Influence of acquisition parameters on the magnitude of cone beam computed tomography artifacts

Influence of tube current and metal artifact reduction on the diagnosis of external cervical resorption in teeth adjacent to a dental implant in CBCT: an ex-vivo study

OBJECTIVES

This ex-vivo study aimed to assess the influence of tube current (mA) and metal artifact reduction (MAR) on the diagnosis of early external cervical resorption (EECR) in cone-beam computed tomography (CBCT) in the presence of an adjacent dental implant.

MATERIALS AND METHODS

Twenty-three single-rooted teeth were sectioned longitudinally and EECR was induced using a spherical drill and 5% nitric acid in 10 teeth. Each tooth was positioned in the socket of the lower right canine of a dry human mandible and CBCT scans were acquired using 90 kVp, voxel of 0.085 mm, field of view of 5 x 5 cm, and varying tube current (4, 8 or 12 mA), MAR (enabled or disabled) and implant conditions (with a zirconia implant in the socket of the lower right first premolar or without). Five oral radiologists evaluated the presence of EECR in a 5-point scale and the diagnostic values (area under the receiver operating characteristic curve - AUC, sensitivity, and specificity) were compared using multi-way Analysis of Variance (α = 0.05). Kappa test assessed intra-/inter-evaluator agreement.

RESULTS

The tube current only influenced the AUC values in the presence of the implant and when MAR disabled; in this case, 8 mA showed lower values (p<0.007). MAR did not influence the diagnostic values (p>0.05). In general, the presence of an implant reduced the AUC values (p<0.0001); sensitivity values with 8 mA and MAR disabled, and specificity values with 4 mA and MAR enabled and 8 mA regardless MAR were also decreased (p<0.0001).

CONCLUSIONS

Variations in tube current and MAR were unable to improve EECR detection, which was impaired by the presence of an adjacent implant.

CLINICAL RELEVANCE

Increasing tube current or activating MAR tool does not improve EECR diagnosis, which is hampered by the artifacts generated by dental implants.

Assessing the Impact of the Metal Artifact Reduction Tool on Detecting Furcation Lesions in Maxillary Molars with Different Intracanal Posts: An Ex Vivo Cone-beam Computed Tomography Study

INTRODUCTION

Considering the potential image compromise and diagnostic challenges posed by metals, this study aimed to assess the efficacy of the metal artifact reduction (MAR) tool in cone-beam computed tomography examinations for detecting furcation lesions in upper molars treated endodontically and restored with different intracanal posts.

METHODS

This ex vivo study used 45 endodontically treated maxillary first molars, categorized into the following3 groups (n = 15): control (without intracanal post), metal post, and fiberglass post. Simulations were conducted in the laboratory to replicate alveolar bone, periodontal ligament, and grade I, II, and III furcation lesions. Cone-beam computed tomography scans were obtained with and without the MAR tool, and the furcation lesions were evaluated considering a 5-point Likert scale. Data were analyzed at 5%.

RESULTS

In the control group, there was no influence of MAR (P > .05); grade II lesions were not diagnosed, and grade III lesions were the most detected (P < .05). In the metal post group with MAR, grade III lesions were diagnosed more frequently than I and II (P < .05) and grade III without MAR (P < .05). In the fiberglass post group, the diagnosis of grade I lesions decreased with MAR (P < .05), and without MAR, grade III was most diagnosed (P < .05); grade III lesions were the most diagnosed (P < .05).

CONCLUSIONS

The MAR tool was only effective for diagnosing grade III furcation lesions, regardless of the intracanal material. Its application for grade I and II lesions did not contribute to improved diagnosis. Furthermore, in the fiberglass post group with grade I lesions, the MAR tool negatively affected the detection of the lesions.

Introducing a new auto edge detection technique capable of revealing cervical root resorption in CBCT scans with pronounced metallic artifacts

Cervical resorption is a serious threat to the longevity of the teeth. In this study, the Canny edge-detection algorithm was applied on CBCT images to compare the accuracy of original and Canny views for diagnosing cervical resorption in endodontically treated teeth. Intracanal metallic posts were inserted in 60 extracted teeth being randomly divided into three groups: control, 0.5 mm, and 1 mm cervical resorption. CBCT scans of the teeth were presented to three observers in both original and Canny formats with the accuracy being determined by receiver operating characteristic (ROC) analysis. The DeLong test was used for paired comparisons with the significance level set at 0.05. The highest accuracy belonged to Canny images in 1 mm resorption, followed by Canny images in 0.5 mm resorption, original images in 1 mm resorption, and original images in 0.5 mm resorption, respectively. The Canny images were significantly more accurate in the diagnosis of 0.5 mm (p < 0.001) and 1 mm (p = 0.009) resorption. Application of the Canny edge-detection algorithm could be suggested as a new technique for facilitating the diagnosis of cervical resorption in teeth that are negatively affected by metallic artifacts.

Influence of an adjacent zirconium implant, tube current, and metal artifact reduction algorithm on horizontal root fracture diagnosis in cone beam computed tomography

OBJECTIVE

We evaluated the influence of an adjacent zirconium implant, tube current (mA), and a metal artifact reduction algorithm (MARA) on horizontal root fracture (HRF) diagnosis in cone beam computed tomography (CBCT).

STUDY DESIGN

Nineteen teeth (9 with HRF, 10 without) were individually placed in a human maxilla. Scan volumes were acquired without and with a zirconium implant adjacent to the tooth at settings of 4, 8, and 10 mA, with MARA disabled and enabled, using a 5×5 cm field of view, 0.085-mm voxel size, and 90 kV. Four maxillofacial radiologists individually assessed the scans. Diagnostic metrics were compared by multiway analysis of variance (α=5%). Inter- and intraexaminer agreements for HRF diagnosis were evaluated with the weighted kappa test.

RESULTS

Area under the receiver operating characteristic curve (AUC), sensitivity, and specificity were significantly lower in the presence of the implant (P≤.005). AUC values were higher in scans obtained with 8 and 10 mA compared with 4 mA (P=0.010), but 10 mA without MARA was better with the implant present. MARA did not significantly influence outcomes (P≥0.240). Inter- and intraexaminer agreements ranged from moderate to almost perfect.

CONCLUSIONS

The presence of the zirconium implant impairs HRF detection. Settings of 8 or 10 mA improve HRF detection regardless MARA condition without the implant. With an adjacent implant, 10 mA without MARA is recommended to improve diagnostic performance.

Influence of the metal post material, tooth location in the dental arch, and metal artifact reduction tool on vertical root fracture diagnosis in cone beam CT

This study aimed to evaluate the influence of the metal post composition, tooth location in the dental arch, and metal artifact reduction (MAR) on vertical root fracture (VRF) diagnosis in cone beam computed tomography (CBCT). Twenty-two unirradicular premolars (12 sound and 10 fractured) and two alveolar sockets of a mandible (anterior and posterior regions) composed the sample. CBCT scans of each tooth with a metal post placed into the root canal-silver-palladium (Ag-Pd), cobalt-chromium (Co-Cr), or nickel-chromium (Ni-Cr)-were individually acquired for each mandibular region, and two conditions of MAR, using a OP300 device (Instrumentarium, Finland). Images were assessed by five evaluators independently for VRF detection. Diagnostic values were calculated and compared among all groups using multi-way ANOVA with Tukey post hoc test to investigate the effect of post material, anatomical region, and MAR on VRF diagnosis (α = 0.05). Values of area under the receiver operating curve and specificity were not influenced by the studied factors (p > 0.05). Sensitivity was influenced by the MAR in both mandibular regions (p < 0.05). In the anterior region, sensitivity values increased when the MAR was enabled, regardless of the metal post material (p < 0.05). Similar behavior was noticed in the posterior region for Ni-Cr (p < 0.05) but not for Ag-Pd and Co-Cr posts (p > 0.05). The MAR improved the sensitivity in VRF diagnosis for all tested metal posts in the mandibular anterior region and for the Ni-Cr post in the mandibular posterior region. Therefore, for images obtained in the OP300 CBCT device, activation of the MAR is suggested in these cases.

Assessment of the root filling volume in C-shaped root canal on cone-beam CT and micro-CT in relation to nano-CT

AIM

To assess the observed volume of filled C-shaped root canals from different CBCT and micro-CT having nano-CT as a reference.

MATERIALS AND METHODS

Twelve extracted mandibular molars with C-shaped root canals were endodontically treated using Reciproc Blue R25 (VDW GMBH, Munich, Germany) in a reciprocating system and filled with gutta-percha (Dentsply Maillefer) and AH Plus sealer (Dentsply DeTrey, Konstanz, Germany). CBCT scans were performed using 3 units-3D Accuitomo 170 (J. Morita, Kyoto, Japan), ProMax 3D Max (Planmeca, Helsinki, Finland), and NewTom VGi EVO (Cefla QR, Verona, Italy)-at two resolution modes: standard and high. Micro-CT and nano-CT scans were also obtained. The volume of all filled C-shaped root canals was obtained using CTAn software (Bruker, Kontich, Belgium), and the blooming artifact, in relation to nano-CT volume, was calculated. The data were evaluated by the Bland-Altman plots and ANOVA two-way for repeated measures (α = 0.05).

RESULTS

All CBCT units and micro-CT showed significantly larger observed volume of root canal filling when compared to nano-CT. The blooming artifact of root canal filling in standard resolution was significantly larger than that in high resolution (p < 0.05) in all CBCT units.

CONCLUSIONS

Endodontic filling material with AH Plus sealer causes blooming artifacts in CBCT units and micro-CT.

CLINICAL RELEVANCE

Considering the anatomical complexity of C-shaped root canals and the challenges associated with endodontic treatment, CBCT is frequently recommended for follow-up evaluations. However, the presence of endodontic filling material can result in blooming artifacts that may potentially impact the accurate diagnosis of endodontic complications.

Filtered back projection vs. iterative reconstruction for CBCT: effects on image noise and processing time

OBJECTIVES

To assess the effect of standard filtered back projection (FBP) and iterative reconstruction (IR) methods on CBCT image noise and processing time (PT), acquired with various acquisition parameters with and without metal artefact reduction (MAR).

METHODS

CBCT scans using the Midmark EIOS unit of a human mandible embedded in soft tissue equivalent material with and without the presence of an implant at mandibular first molar region were acquired at various acquisition settings (milliamperages [4mA-14mA], FOV [5 × 5, 6 × 8, 9 × 10 cm], and resolutions [low, standard, high] and reconstructed using standard FBP and IR, and with and without MAR. The processing time was recorded for each reconstruction. ImageJ was used to analyze specific axial images. Radial transaxial fiducial lines were created relative to the implant site. Standard deviations of the gray density values (image noise) were calculated at fixed distances on the fiducial lines on the buccal and lingual aspects at specific axial levels, and mean values for FBP and IR were compared using paired t-tests. Significance was defined as p < 0.05.

RESULTS

The overall mean for image noise (± SD) for FBP was 198.65 ± 55.58 and 99.84 ± 16.28 for IR. IR significantly decreased image noise compared to FBP at all acquisition parameters (p < 0.05). Noise reduction among different scanning protocols ranged between 29.7% (5 × 5 cm FOV) and 58.1% (5mA). IR increased processing time by an average of 35.1 s.

CONCLUSIONS

IR significantly reduces CBCT image noise compared to standard FBP without substantially increasing processing time.

Influence of Windowing and Evaluation of Metal Artifact Reduction Algorithm on Five Different Restorative Materials by Using Different Cone Beam Computed Tomography (CBCT) Scanners: A CBCT Study

OBJECTIVES

To assess the influence of windowing, and to evaluate, and compare the effect of the metal artifact reduction (MAR) and non-metal artifact reduction (non-MAR) algorithms on different high-density restorative dental materials using different cone beam computed tomography (CBCT) devices.

MATERIAL AND METHOD

Height and diameter of all cylindrical shape metals including amalgam, cobalt-chromium, composite, gutta-percha, and titanium were measured using a digital caliper device. Polymethylmethacrylate block and arch phantom with a cylindrical-shaped perforation containing five different metals were submitted to tomographic acquisition with six different cone beam computed tomographic devices in small fields of view with their MAR enabled and disabled. Windowing was done using ITK-SNAP software (3.8.2) which was used as a contrast medial tool for window level and window width. The data was analyzed for probability distribution using the Kolmogorov-Smirnov test, where a p-value of <0.05 indicated that the data were not normally distributed. The comparison of length and width was done using the Wilcoxon sign rank test. Comparison of categorical variables was done using the Chi-square test where a p-value of <0.05 was considered statistically significant.

RESULTS

Length and width of all these metals measured using MAR and non-MAR CBCT were found to be statistically non-significant (p-value of >0.05). MAR algorithm significantly reduces metals artifact produced by high-density restorative materials (p-value of <0.05).

CONCLUSION

Amalgam and cobalt-chromium produced more artifacts while composite and gutta-percha did not produce enough artifacts to be reduced by the MAR algorithm. Large window width and high window level would be beneficial to reduce the metal artifact.

Influence of metal artefact reduction on the diagnosis of contact between implant and mandibular canal in cone beam computed tomography: An ex-vivo study

OBJECTIVE

To evaluate the influence of metal artefact reduction (MAR) in the diagnosis of dental implant contact with the mandibular canal (MC) using cone beam computed tomography (CBCT).

METHODS

Dental implants were installed with surgical guides in the posterior hemiarches of 10 dry human mandibles: 0.5 mm above to the MC cortex (G1/n = 8) and 0.5 mm inside the MC (G2/n = 10). The experimental set-up was scanned with two CBCT equipment using 85 kV and 90 kV, MAR ON or OFF, and different tube currents (4 mA, 8 mA and 10 mA). Two dentomaxillofacial radiologists (DMFRs) and two dentists (DDS) scored the relation between the dental implant and MC. Descriptive statistics were used to observe the absolute frequency of scores. Sensitivity, specificity and accuracy were calculated considering the known relation between the dental implant and the MC interior. McNemar's test (α = .05) was applied to compare the diagnostic efficacy of MAR ON versus MAR OFF.

RESULTS

Overall specificity was higher than sensitivity for both DDS and DMFR (97% vs. 50% and 92.0% vs. 78.0% respectively). There was a significant effect of MAR (p = .031) for DMFR in the case of contact between the dental implant with the MC interior, in which sensitivity decreased with MAR activation from 90% to 40%. DMFR observers showed a better diagnostic performance compared with the DDS observers (accuracy of 84.0% and 71.0%, respectively).

CONCLUSIONS

Due to the limited efficacy of MAR, it should not be used when conducting CBCT scans for the evaluation of contact between the implant and the mandibular canal.

Influence of CBCT parameters on image quality and the diagnosis of vertical root fractures in teeth with metallic posts: an ex vivo study

Objectives

The aim of this study was to evaluate the influence of peak kilovoltage (kVp) and a metal artifact reduction (MAR) tool on image quality and the diagnosis of vertical root fracture (VRF) in cone-beam computed tomography (CBCT).

Materials and Methods

Twenty single-rooted human teeth filled with an intracanal metal post were divided into 2 groups: control (n = 10) and VRF (n = 10). Each tooth was placed into the socket of a dry mandible, and CBCT scans were acquired using a Picasso Trio varying the kVp (70, 80, 90, or 99), and the use of MAR (with or without). The examinations were assessed by 5 examiners for the diagnosis of VRF using a 5-point scale. A subjective evaluation of the expression of artifacts was done by comparing random axial images of the studied protocols. The results of the diagnoses were analyzed using 2-way analysis of variance and the Tukey post hoc test, the subjective evaluations were compared using the Friedman test, and intra-examiner reproducibility was evaluated using the weighted kappa test (α = 5%).

Results

The kVp and MAR did not influence the diagnosis of VRF (p > 0.05). According to the subjective classification, the 99 kVp protocol with MAR demonstrated the least expression of artifacts, while the 70 kVp protocol without MAR led to the most artifacts.

Conclusions

Protocols with higher kVp combined with MAR improved the image quality of CBCT examinations. However, those factors did not lead to an improvement in the diagnosis of VRF.

Application of 3D-printed guide for locating screw access channels in cement-retained complete arch implant-supported zirconia restorations

Removal of cement-retained complete arch implant-supported zirconia restorations can be challenging. A predictable and minimally invasive technique combining cone beam computed tomography (CBCT) and intraoral scans with a virtual implant planning software program is described to identify the location of the screw access channels during the retrieval, thus minimizing damage to the existing restoration and allowing reuse.

Assessing the Efficacy of Planmeca ProMax® 3D Cone-Beam CT Machine in the Detection of Root Fractures With Varied Metal Artifact Reduction Settings and Three Kilovoltage Peak Levels

BACKGROUND

This study aims to examine the accuracy of cone-beam computed tomography (CBCT) machines in detecting root fracture when using different metal artifact reduction (MAR) settings at different kilovoltage peak (kVp) levels.

METHODOLOGY

Sixty-six tooth roots were treated endodontically using a standardized technique. Of these, 33 roots were randomly selected to be fractured; the other 33 roots were intact and used as controls. The roots were placed randomly in prepared beef ribs to mimic the alveolar bone. Imaging was performed by Planmeca ProMax® 3D (Planmeca, Helsinki, Finland) using different MAR settings (no, low, mid, and high) at three different levels of kVp: 70, 80, and 90. Sensitivity, specificity, and area under the receiver operating characteristic curve (AUC) were calculated.

RESULTS

There was a significant difference in accuracy when using different MAR settings within the group of 70 kVp. Likewise, within the group of 90 kVp. There was no significant difference between different MAR settings at 80 kVp. Using low MAR/90 kVp had significantly higher accuracy relative to other MAR settings at 90 kVp; it also had the highest values of sensitivity, specificity, and AUC in the study. Using mid and high MAR at 70 kVp or 90 kVp decreased accuracy significantly. Mid MAR/90 kVp was the least effective setting in this study.

CONCLUSIONS

 Using low MAR at 90 kVp significantly increased the accuracy within the group of 90 kVp. In contrast, mid MAR and high MAR in 70 and 90 kVp, respectively, decreased accuracy significantly.

Assessment of marginal gaps and image quality of crowns made of two different restorative materials: An in vitro study using CBCT images

Background

The present study assessed the quality of images and the presence of marginal gaps on cone-beam computed tomography (CBCT) images of teeth restored with all-ceramic and metal-ceramic crowns and compared the gap sizes observed on CBCT images with those obtained on micro-CT images.

Methods

Thirty teeth restored with metal-ceramic and all-ceramic crowns, properly adapted and with gaps of 0.30 and 0.50 mm, were submitted to micro-CT and CBCT scans. Linear measurements corresponding to the marginal gap (MG) and the absolute marginal discrepancy (AMD) were obtained. The objective assessment of the quality of CBCT images was performed using the contrast-to-noise ratio (CNR), and the subjective assessment was defined by the diagnoses made by five examiners regarding the presence or absence of gaps.

Results

The measurements were always higher for CBCT, with a significant difference regarding AMD. No significant difference in image quality was observed using CNR between the crowns tested. Low accuracy and sensitivity values could be observed for both crowns.

Conclusion

Marginal mismatch measures were overestimated in CBCT images. No difference in image quality was observed between the crowns. The correct diagnosis of gaps was considered low, irrespective of crown type and gap size.

Efficacy of low-dose cone beam computed tomography and metal artifact reduction tool for assessment of peri-implant bone defects: an in vitro study

BACKGROUND

Early accurate radiographic assessment of peri-implant bone condition is highly important to avoid excessive loss of supporting bone and implant failure. Cone beam computed tomography (CBCT) is the radiographic technique of choice if peri-implant dehiscence and fenestration defects are suspected. The higher radiation dose and the presence of beam hardening artifacts are the main drawbacks of CBCT imaging techniques. This study aims to evaluate the influence of low-dose cone beam computed tomography (LD-CBCT) and metal artifact reduction (MAR) tool on the assessment of peri-implant dehiscence and fenestration.

METHODOLOGY

Thirty titanium implants were inserted into bovine rib blocks. Twenty had standardized bone defects (10 with dehiscence and 10 with fenestration), while the remaining 10 were used as control group with no defects. Radiographic examinations held with high-definition CBCT (HD-CBCT) and LD-CBCT with and without application of MAR tool. Images were assessed by four examiners for the presence or absence of peri-implant defects. The area under the area under the receiver operating characteristic (ROC) curve (AUC), sensitivity, specificity, and accuracy were calculated for all radiographic protocols.

RESULTS

In the absence of MAR tool, there was no difference in AUC and diagnostic values between LD-CBCT and HD-CBCT for detection of both defects. When the MAR tool was applied, the AUC values, sensitivity, and accuracy were higher in HD-CBCT than in LD-CBCT for the detection of both defects, especially for the dehiscence, while specificity remained the same.

CONCLUSION

LD-CBCT can be used in the evaluation of peri-implant dehiscence and fenestration without any decrease in diagnostic accuracy. The application of MAR tool decrease the diagnostic ability of both defects, especially for the detection of dehiscence defects.

Influence of artefacts generated by titanium and zirconium implants in the study of trabecular bone architecture in cone-beam CT images

OBJECTIVES

To evaluate the influence of artefacts generated by titanium and zirconium implants on trabecular bone architecture assessment through cone-beam CT (CBCT). The influence of kilovoltage (kVp) and metal artefact reduction (MAR) in such analysis was also assessed.

METHODS

CBCT scans were obtained with Picasso Trio with or without a titanium or zirconium implants in a posterior region of a mandible using 70, 80 or 90 kVp, with or without MAR. The other acquisition settings were constant: field of view 8 × 5 cm, voxel size 0.2 mm, 5 mA, 24 s and 720 frames. Two volumes of interest (VOIs) were determined comprising trabecular bone mesial and distal to the implant area. The following morphometric parameters were measured: connectivity density (Conn. Dn.), fractal dimension (FD), bone volume fraction (BV/TV), bone surface density (BS/TV), trabecular thickness (Tb. Th.), and trabecular spacing (Tb. Sp.), and compared by multiway ANOVA (α = 0.05).

RESULTS

For Conn. Dn. and FD, with MAR, the zirconium group showed values significantly lower than the other groups (p < 0.05). For BV/TV, BS/TV, Tb. Th. and Tb. Sp., the zirconium group showed the highest values, regardless of MAR condition (p < 0.05). MAR increased BS/TV and Tb. Th. values, and decreased FD values for zirconium group. In general, the kVp level did not influence trabecular morphometric parameters.

CONCLUSION

The assessment of the trabecular bone architecture was mainly influenced by the expression of the artefacts generated by zirconium implants. MAR decreased the FD and increased the BS/TV and Tb.Th. values regardless of the kVp level.

The metal post material influences the performance of artefact reduction algorithms in CBCT images

Abstract This study aimed to assess the effect of the MAR tool on the expression of artefacts in different regions of a tooth restored with different types of metal posts. Alveolar sockets (anterior, and posterior region) of a mandible and an unirradicular tooth were used. Cone beam computed tomography scans of the tooth without a metal post, and with cobalt-chromium (Co-Cr), nickel-chromium (Ni-Cr), or silver-palladium (Ag-Pd) were individually obtained, with 2 MAR conditions: disabled, and enabled. In an axial reconstruction, lines of interest (LOIs) were set around the canal: 4 in oblique (mesiobuccal, distobuccal, mesiolingual, distolingual) directions, and 4 in orthogonal (mesial, distal, buccal, lingual) directions. Beam-hardening artefacts expression was determined by calculating the difference in the mean of gray values (DMGV) between the experimental and control groups for each LOI. There was no significant difference in the DMGV values between “without MAR” and “with MAR” for any LOI, in neither anterior nor posterior mandible (p>0.05), for the Ni-Cr and Co-Cr groups. For the Ag-Pd, significant differences in the DMGV values were observed between “without MAR” and “with MAR” for most LOIs (p<0.05), mainly in oblique directions in the anterior region, and mesio-distal direction in the posterior region. MAR acted mostly in hypodense artefacts (negative DMGV). The effectiveness of the MAR tool of the OP300 CBCT unit varied according to the post material tested. It was effective in reducing the expression of artefacts raised by the Ag-Pd post, mainly in the tooth regions affected by hypodense artefacts, regardless of the mandibular region.

CBCT image artefacts generated by implants located inside the field of view or in the exomass

OBJECTIVES

To compare artefacts in cone-beam computed tomography (CBCT) arising from implants of different materials located either inside the field of view (FOV) or in the exomass, and to test different image-acquisition parameters to reduce them.

METHODS

CBCT scans of a human mandible prepared with either a titanium, titanium-zirconium, or zirconia implant were acquired with the Planmeca ProMax utilizing FOV sizes of 8 × 5 cm and 4 × 5 cm, which placed the implant inside the FOV (8 × 5 cm) or in the exomass (4 × 5 cm). The scanning parameters considered three conditions of metal artefact reduction (MAR), disabled, low, and high, and 2 kVp levels (80 and 90). The standard deviation (SD) of grey values of regions of interest was obtained. The effects of implant material, implant position, MAR condition, kVp level, and their interactions were evaluated by Analysis of Variance (α = 5%).

RESULTS

The zirconia implant produced the highest SD values (more heterogeneous grey values, corresponding to greater artefact expression), followed by titanium-zirconium, and titanium. In general, implants in the exomass produced images with higher SD values than implants inside the FOV. MAR was effective in decreasing SD values, especially from the zirconia implant, only when the implant was inside the FOV. Images with 80 kVp had higher SD values than those with 90 kVp, regardless of the other factors (p < 0.05).

CONCLUSIONS

Implants in the exomass lead to greater artefact expression than when they are inside the FOV. Special attention should be paid to scanning parameters that reduce metal-related artefacts, such as MAR activation and increasing kVp. This is especially important with a zirconia implant inside the FOV.

Effect of cone-beam computed tomography metal artefact reduction on incomplete subtle vertical root fractures

Purpose

This study compared the accuracy of detection of incomplete vertical root fractures (VRFs) in filled and unfilled teeth on cone-beam computed tomography images with and without a metal artefact reduction (MAR) algorithm.

Materials and Methods

Forty single-rooted maxillary premolars were selected and, after endodontic instrumentation, were categorized as unfilled teeth without fractures, filled teeth without fractures, unfilled teeth with fractures, or filled teeth with fractures. Each VRF was artificially created and confirmed by operative microscopy. The teeth were randomly arranged, and images were acquired with and without the MAR algorithm. The images were evaluated with OnDemand software (Cybermed Inc., Seoul, Korea). After training, 2 blinded observers each assessed the images for the presence and absence of VRFs 2 times separated by a 1-week interval. P-values<0.05 were considered to indicate significance.

Results

Of the 4 protocols, unfilled teeth analysed with the MAR algorithm had the highest accuracy of incomplete VRF diagnosis (0.65), while unfilled teeth reviewed without MAR were associated with the least accurate diagnosis (0.55). With MAR, an unfilled tooth with an incomplete VRF was 4 times more likely to be identified as having an incomplete VRF than an unfilled tooth without this condition, while without MAR, an unfilled tooth with an incomplete VRF was 2.28 times more likely to be identified as having an incomplete VRF than an unfilled tooth without this condition.

Conclusion

The use of the MAR algorithm increased the diagnostic accuracy in the detection of incomplete VRF on images of unfilled teeth.

Influence of kilovoltage-peak and the metal artifact reduction tool in cone-beam computed tomography on the detection of bone defects around titanium-zirconia and zirconia implants

Purpose

The aim of this study was to assess the influence of kilovoltage-peak (kVp) and the metal artifact reduction (MAR) tool on the detection of buccal and lingual peri-implant dehiscence in the presence of titanium-zirconia (Ti-Zr) and zirconia (Zr) implants in cone-beam computed tomography (CBCT) images.

Materials and Methods

Twenty implant sites were created in the posterior region of human mandibles, including control sites (without dehiscence) and experimental sites (with dehiscence). Individually, a Ti-Zr or Zr implant was placed in each implant site. CBCT scans were performed using a Picasso Trio device, with variation in the kVp setting (70 or 90 kVp) and whether the MAR tool was used. Three oral radiologists scored the detection of dehiscence using a 5-point scale. The area under the receiver operating characteristic (ROC) curve, sensitivity, and specificity were calculated and compared by multi-way analysis of variance (α=0.05).

Results

The kVp, cortical plate involved (buccal or lingual cortices), and MAR did not influence any diagnostic values (P>0.05). The material of the implant did not influence the ROC curve values (P>0.05). In contrast, the sensitivity and specificity were statistically significantly influenced by the implant material (P<0.05) with Zr implants showing higher sensitivity values and lower specificity values than Ti-Zr implants.

Conclusion

The detection of peri-implant dehiscence was not influenced by kVp, use of the MAR tool, or the cortical plate. Greater sensitivity and lower specificity were shown for the detection of peri-implant dehiscence in the presence of a Zr implant.

Influence of metal artefact reduction tool on the detection of vertical root fractures involving teeth with intracanal materials in cone beam computed tomography images: A systematic review and meta-analysis

BACKGROUND

The effectiveness of the metal artefact reduction (MAR) tool for the detection of vertical root fracture (VRF) by cone beam computed tomography (CBCT) images is controversial.

OBJECTIVE

To evaluate the effectiveness of the MAR tool on VRF detection involving teeth with intracanal materials in CBCT images.

METHODOLOGY

In September 2019, an electronic search was performed in six databases (PubMed, Scopus, Web of Science, Cochrane, Lilacs and Embase). The electronic search was updated in May 2020 through searches in Google Scholar and references of included studies (embracing the electronic and gray literature searches). No language or year restrictions were applied. Independently, two reviewers examined titles, abstracts and full texts according to the eligibility criteria that were as follows: diagnostic studies that evaluated the effectiveness of the MAR tool on the diagnosis of VRF in human teeth (laboratory or in vivo studies) on CBCT images. The risk of bias was evaluated using the Quality Assessment Tool for Diagnostic of Accuracy Studies-2 (QUADAS-2). For conducting the meta-analysis, the values of sensitivity, specificity, diagnostic odds ratio (DOR) and area under the ROC curve (AUC) were obtained, considering the subgroups with and without MAR active. The Grading of Recommendation, Assessment, Development and Evaluation instrument was applied to assess the level of evidence across the studies using GRADEpro software.

RESULTS

A total of 8 laboratory studies were included in both systematic review and meta-analysis. The values of sensitivity, specificity, DOR and AUC to VRF diagnosis with and without MAR active were, respectively, 0.586 and 0.603; 0.699 and 0.713, 3.037 and 3.767; 0.67 and 0.71. The quality of the evidence suggested low confidence in estimating the outcomes.

DISCUSSION

The MAR tool decreased slightly the diagnostic values of VRF involving teeth with intracanal materials in laboratory studies. However, it is important to highlight that most studies had an uncertain risk of bias.

CONCLUSIONS

Although a low level of evidence and high heterogeneity were observed in the included studies, the meta-analysis revealed better diagnosis values for VRF detection when the MAR was deactivated when analysing extracted teeth in a laboratory setting.

REGISTRATION

PROSPERO-CRD42020145222.

FUNDING

This study was financed in party by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (CAPES).

Application of an auto-edge counting method for quantification of metal artifacts in CBCT images: a multivariate analysis of object position, field of view size, tube voltage, and metal artifact reduction algorithm

OBJECTIVE

The objective was to assess the effects of object position, field of view (FOV) size, peak kilovoltage (kVp), and a metal artifact reduction (MAR) algorithm on metal artifacts in cone beam computed tomography (CBCT) as measured with an auto-edge counting method.

STUDY DESIGN

A titanium implant and a stainless steel intracanal post in a root were inserted in bovine rib blocks. CBCT scans were acquired with changes in object position (incisor, canine, and premolar-molar areas), FOV, kVp, and MAR (on or off) mode. Images were quantitatively analyzed in MATLAB by using the Canny edge detection algorithm. Four-way analysis of variance and Tukey tests were applied for data analysis.

RESULTS

The implant produced no significant differences in number of artifacts among the object positions through changing the kVp and MAR mode for all FOV sizes (P > .05). The intracanal post scanned with the medium-sized FOV, high kVp, and MAR off mode generated significant differences among object positions (P = .033). Among the variables assessed, FOV size and MAR mode had a significant influence on the number of artifacts (P ≤ .039).

CONCLUSION

Reduction of FOV size and application of the MAR tool significantly decreased the number of streak artifacts. The Canny edge detection algorithm could be an efficient method of metal artifact quantification.

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.

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.

Effectiveness of Commercial Software-Enhanced Image Artifact Reduction Software

INTRODUCTION

Artifact reduction (AR) software has been incorporated into some cone-beam computed tomographic (CBCT) systems to reduce the severity of beam hardening (BH) artifacts and improve image quality. This study quantifies BH artifact and evaluates the effectiveness of AR in 2 CBCT systems.

METHODS

Palatal roots of Dent-Alike (Dentsply Sirona, Tulsa, OK) teeth were prepared and root filled with gutta-percha and EndoSequence BC Sealer (Brasseler, Savannah, GA). Six teeth were imaged with and without AR software using the ProMax3D (Planmeca Oy, Helsinki, Finland) and the Pax-i3D (Vatech, Hwaseong-si, South Korea) systems. FSL (FMRIB, Oxford, UK) software was used to quantify the light and dark components of the BH artifact along the tooth root using a specific region of interest approach and an image-wide analysis approach. Statistical analysis was performed using paired t tests and corrected for multiple comparisons with cluster mass correction using a nonparametric statistical analysis to evaluate the differences in the artifact volumes and areas with and without AR.

RESULTS

A significant reduction in the light artifact was observed with the Planmeca system (P < .05), but no significant differences were observed for either the light or dark artifacts with the Vatech system when AR was applied. There were also significant reductions in the volumes of light and dark artifacts along the entire root length when the AR was applied with the Planmeca system (cluster mass P < .05), but no significant differences were observed with the Vatech system.

CONCLUSIONS

Proprietary AR software is not equally effective in reducing the light and/or dark components of CBCT BH artifacts.

Influence of zirconia crown artifacts on cone beam computed tomography scans and image superimposition of tomographic image and tooth surface scan: An in vitro study

STATEMENT OF PROBLEM

Zirconia restorations create significant artifacts on 3D cone beam computed tomography (CBCT) imaging. Static computer-assisted implant surgery (s-CAIS) relies on the accuracy of superimposition between an intraoral surface scan and CBCT imaging. However, how the artifacts from zirconia on the tomographic image might affect the predictability of s-CAIS is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of zirconia crown restorations on the superimposition process for s-CAIS.

MATERIAL AND METHODS

Four stone casts generated 4 groups: a control group (CG) with no crowns and 3 experimental groups with 4 (TG4), 7 (TG7), and 13 (TG13) zirconia crowns. A total of 40 CBCT scans were made for the 4 groups (n=10). All CBCTs were imported into a computer planning software program, and the casts from all 4 groups were scanned by using a high-resolution laboratory scanner. The standard tessellation language (STL) files were imported, segmented, and the 3 files superimposed for all groups. The accuracy of the superimposition was assessed, in millimeters, in 3 planes corresponding to anterior-posterior, horizontal, and vertical, as well as the overall measurement, and the results were analyzed statistically (α=.05).

RESULTS

The overall analysis demonstrated statistically significant differences between all groups (P<.001), except between CG and TG4. The anterior-posterior dimension demonstrated significant differences between CG and TG7 (P<.001), CG and TG13 (P<.001), TG4 and TG7 (P=.004), and TG4 and TG13 (P=.001). For the vertical dimension analysis, significant differences were found between CG and TG7 (P=.001), CG and TG13 (P<.001), and TG4 and TG13 (P<.001). For the horizontal variable, statistically significant differences were found between CG and TG7 (P=.049), CG and TG13 (P<.001), TG4 and TG13 (P<.001), and TG7 and TG13 (P=.003).

CONCLUSIONS

The accuracy of the superimposition of the images was influenced by the number of zirconia crowns, with an increased number reducing the superimposition accuracy.

Development of a model of soft tissue simulation using ballistic gelatin for CBCT acquisitions related to dentomaxillofacial radiology research

OBJECTIVES

To present the ballistic gelatin as a new material capable of simulating the soft tissues in cone-beam CT (CBCT) images.

METHODS

CBCT images of three piglet heads were acquired with their soft tissues intact (standard group). Subsequently, the piglet heads were fixed in a container using metallic pins and moulded with acrylic resin; the soft tissues were then removed and replaced by ballistic gelatin, with the same thickness of the original soft tissues. The images were evaluated by two oral radiologists, to check the adaptation on bone surfaces, thickness and density, penetration into large bone cavities and cancellous bone, and the presence of air bubbles using a 5-score scale. Additionally, an objective analysis was carried out by one oral radiologist. For each CBCT scan, three axial reconstructions were selected to represent the mandibular, occlusal, and maxillary levels. The mean and standard deviation (SD) of the grey values were calculated in four regions of interest determined on soft tissue areas and compared by two-way ANOVA.

RESULTS

The ballistic gelatin showed subjective scores ranging from good to excellent for all parameters evaluated. There was no significant difference in the mean and SD values of the grey values between ballistic gelatin and the gold standard groups for all levels (p > 0.05). Higher SD values were observed in the occlusal level for both groups (p < 0.05).

CONCLUSIONS

Ballistic gelatin has visual and objective similarity with the gold standard. Thus, the ballistic gelatin is a promising material capable of simulating soft tissues in CBCT images.

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.

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.

Do the tube current and metal artifact reduction influence the diagnosis of vertical root fracture in a tooth positioned in the vicinity of a zirconium implant? A CBCT study

AIM

To evaluate the influence of the tube current and metal artifact reduction (MAR) tool on the diagnosis of vertical root fractures (VRF) in a tooth adjacent to a zirconium implant, in cone-beam computed tomography (CBCT) images.

METHODOLOGY

Thirty single-rooted teeth (15 with VRF and 15 control group) were individually positioned in a mandible, and scanned with the OP300 CBCT unit. Images were acquired using a standardized protocol: 5 × 5 cm field of view, 0.08-mm voxel size, and 90 kVp. Each tooth was scanned with and without a zirconium implant in its vicinity, using different tube currents (4 mA, 8 mA, and 10 mA) and conditions of MAR (enabled × disabled). Diagnostic values were calculated for each protocol, and compared by multi-way analysis of variance.

RESULTS

The ROC curve and sensitivity values did not differ significantly among the tube currents, regardless of the presence of the implant and MAR condition (p > 0.05). There were also no significant differences among the tube currents for the specificity values (p > 0.05); however, the specificity differed significantly between the "with implant" and "without implant" conditions, within the same MAR condition and tube current (p < 0.05). Specificity was significantly lower when the implant was present (p < 0.05).

CONCLUSION

The presence of a zirconium implant impairs the diagnosis of VRF in teeth adjacent to the artifact-generator material. Neither the tube current nor the MAR tool is effective in improving this diagnostic task. Therefore, in this clinical scenario, the use of the lowest tube current (4 mA), without MAR activation, is recommended.

CLINICAL RELEVANCE

Considering that the tube current is one of the main factors that influence the radiation dose and image quality in CBCT, and that metal artifacts negatively influence the diagnosis of VRF in areas adjacent to the artifact-generator material, it is important to evaluate the effect of this energetic parameter in the diagnosis of VRF in teeth adjacent to zirconium implants.

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.

A quantitative analysis of metal artifact reduction algorithm performance in volume correction with 3 CBCT devices

OBJECTIVE

The aim of this study was to quantitatively assess the performance of metal artifact reduction (MAR) algorithms on the volume of metal cylinders, considering the influence of materials, positions, and fields of view (FOVs), by using 3 cone beam computed tomography (CBCT) devices (NewTom VGi evo, Picasso Trio, and ProMax 3-D Max).

STUDY DESIGN

Nine phantoms containing cylinders of amalgam, copper-aluminum (CuAl) metal alloy, and titanium, combined in up to 3 positions, were scanned by using 2 different FOVs. MATLAB software was used to evaluate the differences between volumes before and after MAR application, and the possible interference of materials, positions, and FOVs. Wilcoxon's test and the Kruskal-Wallis test were used at a level of significance of 5%.

RESULTS

In general, images containing amalgam and CuAl showed a significant difference in volume before and after MAR application. However, no significant difference after MAR was observed (P > .05) relative to positions and FOVs. MAR had an impact on the cylinder volumes only in the NewTom VGi evo and ProMax 3-D Max scanners.

CONCLUSIONS

The performance of MAR algorithms in volume correction of metal objects is dependent on the materials and the CBCT unit.

Magnitude of beam-hardening artifacts produced by gutta-percha and metal posts on cone-beam computed tomography with varying tube current

Purpose

This study was performed to evaluate the magnitude of artifacts produced by gutta-percha and metal posts on cone-beam computed tomography (CBCT) scans obtained with different tube currents and with or without metal artifact reduction (MAR).

Materials and Methods

A tooth was inserted in a dry human mandible socket, and CBCT scans were acquired after root canal instrumentation, root canal filling, and metal post placement with various tube currents with and without MAR activation. The artifact magnitude was assessed by the standard deviation (SD) of gray values and the contrast-to-noise ratio (CNR) at the various distances from the tooth. Data were compared using multi-way analysis of variance.

Results

At all distances, a current of 4 mA was associated with a higher SD and a lower CNR than 8 mA or 10 mA (P<0.05). For the metal posts without MAR, the artifact magnitude as assessed by SD was greatest at 1.5 cm or less (P<0.05). When MAR was applied, SD values for distances 1.5 cm or closer to the tooth were reduced (P<0.05). MAR usage did not influence the magnitude of artifacts in the control and gutta-percha groups (P>0.05).

Conclusion

Increasing the tube current from 4 mA to 8 mA may reduce the magnitude of artifacts from metal posts. The magnitude of artifacts arising from metal posts was significantly higher at distances of 1.5 cm or less than at greater distances. MAR usage improved image quality near the metal post, but had no significant influence farther than 1.5 cm from the tooth.

Does the metal artifact reduction algorithm activation mode influence the magnitude of artifacts in CBCT images?

Purpose

This study was conducted to assess the effectiveness of a metal artifact reduction (MAR) algorithm activated at different times during cone-beam computed tomography (CBCT) acquisition on the magnitude of artifacts generated by a zirconium implant.

Materials and Methods

Volumes were obtained with and without a zirconium implant in a human mandible, using the OP300 Maxio unit. Three modes were tested: without MAR, with MAR activated after acquisition, and with MAR activated before acquisition. Artifacts were assessed in terms of the standard deviation (SD) of gray values and the contrast-to-noise ratio (CNR) in 6 regions of interest with different distances (10 to 35 mm, from the nearest to the farthest) and angulations (70° to 135°) from the implant region.

Results

In the acquisitions without MAR, the regions closer to the implant (10 and 15 mm) had a higher SD and lower CNR than the farther regions. When MAR was activated (before or after), SD values did not differ among the regions (P>0.05). The region closest to the implant presented a significantly lower CNR in the acquisitions without MAR than when MAR was activated after the acquisition; however, activating MAR before the acquisition did not yield significant differences from either of the other conditions.

Conclusion

Both modes of MAR activation were effective in decreasing the magnitude of CBCT artifacts, especially when the effects of the artifacts were more noticeable.

Evaluation of metal artefacts for two CBCT devices with a new dental arch phantom

OBJECTIVES

To create a new phantom design to evaluate the real impact of artefacts caused by titanium on bone structures in cone beam CT images considering different positions and quantity of metals in the dental arch, with and without metal artefact reduction (MAR).

METHODS

A three cylindrical polymethyl methacrylate (PMMA) plate phantom was designed containing eight perforations arranged to simulate the lower dental arch in the intermediate plate. Three titanium cylinders were positioned in different locations and quantities to test different clinical conditions and to quantify the impact of the metal artefact around five bone cylinders. Scans were carried out in seven different protocols (Control, A-F) in two cone beam CT devices (OP300 Maxio and Picasso Trio). Eight regions of interest around each cortical and trabecular bone were used to measure the grey value standard deviation corresponding the artefact expression in the Image J software. Both the artefact expression and the MAR effect were assessed using the Wilcoxon, Friedman (Dunn) and Kruskal-Wallis tests (significance level of 5%).

RESULTS

For both devices, MAR was statistically efficient only for the protocols E, and F. Protocol F (three metals on the adjacent area of the analysis region) showed higher artefact expression when compared to the others.

CONCLUSION

In conclusion, the new phantom design allowed the quantification of the metal artefact expression caused by titanium. The metal artefact expression is higher when more metal objects are positioned in the adjacent bone structures. MAR may not be effective to reduce artefact expression on the adjacencies of those objects for the devices studied.

Distribution of metal artifacts arising from the exomass in small field-of-view cone beam computed tomography scans

OBJECTIVES

To evaluate the distribution of metal artifacts from the exomass in small field-of-view (FOV) cone beam computed tomography (CBCT) scans.

STUDY DESIGN

An image phantom was scanned by using 3 CBCT units. Metal objects were positioned in the exomass, and additional CBCT scans were obtained. Mean gray values were obtained from 16 homogeneous areas and the standard deviation was calculated to quantify gray level inhomogeneity according to distinct zones of the FOV: total area and outer, inner, right, left, and mid-zones. The discrepancy between each zone and the total area was calculated to compare different CBCT units. Mean gray, gray level inhomogeneity, and discrepancy values were separately assessed by using analysis of variance (ANOVA) and Tukey's test (α = 0.05).

RESULTS

Overall, the mean gray values were significantly lower in the inner zone, and the gray level inhomogeneity values were significantly higher in the inner and mid-zones irrespective of the presence of metal objects in the exomass. The 3 CBCT units presented significantly different discrepancy values in most conditions.

CONCLUSIONS

The distribution of metal artifacts from the exomass follows the inherent gray value dispersion of CBCT images, with greater inhomogeneity in the inner zone of the FOV. This is exacerbated when metal objects are in the exomass.

Difference in the artefacts production and the performance of the metal artefact reduction (MAR) tool between the buccal and lingual cortical plates adjacent to zirconium dental implant

OBJECTIVES

To quantify the artefacts production and the performance of the metal artefact reduction (MAR) tool, enabled before or after the acquisition, in cortical plates (buccal and lingual) and other regions adjacent to zirconium implants.

METHODS

Cone beam CT scans were acquired using the OP300 Maxio unit before (control group) and after (implant group) the insertion of a zirconium implant into the posterior region of a dry mandible. Three conditions of MAR tool were tested: "without MAR", with "MAR activated after acquisition", and with "MAR activated before acquisition". The standard deviation (SD), contrast-to-noise ratio (CNR) and voxel values were calculated in the buccal and lingual cortical plates, medullary bone and water region, close to the implant. The structural bone analysis was performed in the medullary bone close to the implant.

RESULTS

Overall, in control and implant groups, the lingual cortical had higher SD, lower CNR and lower voxel values than the buccal cortical, regardless of the MAR condition (p < 0.05). Implant caused higher SD values and lower voxel values in adjacent regions "without MAR" (p < 0.05). MAR activation decreased SD and changed voxel values when the implant was present, regardless of MAR activation mode (p < 0.05). The activation of MAR increased the trabecular thickness values for the implant group (p < 0.05).

CONCLUSION

The expression of artefacts adjacent to zirconium implants is greater in the lingual than in the buccal cortical. The greater the expression of artefacts in this region, the greater the effectiveness of the MAR tool in homogenizing the grey values, regardless of the time of its activation.

Optimization of exposure parameters and relationship between subjective and technical image quality in cone-beam computed tomography

Purpose

This study was performed to investigate the effect of exposure parameters on image quality obtained using a cone-beam computed tomography (CBCT) scanner and the relationship between physical factors and clinical image quality depending on the diagnostic task.

Materials and Methods

CBCT images of a SedentexCT IQ phantom and a real skull phantom were obtained under different combinations of tube voltage and tube current (Alphard 3030 CBCT scanner, 78–90 kVp and 2–8 mA). The images obtained using a SedentexCT IQ phantom were analyzed technically, and the physical factors of image noise, contrast resolution, spatial resolution, and metal artifacts were measured. The images obtained using a real skull phantom were evaluated for each diagnostic task by 6 oral and maxillofacial radiologists, and each setting was classified as acceptable or unacceptable based on those evaluations. A statistical analysis of the relationships of exposure parameters and physical factors with observer scores was conducted.

Results

For periapical diagnosis and implant planning, the tube current of the acceptable images was significantly higher than that of the unacceptable images. Image noise, the contrast-to-noise ratio (CNR), the line pair chart on the Z axis, and modulation transfer function (MTF) values showed statistically significant differences between the acceptable and unacceptable image groups. The cut-off values obtained using receiver operating characteristic curves for CNR and MTF 10 were useful for determining acceptability.

Conclusion

Tube current had a major influence on clinical image quality. CNR and MTF 10 were useful physical factors that showed significantly associations with clinical image quality.

Are metal artefact reduction algorithms effective to correct cone beam CT artefacts arising from the exomass?

The aim of this study was to evaluate the effectiveness of metal artefact reduction (MAR) in cone beam CT (CBCT) artefacts arising from metallic objects in the exomass. A radiographic phantom composed of 16 polypropylene tubes filled with a homogeneous radiopaque solution was created. CBCT scans were obtained with two units: Picasso Trio (Vatech, South Korea) and ProMax (Planmeca, Finland). The phantom was centred in a 5 × 5 cm field-of-view (FOV) with titanium and CoCr inserts in the exomass. All scans were repeated after enabling MAR. Mean voxel values were obtained from the 16 tubes and standard deviation was calculated as a way of measuring voxel value variability. Mean values and voxel value variability were compared individually in the presence and absence of MAR by means of analysis of variance, followed by Tukey's test (α = 0.05). In the Picasso Trio, MAR significantly decreased mean voxel values (p ≤ 0.05) and increased voxel value variability (p > 0.05) in the presence of titanium. When CoCr was present, no statistical difference (p > 0.05) was observed. In the ProMax, MAR increased significantly mean voxel values (p ≤ 0.05) in the presence of titanium, and presented no significant difference (p > 0.05) for CoCr. Voxel value variability did not differ significantly (p > 0.05) for both materials. In conclusion, MAR was not effective to correct CBCT artefacts arising from metallic objects in the exomass in the two CBCT units used.

Influence of scan mode (partial/full rotations) and FOV size in the formation of artefacts in cone beam CT

OBJECTIVE

To evaluate the influence of rotation degree and field of view (FOV) size on the amount of artefacts produced in cone beam CT (CBCT) images.

METHODS

A cylindrical wax utility phantom, with a metallic sample in its interior, was scanned with two FOV sizes (100 x 100 and 40 x 40 mm) and in full (360°) and partial (~180°) rotations. After the acquisitions, images were objectively assessed in the ImageJ software, obtaining the standard deviation in areas around the metal sample. The influence of artefacts produced by the several FOVs and rotation degrees was compared by two-way analysis of variance (α = 0.05).

RESULTS

The images obtained with a large FOV presented a higher amount of noise compared to a restricted FOV, both for partial (p = 0.0037) and full (p = 0.0023) rotation degrees. For images obtained with a restricted FOV, full rotation resulted in images with less noise (p = 0.0259). For images obtained with large FOV, there was no statistically significant difference (p = 0.1494) in noise for both rotation protocols.

CONCLUSIONS

As there were no significant differences in the amount of artefacts in rotation protocols for large FOVs, the partial rotation can be indicated due to its lower exposure to radiation. For acquiring images with restricted FOVs, the full rotation is recommended.

Diagnosis of external root resorption in teeth close and distant to zirconium implants: influence of acquisition parameters and artefacts produced during cone beam computed tomography

AIM

To assess the influence of artefacts, the metal artefact reduction (MAR) tool and kilovoltage (kVp) on the diagnosis of simulated external root resorption (ERR) in teeth close and distant to zirconium implants in cone beam computed tomography (CBCT) images.

METHODOLOGY

Cavities (0.62 mm in diameter and 0.19 mm deep) were created in the apical thirds of 12 roots on the buccal, lingual, distal or mesial surface; ten roots served as controls. The roots were randomly positioned in the first and second right and left premolar sockets of a dry human mandible, and a zirconium implant was placed in the socket of the first right molar. A ProMax 3D unit varying kVp (70, 80, or 90 kVp) and with the MAR tool activated or not was used to obtain CBCT scans. Five examiners evaluated all images to determine the area under the receiver operating characteristic (ROC) curve, sensitivity and specificity.

RESULTS

The ROC values and sensitivity were not affected by MAR or artefacts regardless of the distance to the implant (P > 0.05), whilst increasing kVp from 70 to 90 led to a significant increase in these values (P = 0.0202 and 0.0199, respectively). Specificity was not affected by the factors studied (P > 0.05).

CONCLUSIONS

Amongst the factors studied, only kVp influenced the diagnosis of simulated external root resorption in CBCT images. Increasing kVp from 70 to 90 improved the accuracy in diagnosing the simulated lesions.