiation delivery and a smaller PTV margin might be adopted.

BackgroundThe emergence of robotic Cone Beam Computed Tomography (CBCT) imaging systems in trauma departments has enabled 3D anatomical assessment of musculoskeletal injuries, supplementing conventional 2D fluoroscopic imaging for examination, diagnosis, and treatment planning. To date, the primary focus has been on trauma sites in the extremities.PurposeTo determine if CBCT images can be used during the treatment planning process in spinal instrumentation and laminectomy procedures, allowing accurate 3D‐printed pedicle screw and laminectomy drill guides to be generated for the cervical and thoracic spine.MethodsThe accuracy of drill guides generated from CBCT images was assessed using animal cadavers (ovine and porcine). Preoperative scans were acquired using a robotic CBCT C‐arm system, the Siemens ARTIS pheno (Siemens Healthcare, GmbH, Germany). The CBCT images were imported into 3D‐Slicer version 4.10.2 (www.slicer.org) where vertebral models and specific guides were developed and subsequently 3D‐printed. In the ovine cadaver, 11 pedicle screw guides from the T1–T5 and T7–T12 vertebra and six laminectomy guides from the C2–C7 vertebra were planned and printed. In the porcine cadaver, nine pedicle screw guides from the C3–T4 vertebra were planned and printed. For the pedicle screw guides, accuracy was assessed by three observers according to pedicle breach via the Gertzbein–Robbins grading system as well as measured mean axial and sagittal screw error via postoperative CBCT and CT scans. For the laminectomies, the guides were designed to leave 1 mm of lamina. The average thickness of the lamina at the mid‐point was used to assess the accuracy of the guides, measured via postoperative CBCT and CT scans from three observers. For all measurements, the intraclass correlation coefficient (ICC) was calculated to determine observer reliability.ResultsCompared with the planned screw angles for both the ovine and porcine procedures (n = 32), the mean axial and sagittal screw error measured on the postoperative CBCT scans from three observers were 3.9 ± 1.9° and 1.8 ± 0.8°, respectively. The ICC among the observes was 0.855 and 0.849 for the axial and sagittal measurements, respectively, indicating good reliability. In the ovine cadaver, directly comparing the measured axial and sagittal screw angle of the visible screws (n = 14) in the postoperative CBCT and conventional CT scans from three observers revealed an average difference 1.9 ± 1.0° in axial angle and 1.8 ± 1.0° in the sagittal angle. The average thickness of the lamina at the middle of each vertebra, as measured on‐screen in the postoperative CBCT scans by three observes was 1.6 ± 0.2 mm. The ICC among observers was 0.693, indicating moderate reliability. No lamina breaches were observed in the postoperative images.ConclusionHere, CBCT images have been used to generate accurate 3D‐printed pedicle screw and laminectomy drill guides for use in the cervical and thoracic spine. The results demonstrate sufficient precision compared with those previously reported, generated from standard preoperative CT and MRI scans, potentially expanding the treatment planning capabilities of robotic CBCT imaging systems in trauma departments and operating rooms.