Keith Horner

Effective dose range for dental cone beam computed tomography scanners

OBJECTIVE To estimate the absorbed organ dose and effective dose for a wide range of cone beam computed tomography scanners, using different exposure protocols and geometries. MATERIALS AND METHODS Two Alderson Radiation Therapy anthropomorphic phantoms were loaded with LiF detectors (TLD-100 and TLD-100 H) which were evenly distributed throughout the head and neck, covering all radiosensitive organs. Measurements were performed on 14 CBCT devices: 3D Accuitomo 170, Galileos Comfort, i-CAT Next Generation, Iluma Elite, Kodak 9000 3D, Kodak 9500, NewTom VG, NewTom VGi, Pax-Uni3D, Picasso Trio, ProMax 3D, Scanora 3D, SkyView, Veraviewepocs 3D. Effective dose was calculated using the ICRP 103 (2007) tissue weighting factors. RESULTS Effective dose ranged between 19 and 368 μSv. The largest contributions to the effective dose were from the remainder tissues (37%), salivary glands (24%), and thyroid gland (21%). For all organs, there was a wide range of measured values apparent, due to differences in exposure factors, diameter and height of the primary beam, and positioning of the beam relative to the radiosensitive organs. CONCLUSIONS The effective dose for different CBCT devices showed a 20-fold range. The results show that a distinction is needed between small-, medium-, and large-field CBCT scanners and protocols, as they are applied to different indication groups, the dose received being strongly related to field size. Furthermore, the dose should always be considered relative to technical and diagnostic image quality, seeing that image quality requirements also differ for patient groups. The results from the current study indicate that the optimisation of dose should be performed by an appropriate selection of exposure parameters and field size, depending on the diagnostic requirements.

Mandibular radiomorphometric indices in the diagnosis of reduced skeletal bone mineral density

Abstract: Diagnosis of osteoporosis allows the delivery of preventive and therapeutic intervention and is usually achieved using bone densitometric techniques. One referral criterion for densitometry is osteopenia on radiographs. The aim of this study was to measure the validity of mandibular cortical indices measured on panoramic radiographs in the diagnosis of reduced skeletal bone density. Seventy-four women underwent bone densitometry of the femoral neck, lumbar spine and the forearm. Fifty-five patients (74%) were classified as having a reduced bone density (T-score ≤–1). Twenty-seven patients had a T-score of <–2.5 observed at one or more of the three measurement sites. A panoramic radiograph was taken of each patient and two observers made measurements of cortical thickness at the mental foramen (mental index, MI), antegonion (antegonial index, AI) and gonion (gonial index, GI) regions. Logistic regression and receiver operating characteristic (ROC) curve analyses were used to measure the validity of cortical indices in the diagnosis of reduced bone mineral density. Only MI contributed significantly to a diagnosis of low skeletal bone mineral density (T-score ≤–1). The 95% limits of agreement between observers in measurement of MI were 1.32 to +1.32 mm. When data for both observers were combined, the area under the ROC curve was 0.733 (SE = 0.072; 95% confidence interval = 0.618 to 0.83), indicating moderate accuracy. A diagnostic threshold for MI of 3 mm (or less) is suggested as the most appropriate threshold for referral for bone densitometry. However, the study provided only limited support for the use of panoramic radiomorphometric indices in diagnosing low skeletal bone mineral density. They might, questionably, be used as part of a method of osteoporosis risk assessment.

E.A.O. guidelines for the use of diagnostic imaging in implant dentistry 2011. A consensus workshop organized by the European Association for Osseointegration at the Medical University of Warsaw

Diagnostics imaging is an essential component of patient selection and treatment planning in oral rehabilitation by means of osseointegrated implants. In 2002, the EAO produced and published guidelines on the use of diagnostic imaging in implant dentistry. Since that time, there have been significant developments in both the application of cone beam computed tomography as well as in the range of surgical and prosthetic applications that can potentially benefit from its use. However, medical exposure to ionizing radiation must always be justified and result in a net benefit to the patient. The as low a dose as is reasonably achievable principle must also be applied taking into account any alternative techniques that might achieve the same objectives. This paper reports on current EAO recommendations arising from a consensus meeting held at the Medical University of Warsaw (2011) to update these guidelines. Radiological considerations are detailed, including justification and optimization, with a special emphasis on the obligations that arise for those who prescribe or undertake such investigations. The paper pays special attention to clinical indications and radiographic diagnostic considerations as well as to future developments and trends.

Detecting patients with low skeletal bone mass

OBJECTIVES The object of this study was to determine the relative usefulness of clinical and radiographic indices in the diagnosis of patients with low skeletal bone mass amongst 135 healthy perimenopausal women, aged 45-55 years, attending for routine dental treatment. METHODS Bone mineral density was measured for the spine and femoral neck, using dual energy X-ray absorptiometry. Each patients osteoporosis status was calculated according to the WHO criteria for Caucasian women. Each patient received a dental panoramic tomogram, and the width of the inferior mandibular cortex (mental index, (MI)) was measured. The body mass index (BMI) and simple calculated osteoporosis risk estimation (SCORE) indices were calculated. RESULTS The SCORE index was a significant factor in predicting low bone mass, but with the weight of the patient being the only significant constituent factor. MI, BMI and SCORE indices were significantly correlated with skeletal bone density. When the logistic regression model included MI, BMI and SCORE indices, all three variables were significant predictors of low skeletal bone mass. CONCLUSIONS A thinning of the mandibular cortices (MI<3mm) in a normal perimenopausal female is associated with low skeletal bone mass. If, in addition, the patient is underweight (BMI is below 20kg/m(2)) or has a high SCORE index (> or =6) then this increases their risk of osteoporosis.

Radiovisiography: an initial evaluation

An initial evaluation of the latest dental radiographic imaging system, radiovisiography, is reported. Despite limitations in its possible clinical applications and problems inherent within the system design, radiovisiography has been found to be a rapid imaging system capable of producing clinically acceptable periapical images. It is suggested that this system may be of particular value in endodontics and in its present form should be considered as an adjunct rather than as a replacement for conventional intra-oral film. Further studies are now required into recent system modifications which are described

Estimation of paediatric organ and effective doses from dental cone beam CT using anthropomorphic phantoms

OBJECTIVES Cone beam CT (CBCT) is an emerging X-ray technology applied in dentomaxillofacial imaging. Previous published studies have estimated the effective dose and radiation risks using adult anthropomorphic phantoms for a wide range of CBCT units and imaging protocols. METHODS Measurements were made five dental CBCT units for a range of imaging protocols, using 10-year-old and adolescent phantoms and thermoluminescent dosimeters. The purpose of the study was to estimate paediatric organ and effective doses from dental CBCT. RESULTS The average effective doses to the 10-year-old and adolescent phantoms were 116 μSv and 79 μSv, respectively, which are similar to adult doses. The salivary glands received the highest organ dose and there was a fourfold increase in the thyroid dose of the 10-year-old relative to that of the adolescent because of its smaller size. The remainder tissues and salivary and thyroid glands contributed most significantly to the effective dose for a 10-year-old, whereas for an adolescent the remainder tissues and the salivary glands contributed the most significantly. It was found that the percentage attributable lifetime mortality risks were 0.002% and 0.001% for a 10-year-old and an adolescent patient, respectively, which are considerably higher than the risk to an adult having received the same doses. CONCLUSION It is therefore imperative that dental CBCT examinations on children should be fully justified over conventional X-ray imaging and that dose optimisation by field of view collimation is particularly important in young children.

Tooth loss and osteoporosis: the OSTEODENT Study

AIM To determine the cross-sectional association of the osteoporotic status of patients with the number of their teeth, with and without taking into account age and/or smoking. MATERIAL & METHODS At four centres, the study recruited 665 females aged 45-70 years and the number of teeth was counted for 651 subjects. Bone density was measured at the total hip, femoral neck and lumbar spine. RESULTS The mean number of teeth in the osteoporotic subjects was 3.3 fewer than normal subjects and 2.1 fewer if those with no teeth were excluded. The association between osteoporosis and having <6 or having <28 teeth remained significant after adjusting for age, smoking and centre with p-values of 0.016 and 0.011, respectively. A single regression model for tooth count with normal errors would not fit all the data. By fitting mixture regression models to subjects with tooth count >0, three clusters were identified corresponding to different degrees of tooth loss. The overall effect of osteoporosis was as follows: -1.8 teeth before and after adjusting for smoking, -1.2 teeth after adjusting for age, and -1.1 teeth after adjusting for both age and smoking. CONCLUSIONS We have established a significant association between osteoporosis and tooth loss after adjusting the effect for age and smoking.

Quantification of metal artifacts on cone beam computed tomography images

OBJECTIVES To quantify metal artifacts obtained from a wide range of cone beam computed tomography (CBCT) devices and exposure protocols, to compare their tolerance to metals of different densities, and to provide insights regarding the possible implementation of metal artifact analysis into a QC protocol for CBCT. MATERIALS AND METHODS A customized polymethyl methacrylate (PMMA) phantom, containing titanium and lead rods, was fabricated. It was scanned on 13 CBCT devices and one multi-slice computed tomography (MSCT) device, including high-dose and low-dose exposure protocols. Artifacts from the rods were assessed by two observers by measuring the standard deviation of voxel values in the vicinity of the rods, and normalizing this value to the percentage of the theoretical maximum standard deviation. RESULTS For CBCT datasets, artifact values ranged between 6.1% and 27.4% for titanium, and between 10.% and 43.7% for lead. Most CBCT devices performed worse than MSCT for titanium artifacts, but all of them performed better for lead artifacts. In general, no clear improvement of metal artifacts was seen for high-dose protocols, although certain devices showed some artifact reduction for large FOV or high exposure protocols. CONCLUSIONS Regions in the vicinity of the metal rods were moderately or gravely affected, particularly in the area between the rods. In practice, the CBCT user has very limited possibilities to reduce artifacts. Researchers and manufacturers need to combine their efforts in optimizing exposure factors and implementing metal artifact reduction algorithms.

Variability of dental cone beam CT grey values for density estimations

OBJECTIVE The aim of this study was to investigate the use of dental cone beam CT (CBCT) grey values for density estimations by calculating the correlation with multislice CT (MSCT) values and the grey value error after recalibration. METHODS A polymethyl methacrylate (PMMA) phantom was developed containing inserts of different density: air, PMMA, hydroxyapatite (HA) 50 mg cm(-3), HA 100, HA 200 and aluminium. The phantom was scanned on 13 CBCT devices and 1 MSCT device. Correlation between CBCT grey values and CT numbers was calculated, and the average error of the CBCT values was estimated in the medium-density range after recalibration. RESULTS Pearson correlation coefficients ranged between 0.7014 and 0.9996 in the full-density range and between 0.5620 and 0.9991 in the medium-density range. The average error of CBCT voxel values in the medium-density range was between 35 and 1562. CONCLUSION Even though most CBCT devices showed a good overall correlation with CT numbers, large errors can be seen when using the grey values in a quantitative way. Although it could be possible to obtain pseudo-Hounsfield units from certain CBCTs, alternative methods of assessing bone tissue should be further investigated. ADVANCES IN KNOWLEDGE The suitability of dental CBCT for density estimations was assessed, involving a large number of devices and protocols. The possibility for grey value calibration was thoroughly investigated.

The use of cone beam computed tomography in endodontics

Introduction The American Association of Endodontists and the American Academy of Oral and Maxillofacial Radiology have jointly developed this position statement. It is intended to provide scientifically based guidance to clinicians regarding the use of cone-beam-computed tomography in endodontic treatment as an adjunct to planar imaging. This document will be periodically revised to reflect new evidence.