Artefacts in CBCT: a review

Three-Dimensional Planning in Maxillofacial Fracture Surgery: Computer-Aided Design/Computer-Aided Manufacture Surgical Splints by Integrating Cone Beam Computerized Tomography Images Into Multislice Computerized Tomography Images

This study aimed to evaluate an innovative workflow for maxillofacial fracture surgery planning and surgical splint designing. The maxillofacial multislice computerized tomography (MSCT) data and dental cone beam computerized tomography (CBCT) data both were obtained from 40 normal adults and 58 adults who suffered fractures. The each part of the CBCT dentition image was registered into MSCT image by the use of the iterative closest point algorithm. Volume evaluation of the virtual splints that were designed by the registered MSCT images and MSCT images of the same object was performed. Eighteen patients (group 1) were operated without any splint. Twenty-one (group 2) and 19 patients (group 3) used the splints designed according to the MSCT images and registered MSCT images, respectively. The authors' results showed that the mean errors between the 2 models ranged from 0.53 to 0.92 mm and the RMS errors ranged from 0.38 to 0.69 mm in fracture patients. The mean errors between the 2 models ranged from 0.47 to 0.85 mm and the RMS errors ranged from 0.33 to 0.71 mm in normal adults. 72.22% patients in group 1 recovered occlusion. 85.71% patients in group 2, and 94.73% patients in group 3 reconstructed occlusion. There was a statistically significant difference between the MSCT images based splints' volume and the registered MSCT splints' volume in patients (P <0.05). The MSCT images based splints' volume was statistically significantly distinct from the registered MSCT splints' volume in normal adults (P <0.05). There was a statistically significant difference between the MSCT images based splints' volume and the registered MSCT splints' volume in patients and normal adults (P <0.05). The occlusion recovery rate of group 3 was better than that of group 1 and group 2. The way of integrating CBCT images into MSCT images for splints designing was feasible. The volume of the splints designed by MSCT images tended to be smaller than the splints designed by the integrated MSCT images. The patients operated with splints tended to regain occlusion. The patients who were operated with the splints which were designed according to registered MSCT images tended to get occlusal recovered.

Effect of Exposure Parameters on Metal Artifacts in Cone Beam Computed Tomography

OBJECTIVES

The aim of this study was to assess the effect of tube current, kilovoltage peak (kVp), metal type, and the position of metal objects on metal artifacts in cone-beam computed tomography (CBCT) images.

MATERIALS AND METHODS

Titanium and cobalt-chromium rods were fabricated and placed in a dry human mandible. Samples were scanned using a Promax 3D CBCT unit with different milli-amperages and kVp. The artifacts induced by metal objects were evaluated using the Image J software in four regions of interest (ROIs) on each image.

RESULTS

A higher kVp decreased artifacts of the buccal surface of the rods in 97% of the cases (P=0.046) but did not affect the severity of artifacts between the two metal objects (P>0.05). Increasing the tube current had no effect on metal artifacts in 93% of the cases (P>0.05). Artifacts induced by a cobalt-chromium alloy were more severe than those with titanium (P<0.001). Artifacts were more intense in the buccal surface of anterior rods compared to the posterior rods (P<0.003).

CONCLUSIONS

Tube voltage, metal type and the position of metal objects affected the severity of metal artifacts on CBCT images. The metal type had the greatest effect on metal artifact intensity in this study.

Influence of image-viewers and artifacts on implant length measurements in cone-beam computed tomography: an in vitro study

This preclinical in vitro study compared the accuracy of implant lengths measured in two different image-viewers, and examined whether implant-induced artifacts affected the implant length measurements on CBCT images. A resin edentulous mandibular model, with multiple adjacent implants in the posterior segments, was acquired with a CBCT machine. In two different image-viewers, two observers independently measured the implant length. Vertical measurements on CBCT images were carried out twice at each session, and repeated one week later. The results demonstrated no significant differences between actual and measured implant lengths. The differences in the mean error for vertical measurements using the two different image-viewers (cross-sectional images: OsiriX viewer = -0.01 ± 0.03 mm, NewTom viewer = -0.05 ± 0.09 mm, p-value = 0.056; sagittal images: OsiriX viewer = -0.03 ± 0.04 mm; NewTom viewer = -0.04 ± 0.10 mm, p-value = 0.24) were not statistically significant. This in vitro investigation suggests that the accuracy of implant length measurements on CBCT images was not influenced by image-viewers or by the presence of implant-induced artifacts. The presence of multiple adjacent implants in the posterior segments of the mandible is not likely to impact the measurements made between the implant apex and vital structures on CBCT images.

Comparative Evaluation of the Artefacts Index of Dental Materials on Two-Dimensional Cone-beam Computed Tomography

The aim of the study was to propose the artefact index on cone-beam computed tomography (CBCT) images of clinical prosthodontics materials, and to compare the effect of the artefacts on CBCT image clarity of normal oral tissues. Seven spheres of different materials were secured on the centre of a resin baseboard, respectively, and four human molars in vitro were placed at 10 mm front, back, left and right of the sphere. The board was scanned using CBCT with the same setting. 10 tomographic images from each of the seven data sets with clear artefacts was selected. The grayscale measuring tool of Photoshop software was used to measure the grayscale (G0) within the boundary of tomographic image and the grayscales of the streaky artefacts that were 1 mm and 20 mm outside the circular boundary (G1 and G2). The arc length, L1, of the circular boundary with artefacts was measured; the circumference, L2, was calculated. The artefact index, A, was determined as (G1/G0) × 0.5 + (G2/G1) × 0.4 + (L2/L1) × 0.1. The artefact index A can comprehensively represent the effect of artefacts on CBCT image clarity for oral tissue.

Effect of Amperage and Field of View on Detection of Vertical Root Fracture in Teeth with Intracanal Posts

INTRODUCTION

This study sought to assess the effects of amperage (mA) and field of view (FOV) on intracanal metal post artifacts and the diagnostic parameters for detection of vertical root fracture (VRF) in teeth with intracanal posts.

METHODS AND MATERIALS

In this diagnostic study, 80 human single-canal teeth were evaluated by cone-beam computed tomography (CBCT). Nickel chrome cast posts were placed into root canals after root canal therapy and canal preparation. In the test group, fracture was induced by an instron machine while no fracture was induced in the control group. Deterministic and probabilistic sensitivity and specificity values at different exposure settings were statistically analyzed using the one-way ANOVA and pairwise comparisons were performed by Tukey's test.

RESULTS

Significant differences were found between the two groups in terms of deterministic (P<0.0001) and probabilistic (P<0.013) sensitivity and deterministic (P<0.037) and probabilistic (P<0.0001) specificity at different FOV and mA combinations.

CONCLUSION

A smaller FOV and lower mA should be preferably used for detection of VRFs in teeth with intracanal posts.

Influence of Head Motion on the Accuracy of 3D Reconstruction with Cone-Beam CT: Landmark Identification Errors in Maxillofacial Surface Model

PURPOSE

The purpose of this study was to investigate the influence of head motion on the accuracy of three-dimensional (3D) reconstruction with cone-beam computed tomography (CBCT) scan.

MATERIALS AND METHODS

Fifteen dry skulls were incorporated into a motion controller which simulated four types of head motion during CBCT scan: 2 horizontal rotations (to the right/to the left) and 2 vertical rotations (upward/downward). Each movement was triggered to occur at the start of the scan for 1 second by remote control. Four maxillofacial surface models with head motion and one control surface model without motion were obtained for each skull. Nine landmarks were identified on the five maxillofacial surface models for each skull, and landmark identification errors were compared between the control model and each of the models with head motion.

RESULTS

Rendered surface models with head motion were similar to the control model in appearance; however, the landmark identification errors showed larger values in models with head motion than in the control. In particular, the Porion in the horizontal rotation models presented statistically significant differences (P < .05). Statistically significant difference in the errors between the right and left side landmark was present in the left side rotation which was opposite direction to the scanner rotation (P < .05).

CONCLUSIONS

Patient movement during CBCT scan might cause landmark identification errors on the 3D surface model in relation to the direction of the scanner rotation. Clinicians should take this into consideration to prevent patient movement during CBCT scan, particularly horizontal movement.

A retrospective, semi-quantitative image quality analysis of cone beam computed tomography (CBCT) and MSCT in the diagnosis of distal radius fractures

OBJECTIVE

To compare image quality and diagnostic validity of CBCT and MSCT for distal radius fractures.

METHODS

35 CBCT and 33 MSCT scans were retrospectively reviewed with a visual grading scale regarding the depiction of cortical bone, trabecular bone, articular surfaces, and soft tissue. The extent and type of artefacts was analyzed. Agreement on AO classification and measurement of cortical disruption and length of the fracture gap was determined. Fracture reduction was evaluated in post-treatment x-rays. Statistical analysis was performed with visual grading characteristics (VGC), chi square tests, and Kendall's coefficient of concordance.

RESULTS

CBCT performed significantly worse for cortical bone, articular surfaces, and especially soft tissue. Trabecular bone showed no significant difference. Significantly more CBCT images showed artefacts. Physics-based artefacts were the most common. CBCT scans also showed motion artefacts. There was no significant difference in agreement on AO classification. The agreement on measurements was substantial for both modalities. Slightly more fractures that had undergone MSCT imaging showed adequate reduction.

CONCLUSION

This initial study of an orthopaedic extremity CBCT scanner showed that the image quality of a CBCT scanner remains inferior for most structures at standard settings. Diagnostic validity of both modalities for distal radius fractures seems similar.

KEY POINTS

• Subjectively, CBCT remains inferior to MSCT in depicting most structures. • Similar diagnostic validity for CBCT and MSCT imaging of distal radius fractures. • CBCT is a possible alternative to MSCT in musculoskeletal imaging. • Visual grading characteristics (VGC) analysis proves useful in analyzing visual grading scales.

Obstacles in spatial evaluation of CBCT-reformatted panoramic imaging

OBJECTIVES

Conventional panoramic radiography (cPR) underlines procedure-related limitations in the display of objects. CBCT is presumed to overcome these constraints. To virtualize a cPR view, reformatted panoramic images (rPIs) can be generated. This study evaluated the rPI with regard to its susceptibility to sterical object deposition in comparison with cPR.

METHODS

A specially developed implant model with dental implants each of 4.0-mm diameter and 11.0-mm length was depositioned by shift, rotation and tilt of 5.00 mm (±0.01 mm) of horizontal shift and 5.0° (±0.167°), respectively, on a highly precise goniometer rotation table, and cPRs and rPIs were generated. Automated evaluation of the cPRs was carried out using a specially developed software. rPIs were processed and analyzed by a semi-automated image analysis.

RESULTS

Object deposition lead to distortive effects in the rPI analogue to cPR, but they appear in display only. Objects illustrated in the rPI were dimensionally correct, but sterical relations are elusive. Results are obtained for the horizontal shift, declination and reclination, lateral tilt and rotation.

CONCLUSIONS

Distortions within the rPI represent the illustration of the hyperbolic-shaped layer out of the three-dimensional data set. With this study, we demonstrated these procedure-related inherent but practically underestimated consequences. Effects of sterical object malpositioning must be compensated by the observer by adequate virtual adjustment of the processed layer. Accurate virtual adjustment leads to vertical dimensions. Sterical relations, e.g. angulation of two objects, are irretraceable unless precisely referenced.

Movement characteristics in young patients and the impact on CBCT image quality

OBJECTIVES

To assess patient movement characteristics in children and young adults and the impact on CBCT image quality.

METHODS

During 33 CBCT examinations, the patients (age: average, 14 years; range, 9-25 years) who had moved were identified by video observation [movement group (MG)]. The CBCT data sets were matched with those of 33 non-moving patients according to age, diagnostic task, examined region, field of view and voxel resolution [non-movement group (N-MG)]. Three observers scored the videos of MG, regarding motional state second by second (moving/non-moving), and movement characteristics: duration (in seconds), complexity (uniplanar or multiplanar) and distance (<3/≥3 ≤ 10/>10 mm). The observers blindly assessed axial sections of the 66 examinations individually, categorizing the image quality (appropriate/acceptable/inappropriate). Next, the observers blindly assessed axial sections of the matched-pairs images simultaneously, deciding which image in the pair had the highest image quality or if it was impossible to decide. The relationship between image quality and movement/movement characteristics was evaluated.

RESULTS

When the 66 CBCT images were evaluated individually, no relationship between image quality and movement was found. However, based on the matched-pairs assessment, accumulated number (≤2 vs ≥3, p = 0.039), duration (≤5 s vs ≥6 s, p = 0.024) and complexity (uniplanar vs multiplanar, p = 0.046) of movements had an impact on image quality; the more severe the movement, the more often the image quality was assessed lower in the MG.

CONCLUSIONS

Axial CBCT images of young patients who moved during examination did not always present lower quality than images originating from non-moving patients. Image quality was, however, significantly lower in the moving patients when movement occurred several times, had a long duration or was multiplanar.

Cone-Beam Computed Tomography for Detection of Intrabony and Furcation Defects: A Systematic Review Based on a Hierarchical Model for Diagnostic Efficacy

BACKGROUND

The aim of this review is to assess the diagnostic efficacy of cone-beam computed tomography (CBCT) for the diagnosis of and/or treatment planning for intrabony and furcation defects, using a well-known six-tiered hierarchical model for diagnostic efficacy.

METHODS

The MEDLINE, EMBASE, and Cochrane Library bibliographic databases were searched until August 2015 for studies evaluating CBCT imaging for the diagnosis of and/or treatment planning for intrabony and/or furcation defects. The search strategy was restricted to English language publications using the combination of MeSH terms, free terms, and key words.

RESULTS

The search strategy yielded 16 publications that qualitatively or quantitatively evaluated the use of CBCT for the detection of intrabony and/or furcation defects and how CBCT influenced the diagnosis and/or treatment plan. According to Quality Assessment of Studies of Diagnostic Accuracy-2, all included studies were medium to low risk of bias. The review identified only one study that investigated the societal efficacy, and none evaluated the patient outcome efficacy or therapeutic efficacy. One study investigated the diagnostic thinking efficacy. All other included studies investigated the diagnostic accuracy of CBCT.

CONCLUSIONS

From the assessed studies, it can be concluded that there is not sufficient scientific evidence to justify the use of CBCT for the diagnosis of and/or treatment planning for intrabony and furcation defects. Furthermore, the effectiveness of CBCT for such diagnostic tasks has been assessed only at low diagnostic efficacy levels.

Towards clinical implementation of ultrafast combined kV-MV CBCT for IGRT of lung cancer : Evaluation of registration accuracy based on phantom study

PURPOSE

Combined kV-MV cone-beam CT (CBCT) is a promising approach to accelerate imaging for patients with lung tumors treated with deep inspiration breath-hold. During a single breath-hold (15 s), a 3D kV-MV CBCT can be acquired, thus minimizing motion artifacts and increasing patient comfort. Prior to clinical implementation, positioning accuracy was evaluated and compared to clinically established imaging techniques.

METHODS AND MATERIALS

An inhomogeneous thorax phantom with four tumor-mimicking inlays was imaged in 10 predefined positions and registered to a planning CT. Novel kV-MV CBCT imaging (90° arc) was compared to clinically established kV-chest CBCT (360°) as well as nonclinical kV-CBCT and low-dose MV-CBCT (each 180°). Manual registration, automatic registration provided by the manufacturer and an additional in-house developed manufacturer-independent framework based on the MATLAB registration toolkit were applied.

RESULTS

Systematic setup error was reduced to 0.05 mm by high-precision phantom positioning with optical tracking. Stochastic mean displacement errors were 0.5 ± 0.3 mm in right-left, 0.4  ± 0.4 mm in anteroposterior and 0.0 ± 0.4 mm in craniocaudal directions for kV-MV CBCT with manual registration (maximum errors of no more than 1.4 mm). Clinical kV-chest CBCT resulted in mean errors of 0.2 mm (other modalities: 0.4-0.8 mm). Similar results were achieved with both automatic registration methods.

CONCLUSION

The comparison study of repositioning accuracy between novel kV-MV CBCT and clinically established volume imaging demonstrated that registration accuracy is maintained below 1 mm. Since imaging time is reduced to one breath-hold, kV-MV CBCT is ideal for image guidance, e.g., in lung stereotactic ablative radiotherapy.

Efficacy of a cone beam computed tomography metal artifact reduction algorithm for the detection of peri-implant fenestrations and dehiscences

OBJECTIVE

To determine whether the use of a metal artifact reduction (MAR) algorithm improves the detection of peri-implant fenestrations and dehiscences on cone beam computed tomography scans.

STUDY DESIGN

One hundred titanium fixtures were implanted into bovine ribs after the creation of defects simulating fenestrations and dehiscences. Images were acquired using four different protocols, namely, A2 (MAR on, voxel 0.2 mm), A3 (MAR on, voxel 0.3 mm), B2 (MAR off, voxel 0.2 mm), and B3 (MAR off, voxel 0.3 mm). For all protocols, receiver operating characteristic (ROC) curves were determined. Values for the areas under the ROC curves (Az) were subjected to analysis of variance.

RESULTS

Az values were not statistically different among protocols regardless of the defect type (P > .05).

CONCLUSIONS

The MAR algorithm tested by us did not improve the diagnosis of peri-implant fenestrations and dehiscences with use of either the 0.2 mm or the 0.3 mm voxel sizes.

Artifacts in orthodontic bracket systems in cone-beam computed tomography and multislice computed tomography

OBJECTIVES

The purpose of this study was to quantify artifacts caused by different bracket systems in cone-beam computed tomography (CBCT) and multislice computed tomography (MSCT) scans.

METHODS

Orthodontic brackets of four different systems were consecutively bonded to the surface of a residual molar on a human cadaveric mandible. One MSCT system and three CBCT units were used to scan each of the four bonded brackets, in addition to obtaining a blank reference scan of the tooth surface. All datasets were registered to the reference dataset using visualization software (Analyze 11.0® by AnalyzeDirect). Artifact-related reductions in image quality were expressed in percent of theoretical maximum standard deviations (SD) obtained for the gray values of the adjacent voxels, with higher percentages correlating more pronounced artifacts.

RESULTS

Both the SD percentages for three defined line profiles and their mean values were almost invariably higher with the MSCT system than with the CBCT units. Looking into the individual SD percentages, two of the CBCT units (Pax Zenith 3D® and Picasso Trio®; both Vatech) produced higher values than the MSCT system (SOMATOM Definition AS+®; Siemens) in some line profiles. The titanium bracket, in particular, was associated with marked differences between the two scanner technologies, as the mean artifact intensities from this bracket were particularly high with the MSCT unit and relatively low with the CBCT units. The artifact intensities observed with the other three bracket systems varied widely depending on which scanner was used.

CONCLUSION

Different artifact intensities were noted depending on the composition of the bracket system and on the scanner technology (MSCT/CBCT). While the artifacts manifested themselves differently with different scanners, their adverse effects were comparable. However, given the variable severity of the artifacts observed depending on the materials scanned and the scanners used, a blanket recommendation for or against MSCT or CBCT units cannot be given on the basis of this study.

Quantification of dental prostheses on cone-beam CT images by the Taguchi method

The gray values accuracy of dental cone‐beam computed tomography (CBCT) is affected by dental metal prostheses. The distortion of dental CBCT gray values could lead to inaccuracies of orthodontic and implant treatment. The aim of this study was to quantify the effect of scanning parameters and dental metal prostheses on the accuracy of dental cone‐beam computed tomography (CBCT) gray values using the Taguchi method. Eight dental model casts of an upper jaw including prostheses, and a ninth prosthesis‐free dental model cast, were scanned by two dental CBCT devices. The mean gray value of the selected circular regions of interest (ROIs) were measured using dental CBCT images of eight dental model casts and were compared with those measured from CBCT images of the prosthesis‐free dental model cast. For each image set, four consecutive slices of gingiva were selected. The seven factors (CBCTs, occlusal plane canting, implant connection, prosthesis position, coping material, coping thickness, and types of dental restoration) were used to evaluate scanning parameter and dental prostheses effects. Statistical methods of signal to noise ratio (S/N) and analysis of variance (ANOVA) with 95% confidence were applied to quantify the effects of scanning parameters and dental prostheses on dental CBCT gray values accuracy. For ROIs surrounding dental prostheses, the accuracy of CBCT gray values were affected primarily by implant connection (42%), followed by type of restoration (29%), prostheses position (19%), coping material (4%), and coping thickness (4%). For a single crown prosthesis (without support of implants) placed in dental model casts, gray value differences for ROIs 1–9 were below 12% and gray value differences for ROIs 13–18 away from prostheses were below 10%. We found the gray value differences set to be between 7% and 8% for regions next to a single implant‐supported titanium prosthesis, and between 46% and 59% for regions between double implant‐supported, nickel‐chromium alloys (Ni‐Cr) prostheses. Quantification of the effect of prostheses and scanning parameters on dental CBCT gray values was assessed.

PACS numbers: 87.59.bd, 87.57Q

The Utility of Cloud Computing in Analyzing GPU-Accelerated Deformable Image Registration of CT and CBCT Images in Head and Neck Cancer Radiation Therapy

The images generated during radiation oncology treatments provide a valuable resource to conduct analysis for personalized therapy, outcomes prediction, and treatment margin optimization. Deformable image registration (DIR) is an essential tool in analyzing these images. We are enhancing and examining DIR with the contributions of this paper: 1) implementing and investigating a cloud and graphic processing unit (GPU) accelerated DIR solution and 2) assessing the accuracy and flexibility of that solution on planning computed tomography (CT) with cone-beam CT (CBCT). Registering planning CTs and CBCTs aids in monitoring tumors, tracking body changes, and assuring that the treatment is executed as planned. This provides significant information not only on the level of a single patient, but also for an oncology department. However, traditional methods for DIR are usually time-consuming, and manual intervention is sometimes required even for a single registration. In this paper, we present a cloud-based solution in order to increase the data analysis throughput, so that treatment tracking results may be delivered at the time of care. We assess our solution in terms of accuracy and flexibility compared with a commercial tool registering CT with CBCT. The latency of a previously reported mutual information-based DIR algorithm was improved with GPUs for a single registration. This registration consists of rigid registration followed by volume subdivision-based nonrigid registration. In this paper, the throughput of the system was accelerated on the cloud for hundreds of data analysis pairs. Nine clinical cases of head and neck cancer patients were utilized to quantitatively evaluate the accuracy and throughput. Target registration error (TRE) and structural similarity index were utilized as evaluation metrics for registration accuracy. The total computation time consisting of preprocessing the data, running the registration, and analyzing the results was used to evaluate the system throughput. Evaluation showed that the average TRE for GPU-accelerated DIR for each of the nine patients was from 1.99 to 3.39 mm, which is lower than the voxel dimension. The total processing time for 282 pairs on an Amazon Web Services cloud consisting of 20 GPU enabled nodes took less than an hour. Beyond the original registration, the cloud resources also included automatic registration quality checks with minimal impact to timing. Clinical data were utilized in quantitative evaluations, and the results showed that the presented method holds great potential for many high-impact clinical applications in radiation oncology, including adaptive radio therapy, patient outcomes prediction, and treatment margin optimization.

Ex vivo evaluation of new 2D and 3D dental radiographic technology for detecting caries

OBJECTIVES

Proximal dental caries remains a prevalent disease with only modest detection rates by current diagnostic systems. Many new systems are available without controlled validation of diagnostic efficacy. The objective of this study was to evaluate the diagnostic efficacy of three potentially promising new imaging systems.

METHODS

This study evaluated the caries detection efficacy of Schick 33 (Sirona Dental, Salzburg, Austria) intraoral digital detector images employing an advanced sharpening filter, Planmeca ProMax(®) (Planmeca Inc., Helsinki, Finland) extraoral "panoramic bitewing" images and Sirona Orthophos XG3D (Sirona Dental) CBCT images with advanced artefact reduction. Conventional photostimulable phosphor images served as the control modality. An ex vivo study design using extracted human teeth, ten expert observers and micro-CT ground truth was employed.

RESULTS

Receiver operating characteristic analysis indicated similar diagnostic efficacy of all systems (ANOVA p > 0.05). The sensitivity of the Schick 33 images (0.48) was significantly lower than the other modalities (0.53-0.62). The specificity of the Planmeca images (0.86) was significantly lower than Schick 33 (0.96) and XG3D (0.97). The XG3D showed significantly better cavitation detection sensitivity (0.62) than the other modalities (0.48-0.57).

CONCLUSIONS

The Schick 33 images demonstrated reduced caries sensitivity, whereas the Planmeca panoramic bitewing images demonstrated reduced specificity. XG3D with artefact reduction demonstrated elevated sensitivity and specificity for caries detection, improved depth accuracy and substantially improved cavitation detection. Care must be taken to recognize potential false-positive caries lesions with Planmeca panoramic bitewing images. Use of CBCT for caries detection must be carefully balanced with the presence of metal artefacts, time commitment, financial cost and radiation dose.

Motion artefacts in cone beam CT: an in vitro study about the effects on the images

OBJECTIVE

In cone beam CT (CBCT), imperfect patient immobility, caused by involuntary movements, is one of the most important causes of artefacts and image quality degradation. Various works in literature address this topic, but seldom is the nature of the movement correlated with the type of artefact and the image degradation in a systematic manner, and the correlation analyzed and explained.

METHODS

All three types of movements that can occur during a scan-nodding, tilting and rolling-were applied to a dry skull, in various manners from abrupt to gradual through the entire scan, at different times and angles, over a wide range of displacements. 84 scans were performed, with different skull movements, and the resulting images examined by two skilled radiologists, rated in a four-point scale and statistically analyzed. A commercial CBCT machine was used, featuring supine patient positioning.

RESULTS

Different types of movements induce different artefacts, in different parts of the anatomy. In general, movement of short duration may lead to double contours (bilateral or monolateral depending upon the angle of the scan at which they occur), whereas gradual movements result into blurring.

CONCLUSION

Not all movements cause motion artefacts that equally jeopardize the image. Rolling is the type of movement that most severely affects the image diagnostic value.

ADVANCES IN KNOWLEDGE

These findings may help practitioners to identify the causes of motion artefacts and the resulting image degradation, and remediate them, and manufacturers to improve the patient-positioning devices.

Artifacts: The downturn of CBCT image

Cone-beam computed tomography (CBCT) has been accepted as a useful tool for diagnosis and treatment planning in dentistry. Despite a growing trend of CBCT in dentistry, it has some disadvantages like artifacts. Artifacts are discrepancies between the reconstructed visual image and the actual content of the subject which degrade the quality of CBCT images, making them diagnostically unusable. Additionally, structures that do not exist in the subject may appear within images. Such structures can occur because of patient motion, the image capture and reconstruction process. To optimize image quality, it is necessary to understand the types of artifacts. This article aims to throw light on the various types of artifacts associated with CBCT images.

Dental cone beam CT: A review

For the maxillofacial region, there are various indications that cannot be interpreted from 2D images and will benefit from multiplanar viewing. Dental cone beam CT (CBCT) utilises a cone- or pyramid-shaped X-ray beam using mostly flat-panel detectors for 3D image reconstruction with high spatial resolution. The vast increase in availability and amount of these CBCT devices offers many clinical benefits, and their ongoing development has potential to bring various new clinical applications for medical imaging. Additionally, there is also a need for high quality research and education. European guidelines promote the use of a medical physics expert for advice on radiation protection, patient dose optimisation, and equipment testing. In this review article, we perform a comparison of technical equipment based on manufacturer data, including scanner specific X-ray spectra, and describe issues concerning CBCT image reconstruction and image quality, and also address radiation dose issues, dosimetry, and optimisation. We also discuss clinical needs and what type of education users should have in order to operate CBCT systems safely. We will also take a look into the future and discuss the issues that still need to be solved.

Reduction of scatter-induced image noise in cone beam computed tomography: effect of field of view size and position

OBJECTIVE

To measure the effect of field of view (FOV) size and position on scatter-induced image noise in cone beam computed tomography (CBCT).

STUDY DESIGN

A polymethyl methacrylate (PMMA) phantom containing air and aluminum underwent CBCT scanning, using seven FOVs ranging between 4 × 4 cm and 14 × 10 cm, positioned both centrally and according to a dental scan. Signal difference to noise ratio (SDNR) was measured on two-dimensional (2-D) projection images.

RESULTS

At a central position, SDNR decreased with increasing FOV size, ranging between 9.8 (14 × 10 cm) and 10.9 (4 × 4 cm). For dental FOV positions, SDNR values were between 6.3 (14 × 10 cm) and 9.5 (4 × 4 cm). To reach a constant SDNR, a dose reduction up to 76% was possible for small FOVs compared with the 14 × 10 cm FOV.

CONCLUSIONS

The use of small FOVs and peripheral FOV positioning decreases scatter at the detector, resulting in a considerable potential for reduction of radiation dose to the patient.

Indications of cone beam CT in head and neck imaging

CONCLUSION

Cone Beam Computed Tomography (CBCT) can be widely used in imaging of bony structures of the anterior and lateral skull base. Significant differences of applied dosages result from the different protocols of the various indications.

OBJECTIVES

CBCT is increasingly being used in head and neck imaging. Until now, no precise knowledge about its dedicated usage existed.

METHODS

All CBCT of 2012 and 2013 were analysed with regard to the technical parameters, the performance, and the indication for imaging.

RESULTS

In total, 1862 patients were examined in 2012 and 2013. The top eight indications of the anterior skull were (1) chronic rhinosinusitis with disturbed nasal breathing (30.3%); (2) chronic rhinosinusitis (17.6%); (3) midfacial traumatology (13.7%); (4) disturbed nasal breathing (12.8%); (5) acute rhinosinusitis (7.9%); (6) polyposis nasi (6.3%); (7) search for focus (3.9%); and (8) persistent rhinorrhea (1.2%). For the lateral skull base, the top eight were (1) control after cochlear implantation (28.4%); (2) cholesteatoma (19.7%); (3) visualization of ear anatomy (8.7%); (4) chronic otitis media mesotympanalis (6.3%); (5) conductive hearing loss (5.1%); (6) suspected mastoiditis (4.8%); (7) pathology of external auditory canal (4.8%); and (8) otosclerosis (3.3%). Applied dosage for the anterior skull base was significantly lower than for the lateral skull base (2.90 mGy vs 5.92 mGy, p < 0.05); 2.4% and 3.6% of patients' images, respectively, had to be repeated.

An innovative approach in osteoporosis opportunistic screening by the dental practitioner: the use of cervical vertebrae and cone beam computed tomography with its viewer program

OBJECTIVES

To investigate the use of cone beam computed tomography (CBCT) for predicting osteoporosis based on the cervical vertebrae CBCT-derived radiographic density (RD) using the CBCT-viewer program.

STUDY DESIGN

CBCT scans (WhiteFox, de Gotzen S.r.l device, distributed by Satelec-Acteon Group, Italy) and dual-energy X-ray absorptiometry examinations of 38 women who participated in an earlier investigation were examined. A coronal slice, subjectively determined from the cervical vertebrae, was selected and the RD as gray values for the first and second vertebrae, and the dens was calculated by using CBCT-viewer software (WhiteFox imaging).

RESULTS

The CBCT-derived RD values of the dens and the left part of the first cervical vertebra showed the strongest correlation coefficients (r=0.7, 0.6; P<.001) and the highest sensitivity (76.9%, 70%), specificity (92%, 92.9%), and accuracy (90.8%, 86.4%) in predicting osteoporosis in the lumbar vertebrae and the femoral neck, respectively.

CONCLUSIONS

CBCT-derived RD of cervical vertebrae can predict osteoporosis status using a CBCT-viewer program. This finding should be confirmed on other CBCT devices.

CBCT-based bone quality assessment: are Hounsfield units applicable?

CBCT is a widely applied imaging modality in dentistry. It enables the visualization of high-contrast structures of the oral region (bone, teeth, air cavities) at a high resolution. CBCT is now commonly used for the assessment of bone quality, primarily for pre-operative implant planning. Traditionally, bone quality parameters and classifications were primarily based on bone density, which could be estimated through the use of Hounsfield units derived from multidetector CT (MDCT) data sets. However, there are crucial differences between MDCT and CBCT, which complicates the use of quantitative gray values (GVs) for the latter. From experimental as well as clinical research, it can be seen that great variability of GVs can exist on CBCT images owing to various reasons that are inherently associated with this technique (i.e. the limited field size, relatively high amount of scattered radiation and limitations of currently applied reconstruction algorithms). Although attempts have been made to correct for GV variability, it can be postulated that the quantitative use of GVs in CBCT should be generally avoided at this time. In addition, recent research and clinical findings have shifted the paradigm of bone quality from a density-based analysis to a structural evaluation of the bone. The ever-improving image quality of CBCT allows it to display trabecular bone patterns, indicating that it may be possible to apply structural analysis methods that are commonly used in micro-CT and histology.

Technical aspects of dental CBCT: state of the art

As CBCT is widely used in dental and maxillofacial imaging, it is important for users as well as referring practitioners to understand the basic concepts of this imaging modality. This review covers the technical aspects of each part of the CBCT imaging chain. First, an overview is given of the hardware of a CBCT device. The principles of cone beam image acquisition and image reconstruction are described. Optimization of imaging protocols in CBCT is briefly discussed. Finally, basic and advanced visualization methods are illustrated. Certain topics in these review are applicable to all types of radiographic imaging (e.g. the principle and properties of an X-ray tube), others are specific for dental CBCT imaging (e.g. advanced visualization techniques).

Comparison of Multidetector Computed Tomography and Flat-Panel Computed Tomography Regarding Visualization of Cortical Fractures, Cortical Defects, and Orthopedic Screws: A Phantom Study

To compare the visualization of cortical fractures, cortical defects, and orthopedic screws in a dedicated extremity flat-panel computed tomography (FPCT) scanner and a multidetector computed tomography (MDCT) scanner.We used feet of European roe deer as phantoms for cortical fractures, cortical defects, and implanted orthopedic screws. FPCT and MDCT scans were performed with equivalent dose settings. Six observers rated the scans according to number of fragments, size of defects, size of defects opposite orthopedic screws, and the length of different screws. The image quality regarding depiction of the cortical bone was assessed. The gold standard (real number of fragments) was evaluated by autopsy.The correlation of reader assessment of fragments, cortical defects, and screws with the gold standard was similar for FPCT and MDCT. Three readers rated the subjective image quality of the MDCT to be higher, whereas the others showed no preferences.Although the image quality was rated higher in the MDCT than in the FPCT by 3 out of 6 observers, both modalities proved to be comparable regarding the visualization of cortical fractures, cortical defects, and orthopedic screws and of use to musculoskeletal radiology regarding fracture detection and postsurgical evaluation in our experimental setting.

Evaluation of peri-implant buccal bone by computed tomography: an experimental study

OBJECTIVES

To evaluate the accuracy of measuring peri-implant buccal bone when using three different computed tomography devices.

MATERIALS AND METHODS

Sixty tissue-level or bone-level dental implants were placed in bovine ribs with either buccal bone full coverage, dehiscence or fenestration. For each site, the distance from the bone defect to the implant neck and the buccal bone thickness 1 mm apical to the crest were measured using a calliper. Subsequently, all sites were scanned in a reproducible position using a multi-slice computed tomography (CT) (Brightspeed, voxel size 0.625 mm) and two cone-beam computed tomography devices (i-CAT NG, voxel size 0.3 mm and Newtom VGi, voxel size 0.2 mm). Bone thickness was measured on images from the three systems similar to direct measurements and differences were evaluated. Factors that could influence the buccal bone identification were assessed by multiple binary logistic regression.

RESULTS

Buccal bone ranged from 0.1 mm to 2.75 mm in thickness and was not visible in 68%, 63% and 60% of cases when using CT, i-CAT and Newtom, respectively. For each mm of bone thickness increment, the odds of radiographic identification increased by 30.6 (P < 0.001). Bone defects negatively affected radiographic visibility (P < 0.05). All devices underestimated bone dimensions although differences among them were not significant.

CONCLUSIONS

Within these experimental conditions, the investigated devices have equivalent low accuracy in diagnosing peri-implant buccal bone. Accuracy was significantly influenced by buccal bone thickness, especially if <1 mm, and in presence of peri-implant marginal defects.

Effect of Cone-Beam Computed Tomography Field of View and Acquisition Frame on the Detection of Chemically Simulated Peri-Implant Bone Loss In Vitro

BACKGROUND

The aim of this study is to determine the influence of field of view (FOV) and number of acquisition projection images (frames) on the detection of chemically simulated peri-implant defects by cone-beam computed tomography (CBCT) using an in vitro bovine rib bone model.

METHODS

Eighty implants were placed in bovine ribs in which small and large bone defects were created using 70% perchloric acid. CBCT images were acquired at three acquisition protocols: protocol 1 (FOV 4 × 4 cm, 0.08-mm voxel size, 1,009 frames [high fidelity]; protocol 2 (same as protocol 1 except 512 frames [standard]); and protocol 3 (FOV 14 × 5 cm, 0.25-mm voxel size; high fidelity). Two oral and maxillofacial radiologists (OMRs) and two oral and maxillofacial surgeons (OMSs) rated the presence or absence of bone defects on a five-point scale. κ and area under the curve (AUC) were calculated and compared using analysis of variance with post hoc Tukey test at P ≤ 0.05.

RESULTS

Intra- and interobserver agreement for OMRs ranged from moderate to good and from slight to moderate for OMSs. For the detection of small lesions, protocol 1 (AUC 0.813 ± 0.045) provided higher detection rates than protocol 2 (AUC 0.703 ± 0.02) and protocol 3 (AUC 0.773 ± 0.55) [F(2,9) = 1.6377]. For larger defects, the trends were similar, with protocol 1 (AUC 0.852 ± 0.108) providing higher detection rates than protocol 2 (AUC 0.730 ± 0.045) and protocol 3 (AUC 0.783 ± 0.058) [F(2,9) = 1.9576].

CONCLUSION

Within the limits of this study, optimal detection of chemically simulated pericircumferential implant crestal bone defects is achieved at the least radiation detriment using the smallest FOV, the highest number of acquisition frames, and the smallest voxel.

Using cone-beam CT as a low-dose 3D imaging technique for the extremities: initial experience in 50 subjects

PURPOSE

To prospectively evaluate a dedicated extremity cone-beam CT (CBCT) scanner in cases with and without orthopedic hardware by (1) comparing its imaging duration and image quality to those of radiography and multidetector CT (MDCT) and (2) comparing its radiation dose to that of MDCT.

MATERIALS AND METHODS

Written informed consent was obtained for all subjects for this IRB-approved, HIPAA-compliant study. Fifty subjects with (1) fracture of small bones, (2) suspected intraarticular fracture, (3) fracture at the site of complex anatomy, or (4) a surgical site difficult to assess with radiography alone were recruited and scanned on an extremity CBCT scanner prior to FDA approval. Same-day radiographs were performed in all subjects. Some subjects also underwent MDCT within 1 month of CBCT. Imaging duration and image quality were compared between CBCT and radiographs. Imaging duration, effective radiation dose, and image quality were compared between CBCT and MDCT.

RESULTS

Fifty-one CBCT scans were performed in 50 subjects. Average imaging duration was shorter for CBCT than radiographs (4.5 min vs. 6.6 min, P = 0.001, n = 51) and MDCT (7.6 min vs. 10.9 min, P = 0.01, n = 7). Average estimated effective radiation dose was less for CBCT than MDCT (0.04 mSv vs. 0.13 mSv, P =  .02, n = 7). CBCT images yielded more diagnostic information than radiographs in 23/51 cases and more diagnostic information than MDCT in 1/7 cases, although radiographs were superior for detecting hardware complications.

CONCLUSION

CBCT performs high-resolution imaging of the extremities using less imaging time than radiographs and MDCT and lower radiation dose than MDCT.

Comparison of intraoral radiography and cone-beam computed tomography for the detection of periodontal defects: an in vitro study

Background

This study aimed to compare the diagnostic accuracy of cone-beam computed tomography (CBCT) unit with digital intraoral radiography technique for detecting periodontal defects.

Methods

The study material comprised 12 dry skulls with maxilla and mandible. Artificial defects (dehiscence, tunnel, and fenestration) were created on anterior, premolar and molar teeth separately using burs. In total 14 dehiscences, 13 fenestrations, eight tunnel and 16 without periodontal defect were used in the study. These were randomly created on dry skulls. Each teeth with and without defects were images at various vertical angles using each of the following modalities: a Planmeca Promax Cone Beam CT and a Digora photostimulable phosphor plates. Specificity and sensitivity for assessing periodontal defects by each radiographic technique were calculated. Chi-square statistics were used to evaluate differences between modalities. Kappa statistics assessed the agreement between observers. Results were considered significant at P < 0.05.

Results

The kappa values for inter-observer agreement between observers ranged between 0.78 and 0.96 for the CBCT, and 0.43 and 0.72 of intraoral images. The Kappa values for detecting defects on anterior teeth was the least, following premolar and molar teeth both CBCT and intraoral imaging.

Conclusions

CBCT has the highest sensitivity and diagnostic accuracy for detecting various periodontal defects among the radiographic modalities examined.

Linear accuracy and reliability of volume data sets acquired by two CBCT-devices and an MSCT using virtual models: a comparative in-vitro study

OBJECTIVE

To discriminate clinically relevant aberrance, the accuracy of linear measurements in three-dimensional (3D) reconstructed datasets was investigated.

MATERIALS AND METHODS

Three partly edentulous human skulls were examined. Landmarks were defined prior to acquisition. Two CBCT-scanners and a Quad-slice CT-scanner were used. Actual distances were physically measured with calipers and defined as a reference. Subsequently, from digital DICOM datasets, 3D virtual models were generated using maximum intensity projections (MIPs). Linear measurements were performed by semi-automated image analysis. Virtual and analogue linear measurements were compared using repeated measurements in a mixed model (p ≤ 0.05).

RESULTS

No significant difference was found among all of the digital measurements when compared to one another, whereas a significant difference was found in matched-pairs analysis between CBCT and calipers (p = 0.032). All digitally acquired data resulted in lower mean values compared to the measurements via calipers. A high level of inter-observer reliability was obtained in the digital measurements (inter-rater correlation = 0.988-0.993).

CONCLUSIONS

The reconstructed datasets led to highly consistent values among linear measurements. Yielding sub-millimeter precision, these modalities are assumed to reflect reality in a clinically irrelevant altered manner. During data acquisition and evaluation, a maximum of precision must be achieved.

How do dentists use CBCT in dental clinics? A Norwegian nationwide survey

OBJECTIVES

Cone beam computed tomography (CBCT) was introduced to Norwegian dental clinics in 2007. The aim of the study was to investigate how dental clinics use this imaging modality, including factors related to workflow and image quality, and to evaluate dentists' opinions on and experiences of using it.

MATERIALS AND METHODS

A web-based 59-item questionnaire regarding the clinical use of CBCT was sent to all 39 CBCT clinics in Norway.

RESULTS

Twenty-nine clinics (74%) responded. Most respondents (93%) were from clinics with more than one dentist and 83% had at least one specialist. All clinics had digital intraoral x-ray receptors and all but one had panoramic imaging. The most common indications for CBCT were implant treatment planning (34% of all clinics) and localization of impacted teeth (43% of specialist clinics). Seventy-two per cent of clinics reported an average of four or fewer CBCT examinations each week and 83% of respondents were subjectively satisfied with the image quality. The most commonly used enhancement functions were contrast (97%), brightness (90%) and zoom (86%).

CONCLUSIONS

The Norwegian CBCT clinics surveyed were fully digitized and had multiple dentists. Periodontists and oral and maxillofacial surgeons were the most frequent specialties represented in the clinics. Clinics with only dental specialists performed more CBCT examinations/week than clinics with general practitioners or both general practitioners and specialists. The most common indications for CBCT examinations were related to treatment planning. This study found some challenges related to image quality and communication within the radiological team.

Metallic artifacts from internal scaphoid fracture fixation screws: comparison between C-arm flat-panel, cone-beam, and multidetector computed tomography

OBJECTIVES

The aim of this study was to compare image quality and extent of artifacts from scaphoid fracture fixation screws using different computed tomography (CT) modalities and radiation dose protocols.

MATERIALS AND METHODS

Imaging of 6 cadaveric wrists with artificial scaphoid fractures and different fixation screws was performed in 2 screw positions (45° and 90° orientation in relation to the x/y-axis) using multidetector CT (MDCT) and 2 flat-panel CT modalities, C-arm flat-panel CT (FPCT) and cone-beam CT (CBCT), the latter 2 with low and standard radiation dose protocols. Mean cartilage attenuation and metal artifact-induced absolute Hounsfield unit changes (= artifact extent) were measured. Two independent radiologists evaluated different image quality criteria using a 5-point Likert-scale. Interreader agreements (Cohen κ) were calculated. Mean absolute Hounsfield unit changes and quality ratings were compared using Friedman and Wilcoxon signed-rank tests.

RESULTS

Artifact extent was significantly smaller for MDCT and standard-dose FPCT compared with CBCT low- and standard-dose acquisitions (all P < 0.05). No significant differences in artifact extent among different screw types and scanning positions were noted (P > 0.05). Both MDCT and FPCT standard-dose protocols showed equal ratings for screw bone interface, fracture line, and trabecular bone evaluation (P = 0.06, 0.2, and 0.2, respectively) and performed significantly better than FPCT low- and CBCT low- and standard-dose acquisitions (all P < 0.05). Good interreader agreement was found for image quality comparisons (Cohen κ = 0.76-0.78).

CONCLUSIONS

Both MDCT and FPCT standard-dose acquisition showed comparatively less metal-induced artifacts and better overall image quality compared with FPCT low-dose and both CBCT acquisitions. Flat-panel CT may provide sufficient image quality to serve as a versatile CT alternative for postoperative imaging of internally fixated wrist fractures.

Influence of the artefact reduction algorithm of Picasso Trio CBCT system on the diagnosis of vertical root fractures in teeth with metal posts

OBJECTIVES

To assess the influence of the artefact reduction algorithm (AR) available on the Picasso Trio 3D(®) imaging system (Vatech, Hwaseong, Republic of Korea) on image quality [greyscale values, contrast-to-noise ratio (CNR) and artefact formation] and diagnosis of vertical root fractures (VRFs) in the teeth with intracanal metal posts.

METHODS

30 uniradicular teeth had their crowns removed and their roots endodontically treated to receive intracanal metal posts. In 20 teeth, both complete (n = 10) and incomplete (n = 10) VRFs were created. Each tooth was scanned twice, with and without AR activation. The mean and variation of greyscale values, as well as CNR, were calculated for all images. Subsequently, an evaluator compared the amount of artefact (cupping, white streaks and dark bands) in all images. Five evaluators rated for VRF presence using a five-point scale.

RESULTS

Mean greyscale values and CNR were significantly decreased in images acquired with the AR. The usage of the algorithm promoted an overall reduction of image artefacts. Regarding the diagnosis of complete and incomplete VRFs, the use of the AR had an overall negative impact on specificity and accuracy.

CONCLUSIONS

While indeed reducing artefact formation, the use of the AR, instead of improving the impact on the diagnosis of VRFs in teeth with intracanal metal posts, had a negative impact on the diagnosis.

Three-dimensional monitoring of root movement during orthodontic treatment

INTRODUCTION

A significant objective of orthodontic treatment is to achieve proper and stable tooth positions that involve not only the crowns, but also their roots. However, the current methods of clinically monitoring root alignment are unreliable and inaccurate. Therefore, the purpose of this study was to develop a methodology that can accurately identify root position in a clinical situation.

METHODS

Pretreatment and posttreatment cone-beam computed tomography (CBCT) and extraoral laser scans of study models of a patient were obtained. Threshold segmentation of the CBCT scans was performed, resulting in 3-dimensional surface models. The pretreatment CBCT teeth were isolated from their respective arches for individual tooth manipulation. These isolated pretreatment CBCT teeth were superimposed onto the posttreatment surface scan depicting the expected root position setup. To validate the accuracy of the expected root position setup, it was compared with the true root position represented by the posttreatment CBCT scan. Color displacement maps were generated to measure any differences between the expected and true root positions.

RESULTS

Color map analysis through crown superimposition showed displacement differences of 0.148 ± 0.411 mm for the maxillary roots and 0.065 ± 0.364 mm for the mandibular roots.

CONCLUSIONS

This methodology has been demonstrated to be an accurate and reliable approach to visualize the 3-dimensional positions of all teeth, including the roots, with no additional radiation applied.