Sparse-view CBCT reconstruction using meta-learned neural attenuation field and hash-encoding regularization.

Real-time Intraoperative Computed Tomography Assessment of Quality of Permanent Interstitial Seed Implantation for Prostate Cancer

Cone‐beam CT (CBCT) has been widely used in image guided radiation therapy (IGRT) to acquire updated volumetric anatomical information before treatment fractions for accurate patient alignment purpose. However the excessive x‐ray imaging doses (a few cGy per scan) delivered to patients from serial CBCT scans raise a clinical concern in most IGRT procedures. This fact has greatly limited exploitation of IGRT's maximal potential. The imaging dose can be effectively reduced by reducing the number of x‐ray projections and/or lowering mAs levels in a CBCT scan. The image quality reconstructed from conventional FDK‐type algorithms however will be highly degraded. Recently total variation (TV) method has demonstrated its ability to reconstruct CBCT images from a few number of noisy x‐ray projections. Nonetheless such a method can hardly be applied in real clinical environments due to its long computational time (a few hours). It is highly desirable to develop a fast reconstruction scheme to obtain high quality CBCT images from undersampled and noisy projection data so as to lower the imaging dose.Utilizing GPU to speed up the computationally intensive tasks in CBCT reconstruction problems has drawn a lot of attention recently. In this talk GPU‐based CBCT reconstruction algorithms will be reviewed with an emphasis on an iterative CBCT reconstruction algorithm via TV regularization. We have recently developed a GPU‐friendly version of the forward‐backward splitting algorithm to solve the TV‐based reconstruction problem. Multi‐grid technique is also employed. It is found that 40 x‐ray projections are sufficient to reconstruct CBCT images with satisfactory quality for IGRT patient alignment purpose. Phantom studies indicate that CBCT images can be successfully reconstructed with our algorithm under as low as 0.1 mAs/projection level. Comparing with currently widely used full‐fan head‐and‐neck scanning protocol of about 360 projections with 0.4 mAs/projection it is estimated that an overall 36 times dose reduction has been achieved. Moreover the reconstruction time is about 130 sec on an NVIDIA Tesla C1060 GPU card which is estimated ∼100 times faster than similar iterative reconstruction approaches. The high computational efficiency and satisfactory image quality make the iterative low dose CBCT reconstruction approach feasible in real clinical environments.Learning Objectives:1. Understand basic concepts of GPU‐based CBCT reconstruction.2. Understand main challenges in GPU‐based iterative CBCT reconstruction approach and how an iterative CBCT reconstruction problem is solved on GPU.Conflict of Interest: The research presented here is partially supported by NVIDIA.

Comparison between effective radiation dose of CBCT and MSCT scanners for dentomaxillofacial applications

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.

Positional accuracy of a prosthetic treatment plan incorporated into a cone beam computed tomography scan using surface scan registration

ObjectivesSegmentation of anatomical structures on dento-maxillo-facial (DMF) computed tomography (CT) or cone beam computed tomography (CBCT) scans is increasingly needed in digital dentistry. The main aim of this research was to propose and evaluate a novel open source tool called DentalSegmentator for fully automatic segmentation of five anatomical structures on DMF CT and CBCT scans: maxilla/upper skull, mandible, upper teeth, lower teeth, and the mandibular canal. MethodsA retrospective sample of 470 CT and CBCT scans was used as a training/validation set. The performance and generalizability of the tool was evaluated by comparing segmentations provided by experts and automatic segmentations in two hold-out test datasets: an internal dataset of 133 CT and CBCT scans acquired before orthognathic surgery and an external dataset of 123 CBCT scans randomly sampled from routine examinations in 5 institutions. ResultsThe mean overall results in the internal test dataset (n = 133) were a Dice similarity coefficient (DSC) of 92.2 ± 6.3 % and a normalised surface distance (NSD) of 98.2 ± 2.2 %. The mean overall results on the external test dataset (n = 123) were a DSC of 94.2 ± 7.4 % and a NSD of 98.4 ± 3.6 %. ConclusionsThe results obtained from this highly diverse dataset demonstrate that this tool can provide fully automatic and robust multiclass segmentation for DMF CT and CBCT scans. To encourage the clinical deployment of DentalSegmentator, the pre-trained nnU-Net model has been made publicly available along with an extension for the 3D Slicer software. Clinical significanceDentalSegmentator open source 3D Slicer extension provides a free, robust, and easy-to-use approach to obtaining patient-specific three-dimensional models from CT and CBCT scans. These models serve various purposes in a digital dentistry workflow, such as visualization, treatment planning, intervention, and follow-up.

Our aim was to evaluate the effects of balloon sinuplasty on the size of the ostium in the maxillary sinuses in patients with chronic rhinosinusitis from cone beam computer tomography (CBCT) scans of the sinus. This is a blinded retrospective trial in patients who had undergone balloon sinuplasty of the maxillary sinus. CBCT scans were taken and SNOT-22 Quality of Life questionnaire completed before and 12 months after the operation. The size of the maxillary ostium was measured from the CBCT scans three-dimensionally. The association of changes in the SNOT-22 scores of the ostium was analysed. We discovered that the balloon sinuplasty increased the size of the maxillary ostium in all dimensions. The changes were statistically significant (p<0.05) in the axial diameter and the ostium area. The number of patent ostia increased after the intervention. The association between SNOT-22 score and ostium patency were statistically significant before the operation. Our conclusion is that the threedimensional measuring technique provides a reliable method to evaluate ostium dimensions. Balloon sinuplasty increased the size of the maxillary ostium and the result was maintained for 12 months after the operation.

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.

Objectives. To investigate the availability of correction of mandibular plane using software for vertical measurements in cone beam computed tomography (CBCT) according to the sites of the mandible. Methods. CBCT scans of six dry mandibles were performed at 0-, 5-, 10-, 15-, and 20-degree angles relative to CBCT scanning table. Using the imaging software, mandibular planes of the different angles were corrected to that of 0-degree angle on the CBCT images. Before and after correction of the mandibular planes, the distance from the mandibular canal to the alveolar crest was measured at M1, M2, and M3 areas of the mandible and vertical measurements were statistically compared with those of 0-angle location using the paired t-test. Results. Prior to correction, the vertical measurements increased as the angle increased. The greatest differences of measurements were observed in M3 areas (P < 0.05). After correction, a strong correlation was found in measurements between the 0-degree angle and the other angles in all sites of the mandible (P > 0.05). Conclusions. The vertical measurements of CBCT were significantly influenced by mandibular positioning. When CBCT scans are performed at angles other than 0-degree angle, software-based correction of the mandibular plane can be a reliable tool for the accurate vertical measurements in CBCT.

Letters to the Editor.

Introduction A radiological evaluation is essential in endodontics, for diagnostic purposes, planning and execution of the treatment, and evaluation of the success of therapy. The periapical radiography is nowadays the main radiographic investigations used but presents some limits as 3D anatomic alteration, geometric compression, and possible anatomical structures overlapping that can obscure the area of interest. CBCT (cone beam computed tomography) in endodontics allows a detailed assessment of the teeth and surrounding alveolar anatomy for endodontic diagnosis, treatment planning, and follow-up. Objective The purpose of this study was to evaluate the accuracy of CBCT in comparison with conventional intraoral radiographs used in endodontic procedures. Materials and Methods Statistical analysis was performed on 101 patients with previous endodontic treatments with the relative radiographic documentation (preoperative, postoperative, and follow-up intraoral X-ray) that had underwent at CBCT screening for surgical reasons. The CBCT scans were evaluated independently by two operators and compared with the corresponding periapical images. Results Our analysis shows that the two radiological investigations statistically agree in 100% of cases in the group of patients without any endodontic sign. In the group of patients with an endodontic pathology, detected with CBCT, endodontic under extended treatments (30.6%), MB2 canals in nontreated maxillary molars (20.7%), second canals in nontreated mandibular incisors (9%), root fractures (2.7%), and root resorption (2.7%) were not always visible in intraoral X-ray. Otherwise, positivity in the intraoral X-ray was always confirmed in CBCT. A radiolucent area was detected in CBCT exam in 46%, while the intraoral X-ray exam was positive only in 18%. Conclusions Our study shows that some important radiological signs acquired using CBCT are not always visible in periapical X-ray. Furthermore, CBCT is considered as a II level exam and could be used to solve diagnostic questions, essential to a proper management of the endodontic problems.

BackgroundDental radiographs are essential tools for diagnosis. However, there are significant concerns about the dangerous effect of radiation especially on children. The aim of this study was to evaluate genotoxicity and cytotoxicity in the exfoliated cells of buccal mucosa of children subjected to Cone Beam Computed Tomography (CBCT).Methods The study included 18 healthy children aged (9–12 years) who were exposed to CBCT. All CBCT scans were performed with the i-CAT CBCT. Exfoliated buccal cells were scraped from the left and right cheek immediately before the exposure, after 10 ± 2 days, and after 1 month. Cells were stained using Feulgen/fast green stain and examined under light microscopy. Genotoxicity (Micronuclei) and cytotoxicity (condensed chromatin, karyorrhexis, pyknosis, and karyolysis) were scored. Statistical analysis was performed using the McNemar test, Wilcoxon Signed-Rank test, and Mann-Whitney U test at a significance level of p < 0.05.ResultsThere were statistically significant differences in the mean percentages of micronuclei, condensed chromatin, karyorrhexis, pyknosis, and karyolysis before and 10 ± 2 days after the CBCT scan (p < 0.05). There were no statistically significant differences in the frequency of micronuclei, condensed chromatin, karyorrhexis, or pyknosis before and 1 month after the exposure (p > 0.05) except for karyolysis (p < 0.05).ConclusionsCBCT may induce genotoxicity and cytotoxicity in buccal mucosa cells of children. Therefore, CBCT should not be prescribed unless necessary as it cannot be considered a risk-free procedure.

Part 2 of this prospective clinical study aimed to compare the 1-year outcome of root canal retreatments, when individual roots and teeth were assessed by periapical radiographs and cone beam computed tomography (CBCT). Subjects participating in this study had been referred for management of an endodontic problem associated with one or more root filled teeth. Root canal retreatment was performed by Specialists or postgraduate students under the direct supervision of Specialist endodontic staff. A total of 98 teeth (84 patients) were reassessed clinically and radiographically 1year after completion of root canal retreatment. The postoperative periapical radiographs and CBCT scans were compared with their respective pre-treatment (diagnostic) periapical radiographs and CBCT scans. The increase or decrease in size of existing periapical radiolucencies and development of new radiolucencies were assessed by a consensus panel consisting of two calibrated examiners. They also determined an appropriate management plan for each case based on the radiographical findings. Comparison of the outcome diagnosis of individual roots and teeth and case management, when assessed by periapical radiographs and CBCT scans, was performed using chi-squared and McNemar's tests. An overall favourable result of 93% success for teeth (96% roots) was recorded when the assessment was undertaken by periapicals compared with 77% success for teeth (87% roots) when assessed by CBCT. A significant difference in outcome diagnosis of single paired roots (P<0.0001) and teeth (P= 0.0001) was observed when comparing periapicals to CBCT for the cohort of teeth as a whole. When comparing the future management plan on the basis of radiographic information alone, there was a significant difference between periapicals and CBCT-based management (P=0.01). Diagnosis using CBCT revealed a significantly lower number of favourable outcomes than periapicals in root canal retreatment. This significantly affected the future management of cases attending for a review.

Purpose: To investigate the accuracy and feasibility of cone beam computed tomography (CBCT) for stereotactic radiosurgery (SRS) setup. Method and Materials: A stereotactic BRW frame was attached to a Rando head phantom with imbedded radio-opaque markers (1mm in diameter) simulating the target locations. The head phantom with a CT localizer was first simulated for radiosurgery planning on a conventional CT scanner and then scanned on a treatment machine using CBCT. The differences between the conventional and CBCT localizations of the target positions were computed using a radiosurgery planning software. The translational corrections for target positions were calculated as the differences between the CBCT coordinates of the machine isocenter and the planned isocenters, which were the planned BRW coordinates from the conventional CT scan multiplied by the transformation matrix between the BRW and CBCT coordinate systems on the CBCT scan. The setup accuracy of CBCT was assessed from the analysis of orthogonal projection images for each radio-opaque target at the machine isocenter. Results: All nine fiducial markers of BRW localizer were successfully identified on all but one slice of the CBCT scan. The average localization difference between the conventional CT and CBCT BRW target coordinates was 0.28mm (SD 0.10mm). The mean distance error for all the radio-opaque targets localized using the CBCT and orthogonal projection images was 1.28mm (SD 0.61 mm). The major contributing factor to this cumulative setup error was the uncertainty in the superior-inferior direction due to the 2mm slice thickness in conventional CT. Conclusion: The CBCT image guidance can be used to setup SRS patients within accuracy comparable to the current SRS standard using an external fiducial system. The technique described here can serve as a gold standard for evaluating the accuracy of alternative immobilization and setup devices for SRS.

Objective: To assess the correlation between alveolar cleft measurements obtained from conventional radiography and cone-beam computed tomography (CBCT). Method: Eleven patients treated at ‘Associacao Maranhense da Alegria’, a non-profit organization that offers treatment to patients with cleft lip and palate, were included in this cross-sectional, descriptive study. All patients presented pre-incisive and trans-incisive foramen clefts and had not been treated with bone grafting. Periapical and occlusal radiographs and CBCT scans were obtained from all patients. The following measurements were determined: on periapical radiographs, cleft width in relation to the adjacent teeth in the a) apical, b) middle, and c) cervical thirds; on occlusal radiographs, cleft width based on the d) buccal, e) middle, and f) palatal aspects of the cleft; on CBCT scans, cleft width in relation to the adjacent teeth in the g) apical, h) middle, and i) cervical thirds, in a panoramic longitudinal section, for the assessment of correlation with periapical radiographic findings, and cleft width based on the j) buccal, l) middle, and m) palatal aspects of the cleft, in axial sections, for the assessment of correlation with occlusal radiographic findings. Radiographic measurements were calculated using a millimeter ruler and CBCT measurements were made using the i-CAT Vision software. Statistical analysis was performed by Spearman’s rank correlation test using and the software SPSS Statistics 17 for Windows. Results: The following correlation coefficients were found between periapical radiography and CBCT: 0.618 in the apical third (significance ρ=0.05), 0.556 in the middle third (significance ρ=0.05), and 0.963 in the cervical third (significance ρ=0.01). Results between occlusal radiography and CBCT were as follows: 0.712 on the buccal aspect (significance ρ=0.01), 0.568 on the middle aspect, and 0.679 on the palatal aspect (both significant at ρ=0.05). Conclusion: These findings indicate different positive correlation coefficients between measurements obtained from conventional radiography vs. CBCT, especially between periapical radiography and CBCT in the cervical third, and between occlusal radiography and CBCT on the buccal aspect of the cleft.