Artefacts in CBCT: a review

Quantitative analysis of metal artefacts of dental implant in CBCT image by correlation analysis to micro-CT: A microstructural study

OBJECTIVES

Quantification of dental implant metal artefacts in CBCT images using correlation analysis of trabecular microstructural parameters from CBCT and micro-CT, and analysis of the effect of varying the angular position of the subject.

METHODS

Polyurethane synthetic bone blocks were first scanned without implants by micro-CT and CBCT. Two dental implants were then placed parallel in the bone blocks and these specimens were scanned by CBCT with different alpha angles. Three volumes of interest (VOI) were set for further analysis. Six microstructural parameters were measured: trabecular thickness (Tb_Th), trabecular spacing (Th_Sp), bone volume per total volume (BV/TV), bone surface per total volume (BS/TV), connectivity density (CD) andfractal dimension (FD). Micro-CT measurements were used as a gold standard for CBCT. Spearman correlation coefficients for each microstructural parameter from CBCT and micro-CT were calculated and compared using Steiger's Z test.

RESULTS

Without the implants, in VOI₁, the Spearman correlation coefficients of Tb_Th, Tb_Sp, BV/TV, BS/TV, CD and FD were 0.599, 0.76, 0.552, 0.566, 0.664 and 0.607, respectively. With the implants, the correlation coefficients decreased sharply in VOI₁. As the alpha angle increased from zero to 90°, the correlation coefficients increased and became significant. Similar results appeared in VOI₂. In contrast, in VOI₃, the correlation coefficient decreased as the alpha angle increased.

CONCLUSIONS

Metal artefacts were successfully quantified using microstructural parameters in terms of the image quality of the CBCT. Changes in alpha angle affected the quality of the CBCT image.

Do the number of basis images and metal artifact reduction affect the production of artifacts near and far from zirconium dental implants in CBCT?

OBJECTIVES

This study aimed to evaluate the influence of the number of basis images and the metal artifact reduction (MAR) tool on the production of artifacts near and far from a zirconium implant in cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

CBCT scans of a mandible were acquired before and after insertion of an implant, using 450 and 720 basis images, with and without MAR activation. The mean and standard deviation (SD) of the gray values of the regions of interest (ROIs) located on the cortices adjacent to the implant and at different distances from it (in the soft tissue) were calculated. The mean of the gray values was used to calculate the absolute contrast difference (ACD) between the control and implant scans.

RESULTS

In general, the number of basis images did not affect the SD and the ACD values of the buccal and lingual ROIs (p > 0.05). The implant increased the SD in the lingual cortical plate (p < 0.05). In this case, MAR activation decreased SD (p < 0.05). All ROIs located at different distances from the implant showed higher SD on scans acquired with 450 basis images (p < 0.05), regardless of MAR condition.

CONCLUSIONS

A higher number of basis images reduces the magnitude of artifacts but does not influence the image quality in bone cortical plates. MAR improves the image in the areas most affected by artifacts.

CLINICAL RELEVANCE

The number of basis images is known as a factor capable of influencing the image quality and radiation dose for the patient. Therefore, it is important to investigate its effect on the expression of artifacts in the CBCT images.

Root canal sealers affect artifacts on cone-beam computed tomography images

The purpose of this study was to evaluate the appearance of artifacts by four types of root canal filling sealers on cone-beam computed tomography (CBCT) images. Thirty standardized tooth models were given the radiopacity equivalent to human teeth, and root canal preparation was performed using WaveOne Gold. Root canal filling by a single-point method was performed using WaveOne Gold gutta-percha points and four types of root canal sealers: AH Plus (AH), CANALS (CA), BioRoot RCS (BR), and MTA Fillapex (MTA). Samples were taken by periapical radiography at 60 kV and scanned by CBCT at three tube voltages (70, 85, and 100 kV). The gray-scale values (GVs) of the periapical radiographs were measured and the aluminum equivalents were calculated. On the CBCT axial images, the artifact and dentin area GVs were measured and the rate of change in the GV (RCGV) was calculated as follows: RCGV (%) = (dentin area GV - artifact GV)/dentin area GV × 100. High-density areas with artifacts on the CBCT images were also measured. On the periapical radiographs, the aluminum equivalent was largest for AH and smallest for MTA. On the CBCT images, AH showed the largest values for both RCGV and the high-density areas, while BR and MTA showed comparable values. Correlations were found between the radiopacity on the periapical radiographs and the degree of artifacts on the CBCT images. These findings suggest that the greater the contrast in the 2D image, the higher the artifacts in the 3D image.

Artefacts at different distances from titanium and zirconia implants in cone-beam computed tomography: effect of tube current and metal artefact reduction

OBJECTIVES

To evaluate the effect of cone-beam computed tomography (CBCT) tube current (mA) on the magnitude of artefacts at different distances from titanium or zirconia implants, with and without activation of a proprietary metal artefact reduction (MAR).

MATERIAL AND METHODS

Human mandibles were scanned on an OP300 Maxio CBCT unit (Instrumentarium, Tuusula, Finland) before and after the installation of dental implants, with four different tube currents (4 mA, 6.3 mA, 8 mA and 10 mA), with and without activation of proprietary MAR. The effect of mA on the standard deviation (SD) of gray values and contrast to noise ratio (CNR) were assessed in regions of interest located 1.5 cm, 2.5 cm, and 3.5 cm from implants.

RESULTS

In the presence of titanium implants, a significant decrease in SD was found by increasing tube current from 4 mA to 6.3 mA or 8 mA. For zirconia implants, 8 mA yielded better results for all distances. MAR improved CNR in the presence of zirconia implants at all distances, whereas no differences were observed with the use of MAR for titanium implants.

CONCLUSION

Increased tube current can improve overall image quality in the presence of implants, at all the distances tested. When a zirconia implant is present, such increase in mA should be higher in comparison to that for examinations with titanium implants. Activation of OP300 Maxio proprietary MAR improved image quality only among examinations with zirconia implants.

CLINICAL RELEVANCE

Artefact-generating implants are common in the field of view of CBCT examinations. Optimal exposure parameters, such as tube current, ensure high image quality with lowest possible radiation exposure.

Clinical outcomes of flap versus flapless immediately loaded single dental implants in the mandibular posterior region: One-year follow-up results from a randomized controlled trial

STATEMENT OF PROBLEM

Flapless implant placement with immediate functional loading has been reported in anterior locations. However, data on posterior locations are lacking.

PURPOSE

The purpose of this randomized controlled trial was to determine and compare clinical outcomes of flap versus flapless surgically placed single posterior mandibular dental implants subjected to immediate functional loading.

MATERIAL AND METHODS

Participants with missing mandibular first molar teeth were recruited and randomized into 2 groups (n=51): flapped and flapless. Dental implants were surgically placed and loaded immediately with interim restorations following implant protective occlusion. Outcome measures were implant failure, crestal bone loss, and periodontal parameters: modified plaque index, modified sulcus bleeding index, and pocket depths. Outcome data were recorded at baseline, 6-month, and 12-month follow-up visits. Cone beam computed tomography scans were used to calculate crestal bone loss, and periodontal outcomes were recorded by using a resin covered periodontal probe (α=.05).

RESULTS

After 12 months, similar implant failure rates (P>.05) were found between the groups. Crestal bone loss in the flapped group was statistically higher than in the flapless group at 6 months (0.83 ±0.21 mm versus 0.75 ±0.23 mm) and at 12 months (1.04 ±0.27 mm versus 0.90 ±0.24 mm) from the baseline. The modified plaque index, modified sulcus bleeding index, and peri-implant probing depths (PDs) in both groups increased from the baseline to 6-month follow-ups (Baseline modified plaque index: 0.82 ±0.54 versus 0.79 ±0.21; Baseline modified sulcus bleeding index: 0.74 ±0.21 versus 0.70 ±0.43; Baseline PD: 1.25 ±0.37 mm versus 1.20 ±0.22 mm; 6 months modified plaque index: 1.54 ±0.70 versus 1.21 ±0.45; 6 months modified sulcus bleeding index: 1.93 ±0.54 versus 1.51 ±0.61; 6 months PD: 3.20 ±0.73 mm versus 2.80 ±0.43 mm). At 12-month follow-ups after repeated oral hygiene reinforcements, periodontal parameters had improved (decreased) significantly.

CONCLUSIONS

Flapless implant insertion with immediate functional loading could be considered as an appropriate treatment option for providing functional restorations on the day of implant placement with minimal surgical intervention, reducing crestal bone loss, and periodontal complications.

In vivo detection of vertical root fractures in endodontically treated teeth: Accuracy of cone-beam computed tomography and assessment of potential predictor variables

Background

This study aimed: (a) to determine the diagnostic performance of cone-beam computed tomography (CBCT) for detection of vertical root fractures (VRFs); (b) to evaluate the predictive value of diagnostic criteria regarding the definition of VRFs; and (c) to examine the robustness of the association of patient-, tooth-, and treatment-related variables with VRFs.

Material and Methods

130 root-filled teeth with signs/symptoms of VRFs underwent clinical and CBCT assessments. Definite diagnosis of VRF was confirmed by endodontic microsurgical (EMS) exploration. Determination of diagnostic performance of CBCT was based on standard algorithms derived from two-way contingency table analysis. Predictive value of diagnostic criteria and the association between predictor variables with VRFs were analyzed using logistic regression models.

Results

VRFs were detected during EMS in 50% of the teeth. Based on the finding of fracture lines on CBCT scans, sensitivity, specificity, and accuracy were 86.2%, 13.8%, and 50%, respectively. Teeth having more than three diagnostic criteria present had significant higher odds for VRF diagnosis. After logistic regression analysis, parafunctional habits, one-canal roots, excessive root canal enlargement, and absence of intra-radicular posts remained as robust predictor variables of VRFs.

Conclusions

Although the sensitivity of CBCT for VRFs detection is high, the risk of false-positive results related to its low specificity makes that all suspected cases must be confirmed by surgical exploration. VRFs cannot be reliably diagnosed by isolated clinical signs/symptoms; instead those teeth possessing more than three diagnostic criteria might be considered practically pathognomonic. The parafunctional habits, one-canal roots, excessive root canal enlargement, and the absence of intra-radicular posts may act strongly/independently for the occurrence of VRFs in endodontically treated teeth.

Key words:Cone-beam computed tomography, diagnostic accuracy, diagnostic surgery, predictor variables, root canal treatment, vertical root fracture.

MRI for the display of autologous onlay bone grafts during early healing-an experimental study

OBJECTIVES

Autologous bone grafts are the gold standard to augment deficient alveolar bone. Dimensional graft alterations during healing are not known as they are not accessible to radiography. Therefore, MRI was used to display autologous onlay bone grafts in vivo during early healing.

METHODS AND MATERIALS

Ten patients with alveolar bone atrophy and autologous onlay grafts were included. MRI was performed with a clinical MR system and an intraoral coil preoperatively (t0), 1 week (t1), 6 weeks (t2) and 12 weeks (t3) postoperatively, respectively. The graft volumes were assessed in MRI by manual segmentation by three examiners. Graft volumes for each time point were calculated and dimensional alteration was documented. Cortical and cancellous proportions of bone grafts were assessed. The intraobserver and interobserver variability were calculated. Statistical analysis was performed using a mixed linear regression model.

RESULTS

Autologous onlay bone grafts with cortical and cancellous properties were displayed in vivo in eight patients over 12 weeks. The fixation screws were visible as signal voids with a thin hyperintense fringe. The calculated volumes were between 0.12-0.74 cm³ (t1), 0.15-0.73 cm³ (t2), and 0.17-0.64 cm³ (t3). Median changes of bone graft volumes of -15% were observed. There was no significant difference between the examiners (p = 0.3).

CONCLUSIONS

MRI is eligible for the display and longitudinal observation of autologous onlay bone grafts. Image artifacts caused measurements deviations in some cases and minimized the precise assessment of graft volume. To the knowledge of the authors, this is the first study that used MRI for the longitudinal observation of autologous onlay bone grafts.

A hybrid, image-based and biomechanics-based registration approach to markerless intraoperative nodule localization during video-assisted thoracoscopic surgery

The resection of small, low-dense or deep lung nodules during video-assisted thoracoscopic surgery (VATS) is surgically challenging. Nodule localization methods in clinical practice typically rely on the preoperative placement of markers, which may lead to clinical complications. We propose a markerless lung nodule localization framework for VATS based on a hybrid method combining intraoperative cone-beam CT (CBCT) imaging, free-form deformation image registration, and a poroelastic lung model with allowance for air evacuation. The difficult problem of estimating intraoperative lung deformations is decomposed into two more tractable sub-problems: (i) estimating the deformation due the change of patient pose from preoperative CT (supine) to intraoperative CBCT (lateral decubitus); and (ii) estimating the pneumothorax deformation, i.e. a collapse of the lung within the thoracic cage. We were able to demonstrate the feasibility of our localization framework with a retrospective validation study on 5 VATS clinical cases. Average initial errors in the range of 22 to 38 mm were reduced to the range of 4 to 14 mm, corresponding to an error correction in the range of 63 to 85%. To our knowledge, this is the first markerless lung deformation compensation method dedicated to VATS and validated on actual clinical data.

Cone-beam CT image quality improvement using Cycle-Deblur consistent adversarial networks (Cycle-Deblur GAN) for chest CT imaging in breast cancer patients

Cone-beam computed tomography (CBCT) integrated with a linear accelerator is widely used to increase the accuracy of radiotherapy and plays an important role in image-guided radiotherapy (IGRT). For comparison with fan-beam computed tomography (FBCT), the image quality of CBCT is indistinct due to X-ray scattering, noise, and artefacts. We proposed a deep learning model, “Cycle-Deblur GAN”, combined with CycleGAN and Deblur-GAN models to improve the image quality of chest CBCT images. The 8706 CBCT and FBCT image pairs were used for training, and 1150 image pairs were used for testing in deep learning. The generated CBCT images from the Cycle-Deblur GAN model demonstrated closer CT values to FBCT in the lung, breast, mediastinum, and sternum compared to the CycleGAN and RED-CNN models. The quantitative evaluations of MAE, PSNR, and SSIM for CBCT generated from the Cycle-Deblur GAN model demonstrated better results than the CycleGAN and RED-CNN models. The Cycle-Deblur GAN model improved image quality and CT-value accuracy and preserved structural details for chest CBCT images.

Influence of CBCT-based volumetric distortion and beam hardening artefacts on the assessment of root canal filling quality in isthmus-containing molars

OBJECTIVES

To evaluate the influence of artefacts in cone beam CT (CBCT) images of filled root canals in isthmus-containing molars.

METHODS

10 teeth presenting canals with an isthmus were instrumented and filled with a thermoplasticised obturation technique. The teeth were scanned using a micro-CT device and two CBCT devices: 3D Accuitomo 170 (ACC) and NewTom VGi evo (NT), with different acquisition protocols: larger and smaller voxel size. Three examiners assessed the CBCT images for: (1) detection of filling voids; (2) assessment of under- or overestimation of the filling material and (3) resemblance of CBCT images to the reference standard. Analyses of Task 1 yielded accuracy, sensitivity and specificity for detection of filling voids. For tasks 2 and 3, statistical analysis was performed using Wilcoxon test. The level of significance was set at p < .05.

RESULTS

For Task 1, ACC showed higher sensitivity, whereas NT presented higher specificity. No significant difference was found between the protocols in ACC, however, for NT, differences between protocols were significant for all diagnostic values. In Task 2, visualisation of the filling was overestimated for NT, while for ACC, underestimation was observed. For Task 3, images with smaller voxel size were more similar to the reference image, for both CBCT devices.

CONCLUSIONS

Different artefacts compromise the detection of filling voids on CBCT images of canals in mandibular molars with isthmus. ACC and NT present rather similar diagnostic accuracy, even though artefact expression remains device-specific.

Objective assessment of the combined effect of exomass-related- and motion artefacts in cone beam CT

OBJECTIVES

To assess quantitatively the combined effect of exomass-related- and motion artefacts on voxel value parameters in cone beam CT (CBCT).

METHODS

A cylindrical phantom was manufactured, containing 21 tubes filled with a radiopaque solution, allowing the inclusion of three titanium implants in the periphery to induce exomass-related artefacts. The phantom was mounted on a robot simulating 0.75-, 1.5-, and 3 mm movements (nodding/lateral rotation/tremor). CBCT images with/without exomass and with/without movements were acquired in duplicate in three units: Cranex 3Dx, Orthophos SL-3D, and X1 (with motion-artefact correction). A cylindrical volume of interest was defined in each tube and voxel value mean and standard deviation were assessed. For each CBCT volume, the 21 mean voxel values were averaged providing the overall mean voxel value (MVV), and the standard deviation (among the 21 values) was calculated providing overall voxel value inhomogeneity (VVI). The standard deviation from each of the 21 volumes-of-interest were averaged, providing overall image noise (IN). The effect of the diverse tested situations was inferred from a repeated-measures analysis of variance, followed by Sidak's test (α = 0.05).

RESULTS

Overall, images acquired with exomass showed significantly (p ≤ 0.05) lower MVV, and higher VVI and IN. Motion artefacts aggravated exomass-related alterations. MVV and VVI were mostly affected by 3 mm nodding movements. Motion-artefact correction eliminated the deleterious effect of movement.

CONCLUSIONS

CBCT voxel-value parameters are altered by exomass-related artefacts, and this finding is aggravated in the presence of motion artefacts. Motion-artefact correction effectively eliminated the deleterious impact of movement.

Prevalence and Morphology of C-Shaped Canals: A CBCT Analysis in a Korean Population

This retrospective study of roots with C-shaped canals investigated their prevalence, configuration type, and lingual wall thickness, as well as the panoramic radiographic features of roots in permanent mandibular second molars confirmed to have C-shaped canals on cone-beam computed tomography (CBCT) in a Korean population. In total, 1884 CBCT images of mandibular second molars were examined by two endodontists to analyze the presence of C-shaped canals according to age and sex. The bilateral occurrence of C-shaped roots and their morphology on panoramic radiography were assessed and statistically analyzed using the chi-square test. The classification of Fan et al. was applied to categorize the configurations of C-shaped canals. The lingual wall thickness was calculated in the mesial, middle, and distal areas at the orifice and at 5 mm from the apex. The Mann-Whitney U test was used to analyze the mean difference of lingual wall thickness between the apex and orifice level. A P value of 0.05 was considered to indicate statistical significance in the statistical analyses. Of 2508 mandibular second molars, 924 (36.8%) had C-shaped root canals. The prevalence was significantly lower in the over 61 age group (24.08%) than in the 21-30-year age group (40.02%) and was higher in women (42.32%). Most cases were bilateral (85.9%). The C1 type was the most common (35.3%). The prevalence of C1 type canals decreased, while that of C3b type canals increased with age. In 75.2% of teeth having C-shaped root canals on CBCT, fused roots were observed on panoramic views. The difference in the lingual wall thickness at the orifice and 5 mm from the apex was significant in the middle area in all configurations of C-shaped root canals. When performing nonsurgical or surgical endodontic procedures of the mandibular second molars, clinicians should consider age, sex, ethnicity, and anatomical variations.

Fusion of intra-oral scans in cone-beam computed tomography scans

PURPOSE

The purpose of this study was to evaluate the clinical accuracy of the fusion of intra-oral scans in cone-beam computed tomography (CBCT) scans using two commercially available software packages.

MATERIALS AND METHODS

Ten dry human skulls were subjected to structured light scanning, CBCT scanning, and intra-oral scanning. Two commercially available software packages were used to perform fusion of the intra-oral scans in the CBCT scan to create an accurate virtual head model: IPS CaseDesigner® and OrthoAnalyzer™. The structured light scanner was used as a gold standard and was superimposed on the virtual head models, created by IPS CaseDesigner® and OrthoAnalyzer™, using an Iterative Closest Point algorithm. Differences between the positions of the intra-oral scans obtained with the software packages were recorded and expressed in six degrees of freedom as well as the inter- and intra-observer intra-class correlation coefficient.

RESULTS

The tested software packages, IPS CaseDesigner® and OrthoAnalyzer™, showed a high level of accuracy compared to the gold standard. The accuracy was calculated for all six degrees of freedom. It was noticeable that the accuracy in the cranial/caudal direction was the lowest for IPS CaseDesigner® and OrthoAnalyzer™ in both the maxilla and mandible. The inter- and intra-observer intra-class correlation coefficient showed a high level of agreement between the observers.

CLINICAL RELEVANCE

IPS CaseDesigner® and OrthoAnalyzer™ are reliable software packages providing an accurate fusion of the intra-oral scan in the CBCT. Both software packages can be used as an accurate fusion tool of the intra-oral scan in the CBCT which provides an accurate basis for 3D virtual planning.

Guidelines for reporting on CBCT scans

The aim of a radiographic report is to provide an accurate interpretation of images to facilitate the diagnostic process, and when indicated prompt the appropriate management for the patient. It is part of the patient's clinical records. This paper describes the imaging chain involved in the cone beam computed tomography (CBCT) workflow from referring to reporting on a CBCT scan. It provides guidelines on the essential information required before and immediately after a CBCT scan is taken, and optimizing the viewing conditions. Finally, it describes a framework for a systematic, comprehensive and tailored CBCT radiographic report. It is aimed at endodontists, clinicians and radiologists reporting on CBCT scans of the dentoalveolar region.

The Influence of Surgical Experience and Bone Density on the Accuracy of Static Computer-Assisted Implant Surgery in Edentulous Jaws Using a Mucosa-Supported Surgical Template with a Half-Guided Implant Placement Protocol-A Randomized Clinical Study

The aim of our randomized clinical study was to analyze the influence of surgical experience and bone density on the accuracy of static computer-assisted implant surgery (CAIS) in edentulous jaws using a mucosa-supported surgical template with a half-guided implant placement protocol. Altogether, 40 dental implants were placed in the edentulous jaws of 13 patients (novice surgeons: 18 implants, 6 patients (4 male), age 71 ± 10.1 years; experienced surgeons: 22 implants, 7 patients (4 male), age 69.2 ± 4.55 years). Angular deviation, coronal and apical global deviation and grey level measurements were calculated for all implants by a blinded investigator using coDiagnostiX software. 3DSlicer software was applied to calculate the bone volume fraction (BV/TV) for each site of implant placement. There were no statistically significant differences between the two study groups in either of the primary outcome variables. There was a statistically significant negative correlation between angular deviation and both grey level measurements (R-value: −0.331, p < 0.05) and BV/TV (R-value: −0.377, p < 0.05). The results of the study suggest that surgical experience did not influence the accuracy of implant placement. The higher the bone density at the sites of implant placement, the higher the accuracy of static CAIS.

Assessment of true vertical root fracture line in endodontically treated teeth using a new subtraction software - A Micro-CT and CBCT study

This study aimed to find true facture lines in endodontically treated teeth on CBCT images using digital subtraction and to evaluate the influence of width of facture lines in the diagnosis. Thirty-two endodontically treated teeth with vertical root fractures (VRFs) from 30 patients were included in this study. The CBCT images of the patients and the micro-CT images of extracted teeth were imported into our digital subtraction software to distinguish the true facture lines from the streak artefacts. Of them, 23(71.87%) teeth did not present true fracture lines on the CBCT images (CBCT negative), and 9 (28.13%) teeth presented true fracture lines on the CBCT images (CBCT positive). The width of the facture lines was significantly different between these two groups (P < 0.05). To summarise, for in vivo endodontically treated teeth with subtle VRFs, many true fractures lines could not be demonstrated on CBCT images and wider fractures could be better distinguished.

Metal artifacts reduction in computed tomography: A phantom study to compare the effectiveness of metal artifact reduction algorithm, model-based iterative reconstruction, and virtual monochromatic imaging

The purpose of this study was to compare the effectiveness of a metal artifact reduction algorithm (MAR), model-based iterative reconstruction (MBIR), and virtual monochromatic imaging (VMI) for reducing metal artifacts in CT imaging.A phantom study was performed for quantitatively evaluating the dark bands and fine streak artifacts generated by unilateral hip prostheses. Images were obtained by conventional scanning at 120 kilovolt peak, and reconstructed using filtered back projection, MAR, and MBIR. Furthermore, virtual monochromatic images (VMIs) at 70 kilo-electron volts (keV) and 140 keV with/without use of MAR were obtained by dual-energy CT. The extents and mean CT values of the dark bands and the differences in the standard deviations and location parameters of the fine streak artifacts evaluated by the Gumbel method in the images obtained by each of the methods were statistically compared by analyses of variance.Significant reduction of the extent of the dark bands was observed in the images reconstructed using MAR than in those not reconstructed using MAR (all, P < .01). Images obtained by VMI at 70 keV and 140 keV with use of MAR showed significantly increased mean CT values of the dark bands as compared to those obtained by reconstructions without use of MAR (all, <.01). Significant reduction of the difference in the standard deviations used to evaluate fine streak artifacts was observed in each of the image sets obtained with VMI at 140 keV with/without MAR and conventional CT with MBIR as compared to the images obtained using other methods (all, P < .05), except between VMI at 140 keV without MAR and conventional CT with MAR. The location parameter to evaluate fine streak artifacts was significantly reduced in CT images obtained using MBIR and in images obtained by VMI at 140 keV with/without MAR as compared to those obtained using other reconstruction methods (all, P < .01).In our present study, MAR appeared to be the most effective reconstruction method for reducing dark bands in CT images, and MBIR and VMI at 140 keV appeared to the most effective for reducing streak artifacts.

Influence of the exomass on the detection of simulated root fracture in cone-beam CT - an ex-vivo study

OBJECTIVES

To evaluate the influence of exomass-related metal artefacts on the detection of simulated vertical root fracture (VRF) in cone-beam computed tomography (CBCT).

METHODS

20 teeth were endodontically instrumented and VRF was induced in half of them. All teeth were individually placed in an empty socket of a human mandible. Metallic materials were differently arranged in the exomass [zone outside of the field of view (FOV) but between the X-ray source and the receptor] and/or endomass (zone inside of the FOV), and CBCT scans were obtained. Four radiologists evaluated the presence of VRF using a 5-point scale. Sensitivity, specificity, and area under the receiver operating curve (AUC) were compared using ANOVA. Also, the tooth of interest was replaced with a tube filled with a radiopaque solution and all CBCT scans were repeated to analyse the data objectively. Mean grey and noise values were obtained from the tube and compared using ANOVA followed by Tukey's test (α = 0.05).

RESULTS

Mean grey values were significantly lower and noise was significantly higher when metallic materials were present in the endomass or both the exomass and endomass. Sensitivity, specificity, and AUC were not influenced by the artefacts from the metallic materials irrespective of the arrangement condition.

CONCLUSIONS

Exomass-related metal artefacts did not influence the diagnosis of simulated VRF in CBCT.

Comparison of Cone Beam Computed Tomography and Digital Radiography in Detecting Separated Endodontic Files and Strip Perforation

The separation of endodontic files and strip perforation are among procedural intraoperative complications which may ultimately lead to the failure of root canal treatment. The aim of the present study was to compare the diagnostic potential of cone beam computed tomography (CBCT) and digital periapical radiographs in detecting separated rotary files and strip perforation in filled canals. Fifty human mandibular molars were selected for this study. The teeth were randomly divided into two groups based on endodontic errors (i.e., file separation and strip perforation). In each group, 25 of 50 mesial canals were randomly chosen for simulating the errors, while the other 25 canals were considered as the control group. In group one, a simulation of the separation of rotary files was performed using ProTaper F2 files. Strip perforation of the root canals in group two was achieved by number 2 and 3 Gates Glidden drills in the coronal third of the root canals. Digital periapical radiographs in two different horizontal angles and high-resolution CBCT scans were obtained from the teeth mounted on a dry human mandible with simulated soft tissue covering. Three experienced observers who were unaware of the study groups evaluated the digital periapical and CBCT image sets in two separate readings. Intraobserver and interobserver agreements, as well as accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), were calculated and compared. Intraobserver and interobserver agreements ranged from poor to excellent and poor to good, respectively. The accuracy, sensitivity, specificity, PPV, and NPV for digital radiography in detecting separated files were 0.950, 0.813, 0.957, 0.929, and 0.880, respectively. The same values for CBCT were 0.747, 0.667, 0.900, 0.833, and 0.783, respectively. For the diagnosis of strip perforation, these values were 0.855, 0.800, 0.909, 0.889, and 0.833 for periapical radiography and 0.955, 1.000, 0.920, 0.926, and 1.000 for CBCT. In conclusion, CBCT was superior for diagnosing strip perforation of the filled root canals, while digital periapical radiographs performed better in the detection of separated rotary files.

Synthetic CT in assessment of anatomical and dosimetric variations in radiotherapy - procedure validation

Introduction: One of many procedures to control the quality of radiotherapy is daily imaging of the patient’s anatomy. The CBCT (Cone Beam Computed Tomography) plays an important role in patient positioning, and dose delivery monitoring. Nowadays, CBCT is a baseline for the calculation of fraction and total dose. Thus, it provides the potential for more comprehensive monitoring of the delivered dose and adaptive radiotherapy. However, due to the poor quality and the presence of numerous artifacts, the replacement of the CBCT image with the corrected one is desired for dose calculation. The aim of the study was to validate a method for generating a synthetic CT image based on deformable image registration.

Material and methods: A Head & Torso Freepoint phantom, model 002H9K (Computerized Imaging Reference Systems, Norfolk, USA) with inserts was imaged with CT (Computed Tomography). Then, contouring and treatment plan were created in Eclipse (Varian Medical Systems, Palo Alto, CA, USA) treatment planning system. The phantom was scanned again with the CBCT. The planning CT was registered and deformed to the CBCT, resulting in a synthetic CT in Velocity software (Varian Medical Systems, Palo Alto, CA, USA). The dose distribution was recalculated based on the created CT image.

Results: Differences in structure volumes and dose statistics calculated both on CT and synthetic CT were evaluated. Discrepancies between the original and delivered plan from 0.0 to 2.5% were obtained. Dose comparison was performed on the DVH (Dose-Volume Histogram) for all delineated inserts.

Conclusions: Our findings suggest the potential utility of deformable registration and synthetic CT for providing dose reconstruction. This study reports on the limitation of the procedure related to the limited length of the CBCT volume and deformable fusion inaccuracies.

A Qualitative Assessment of Bone Mineral Density in Individuals With Hemifacial Microsomia: A Cone-Beam Computed Tomography Study

OBJECTIVE

The purpose of this study is to utilize cone-beam computed tomography (CBCT) to compare the bone mineral density (BMD) on the affected versus nonaffected side, among individuals with hemifacial microsomia (HFM).

METHODS

This retrospective study included 9 patients with HFM. Pretreatment CBCT volumes were imported into Invivo5 software, which was used to measure BMD through Hounsfield units (HU) in 3 regions of the mandible; inferior to the lower lateral incisors, inferior to the first molar and at the ramus inferior to the sigmoid notch. Each region was measured at the buccal cortical bone, lingual cortical bone, and cancellous bone. The densities on the right and left sides were compared by Wilcoxon signed-rank test.

RESULTS

Overall, the BMD on the affected side tended to show slightly lower values when compared with the nonaffected side. Differences ranged from 14 HU at the lingual cortical plate of the first molar region to 234 HU at the buccal cortical plate of the ramus region. Differences were only statistically significant at the ramus region for the buccal (P = .002) and lingual (P < .001) cortical plates and at the lower incisor region at the buccal cortical plate (P = .016) and cancellous bone (P = .044). The differences, however, did not seem to be clinically significant.

CONCLUSIONS

The current study shows that the quality of bone on the affected side may be slightly reduced but did not seem to be clinically significant. This should be accounted for during surgical and orthodontic planning for patients with HFM.

Evaluation of a cycle-generative adversarial network-based cone-beam CT to synthetic CT conversion algorithm for adaptive radiation therapy

PURPOSE

Image-guided radiation therapy could benefit from implementing adaptive radiation therapy (ART) techniques. A cycle-generative adversarial network (cycle-GAN)-based cone-beam computed tomography (CBCT)-to-synthetic CT (sCT) conversion algorithm was evaluated regarding image quality, image segmentation and dosimetric accuracy for head and neck (H&N), thoracic and pelvic body regions.

METHODS

Using a cycle-GAN, three body site-specific models were priorly trained with independent paired CT and CBCT datasets of a kV imaging system (XVI, Elekta). sCT were generated based on first-fraction CBCT for 15 patients of each body region. Mean errors (ME) and mean absolute errors (MAE) were analyzed for the sCT. On the sCT, manually delineated structures were compared to deformed structures from the planning CT (pCT) and evaluated with standard segmentation metrics. Treatment plans were recalculated on sCT. A comparison of clinically relevant dose-volume parameters (D₉₈, D₅₀ and D₂ of the target volume) and 3D-gamma (3%/3mm) analysis were performed.

RESULTS

The mean ME and MAE were 1.4, 29.6, 5.4 Hounsfield units (HU) and 77.2, 94.2, 41.8 HU for H&N, thoracic and pelvic region, respectively. Dice similarity coefficients varied between 66.7 ± 8.3% (seminal vesicles) and 94.9 ± 2.0% (lungs). Maximum mean surface distances were 6.3 mm (heart), followed by 3.5 mm (brainstem). The mean dosimetric differences of the target volumes did not exceed 1.7%. Mean 3D gamma pass rates greater than 97.8% were achieved in all cases.

CONCLUSIONS

The presented method generates sCT images with a quality close to pCT and yielded clinically acceptable dosimetric deviations. Thus, an important prerequisite towards clinical implementation of CBCT-based ART is fulfilled.

Correlation of objective image quality and working length measurements in different CBCT machines: An ex vivo study

To investigate potential correlations between objective CBCT image parameters and accuracy in endodontic working length determination ex vivo. Contrast-to-noise ratio (CNR) and spatial resolution (SR) as fundamental objective image parameters were examined using specific phantoms in seven different CBCT machines. Seven experienced observers were instructed and calibrated. The order of the CBCTs was randomized for each observer and observation. To assess intra-operator reproducibility, the procedure was repeated within six weeks with a randomized order of CBCT images. Multivariate analysis (MANOVA) did not reveal any influence of the combined image quality factors CNR and SR on measurement accuracy. Inter-operator reproducibility as assessed between the two observations was poor, with a mean intra-class correlation (ICC) of 0.48 (95%-CI  0.38, 0.59) for observation No. 1. and 0.40 (95%-CI 0.30, 0.51) for observation No. 2. Intra-operator reproducibility pooled over all observers between both observations was only moderate, with a mean ICC of 0.58 (95%-CI 0.52 to 0.64). Within the limitations of the study, objective image quality measures and exposure parameters seem not to have a significant influence on accuracy in determining endodontic root canal lengths in CBCT scans. The main factor of variance is the observer.

Comparative Reliability Assessment of Tooth Volume Measurement with Different Three-Dimensional Imaging Software

Objective. To evaluate the in vivo tooth volume through VRMesh and 3Matic programs and to compare the measurements to the physical volume. So, the aim of the study was to ensure the reliability and sensitivity of the three-dimensional software (VRMesh and 3Matic) in measuring tooth volume. Material and Methods. The volume of 26 extracted upper first premolars from orthodontic patients who had CBCT before orthodontic treatment were measured. Two different commercial programs, which were VRMesh and 3Matic, were used to calculate the volume of the segmented upper first premolar from CBCT. The in vivo tooth volume was compared to the physical tooth volume to examine the accuracy of the two software in measuring the tooth volume. Results. The difference between the mean of the in vivo and in vitro tooth volume measurements was too small, making it clinically nonsignificant. ANOVA test was used as a statistical tool, and no statistically significant difference was noticed among the measurements. The values were normally distributed when tested for normality by Kolmogorov-Smirnov and Shapiro-Wilk test. $\mathit{P}$ value less than or equal to 0.05 ( $\mathit{P}\le 0.05$ ) was considered statistically significant. Conclusion. The assessment of the in vivo tooth volume measurement with different three-dimensional imaging software (VRMesh and 3Matic) programs in comparison with the tooth physical volume is reliable. The use of a mouse pen during the refining stage of the segmentation may have increased the accuracy of the procedure. The determined in vivo tooth volumes are dependable and can be applied in orthodontic diagnosis and treatment planning.

Accuracy of Cone-Beam Computed Tomography in Measuring the Thickness of Radicular Dentin

The purpose of this study was to evaluate the accuracy of Cone-Beam Computed Tomography (CBCT) in measuring radicular dentin thickness focused on intraradicular post placement planning treatment. Ten single-rooted human premolars were selected. The teeth were divided into three segments (cervical, middle and apical). The coronal face of the apical and middle sections was selected for the dentin thickness assessment; which was measured from the external root surface to the root canal wall, on the buccal, lingual, mesial, and distal surfaces of each tooth. In situ anatomical measurement was the reference standard, and the corresponding axial CBCT imaging were evaluated by the i-CAT software. The one-way ANOVA test and the Bonferroni post hoc test were applied to compare the groups (p>0.05). CBCT imaging measurements (p=0.003) overestimated the radicular dentin thickness compared to the reference standard. Descriptive analysis showed that the greatest difference between the reference standard and the tomographic measurement means were 0.20 mm. One-way ANOVA test found the statistical significant difference among group's measurements. Bonferroni correction demonstrated statistically significant difference only related lingual surface for the CBCT imaging measurements. CBCT imaging measurements overestimated the radicular dentin thickness. However, the measurement difference was clinically acceptable.

A learning-based method for online adjustment of C-arm Cone-beam CT source trajectories for artifact avoidance

PURPOSE

During spinal fusion surgery, screws are placed close to critical nerves suggesting the need for highly accurate screw placement. Verifying screw placement on high-quality tomographic imaging is essential. C-arm cone-beam CT (CBCT) provides intraoperative 3D tomographic imaging which would allow for immediate verification and, if needed, revision. However, the reconstruction quality attainable with commercial CBCT devices is insufficient, predominantly due to severe metal artifacts in the presence of pedicle screws. These artifacts arise from a mismatch between the true physics of image formation and an idealized model thereof assumed during reconstruction. Prospectively acquiring views onto anatomy that are least affected by this mismatch can, therefore, improve reconstruction quality.

METHODS

We propose to adjust the C-arm CBCT source trajectory during the scan to optimize reconstruction quality with respect to a certain task, i.e., verification of screw placement. Adjustments are performed on-the-fly using a convolutional neural network that regresses a quality index over all possible next views given the current X-ray image. Adjusting the CBCT trajectory to acquire the recommended views results in non-circular source orbits that avoid poor images, and thus, data inconsistencies.

RESULTS

We demonstrate that convolutional neural networks trained on realistically simulated data are capable of predicting quality metrics that enable scene-specific adjustments of the CBCT source trajectory. Using both realistically simulated data as well as real CBCT acquisitions of a semianthropomorphic phantom, we show that tomographic reconstructions of the resulting scene-specific CBCT acquisitions exhibit improved image quality particularly in terms of metal artifacts.

CONCLUSION

The proposed method is a step toward online patient-specific C-arm CBCT source trajectories that enable high-quality tomographic imaging in the operating room. Since the optimization objective is implicitly encoded in a neural network trained on large amounts of well-annotated projection images, the proposed approach overcomes the need for 3D information at run-time.

Potential of a New Cone-Beam CT Software for Blooming Artifact Reduction

Abstract This study evaluated the dimensions of intraradicular posts using a new cone beam CT (CBCT) software, and verified the potential of blooming artifact reduction. Sixty-three single-rooted human teeth were shaped, obturated, prepared for intracanal post placement and distributed into three groups: G1: anatomically customized prefabricated glass fiber posts; G2: low-fusion alloy posts; G3: gold alloy posts. After post fabrication and luting with RelyX U200®, specimens were sectioned axially at 9 mm from the root apex, and markings were made on the root surfaces (X-, Y- and Z-axes). The dimensions of the original posts (control group) were measured using a digital micrometer. CBCT scans of the teeth were obtained using a PreXion 3D Elite® scanner. Posts were measured on CBCT scans using DICOM files and the e-Vol DX software. A specific filter, Blooming Artefact Reduction (BAR), was developed to analyze intracanal posts. Statistical data were evaluated using the Van de Waerden nonparametric analysis of variance and, after that, normalized data were analyzed using the Tukey test. The level of significance was set at α = 5%. The measures of the anatomical prefabricated, low-fusion alloy and gold alloy intracanal posts obtained using the e-Vol DX CBCT software and a micrometer were not significantly different (p>0.05). The use of the BAR filter of the e-Vol DX software application did not induce any dimensional differences on CBCT scans of intracanal posts when compared with measurements made with a micrometer on original posts. The use of the BAR filter eliminated blooming artifacts.

Head motion and perception of discomfort by young children during simulated CBCT examinations

OBJECTIVES

To assess the frequency and characteristics (number, complexity, and distance) of head movements, and the perception of discomfort during simulated CBCT examinations in children, considering units with different patient positioning method and head immobilization device combinations.

METHODS

Forty children (20 boys/20 girls, age range 10-14 years) were video-recorded during simulated CBCT examinations. Children were randomly allocated to a sequence of five CBCT units: Newtom-5G, Orthophos-SL, Cranex-3Dx (patient standing/sitting), and X1. The child scored his/her discomfort perception (visual scale) and the preferred/ill-favored unit. Three observers scored the videos (20% in duplicate): child movement (yes/no), number (<3/≥3/continuous), complexity (uniplanar/multiplanar) and distance (<3 mm/≥3 mm). κ statistics provided intra-/interobserver reproducibility. Severe/extreme motion was defined based on movement characteristics. Chi-square tests assessed the frequency differences of severe/extreme motion among the units, age and operator. Logistic regression analyses with severe/extreme motion as outcome were performed.

RESULTS

The range of intra- and inter-observer reproducibility for movement observation was 0.78-0.89 and 0.61-0.64, respectively. Between 60% (Newtom-5G) and 100% (X1) of children moved during the examination. Severe/extreme motion was significantly related to unit and age. There was significantly less severe/extreme motion, when the child was in the supine position with a foam headrest as head support. The younger the child, the higher the risk for severe/extreme motion. The majority of the children preferred the unit with the supine position and a foam headrest.

CONCLUSIONS

The prevalence of severe and extreme motion was associated with the unit's patient positioning method and head immobilization devices combined, and child age.

CBCT image quality QA: Establishing a quantitative program

Purpose

Routine quality assurance (QA) of cone‐beam computed tomography (CBCT) scans used for image‐guided radiotherapy is prescribed by the American Association of Physicists in Medicine Task Group (TG)‐142 report. For CBCT image quality, TG‐142 recommends using clinically established baseline values as QA tolerances. This work examined how image quality parameters vary both across machines of the same model and across different CBCT techniques. Additionally, this work investigated how image quality values are affected by imager recalibration and repeated exposures during routine QA.

Methods

Cone‐beam computed tomography scans of the Catphan 604 phantom were taken on four TrueBeam® and one Edge™ linear accelerator using four manufacturer‐provided techniques. TG‐142 image quality parameters were calculated for each CBCT scan using SunCHECK Machine™. The variability of each parameter with machine and technique was evaluated using a two‐way ANOVA test on a dataset consisting of 200 CBCT scans. The impact of imager calibration on image quality parameters was examined for a subset of three machines using an unpaired Student’s t‐test. The effect of artifacts appearing on CBCTs taken in rapid succession was characterized and an approach to reduce their appearance was evaluated. Additionally, a set of baselines and tolerances for all image quality metrics was presented.

Results

All imaging parameters except geometric distortion varied with technique (P < 0.05) and all imaging parameters except slice thickness varied with machine (P < 0.05). Imager calibration can change the expected value of all imaging parameters, though it does not consistently do so. While changes are statistically significant, they may not be clinically significant. Finally, rapid acquisition of CBCT scans can introduce image artifacts that degrade CBCT uniformity.

Conclusions

This work characterized the variability of acquired CBCT data across machines and CBCT techniques along with the impact of imager calibration and rapid CBCT acquisition on image quality.

Imaging Anatomy of the Jaw and Dentition with Cone Beam Computed Tomography

Knowledge of dental, maxillary, and mandibular anatomy and the use of correct nomenclature is critical in the evaluation of a mandibulofacial and/or maxillofacial imaging data set. The use of the correct diagnostic imaging tool tailored to the patient's needs is of equal importance. This article highlights imaging anatomy and cross-sectional imaging modalities mainly focusing on cone beam computed tomography of the mandibulofacial and maxillofacial region.

Dentomaxillofacial CBCT: Clinical Challenges for Indication-oriented Imaging

This critical review discusses the clinical challenges for patient-specific and indication-oriented dentomaxillofacial cone beam computed tomography (CBCT). Large variations among units and protocols may lead to variable degrees of diagnostic and three-dimensional model accuracy, impacting both specific diagnostic tasks and treatment planning. Particular indications, whether diagnostic or therapeutic, may give rise to very specific challenges with regard to CBCT unit and parameter setup, considering the required image quality, segmentation accuracy, and artifact level. Considering that dental materials are in the field of view needed for diagnosis or treatment planning, artifact expression is a dominant factor in proper CBCT selection. The heterogeneity of dental CBCT units and performances may highly impact the scientific results. Thus research findings cannot be simply generalized as published evidence, and a demonstrated clinical applicability for a specific indication should not be simply extrapolated from one CBCT unit to another.

Comparison of the different voxel sizes in the estimation of peri-implant fenestration defects using cone beam computed tomography: an ex vivo study

Background

To examine the influence of voxel sizes to detect of peri-implant fenestration defects on cone beam computed tomography (CBCT) images.

Materials and methods

This study performed with three sheep heads both maxilla and mandible and two types of dental implant type 1 zirconium implant (Zr⁴⁰) (n = 6) and type 2 titanium implant (Ti²²) (n = 10). A total of 14 peri-implant fenestrations (8 buccal surfaces, 6 palatal/lingual surface) were created while 18 surfaces (8 buccal, 10 palatal/lingual) were free of fenestrations. Three observers have evaluated the images of fenestration at each site. Images obtained with 0.75 mm³, 0.100 mm³, 0.150 mm³, 0.200 mm³, and 0.400 mm³ voxel sizes. For intra- and inter-observer agreements for each voxel size, Kappa coefficients were calculated.

Results

Intra- and inter-observer kappa values were the highest for 0.150 mm³, and the lowest in 0.75 mm³ and 0.400 mm³ voxel sizes for all types of implants. The highest area under the curve (AUC) values were found higher for the scan mode of 0.150 mm³, whereas lower AUC values were found for the voxel size for 0.400 mm³. Titanium implants had higher AUC values than zirconium with the statistical significance for all voxel sizes (p ≤ 0.05).

Conclusion

A voxel size of 0.150 mm³ can be used to detect peri-implant fenestration bone defects. CBCT is the most reliable diagnostic tool for peri-implant fenestration bone defects.

Application of 3D tooth model for monitoring of implant space and inter-root distance without radiographs: a proof of concept study

BACKGROUND

Radiographs are integral in evaluating implant space and inter-root distance. The purpose of this report is to introduce a method for evaluating the 3D root position with minimal radiation using a 3D tooth model composed of an intraoral-scanned crown and a cone-beam computed tomography (CBCT)-scanned root.

MATERIALS AND METHODS

Intraoral scan and CBCT scan of the patient were obtained before treatment. In the CBCT image, tooth segmentation was performed by isolating individual teeth from the maxillary and mandibular alveolar bone using software program. The 3D tooth model was fabricated by combining segmented individual teeth with the intraoral scan.

RESULTS

A post-treatment intraoral scan was integrated into the tooth model, and the resulting position of the root could be predicted without additional radiographs. It is possible to monitor the root position after a pretreatment CBCT scan using a 3D tooth model without additional radiographs.

CONCLUSION

The application of the 3D tooth model benefits the patient by reducing repeated radiation exposure while providing the clinician with a precise treatment evaluation to monitor tooth movement.

Accuracy of cone-beam computed tomography is limited at implant sites with a thin buccal bone: A laboratory study

BACKGROUND

To evaluate whether buccal bone thickness (BBT), implant diameter, and abutment/crown material influence the accuracy of cone-beam computed tomography (CBCT) to determine the buccal bone level at titanium implants.

METHODS

Two implant beds (i.e., narrow and standard diameter) were prepared in each of 36 porcine bone blocks. The implant beds were positioned at a variable distance from the buccal bone surface; thus, resulting in three BBT groups (i.e., >0.5 to 1.0; >1.0 to 1.5; >1.5 to 2.0 mm). In half of the blocks, a buccal bone dehiscence of random extent ("depth") was created and implants were mounted with different abutment/crown material (i.e., titanium abutments with a metal-ceramic crown and zirconia abutments with an all-ceramic zirconia crown). The distance from the implant shoulder to the buccal bone crest was measured on cross-sectional CBCT images and compared with the direct measurements at the bone blocks.

RESULTS

While abutment/crown material and implant diameter had no effect on the detection accuracy of the buccal bone level at dental implants in CBCT scans, BBT had a significant effect. Specifically, when BBT was ≤1.0 mm, a dehiscence was often diagnosed although not present, that is, the sensitivity was high (95.8%), but the specificity (12.5%) and the detection accuracy (54.2%) were low. Further, the average measurement error of the distance from the implant shoulder to the buccal bone crest was 1.6 mm.

CONCLUSIONS

Based on the present laboratory study, BBT has a major impact on the correct diagnosis of the buccal bone level at dental titanium implants in CBCT images; in cases where the buccal bone is ≤1 mm thick, detection of the buccal bone level is largely inaccurate.

Head motion during cone-beam computed tomography: Analysis of frequency and influence on image quality

Purpose

Image artifacts caused by patient motion cause problems in cone-beam computed tomography (CBCT) because they lead to distortion of the 3-dimensional reconstruction. This prospective study was performed to quantify patient movement during CBCT acquisition and its influence on image quality.

Materials and Methods

In total, 412 patients receiving CBCT imaging were equipped with a wireless head sensor system that detected inertial, gyroscopic, and magnetometric movements with 6 dimensions of freedom. The type and amplitude of movements during CBCT acquisition were evaluated and image quality was rated in 7 different anatomical regions of interest. For continuous variables, significance was calculated using the Student t-test. A linear regression model was applied to identify associations of the type and extent of motion with image quality scores. Kappa statistics were used to assess intra- and inter-rater agreement. Chi-square testing was used to analyze the impact of age and sex on head movement.

Results

All CBCT images were acquired in a 10-month period. In 24% of the investigations, movement was recorded (acceleration: >0.10 [m/s²]; angular velocity: >0.018 [°/s]). In all examined regions of interest, head motion during CBCT acquisition resulted in significant impairment of image quality (P<0.001). Movement in the horizontal and vertical axes was most relevant for image quality (R²>0.7).

Conclusion

Relevant head motions during CBCT imaging were frequently detected, leading to image quality loss and potentially impairing diagnosis and therapy planning. The presented data illustrate the need for digital correction algorithms and hardware to minimize motion artefacts in CBCT imaging.

A review of virtual planning software for guided implant surgery - data import and visualization, drill guide design and manufacturing

Background

Virtual implant planning systems integrate (cone beam-) computed tomography data to assess bone quantity and virtual models for the design of the implant-retained prosthesis and drill guides. Five commercially available systems for virtual implant planning were examined regarding the modalities of integration of radiographic data, virtual dental models and the design of drill guides for guided implant surgery. The purpose of this review was to describe the limitations of these available systems regarding the import of imaging data and the design and fabrication of a drill guide.

Methods

The following software systems were examined regarding the import of imaging data and the export of the virtual implant planning for the design and fabrication of a drill guide with the help of two clinical situations requiring dental implant therapy: coDiagnostiX™, DentalWings, Canada (CDX); Simplant Pro™, Dentsply, Sweden (SIM); Smop™, Swissmeda, Switzerland (SMP); NobelClinician™, Nobel Biocare, Switzerland (NC); Implant Studio, 3Shape, Denmark (IST). Assessment criteria included data formats and management as well as the workflow for the design and production of drill guides.

Results

All systems have a DICOM-interface (“Digital Imaging and Communication in Medicine”) for the import of radiographic data. Imaging artefacts could be reduced but not eliminated by manual data processing. The import of virtual dental models in a universal format (STL: Standard Tesselation Language) was possible with three systems; one system could only be used with a proprietary data format.

All systems display three-dimensional surface models or two-dimensional cross-sections with varying orientation for virtual implant planning. Computer aided design and manufacturing (CAD/CAM) of drill guides may be performed by the user with the help of default parameters or solely by the provider of the software and thus without the influence of the clinician.

Conclusion

Data bases of commonly used implant systems are available in all tested software, however not all systems allow to plan and execute fully guided implant placement. An individual design and in-house manufacturing of the drill guide is only available in some software systems. However, at the time of publication most recent software versions showed flexibility in individual design and in-house manufacturing of drill guides.

3D cone-beam CT with a twin robotic x-ray system in elbow imaging: comparison of image quality to high-resolution multidetector CT

Background

Elbow imaging is challenging with conventional multidetector computed tomography (MDCT), while cone-beam CT (CBCT) provides superior options. We compared intra-individually CBCT versus MDCT image quality in cadaveric elbows.

Methods

A twin robotic x-ray system with new CBCT mode and a high-resolution clinical MDCT were compared in 16 cadaveric elbows. Both systems were operated with a dedicated low-dose (LD) protocol (equivalent volume CT dose index [CTDI_{vol(16 cm)}] = 3.3 mGy) and a regular clinical scan dose (RD) protocol (CTDI_{vol(16 cm)} = 13.8 mGy). Image quality was evaluated by two radiologists (R1 and R2) on a seven-point Likert scale, and estimation of signal intensity in cancellous bone was conducted. Wilcoxon signed-rank tests and intraclass correlation coefficient (ICC) statistics were used.

Results

The CBCT prototype provided superior subjective image quality compared to MDCT scans (for RD, p ≤ 0.004; for LD, p ≤ 0.001). Image quality was rated very good or excellent in 100% of the cases by both readers for RD CBCT, 100% (R1) and 93.8% (R2) for LD CBCT, 62.6% and 43.8% for RD MDCT, and 0.0% and 0.0% for LD MDCT. Single-measure ICC was 0.95 (95% confidence interval 0.91–0.97; p < 0.001). Software-based assessment supported subjective findings with less “undecided” pixels in CBCT than dose-equivalent MDCT (p < 0.001). No significant difference was found between LD CBCT and RD MDCT.

Conclusions

In cadaveric elbow studies, the tested cone-beam CT prototype delivered superior image quality compared to high-end multidetector CT and showed a potential for considerable dose reduction.

Impacts of Thresholds of Gray Value for Cone-Beam Computed Tomography 3D Reconstruction on the Accuracy of Image Matching with Optical Scan

In cone-beam computed tomography (CBCT), the minimum threshold of the gray value of segmentation is set to convert the CBCT images to the 3D mesh reconstruction model. This study aimed to assess the accuracy of image registration of optical scans to 3D CBCT reconstructions created by different thresholds of grey values of segmentation in partial edentulous jaw conditions. CBCT of a dentate jaw was reconstructed to 3D mesh models using three different thresholds of gray value (-500, 500, and 1500), and three partially edentulous models with different numbers of remaining teeth (4, 8, and 12) were made from each 3D reconstruction model. To merge CBCT and optical scan data, optical scan images were registered to respective 3D reconstruction CBCT images using a point-based best-fit algorithm. The accuracy of image registration was assessed by measuring the positional deviation between the matched 3D images. The Kruskal-Wallis test and a post hoc Mann-Whitney U test with Bonferroni correction were used to compare the results between groups (α = 0.05). The correlations between the experimental factors were calculated using the two-way analysis of variance test. The positional deviations were lowest with the threshold of 500, followed by the threshold of 1500, and then -500. A significant interaction was found between the threshold of gray values and the number of remaining teeth on the registration accuracy. The most significant deviation was observed in the arch model with four teeth reconstructed with a gray-value threshold of -500. The threshold for the gray value of CBCT segmentation affects the accuracy of image registration of optical scans to the 3D reconstruction model of CBCT. The appropriate gray value that can visualize the anatomical structure should be set, especially when few teeth remain in the dental arch.

Influence of Metal Post in Adjacent Teeth in the Detection of Vertical Root Fracture Using Cone-beam Computed Tomography with Different Acquisition Parameters

INTRODUCTION

The aim of the present study was to evaluate the detection of vertical root fracture (VRF) in the presence of adjacent teeth restored with a metal post and the influence of acquisition parameters (tube current and metal artifact reduction [MAR] algorithm) on this diagnostic task.

METHODS

Cone-beam computed tomographic images of 10 single-rooted teeth were acquired before and after the simulation of VRF. The acquisitions were set up to simulate different conditions regarding the presence of adjacent teeth restored with a metal post (control, 1 adjacent tooth, and both adjacent teeth), different tube currents (4, 8, and 10 mA), and the use of MAR (without MAR and with MAR). Images were assessed by 5 oral and maxillofacial radiologists using a 5-point scale for the presence of VRF. Diagnostic values were calculated and compared by 2-way analysis of variance (significance level of 5%).

RESULTS

The area under the receiver operating characteristic curve (Az) values for VRF detection were affected by the presence of adjacent teeth and the variation of milliamperes. For 4 mA, when both restored teeth were present, Az values were significantly lower than the control group (P ≤ .05). In the presence of both restored teeth, 8 mA presented significantly higher Az values compared with 4 mA (P ≤ .05).

CONCLUSIONS

The presence of both adjacent teeth restored with a metal post impairs VRF detection; however, an increase in tube current up to 8 mA may aid in this diagnostic task. Moreover, the MAR tool does not seem to be efficient in those cases.

Comparison of CBCT-based dose calculation methods in head and neck cancer radiotherapy: from Hounsfield unit to density calibration curve to deep learning

PURPOSE

Anatomical variations occur during head and neck (H&N) radiotherapy treatment. kV cone-beam computed tomography (CBCT) images can be used for daily dose monitoring to assess dose variations owing to anatomic changes. Deep learning methods (DLMs) have recently been proposed to generate pseudo-CT (pCT) from CBCT to perform dose calculation. This study aims to evaluate the accuracy of a DLM and to compare this method with three existing methods of dose calculation from CBCT in H&N cancer radiotherapy.

METHODS

Forty-four patients received VMAT for H&N cancer (70-63-56 Gy). For each patient, reference CT (Bigbore, Philips) and CBCT images (XVI, Elekta) were acquired. The DLM was based on a generative adversarial network. The three compared methods were: (a) a method using a density to Hounsfield Unit (HU) relation from phantom CBCT image (HU-D curve method), (b) a water-air-bone density assignment method (DAM), and iii) a method using deformable image registration (DIR). The imaging endpoints were the mean absolute error (MAE) and mean error (ME) of HU from pCT and reference CT (CT_ref ). The dosimetric endpoints were dose discrepancies and 3D gamma analyses (local, 2%/2 mm, 30% dose threshold). Dose discrepancies were defined as the mean absolute differences between DVHs calculated from the CT_ref and pCT of each method.

RESULTS

In the entire body, the MAEs and MEs of the DLM, HU-D curve method, DAM, and DIR method were 82.4 and 17.1 HU, 266.6 and 208.9 HU, 113.2 and 14.2 HU, and 95.5 and -36.6 HU, respectively. The MAE obtained using the DLM differed significantly from those of other methods (Wilcoxon, P ≤ 0.05). The DLM dose discrepancies were 7 ± 8 cGy (maximum = 44 cGy) for the ipsilateral parotid gland D_mean and 5 ± 6 cGy (max = 26 cGy) for the contralateral parotid gland mean dose (D_mean ). For the parotid gland D_mean , no significant dose difference was observed between the DLM and other methods. The mean 3D gamma pass rate ± standard deviation was 98.1 ± 1.2%, 91.0 ± 5.3%, 97.9 ± 1.6%, and 98.8 ± 0.7% for the DLM, HU-D method, DAM, and DIR method, respectively. The gamma pass rates and mean gamma results of the HU-D curve method, DAM, and DIR method differed significantly from those of the DLM.

CONCLUSIONS

For H&N radiotherapy, DIR method and DLM appears as the most appealing CBCT-based dose calculation methods among the four methods in terms of dose accuracy as well as calculation time. Using the DIR method or DLM with CBCT images enables dose monitoring in the parotid glands during the treatment course and may be used to trigger replanning.

Mapping the expression of beam hardening artefacts produced by metal posts positioned in different regions of the dental arch

OBJECTIVES

To objectively assess the expression and direction of artefacts in the vicinity of metal posts positioned in different mandibular regions.

MATERIALS AND METHODS

A human mandible had two sockets prepared-anterior and posterior regions-to accommodate a single-rooted tooth. Two CBCT units, Picasso Trio and OP300, were used. CBCT images of the tooth without metal post, and with silver-palladium, nickel-chromium, or cobalt-chromium posts (experimental groups) were individually acquired. Then, 8 lines of interest (LOIs) were determined around the root canal, in an axial reconstruction: 4 in orthogonal (buccal, lingual, mesial, and distal) directions, and 4 in oblique (mesiobuccal, distobuccal, mesiolingual, and distolingual) directions. The mean of gray values was measured for each LOI.

RESULTS

For the OP300, in general, all experimental groups showed greater expression of hyperdense streaks in orthogonal LOIs and greater expression of hypodense streaks in oblique LOIs. For the Picasso Trio, for both mandibular regions, the buccal LOI showed greater expression of hypodense streaks; conversely, greater expression of hyperdense streaks was observed in the distal and distobuccal LOIs in the anterior region and in the mesiolingual LOI in the posterior region. The silver-palladium group showed significantly greater expression of beam hardening artefacts in the posterior region of the mandible, regardless of the CBCT unit (p < 0.05). The mandibular posterior region showed significantly lower gray values than the anterior region (p < 0.05).

CONCLUSION

The expression and direction of artefacts produced in the vicinity of metal posts vary according to the mandibular region, composition of the post, and CBCT unit.

CLINICAL RELEVANCE

The mapping of artefacts produced by metal posts reveals the root regions with greater expression of hypodense and hyperdense artefacts, which may contribute to recognizing regions more likely to mimic or hide root fracture lines.

Misfit detection in implant-supported prostheses of different compositions by periapical radiography and cone beam computed tomography: An in vitro study

STATEMENT OF PROBLEM

Misfits at the implant-abutment joint (IAJ) can cause the biological and mechanical failure of implant therapy. Standard parallel periapical radiography (PERI) is the method of choice for assessing the fitting of implant-supported prostheses. Although current guidelines do not support the use of cone beam computed tomography (CBCT) solely for misfit detection, CBCT scans can also register misfits as imaging findings. Whether the material used for prostheses manufacturing influences misfit appearance in PERI and CBCT images is unknown.

PURPOSE

The purpose of this in vitro study was to assess the influence of the type of prosthesis material on misfit detection at the IAJ by using PERI and CBCT.

MATERIAL AND METHODS

Thirty-two implants with an external hexagon connection were placed in dried human mandibles. Implant-supported crowns were manufactured with different materials and allocated to 3 experimental groups: metal-ceramic (MC), titanium abutment veneered with acrylic resin (TIT), and zirconia abutment veneered with glass-ceramic (ZIR). All crowns were installed both with and without a simulated 200-μm-thick gap at the IAJ (n=64) and were assessed by PERI and CBCT scans. Four dentists evaluated the images for the presence or absence of misfit. Statistical analysis included the Kappa test and areas under the receiver operating characteristics curve (Az values) comparisons (α=.05).

RESULTS

Kappa values indicated almost perfect intraevaluator and interevaluator reproducibility for PERI and ranged from fair to almost perfect for CBCT. For PERI, Az values were not significantly different among the MC (0.995), TIT (0.997), and ZIR groups (1.000) (P>.05). Regarding CBCT, the Az values found for TIT (0.941) and MC (0.890) were significantly higher than for ZIR (0.762) (P<.05). Az values for PERI were significantly higher than for CBCT (P<.05).

CONCLUSIONS

The type of prosthesis material did not influence misfit detection at the IAJ with PERI; however, ZIR had lower diagnostic accuracy than TIT and MC implant-supported crowns with CBCT.

Computed Tomography (CT)-Assisted 3D Cephalometry in Horses: Interincisal Angulation of Clinical Crowns

The angle encompassed between opposing incisors in horses is assumed to decline with age. Previous studies merely consider the overall profile view of clinical crowns presuming a generalized angle, neglecting potential tooth position-dependent differences. Cephalometric measurements from 3D computed tomographic thick-slab reconstructions of single incisors within a global reference frame were used to determine clinical crown interincisal angulation (IIA) of 48 horses. Based on predefined dentoalveolar landmarks, IIA was defined as the angle enclosed by the respective labial axis of the clinical crown (LACC). A measurement repeatability analysis was conducted including a comparison of third incisor teeth IIA with data obtained by cephalometric implementation of previously described landmarks for third incisor teeth (lingual/palatal border). The age-related angle course and differences between tooth positions were investigated considering LACCs of permanent incisors. Determining IIA by LACCs exhibited a high level of reproducibility applying for all tooth positions (mean coefficient of variation = 0.65 %; mean SD ± 0.89°). The comparison method for third incisor teeth revealed two times higher mean dispersion of repeated measurements, P = 0.017. A non-linear model slightly increased predictability of angular changes over time as against linearity assumption. The angle decline was more distinctive in younger horses and appears to approach a final value in older ones. Third incisor teeth exhibited significantly higher angle decline compared to first and second incisor teeth, P < 0.0001. According to the results, age determination of horses using clinical crown IIA is not recommended. Rather, 3D cephalometry may provide a promising tool to determine interdental and dentofacial angles of distinct tooth positions in health and disease.

Accuracy of mean grey density values obtained with small field of view cone beam computed tomography in differentiation between periapical cystic and solid lesions

AIM

To determine if small and medium field of view (FOV) cone beam computed tomography (CBCT) adjusted grey density values can be used to distinguish between periapical cystic and solid lesions.

METHODOLOGY

Fifty-seven patients with periapical lesions having retrievable small or medium FOV CBCT images and biopsy samples were included. Two oral and maxillofacial pathologists examined the biopsy samples to provide the gold standard diagnosis of cystic or solid lesion. From the CBCT images, two independent examiners recorded the minimum adjusted grey density value of each lesion twice. Intra-examiner and inter-examiner reliability of the measurements were analysed, and sensitivity, specificity and accuracy of the minimum grey values in distinguishing a solid from cystic lesion were calculated. A receiver operating curve for diagnostic ability of adjusted grey density values to differentiate between periapical cystic and solid lesions was obtained, and the area under the curve (AUC) was calculated.

RESULTS

The intra- and inter-examiner reliability of the grey density values of the lesions and dentine were excellent. The AUC was 0.44 (P-value = 0.45). The adjusted grey density value with the greatest accuracy for differentiating between cystic and solid lesions had an accuracy, sensitivity and specificity of 0.54, 1.00 and 0.075, respectively.

CONCLUSIONS

Small FOV CBCT adjusted grey density values obtained by the device used in the study could not distinguish between periapical cystic and solid lesions. Further developments in CBCT devices are needed to improve the accuracy of grey density measurements.

Cone-beam Computed Tomographic-based Assessment of Filled C-shaped Canals: Artifact Expression of Cone-beam Computed Tomography as Opposed to Micro-computed Tomography and Nano-computed Tomography

INTRODUCTION

The present study investigated the assessment of root canal fillings in a series of cone-beam computed tomographic (CBCT) images obtained from endodontically treated mandibular molars with C-shaped canals.

METHODS

Clinically comparable high (HR) and normal (NR) resolution protocols were selected in 3D Accuitomo 170 (J Morita Corporation, Kyoto, Japan), NewTom VGi evo (Cefla QR Verona, Verona, Italy), ProMax 3D Max (Pro; Planmeca, Helsinki, Finland), and Pax-i3D Green Premium (Pax; Vatech, Gyeonggi, South Korea). Micro-computed tomographic and nano-computed tomographic images were considered as the reference standard. The set of images was evaluated according to beam hardening artifact patterns (dark streaks, hypodense areas, and volume distortion).

RESULTS

Regarding dark streaks, the Fleiss kappa test showed that Pax HR and NR and Pro HR images showed the highest artifact expression. Hypodense areas were detected in 100% and 99.1% of the images obtained using Pax HR and NR, respectively. Kappa tests showed highest distortion for images derived from the Pax and Pro CBCT devices. Root canal filling assessment was considered appropriate in 100% of the 3D Accuitomo 170 HR, NewTom VGi evo NR, micro-computed tomographic, and nano-computed tomographic images.

CONCLUSIONS

The present study confirms the large variability in CBCT-derived artifact expression. Highlighting the increased artifact expression for particular CBCT systems, it may be concluded that for diagnosis of endodontically filled molars with C-shaped canals, the choice of CBCT unit and protocol is essential.