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A 6-year-old girl presented with a grossly expansive lesion of the left lower jaw. Radiological investigations revealed a large mixed radiolucent/radio-opaque lesion of the left mandible extending into the ramus. Correlation of biopsy and imaging results lead to the diagnosis of an expansile form of focal cemento-osseous dysplasia. Surgical enucleation was performed, and the patient remained free of recurrence after 6 months of follow-up. When dealing with fibro-osseous lesions of the jaw, correlation of radiological and pathological results is mandatory to make a correct diagnosis and avoid unnecessarily extensive surgery.

Objective: To present patient dose levels for different CBCT scanners, acquired by a dose monitoring tool in a University Hospital, as a function of field of view (FOV), operation mode, and patient age. Methods: An integrated dose monitoring tool was used to collect radiation exposure data [type of CBCT unit, dose-area product (DAP), FOV size, and operation mode] and patient demographic information (age, referral department) performed on a 3D Accuitomo 170 and a Newtom VGI EVO unit. Effective dose conversion factors were calculated and implemented into the dose monitoring system. For each CBCT unit, the frequency of examinations, clinical indications, and effective dose levels were obtained for different age and FOV groups, and operation modes. Results: A total of 5163 CBCT examinations were analyzed. Surgical planning and follow-up were the most frequent clinical indications. For the standard operation mode, effective doses ranged from 35.1 to 300 µSv and 9.26-117 µSv using 3D Accuitomo 170 and Newtom VGI EVO, respectively. In general, effective doses decreased with increasing age and FOV size reduction. Conclusions: Effective dose levels varied notably between systems and operation modes.Operation mode selection and FOV size were indication-oriented, with larger FOV sizes election serving surgical planning and follow-up. Seeing the influence of FOV size on effective dose levels, manufacturers could be advised to move toward patient-specific collimation and dynamic FOV selection. Systematically monitoring patient doses could be recommended for steering future CBCT optimization.

Objectives: As-low-as-diagnostically-acceptable (ALADA) doses are substantially lower than current diagnostic reference levels. To improve dose management, a reference quality approach was tested in which phantom quality metrics of a clinical ALADA dose reference protocol were used to benchmark potential ALADA dose protocols for various scanner models. Methods: Spatial resolution, contrast resolution, contrast-to-noise ratio (CNR) and subjective noise and sharpness were evaluated for a clinical ALADA dose reference protocol at 80 kV and 40 mA (CTDIvol 2.66 mGy) and compared with test protocols of two CT scanners at 100 kV and 35 mA (3.08–3.44 mGy), 80 kV and 54–61 mA (2.65 mGy), 80 kV and 40 mA (1.73–1.92 mGy), and 80 kV and 21–23 mA (1.00–1.03 mGy) using different kernels, filtered backprojection and iterative reconstructions. The test protocols with the lowest dose showing quality metrics non-inferior to the reference protocol were verified in a cadaver study by determining the diagnostic accuracy of detection of maxillofacial fractures and CNR of the optical nerve and rectus inferior muscle. Results: 36 different image series were analysed in the phantom study. Based on the phantom quality metrics, potential ALADA dose protocols at 1.73–1.92 mGy were selected. Compared with the reference images, the selected protocols showed non-inferiority in the detection and classification of maxillofacial fractures and non-inferior CNR of orbital soft tissues in the cadaver study. Conclusions: Reference quality metrics from clinical ALADA dose protocols may be used to guide selection of potential ALADA dose protocols of different CT scanners.

Objectives: To investigate the dose-area product (DAP) of cone-beam computed tomography (CBCT) examinations for different scan settings and imaging indications, and to establish institutional diagnostic reference levels (DRLs) for dose optimisation. Methods: A retrospective analysis of the DAP values of 3568 CBCT examinations taken from two different devices at the Prince Philip Dental Hospital, Hong Kong between 2016 and 2021 was performed. Patient- (age, gender, and imaging indication) and imaging-related (CBCT device, field-of-view (FOV), and voxel size) were correlated with the DAPs. The indication-oriented third-quartile DAP values were compared with DRLs from the UK, Finland, and Switzerland. The obtained third-quartile DAPs lower than the national DRLs and those for which no national DRLs have been proposed were used to establish institutional DRLs. Results: In the investigated CBCTs, the DAP value for large FOV scans was significantly lower than medium/small FOVs. CBCTs with a small voxel size exhibited a significantly higher DAP than those with a medium/large voxel size. CBCTs for endodontic, periodontal, orthodontic, or orthognathic evaluation exhibited a significantly higher DAP than other indications. Twelve indication-oriented institutional DRLs were established and five of them were lower than the national DRLs: third molars (229 mGy×cm2), jaw cysts/tumours (410 mGy×cm2), maxillary sinus pathology (520 mGy×cm2), developing dentition (164 mGy×cm2), and periapical lesions (564 mGy×cm2). Conclusions: CBCT examinations for endodontic, periodontal, orthodontic, or orthognathic evaluation may deliver a higher radiation dose to the patient than other imaging tasks. A periodic review of the patient dose from CBCT imaging and establishment of institutional DRLs for specific clinical settings are needed for monitoring patient dose and to optimise indication-oriented scanning protocols.

Magnetic resonance neurography allows for the selective visualization of peripheral nerves and is increasingly being investigated. Whereas in the past, the imaging of the extracranial cranial and occipital nerve branches was inadequate, more and more techniques are now available that do allow nerve imaging. This basic review provides an overview of the literature with current state of the art, anatomical landmarks and future perspectives. Furthermore, we illustrate the possibilities of the three-dimensional CRAnial Nerve Imaging (3D CRANI) MR-sequence by means of a few case studies. ispartof: BRITISH JOURNAL OF RADIOLOGY vol:94 issue:1119 ispartof: location:England status: published

Objectives: To evaluate the influence of exomass-related metal artefacts on the detection of simulated vertical root fracture (VRF) in cone-beam computed tomography (CBCT). Methods: Twenty teeth were endodontically instrumented and VRF was induced in half of them. All teeth were individually placed in an empty socket of a human mandible. Metallic materials were differently arranged in the exomass [zone outside of the field of view (FOV) but between the X-ray source and the receptor] and/or endomass (zone inside of the FOV), and CBCT scans were obtained. Four radiologists evaluated the presence of VRF using a 5-point scale. Sensitivity, specificity, and area under the receiver operating curve (AUC) were compared using ANOVA. Also, the tooth of interest was replaced with a tube filled with a radiopaque solution and all CBCT scans were repeated to analyse the data objectively. Mean grey and noise values were obtained from the tube and compared using ANOVA followed by Tukey’s test (α = 0.05). Results: Mean grey values were significantly lower and noise was significantly higher when metallic materials were present in the endomass or both the exomass and endomass. Sensitivity, specificity, and AUC were not influenced by the artefacts from the metallic materials irrespective of the arrangement condition. Conclusions: Exomass-related metal artefacts did not influence the diagnosis of simulated VRF in CBCT.

Objectives: This report aims to describe the development of age-specific phantoms for use in paediatric dentomaxillofacial radiology research. These phantoms are denoted DIMITRA paediatric skull phantoms as these have been primarily developed and validated for the DIMITRA European research project (Dentomaxillofacial paediatric imaging: an investigation towards low-dose radiation induced risks). Methods: To create the DIMITRA paediatric phantoms, six human paediatric skulls with estimated ages ranging between 4 and 10 years- old were selected, protected with non-radiopaque tape and immersed in melted Mix-D soft tissue equivalent material, by means of a careful procedure (layer-by-layer). Mandibles were immersed separately and a Mix-D tongue model was also created. For validation purposes, the resulting paediatric phantoms were scanned using a cone-beam CT unit with different exposure parameter settings. Results: Preliminary images deriving from all scans were evaluated by two dentomaxillofacial radiologists, to check for air bubbles, artefacts and inhomogeneities of the Mix-D and a potential effect on the visualization of the jaw bone. Only skulls presenting perfect alignment of Mix-D surrounding the bone surfaces with adequate and realistic soft tissue thickness density were accepted. Conclusions: The DIMITRA anthropomorphic phantoms can yield clinically equivalent images for optimization studies in dentomaxillofacial research. In addition, the layer-by-layer technique proved to be practical and reproducible, as long as recommendations are carefully followed. The research leading to these results has received funding from the European Atomic Energy Community's Seventh Framework Programme FP7/2007-2011 under grant agreement no 604984 (OPERRA: Open Project for the European Radiation Research Area).

Objectives: Dental CBCT exposure parameters should be optimized according to patient-specific indications, mainly for children that are most vulnerable to harmful effects of ionizing radiation. The aim of this study was to determine optimized kV settings for paediatric acquisitions for a dental CBCT device. Methods: Clinical and quantitative evaluations of image quality were performed using 5 and 10 years old (y/o) anthropomorphic phantoms. Technical evaluation was performed with the SEDENTEXCT-IQ phantom. Images were obtained using a PaX-i3D Green CBCT (Vatech, Korea) device, combining tube voltages ranging from 85 to 110 kV and 2 fields of view (FOVs: 21 × 19 and 12 × 9 cm), while maintaining the radiation dose fixed by adjusting the mA accordingly. Clinically, observers assessed images based on overall quality, sharpness, contrast, artefacts, and noise. For quantitative evaluation, mean grey value shift, % increase standard deviation, % beam-hardening and contrast-to-noise ratio were calculated. For technical evaluation, segmentation accuracy, contrast-to-noise ratio and full width at half maximum were measured. Biplot graphs were used to choose representative parameters, from which the best kV was selected for each protocol and evaluation. kV values that had no statistical differences (p > 0.05) with the best kV chosen were considered as having the same quality. Results: Clinically, 95 kV was found as a cut-off value. From the quantitative aspect, 85 kV (p < 0.05) showed the worst quality, except in 12 × 9 cm 5 y/o. Technically, 85 and 110 kV in the large FOV showed significantly worse quality for the large FOV. Conclusion: For paediatric indications, 95 kV or higher (and correspondingly low mA values) was found as optimal.

We aimed to assess the diagnostic accuracy of different cone beam CTs (CBCTs) and the influence of field of view (FOV) in diagnosing simulated periapical lesions.6 formalin-fixed lateral mandibular specimens from pigs were used for creating 20 standardized periapical bone defects. 18 roots were selected for the control group. Three CBCT devices [Accuitomo 3D® (Morita, Kyoto, Japan), NewTom 3G (Quantitative Radiology, Verona, Italy) and Scanora® (Soredex, Tuusula, Finland)] and three FOVs (NewTom 3G® FOV 6, 9 and 12 inches) were used to scan the mandible. Five observers assessed the images, using a five-point probability scale for the presence of lesions. Specificity, sensitivity and areas under the receiver operating characteristic (ROC) curves were calculated.Sensitivity ranged from 72% to 80%. Specificity ranged from 60% to 77%. A difference in scoring between Scanora and the other two devices existed only in the control group. ROC analysis for different FOVs showed a decreased sensitivity with an increasing FOV, but this difference was not significant.the control group, there was a difference between the CBCT devices regarding their specificity. FOV size did not show any difference in diagnostic performance. In cases in which conventional radiographic methods in combination with clinical evaluation are not sufficient, CBCT may be the method of choice to assess periapical pathology. CBCT examinations should be complementary to a clinical examination and FOV adaptation can be utilized to keep the dose to the patient as low as possible.

Objectives: To assess the use of three-dimensional (3D) imaging methods to quantify the changes in soft- and hard-tissues in cleft patients after cleft-related treatment during growth. methods: PubMed, EMBASE, Web of Science and the Cochrane Library were searched up to 1 June 2018. Included publications were those using 3D imaging to quantify soft- and hard-tissue changes after cleft-related treatments in patients with any type of cleft, during growth. Data extraction and qualitative analysis were performed by two reviewers. The methodological quality of each study was reviewed using the QUADAS-2 tool. Results: From 4 databases, 2315 articles were found. Full texts of 422 articles were analyzed and finally 12 articles were included for qualitative analysis. CT was performed in the majority of studies for hard-tissue quantification. Stereophotogrammetry, Laser scanner and 3D digitizer were identified as viable methods to quantify both soft- and hard-tissue changes, depending on whether the scan was made of the facial surface or the cast surface. Most studies conducted imaging analysis without registration between multitemporal images, which is the reason why they did not fulfil the inclusion criteria. conclusions: Although several imaging modalities have the potential to quantify cleft-related treatment follow-up, there is an urgent need to assess the imaging methods and related analyses allowing to standardise a 3D imaging protocol to quantify hard- and soft-tissue treatment follow-up.

OBJECTIVES: To systematically review the existing literature on the three-dimensional (3D) radiological evaluation of secondary alveolar bone grafting (SABG) in cleft lip and palate (CLP) patients, with specific interest in 3D imaging protocols and assessment methods. METHODS: A comprehensive literature search on PubMed, Embase and the Cochrane Library was conducted. Included publications concerned 3D imaging for evaluation of SABG in CLP patients while articles about primary or tertiary bone grafting or using of two-dimensional images only were excluded. Study quality was evaluated using the Methodological Index for Non-Randomized Studies or the Cochrane Collaboration tool for assessing risk of bias. RESULTS: The search yielded 1735 citations, of which 38 met the inclusion criteria. We noticed a large variability in imaging protocols and bone graft evaluation methods between studies. Most articles were observational studies with medium to low methodological quality, except for the one randomised clinical trial having a low risk of bias. CONCLUSIONS: There is a lack of prospective, controlled trials based on a consistent imaging protocol with a sufficiently long follow-up period. A pressing need exists for the development of a consistent optimized imaging protocol for diagnosis and follow up of SABG in CLP patients. Although 3D evaluation methods seem to be more precise than two-dimensional methods, we should be careful when comparing the outcomes arising from different 3D measuring techniques.

Buccal bifurcation cyst is a rare, uncommon buccal cystic lesion associated with the permanent mandibular first molar in children just prior to tooth eruption, and is categorized by the World Health Organization as an odontogenic cyst occurring in a vital tooth, near the buccal cervical margin of the lateral aspect of a root, as a result of an inflammatory process in a periodontal pocket. The aim of this study is to present a series of three similar mandibular buccal bifurcation cyst cases, by providing clinical, radiological and histological characterization of the lesion, in order to lead clinicians through the diagnosis, treatment and follow-up process and contribute to deeper knowledge of this rare pathological entity. ispartof: BJR CASE REPORTS vol:4 issue:2 ispartof: location:England status: published

To explore the diagnostic values of digital intraoral radiography and cone beam CT (CBCT) in the determination of periodontal bone loss, infrabony craters and furcation involvements.Accuracy assessment of the imaging modalities was conducted through bone level measurements, infrabony crater and furcation involvement classifications. For CBCT, images were obtained at 120 kV and 23.87 mAs, and observations were made on a 5.2 mm panoramic reconstruction view and on 0.4 mm thick cross-sectional slices. Intraoral radiographs of a size 2 charge-coupled device (CCD) sensor were obtained using the paralleling technique, at 60 kV (DC) and 0.28 mAs exposure. 71 human cadaver and dry skull bony defects were measured and evaluated by 3 observers. Comparison was made with the gold standard.The mean error (gold standard deviation) of bone level measurements was 0.56 mm for intraoral radiography and 0.47 mm for the CBCT panoramic 5.2 mm reconstruction view. There were no significant differences (P = 0.165) between the two methods. However, on 0.4 mm thick cross-sections, the mean error was 0.29 mm and the Wilcoxon signed-rank test indicated a significant difference when compared with the CCD (P = 0.006). The detection of crater and furcation involvements failed in 29% and 44% for the CCD, respectively, in contrast to 100% detectability for both defects with CBCT.CBCT on the panoramic 5.2 mm reconstruction view allowed comparable measurements of periodontal bone levels and defects as with intraoral radiography. CBCT with 0.4 mm thick cross-sections demonstrated values closer to the gold standard, indicating more accurate assessment of periodontal bone loss. Further research is needed to explore these results in vivo and to determine the use of CBCT in periodontal diagnosis.

Objectives: To determine the diagnostic accuracy of mandibular and maxillary bone densityin detecting osteoporosis using receiver operating characteristic (ROC) analysis.Methods: 671 women between 45 years and 70 years of age underwent dual energy X-rayabsorptiometry (DXA) of the hip and lumbar spine. This was the gold standard for diagnosing osteoporosis. Intraoral radiography of the upper and lower right premolar regionwas performed, using an aluminium wedge as a densitometric reference. Jaw bone densitywas determined using dedicated software. Observer differences and ROC curves wereanalysed.Results: For detecting osteoporosis using jaw bone density, the area under the ROC curve(Az) was 0.705. For separate analysis of mandibular and maxillary films, sensitivity variedfrom 33.9% to 38.7% and specificity from 83.5% to 85.3% when using a threshold of 4.3 mm Al equivalent.Conclusions: Density of the premolar region reaches a fair diagnostic accuracy, which might improve when including additional factors in the analysis and refining the densitometric tool.

To measure occupational radiation dose during panoramic exposure from five digital panoramic X-ray units.Exposures were made with five different digital panoramic units, of which four were equipped with a direct digital CCD (charge coupled device, "direct digital" technique), and one used storage phosphor plates ("indirect digital" technique). An anthropomorphic phantom served as the patient. An ionization chamber recorded the scattered radiation at 1 m from the phantom at five different locations around the panoramic units, both at the level of the thyroid gland and the level of the gonads, and effective organ doses were calculated. Exposure parameters were set as recommended by the manufacturers for the particular image and patient size: tube potential settings ranged between 64 kV and 74 kV, exposure times between 8.2 s and 19.0 s, tube current values between 4 mA and 7 mA.The maximum organ equivalent dose at 1 m from the panoramic unit was 0.60 microGy, the maximum organ effective dose was 0.10 microSv. Organ equivalent doses varied between 0.18 microGy and 0.30 microGy and organ effective doses between 0.01 microSv and 0.05 microSv for the different positions around the units (average for the different panoramic units). The variations in organ doses for the various machines were 0.04-0.53 microGy organ equivalent dose and 0.01-0.08 microSv organ effective dose.Assuming that 500 panoramic radiographs per year are taken by a dental practitioner at 1 m distance from the panoramic unit, he or she will receive an annual additional organ effective dose between 5 microSv and 15 microSv for the thyroid gland and between 5 microSv and 40 microSv for the gonads, depending on the type of digital panoramic unit.

To perform a survey of private dental offices in Belgium and gain insight in the knowledge and attitude of Belgian dentists towards quality care in radiography and radiation protection.A questionnaire was distributed among 700 Belgian dental offices, which were included based on demographic data and the use of intraoral radiographic equipment.The response rate was 71%. Implementation of standards for quality care and radiation protection was suboptimal. In most offices, exposure settings of the intraoral radiation tube were 65 kV/kVp to 70 kV/kVp and 10 mA to 12 mA, with an average exposure time of 0.45 s. No reduction of exposure time was noticed when using faster film types. About one-third of the responders worked with digital image receptors. Aiming devices and rectangular collimation were used in a minority of practices (40% and 6%, respectively). The distance of the dentist to the radiation tube during exposure was on average 2.2 m, although 8% of the dentists assisted in holding the image receptor inside the patient's mouth. One quarter of the dentists were standing behind a wall when taking radiographs. Lead aprons were worn more often by female dentists. Dose estimation revealed that male dentists received a significantly larger effective dose per year than female dentists (8.3 mSv vs 3.2 mSv).The implementation of standards of quality care for radiography and radiation protection could be improved among Belgian dentists. An elaborate educational programme in dental radiography is a prerequisite. Furthermore, recommendations could help to attain a change in attitude towards the use of ionizing radiation in order to meet European guidelines.

Handheld portable X-ray devices are increasingly used for intraoral radiography. This development introduces new challenges to staff and patient safety, for which new or revised risk assessments must be made and acted upon prior to use. Major issues might be: difficulties in using rectangular collimation with beam aiming devices, more complex matching of exposure settings to the X-ray receptor used (e.g. longer exposure times), movements owing to the units' weight, protection of the operator and third persons, and the use in uncontrolled environments. These problems may result in violation of the "as low as reasonably achievable'', that is, ALARA principle by an increase in (re)exposures compared with the other available intraoral X-ray devices. Hence, the use of handheld portable X-ray devices should be considered only after careful and documented evaluation (which might be performed based on medical physics support), when there is evidence that handheld operation has benefits over traditional modalities and when no new risks to the operators and/or third parties are caused. It is expected that the use of handheld portable X-ray devices will be very exceptional, and for justified situations only. Special attention should be drawn to beam-aiming devices, rectangular collimation, the section of the X-ray receptor, focus-skin distance, and backscatter shielding, and that the unit delivers reproducible dose over the full set of environmental conditions (e.g. battery status and temperature). ispartof: Dentomaxillofacial Radiology vol:44 issue:6 pages:20140343- ispartof: location:England status: published

To develop a database of paediatric head voxel models intended for Monte Carlo (MC) dosimetric applications.Seventeen head and neck CT image data sets were retrieved from the picture archiving and communicating system of our hospital and were reformed into voxel models. 22 organs were segmented at each data set. The segmented organ masses were compared to the respective age- and gender-specific ICRP reference mass value. Adjustments were made such that segmented and reference mass values coincide within a tolerance of 10%. A dental cone beam CT cleft palate simulation study was set up to demonstrate the applicability of our database to MC frameworks and to investigate the need for age- and gender-specific paediatric models.The designed database covers the age range from 2 months to 14 years old. Each model represents a reference head voxel phantom for its corresponding age and gender category. The simulation study revealed absorbed organ dose differences larger than 50% among the 5, 8 and 12 years old models when exposed to identical conditions.Children cannot be represented by one average phantom covering the entire age range like adults due to the fact that their organs change rapidly in size and shape. A database of paediatric head voxel models was designed to enable dose calculations via MC simulations. Advances in knowledge: The application of each model of the database to MC frameworks provides age- and gender-specific organ dose estimations from medical exposures in the head and neck region.

The aim of this study was to systematically review the existing scientific literature and evidence about (a) the validation of masseter muscle ultrasonography for accurate assessment of muscle thickness and (b) the reproducibility of masseter muscle thickness measures. An electronic literature search was conducted using determined keywords on specific databases. Preliminary search revealed 298 articles listed in Medline, Scopus and Web of Science. 60 duplicates were rejected, leaving 238 articles for review. After reading titles and abstracts, 31 articles remained. 23 articles were assessed for eligibility. These articles were categorized as follows: thickness, cross-section, volume and the length of the masseter muscle measured by ultrasonography. It is possible to verify the thickness of the masseter muscle in males and females in relaxation (10-15 and 9-13 mm, respectively) and contraction (14-19 and 12-15 mm, respectively). A similar tendency can also be evidenced in other measurements. Many studies evaluate masseter muscle dimensions to relate it to cephalometric analysis as such to evaluate morphological variations. It can be concluded that ultrasound is a reliable clinical tool for masseter muscle measurements, yet there is a need for standardization of methods and parameters to be recorded. ispartof: Dentomaxillofacial Radiology vol:46 issue:6 pages:20170052- ispartof: location:England status: published

Objectives:To evaluate the accuracy of CBCT in assessing trabecular structures.Methods:Two human mandibles were scanned by micro-CT (Skyscan 1173 high-energy spiral scan micro-CT; Skyscan NV, Kontich, Belgium) and CBCT (3D Accuitomo 170; Morita, Japan). The CBCT images were reconstructed with 0.5 and 1 mm thicknesses. The condylar images were selected for registration. A parallel algorithm for histogram computation was introduced to perform the registration. A mutual information (MI) value was used to evaluate the match between the images obtained from micro-CT and CBCT.Results:In comparison with the micro-CT image for the two samples, the CBCT image with 0.5 mm thickness has a MI value of 0.873 and 0.903 while that with 1.0 mm thickness has a MI value of 0.741 and 0.752. The CBCT images with 0.5 mm thickness were better matched with micro-CT images.Conclusions:CBCT shows comparable accuracy with high-resolution micro-CT in assessing trabecular structures. CBCT can be a feasible tool to evaluate osseous c...

Objectives: To determine the reliability of reformatted 2D-CT for pre-operative planning of implant placement. Methods: One hundred consecutive partially or fully edentate patients underwent 2-D reformatted CT pre-operative planning and subsequent implant placement. The number, site and size of the implants, the available bone height and anatomical complications were recorded. The pre-operative planning and the outcome at surgery were compared statistically using a percentage agreement and Kendall’s correlation coeAcient. Results: Agreement between the pre- and intra-operative data was good for the number of implants (60%) and the selected sites (70%). From a total of 416 implants planned, 21 implants could not be placed because of intra-operative findings. Agreement was relatively poor for implant size (44%) and anatomical complications (46%). Kendall’s correlation coeAcient was highest for the number of implants (0.80) and implant sites (0.81). It was much lower for implant sizes (0.51) and did not reach significance for anatomical complications (0.09). Conclusions: Reformatted 2D-CT is reliable for the pre-operative assessment of the number and sites of implants in the jaws. It is less predictable for the implant size needed and poor for anatomical complications.

The aim of this study was to evaluate whether application of ultralow dose protocols and iterative reconstruction technology (IRT) influence quantitative Hounsfield units (HUs) and contrast-to-noise ratio (CNR) in dentomaxillofacial CT imaging.A phantom with inserts of five types of materials was scanned using protocols for (a) a clinical reference for navigated surgery (CT dose index volume 36.58 mGy), (b) low-dose sinus imaging (18.28 mGy) and (c) four ultralow dose imaging (4.14, 2.63, 0.99 and 0.53 mGy). All images were reconstructed using: (i) filtered back projection (FBP); (ii) IRT: adaptive statistical iterative reconstruction-50 (ASIR-50), ASIR-100 and model-based iterative reconstruction (MBIR); and (iii) standard (std) and bone kernel. Mean HU, CNR and average HU error after recalibration were determined. Each combination of protocols was compared using Friedman analysis of variance, followed by Dunn's multiple comparison test.Pearson's sample correlation coefficients were all0.99. Ultralow dose protocols using FBP showed errors of up to 273 HU. Std kernels had less HU variability than bone kernels. MBIR reduced the error value for the lowest dose protocol to 138 HU and retained the highest relative CNR. ASIR could not demonstrate significant advantages over FBP.Considering a potential dose reduction as low as 1.5% of a std protocol, ultralow dose protocols and IRT should be further tested for clinical dentomaxillofacial CT imaging.HU as a surrogate for bone density may vary significantly in CT ultralow dose imaging. However, use of std kernels and MBIR technology reduce HU error values and may retain the highest CNR.

Objectives: To investigate the effect of tube current–exposure time (mAs) reduction on clinical and technical image quality for different CBCT scanners, and to determine preliminary minimally acceptable values for the mAs and contrast-to-noise ratio (CNR) in CBCT. Methods: A polymethyl methacrylate (PMMA) phantom and an anthropomorphic skull phantom, containing a human skeleton embedded in polyurethane, were scanned using four CBCT devices, including seven exposure protocols. For all protocols, the mAs was varied within the selectable range. Using the PMMA phantom, the CNRAIR was measured and corrected for voxel size. Eight axial slices and one coronal slice showing various anatomical landmarks were selected for each CBCT scan of the skull phantom. The slices were presented to six dentomaxillofacial radiologists, providing scores for various anatomical and diagnostic parameters. Results: A hyperbolic relationship was seen between CNRAIR and mAs. Similarly, a gradual reduction in clinical image quality was seen at lower mAs values; however, for several protocols, image quality remained acceptable for a moderate or large mAs reduction compared with the standard exposure setting, depending on the clinical application. The relationship between mAs, CNRAIR and observer scores was different for each CBCT device. Minimally acceptable values for mAs were between 9 and 70, depending on the criterion and clinical application. Conclusions: Although noise increased at a lower mAs, clinical image quality often remained acceptable at exposure levels below the manufacturer’s recommended setting, for certain patient groups. Currently, it is not possible to determine minimally acceptable values for image quality that are applicable to multiple CBCT models. Dentomaxillofacial Radiology (2015) 44, 20150108. doi: 10.1259/dmfr.20150108 Cite this article as: Pauwels R, Seynaeve L, Henriques JCG, de Oliveira-Santos C, Souza PC, Westphalen FH, et al. Optimization of dental CBCT exposures through mAs reduction. Dentomaxillofac Radiol 2015; 44: 20150108.

To investigate the influence of bowtie filtration on dedicated cone beam CT (CBCT) of the head and neck.A validated hybrid simulation technique was used to model a commercial CBCT system with offset scanning geometry, 90 kV tube potential and 145×75 mm imaging field of view. Three bowtie filters were formulated to produce uniform flux intensity in the projection image of cylindrical objects of diameter 14, 16 and 18 cm. The influence of these simulated filters was compared with the original flat filtration in terms of the output radiation field, the dose delivered to the object, the scatter distribution in projections and the quality of the reconstructed image.Compared against flat filtration, dose reduction for the bowtie case, examined as a function of radial distance within a 16-cm-diameter water cylinder, varied from 8.7% at the centre to 53.8% at the periphery. Scatter reduction, quantified using scatter-to-primary ratio in projection images, was up to 37.6% for a 14-cm-diameter cylindrical contrast phantom. Using the supplied routine image reconstruction, bowtie filtration resulted in comparable noise appearance, contrast resolution and artefact pattern for computational anatomical phantoms, with5% difference in contrast-to-noise ratio.Bowtie filtration can effectively reduce the dose and scatter in CBCT of the head and neck. For better image quality, corresponding modification to the image pre-processing and reconstruction is needed.The hybrid simulation approach can usefully explore the impact of proposed system component and design changes.

The main purpose of this study was to determine the accuracy of cone beam CT (CBCT) in measuring the trabecular bone microstructure, in comparison with micro-CT. The subobjective was to examine to what extent bone quality assessment is influenced by X-ray tube current and voltage settings as well as soft tissue surrounding the bone.Eight human mandibular bone samples were scanned using three different clinical exposure protocol within water (W1-3) and without water (NW1-3) by a high-resolution (80 µm) CBCT machine (3D Accuitomo 170(®); Morita, Kyoto, Japan). Subsequently, the samples underwent micro-CT scanning (SkyScan 1174®; SkyScan, Antwerp, Belgium). After image acquisition, similar volumes of interest of the trabecular structures captured with CBCT and micro-CT were aligned with each other. Segmentation was then performed, and the morphometric parameters were quantified within the volumes of interest by CTAn software (CTAnalyser(®); SkyScan, Antwerp, Belgium). Descriptive statistical analyses and multiple comparisons between all protocols were applied in R software.High positive Pearson's correlation coefficients were observed between CBCT and micro-CT protocols for all tested morphometric indices except for trabecular thickness. No significant differences were observed between all exposure protocols except for trabecular separation. When examining the soft-tissue effect on trabecular bone structures, no significant differences between NW (1-3) and W (1-3) protocols were observed for all variables.The present study demonstrated the potential of high-resolution CBCT imaging for in vivo applications of quantitative bone morphometry and bone quality assessment. However, the overestimation of morphometric parameters and acquisition settings in CBCT must be taken into account.