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.

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

Purpose of reviewMicroRNAs (miRNAs) play crucial roles in modulating the neoplastic process of cancers including head and neck squamous cell carcinoma (HNSCC). miRNAs modulate pathogenesis by inhibiting target genes. Understanding how aberrant miRNAs are involved in HNSCC pathogenesis should help to

MicroRNA aberrances in head and neck cancer: pathogenetic and clinical significance.

This study aimed at evaluating incidence/degree of metal/motion artifacts and 
CT-dose-index in oral/maxillofacial examinations using Cone-Beam-CT. Interferences caused by metal and motion artifacts were evaluated in 500 patients aged from 6 to 81 years, in dental arches, maxillofacial and splanchocranium Cone-Beam-CT exams. The interferences was divided into four progressive degrees (G0–G3) related to the possibility to answer the clinical query. The parameters considered were field-of-view, scan time, patient’s age, and anatomical area. Furthermore volumetric CT-dose-index was measured. In the presence of metal artifacts the clinical query was always answered (G3 = 0). No artifacts (G0) were found in all cases when metal was beyond 5 cm from interest site and in 18.4 % when metal was inside this distance. Beam hardening and photon starvation due to implants, restoration and orthodontic therapies achieved 56.2 % G1 and 25.4 % G2. Motion artifacts were more frequent in under ten (31.5 %) and over sixty (82.2 %), and in mandible analysis (inferior arch 59.5 %, both arches 47.3 %). Moreover, their incidence and intensity were influenced by scan time (49.1 % at 36 s) but not by field-of-view. Mean volumetric CT-dose-index of all patients was mGy 9.11 (mGy 3.62, 5.78, 8.89, and 13.07 at 18, 24, 26, and 36 s, respectively). In our series Cone-Beam-CT diagnostic evaluation was never inhibited by metal artifacts and only in 1.9 % of the cases by motion artifacts, always with a very low CT-dose-index.

Metal and motion artifacts by cone beam computed tomography (CBCT) in dental and maxillofacial study.

Aim
To evaluate the characteristic artefact patterns associated with teeth root filled with Gutta-percha when scanned with four cone-beam CT devices.

Methodology
Whilst using soft tissue simulation, ten root filled human premolars were placed in empty sockets in a dry human skull. Subsequently, the skull was scanned using 3D Accuitomo 170®, WhiteFox®, Cranex 3D® and Scanora 3D® following clinical protocols with the highest resolution and artefact reduction. After proper image registration in OnDemand3D® software (Cybermed, Seoul, Korea), each image slice was evaluated by three trained and calibrated dentomaxillofacial radiologists, which scored absence (0) and presence (1) of cupping artefact, hypodense halos and streak artefacts. Kappa test was performed for intra- and interobserver agreement.

Results
A moderate to perfect agreement for each observer (intra-observer κ = 0.5–1.0) was found. Agreement between the different observers was moderate to almost perfect for the different artefact patterns (interobserver κ = 0.55–0.9). Cupping artefact was the most prevalent (70%), followed by a hypodense halo (35%) and streak artefacts (16%). The Chi-squared test revealed significantly more streaks in axial slices (P < 0.0001), with some CBCT systems yielding significantly inferior results to others (P < 0.05). The dedicated EndoMode and artefact reduction did not improve the result significantly.

Conclusions
The variation of artefact expression was significantly different amongst CBCT machines for root filled teeth. Continuous efforts are needed to improve CBCT reconstruction algorithms, with a specific focus on reducing artefacts induced by dense dental materials, whilst striving for enhanced image quality at low-radiation doses.

Artefact expression associated with several cone‐beam computed tomographic machines when imaging root filled teeth

Objective
To objectively compare the influence of different cone-beam computed tomography (CBCT) devices, high-density materials and field of views (FOVs) on metal artifact expression.

Material and methods
For this in vitro study, three customized acrylic resin phantoms containing high-density materials cylinders: titanium, copper–aluminum alloy and amalgam were scanned on three CBCT devices using high-resolution protocols, same voxel size (0.2 mm) and different FOVs. After fully automatic segmentation and image registration, the same region of interest was defined for the small and medium FOVs. The difference between the segmented and the real volume of the metal cylinders was assessed. Moreover for each segmented slice, the area difference between the segmented and the real axial section was determined. The artifacts on the background were measured as normalizing standard deviation of voxel values in the vicinity of the cylinder, in three different distances.

Results
Considerable differences were observed in volume measurements for all CBCTs devices and materials for both FOV sizes (up to 67%). The slice per slice area analysis indicated higher artifacts at the edges of the metal cylinder. Within the materials, amalgam and titanium had, respectively, the worst and best artifact expression in all the CBCT devices. Standard deviation values varied differently between the three distances in each device.

Conclusion
Our in vitro study showed that different CBCT devices, high-density materials and FOV should be considered while evaluating CBCT images. More carefully, diagnosis conclusions should be drawn in images containing amalgam and copper–aluminum alloy.

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Quantitative evaluation of metal artifacts using different CBCT devices, high-density materials and field of views.

To quantitatively compare the streak artifacts produced by dental metals in a cone-beam computed tomography (CBCT) device and a multi-detector row computed tomography (MDCT) scanner in relation to metal types and imaging parameters. Cubes of aluminum, titanium, cobalt–chromium alloy, and type IV gold alloy were scanned with CBCT and MDCT scanners at tube voltages of 80 and 100 peak kV (kVp), and currents of 100 and 170 mAs by MDCT, and 102 and 170 mAs by CBCT. Artifact areas were quantified using ImageJ software. Artifact areas for the same metals and imaging parameters were smaller with CBCT than with MDCT under most conditions. Type IV gold alloy caused the largest artifact areas, followed by cobalt–chromium alloy, titanium, and aluminum, respectively. Higher tube voltage was associated with smaller artifact areas under most conditions, whereas increasing tube current had no consistent effect on artifact area using either CT device. CBCT was associated with smaller artifact areas than MDCT for the same parameters. Type IV gold alloy produced the largest artifact areas among the tested metals, but metallic artifacts could be reduced by increasing the tube voltage.

Quantitative analysis of metallic artifacts caused by dental metals: comparison of cone-beam and multi-detector row CT scanners

Objectives: The objective of this study was to compare the accuracy of contrast-enhanced CT (CECT) and contrast-enhanced MRI (CEMRI) in the detection of perineural spread (PNS) of adenoid cystic carcinoma (ACC) in the oral and maxillofacial regions. Methods: This study consisted of 13 ACCs from 13 patients, all of which were histopathologically diagnosed. Both CECT and CEMRI were performed in all patients before the treatment. The images of each patient were retrospectively evaluated for the detection of PNS. The definitions of PNS included abnormal density/signal intensity, contrast enhancement or widening of the pterygopalatine fossa, palatine foramen, incisive canal, mandibular foramen and mandibular canal, and enlargement or excessive contrast enhancement of a nerve. Results: 11 out of 13 cases were proven to exhibit PNS histopathologically. 8 of the 11 cases for which PNS was histopathologically proven exhibited PNS on MR images. Six of the eight cases for which PNS was exhibited on MR images also ex...

Perineural spread of adenoid cystic carcinoma in the oral and maxillofacial regions: evaluation with contrast-enhanced CT and MRI.

The calcifying cystic odontogenic tumor (CCOT) simultaneously occurring with other lesions at different locations in the same patient is rare. We report a patient with CCOT associated with an odontoma, a supernumerary tooth, and a dentigerous cyst simultaneously occurring in the maxilla. Cone-beam computed tomography (CBCT) images showed a well-defined expansile lesion with internal calcification, high-density masses surrounded by low-density area, and a supernumerary tooth at the anterior maxilla. Posterolaterally to these lesions, an embedded canine with pericoronal radiolucency was detected. Histopathologic examination revealed a CCOT associated with an odontoma, a supernumerary tooth, and a dentigerous cyst of the embedded canine. Enucleation was performed, and a 2-year postoperative follow-up was uneventful. CBCT was useful in giving the differential diagnosis by depicting internal calcification of CCOT, and in revealing the extent and complex relationship of these lesions.

Calcifying cystic odontogenic tumor associated with other lesions: case report with cone-beam computed tomography findings.

The calcifying cystic odontogenic tumor is a rare benign odontogenic lesion. This report documents a case of this lesion associated with odontoma arising from the anterior maxilla in a 14-year-old boy. The diagnosis was confirmed based on computerized tomography findings, which clearly depicted the internal structures obscured in conventional images.

Computerized tomography observation of a calcifying cystic odontogenic tumor with an odontoma: case report.

OBJECTIVES The study's objectives were to investigate the correlation between pixel values obtained from a cone-beam computed tomographic (CBCT) scanner and the computed tomographic (CT) values from a multidetector row CT scanner and to determine whether they have a linear relationship at various tube voltages and tube currents. METHODS A phantom with different concentrations of contrast medium at the center of a multidetector row CT and a CBCT scanner was scanned at various imaging parameters. Computed tomographic values and pixel values were measured using ImageJ. Regression analysis was performed, as well as correlation tests with a Pearson correlation coefficient. RESULTS A significant correlation between pixel values and the CT values of the same specimen was observed (P < 0.0001), and a linear relationship was found between the values from the 2 scanners at each parameter. CONCLUSIONS A high correlation and linear relationship between the CT values and pixel values were found at each parameter. Therefore, linear functions can be used to convert a pixel value from the CBCT machine used in this study to the CT values.

Correlation between pixel values in a cone-beam computed tomographic scanner and the computed tomographic values in a multidetector row computed tomographic scanner.

Jira Chindasombatjaroen

Papers

Quantitative analysis of metallic artifacts caused by dental metals: comparison of cone-beam and multi-detector row CT scanners

Perineural spread of adenoid cystic carcinoma in the oral and maxillofacial regions: evaluation with contrast-enhanced CT and MRI.

Calcifying cystic odontogenic tumor associated with other lesions: case report with cone-beam computed tomography findings.

Computerized tomography observation of a calcifying cystic odontogenic tumor with an odontoma: case report.

Correlation between pixel values in a cone-beam computed tomographic scanner and the computed tomographic values in a multidetector row computed tomographic scanner.