Effective dose of dental CBCT-a meta analysis of published data and additional data for nine CBCT units.

OBJECTIVES: This article analyses dose measurement and effective dose estimation of dental CBCT examinations. Challenges to accurate calculation of dose are discussed and the use of dose-height product (DHP) as an alternative to dose-area product (DAP) is explored. METHODS: The English literature on effective dose was reviewed. Data from these studies together with additional data for nine CBCT units were analysed. Descriptive statistics, ANOVA and paired analysis are used to characterize the data. RESULTS: PubMed and EMBASE searches yielded 519 and 743 publications, respectively, which were reduced to 20 following review. Reported adult effective doses for any protocol ranged from 46 to 1073 µSv for large fields of view (FOVs), 9-560 µSv for medium FOVs and 5-652 µSv for small FOVs. Child effective doses from any protocol ranged from 13 to 769 µSv for large or medium FOVs and 7-521 µSv for small FOVs. Effective doses from standard or default exposure protocols were available for 167 adult and 52 child exposures. Mean adult effective doses grouped by FOV size were 212 µSv (large), 177 µSv (medium) and 84 µSv (small). Mean child doses were 175 µSv (combined large and medium) and 103 µSv (small). Large differences were seen between different CBCT units. Additional low-dose and high-definition protocols available for many units extend the range of doses. DHP was found to reduce average absolute error for calculation of dose by 45% in comparison with DAP. CONCLUSIONS: Large exposure ranges make CBCT doses difficult to generalize. Use of DHP as a metric for estimating effective dose warrants further investigation.

3D osteoarthritic changes in TMJ condylar morphology correlates with specific systemic and local biomarkers of disease.

OBJECTIVE: To assess 3D morphological variations and local and systemic biomarker profiles in subjects with a diagnosis of temporomandibular joint osteoarthritis (TMJ OA). DESIGN: Twenty-eight patients with long-term TMJ OA (39.9 ± 16 years), 12 patients at initial diagnosis of OA (47.4 ± 16.1 years), and 12 healthy controls (41.8 ± 12.2 years) were recruited. All patients were female and had cone beam CT scans taken. TMJ arthrocentesis and venipuncture were performed on 12 OA and 12 age-matched healthy controls. Serum and synovial fluid levels of 50 biomarkers of arthritic inflammation were quantified by protein microarrays. Shape Analysis MANCOVA tested statistical correlations between biomarker levels and variations in condylar morphology. RESULTS: Compared with healthy controls, the OA average condyle was significantly smaller in all dimensions except its anterior surface, with areas indicative of bone resorption along the articular surface, particularly in the lateral pole. Synovial fluid levels of ANG, GDF15, TIMP-1, CXCL16, MMP-3 and MMP-7 were significantly correlated with bone apposition of the condylar anterior surface. Serum levels of ENA-78, MMP-3, PAI-1, VE-Cadherin, VEGF, GM-CSF, TGFßb1, IFNγg, TNFαa, IL-1αa, and IL-6 were significantly correlated with flattening of the lateral pole. Expression levels of ANG were significantly correlated with the articular morphology in healthy controls. CONCLUSIONS: Bone resorption at the articular surface, particularly at the lateral pole was statistically significant at initial diagnosis of TMJ OA. Synovial fluid levels of ANG, GDF15, TIMP-1, CXCL16, MMP-3 and MMP-7 were correlated with bone apposition. Serum levels of ENA-78, MMP-3, PAI-1, VE-Cadherin, VEGF, GM-CSF, TGFß1, IFNγ, TNFα, IL-1α, and IL-6 were correlated with bone resorption.

Triaging pregnancies of unknown location: the performance of protocols based on single serum progesterone or repeated serum hCG levels.

STUDY QUESTION: How does a protocol based on a single serum progesterone measurement perform as a triage tool in women with pregnancy of unknown location (PUL) in comparison to protocols based on serial hCG measurement? SUMMARY ANSWER: Triage based on the logistic regression model M4 (using initial hCG and hCG ratio (48 h/0 h)) classifies the majority of PUL into low and high risk groups, in contrast to a progesterone protocol based on a serum level threshold of 10 nmol/l. WHAT IS KNOWN ALREADY: Low progesterone has been shown to identify failing pregnancies and those at low risk of complications. A prediction model (M4) based on the initial hCG and the hCG ratio at 0 and 48 h can successfully classify PUL into low and high risk groups. STUDY DESIGN, SIZE AND DURATION: A multi-centre diagnostic accuracy study of 1271 women was performed retrospectively on data from women at St. George's Hospital (SGH, London, UK) between February 2005 and 2006, Queen Charlottes & Chelsea Hospital (QCCH, London, UK) between April 2009 and August 2012, and the Royal Prince Alfred Hospital (RPAH, Sydney, Australia) between February 2008 and October 2011. The end-points were the final observed outcome for each pregnancy as a failed PUL (low risk), intrauterine pregnancy (IUP, low risk), or ectopic pregnancy (EP, high risk), and any interventions or complications for EP during the follow-up period. PARTICIPANTS/MATERIALS, SETTING AND METHODS: Complete data were available for initial progesterone, 0/48 h hCG and final outcome in 431 of 534 women (81%) at SGH, 396/585 (68%) at QCCH and 96/152 (63%) at RPAH. Missing values were handled using multiple imputation. Three diagnostic approaches were used to classify PUL as high risk: a range of serum progesterone levels were evaluated (>10, 16 and 20 nmol/l) for the progesterone protocol, risk of EP given by the M4 model ≥5% for the M4-based protocol, and hCG ratio was between 0.87 and 1.66 for hCG cut-offs as previously published. Results were analysed using random intercept models or stratified analysis to account for variability between centres. MAIN RESULTS AND THE ROLE OF CHANCE: The progesterone protocol based on levels of >10 nmol/l classified 24% (95% confidence interval 20-28%) of failed PUL, 95% (92-97%) of IUP and 76% (67-83%) of EP as high risk. The M4 protocol classified 14% (11-17%) of failed PUL, 37% (31-43%) of IUP and 84% (76-90%) of EP as high risk. The hCG ratio cut-offs classified 10% (8-12%) of failed PUL, 15% (11-20%) of IUP and 63% (53-71%) of EP as high risk. Using complete cases only, 67% of EP treated with methotrexate (n = 48) and 89% surgically managed (n = 37) were correctly classified by the progesterone protocol, 96 and 81% by M4 protocol and 75 and 65% by hCG ratio cut offs, respectively. LIMITATIONS, REASONS FOR CAUTION: Data were incomplete for 103 (19%), 189 (32%) and 56 (37%) patients at SGH, QCCH and RPAH, respectively; however, we are reassured by the minimal differences seen between the results of complete cases and those following imputation of missing values. The variation in the inclusion criteria between the three centres is also a potential limitation of this study; however, it reflects real clinical practice. Furthermore, the hCG ratio cut-offs were not originally developed to optimize triage. WIDER IMPLICATIONS OF THE FINDINGS: The results show that serum progesterone is less efficient for triage than serial hCG measurements assessed using the M4 model, the striking difference being serum progesterone places nearly all IUP in the high-risk category. A two-step strategy combining single-visit and two-visit approaches should be investigated. STUDY FUNDING/COMPETING INTERESTS: Funding was from Research Foundation-Flanders (FWO). There are no competing interests.

The prediction of pouch of Douglas obliteration using offline analysis of the transvaginal ultrasound 'sliding sign' technique: inter- and intra-observer reproducibility.

STUDY QUESTION: What is the inter-/intra-observer agreement and diagnostic accuracy among gynaecological and non-gynaecological ultrasound specialists in the prediction of pouch of Douglas (POD) obliteration (secondary to endometriosis) at offline analysis of two-dimensional videos using the dynamic real-time transvaginal ultrasound (TVS) 'sliding sign' technique? SUMMARY ANSWER: The inter-/intra-observer agreement and diagnostic accuracy for the interpretation of the TVS 'sliding sign' in the prediction of POD obliteration was found to be very acceptable, ranging from substantial to almost perfect agreement for the observers who specialized in gynaecological ultrasound. WHAT IS KNOWN ALREADY: Women with POD obliteration at laparoscopy are at an increased risk of bowel endometriosis; therefore, the pre-operative diagnosis of POD obliteration is important in the surgical planning for these women. Previous studies have used TVS to predict POD obliteration prior to laparoscopy, with a sensitivity of 72-83% and specificity of 97-100%. However, there have not been any reproducibility studies performed to validate the use of TVS in the prediction of POD obliteration pre-operatively. STUDY DESIGN, SIZE, DURATION: This was a reproducibility study which involved the offline viewing of pre-recorded video sets of 30 women presenting with chronic pelvic pain, in order to determine POD obliteration using the TVS 'sliding sign' technique. The videos were selected on real-time representative quality/quantity; they were not obtained from sequential patients. There were a total of six observers, including four gynaecological ultrasound specialists and two fetal medicine specialists. The study was conducted over a period of 1 month (March 2012-April 2012). PARTICIPANTS/MATERIALS, SETTING, METHODS: The four gynaecological ultrasound observers performed daily gynaecological scanning, while the other two observers were primarily fetal medicine sonologists. Each sonologist viewed the TVS 'sliding sign' video in two anatomical locations (retro-cervix and posterior uterine fundus), i.e. 60 videos in total. The POD was deemed not obliterated, if 'sliding sign' was positive in both anatomical locations (i.e. anterior rectum/rectosigmoid glided smoothly across the retro-cervix/posterior fundus, respectively). If the 'sliding sign' was negative (i.e. anterior rectum/rectosigmoid did not glide smoothly over retro-cervix/posterior fundal region, respectively), the POD was deemed obliterated. Diagnostic accuracy and inter-observer agreement among the six sonologists was evaluated. The same sonologist was also asked to reanalyse the same videos, albeit in a different order, at least 7 days later to assess for intra-observer agreement. A separate analysis of the inter- and intra-observer correlation was also performed to determine the agreement among the four observers who specialized in gynaecological ultrasound. Cohen's κ coefficient <0 meant that there was poor agreement, 0.01-0.20 slight agreement, 0.21-0.40 fair agreement, 0.41-0.60 moderate agreement, 0.61-0.80 substantial agreement and 0.81-0.99 almost perfect agreement. MAIN RESULTS AND THE ROLE OF CHANCE: Agreement (Cohen's κ) between all six observers for the interpretation of the 'sliding sign' for both sets of videos in both regions (retro-cervix and fundus) ranged from 0.354 to 0.927 (fair agreement to almost perfect agreement) compared with 0.630-0.927 (substantial agreement to almost perfect agreement) when only the gynaecological sonologists were included. The overall multiple rater agreement for the interpretation of the 'sliding sign' for both video sets and both regions was Fleiss' κ 0.454 (P-value <0.01) for all six observers and 0.646 (P-value <0.01) for the four gynaecological ultrasound specialists. The multiple rater agreement for all six or all four observers was higher for the retro-cervical region versus the fundal region (Fleiss' κ 0.542 versus 0.370 and 0.732 versus 0.560, respectively). The intra-observer agreement among the six observers for the interpretation of the 'sliding sign' and prediction of POD obliteration ranged from Cohen's κ 0.60-0.95 and 0.46-1.0 (P-value <0.01), respectively. After excluding the fetal medicine specialists, the intra-observer agreement for the interpretation of the 'sliding sign' and the prediction of POD obliteration ranged from Cohen's κ 0.71-0.95 and 0.67-1.0, respectively, indicating substantial to almost perfect agreement. When comparing the four gynaecological observers for the prediction of POD obliteration using the TVS 'sliding sign' (after excluding cases with the POD outcome classified as 'unsure' by the observers), the results for accuracy, sensitivity, specificity, positive and negative predictive value were 93.1-100, 92.9-100, 90.9-100, 77.8-100 and 97.7-100%, respectively. LIMITATIONS, REASONS FOR CAUTION: The 'gold standard' for the diagnosis of POD obliteration is laparoscopy; however, laparoscopic data were available only for 24 out of 30 (80%) TVS 'sliding sign' cases included in this study. Although this should not affect the inter- and intra-observer agreement findings, the ability to draw conclusions regarding the diagnostic accuracy of the TVS 'sliding sign' in the prediction of POD obliteration is somewhat limited. In addition, the diagnostic accuracy findings should be interpreted with the caveat that the cases classified as 'unsure' for the prediction of POD obliteration were excluded from the analysis. WIDER IMPLICATIONS OF THE FINDINGS: We have validated the dynamic real-time TVS 'sliding sign' technique for the prediction of POD obliteration, and this simple ultrasound-based test appears to have very acceptable inter-/intra-observer agreement for those who are experienced in gynaecological ultrasound. Given that women with POD obliteration at laparoscopy have an increased risk of bowel endometriosis and requirement for bowel surgery, the TVS 'sliding sign' test should be considered in the pre-operative imaging work-up for all women with suspected endometriosis, to allow for appropriate surgical planning. We believe the TVS 'sliding sign' technique may be easily learned by sonologists/sonographers who are familiar with performing gynaecological ultrasound, and that further studies are required to confirm the diagnostic accuracy of this new ultrasound technique amongst sonologists/sonographers with various levels of experience. STUDY FUNDING/COMPETING INTEREST(S): This study received no specific grant from any funding agency in the public, commercial or not-for-profit sectors and the authors declare no competing interests.

Correlating cone beam CT results with temporomandibular joint pain of osteoarthritic origin.

OBJECTIVES: The purpose of this study was to determine whether bony changes in temporomandibular joint (TMJ) osteoarthritis (OA) is correlated with pain and other clinical signs and symptoms. METHODS: Clinical data and cone beam CT (CBCT) images of 30 patients with TMJ OA were analysed. The criteria of Koyama et al (Koyama J, Nishiyama H, Hayashi T. Follow-up study of condylar bony changes using helical computed tomography in patients with temporomandibular disorder. Dentomaxillofac Radiol 2007; 36: 472-477.) and Ahmad et al [Ahmad M, Hollender L, Anderson Q, Kartha K, Ohrbach R, Truelove EL, et al. Research diagnostic criteria for temporomandibular disorders (RDC/TMD): development of image analysis criteria and examiner reliability for image analysis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009; 107: 844-860.] were used to classify the condyles observed on the CBCT. Clinical measures included self-reported pain, mandibular range of motion, TMJ sound, pain on palpation of the TMJ and masticatory muscles, and pain on jaw function. Generalized linear modelling was used to correlate the clinical and radiographic findings and Spearman's rho was used to correlate the two classification systems. RESULTS: There was poor correlation between the maximum condyle change and pain rating (Koyama: r² = 0.1443, p = 0.3995; Ahmad: r² = 0.0273, p = 0.9490), maximum mouth opening (Koyama: r² = 0.2910, p = 0.0629; Ahmad: r² = 0.2626, p = 0.0951), protrusion (Koyama: r² = 0.0875, p = 0.7001; Ahmad: r² = 0.1658, p = 0.3612), right lateral motion (Koyama: r² = 0.0394, p = 0.9093; Ahmad: r² = 0.0866, p = 0.6877) and left lateral motion (Koyama: r² = 0.0943, p = 0.6494; Ahmad: r² = 0.1704, p = 0.3236). Strong correlation was observed between Koyama et al's and Ahmad et al's classifications for average (r = 0.9216, p < 0.001) and maximum (r = 0.7694; p < 0.0001) bony change. CONCLUSIONS: There was poor correlation between condylar changes (as observed on CBCT images), pain and other clinical signs and symptoms in TMJ OA.

Comparison of two methods for quantitative assessment of mandibular asymmetry using cone beam computed tomography image volumes.

OBJECTIVES: The aim of this study was to compare two methods of measuring mandibular asymmetry. The first method uses mirroring of the mandible in the midsagittal plane; the second uses mirroring of the mandible and registration on the cranial base. METHODS: Surface models were constructed from cone beam CT (CBCT) scans of 50 patients with asymmetry. For the first approach, a midsagittal plane was defined for each patient as the plane passing through nasion, anterior nasal spine and basion. Mirrors for both halves of the mandible were created. The second approach consisted of mirroring the image volume by flipping the left and right sides and then registering the mirrored image onto the cranial base using a mutual information maximization method. Surface distances between hemimandibles and mirrors were calculated for nine regions. RESULTS: There was no statistically significant difference between the mean surface distance measurements obtained with the two approaches and when comparing both halves in most areas. CONCLUSION: Both mirroring techniques provided similar quantification of mandibular asymmetry in this cohort.

A manufacturer's role in reducing the dose of cone beam computed tomography examinations: effect of beam filtration.

OBJECTIVES: The dosimetry of the Kodak 9500 cone beam CT (CBCT) unit (Carestream Health, Rochester, NY) was measured before and after installation of copper filtration. METHODS: Dosimetry of a pre-production Kodak 9500 CBCT unit was compared with a current production unit with 0.4 mm of added filtration and increased kVp. Thermoluminescent dosimeter 100 chips were placed at 24 locations in a RANDO (radiation analogue dosimetry) head phantom (Nuclear Associates, Hicksville, NY). Small, medium and large adult default exposure settings were used in separate dosimeter runs for large and medium field of view (FOV) examinations with both units. Equivalent dose and effective dose were calculated using International Commission on Radiological Protection (ICRP) 1990 and 2007 tissue weights. RESULTS: Estimations of risk using 2007 ICRP calculations increased by an average of 77% for large FOV scans and 125% for the medium FOV scans in comparison with 1990 calculations. With added filtration, effective dose for medium FOV examinations for default settings were: small adult 76 µSv, medium adult 98 µSv, and large adult 166 µSv. Effective doses for large FOV examinations were: small adult 93 µSv, medium adult 163 µSv, and large adult 260 µSv. Effective dose was reduced by an average of 43% in examinations made with increased filtration and adjusted kVp. CONCLUSION: The manufacturer's installation of additional filtration with the adjustment of kVp in the Kodak 9500 CBCT unit resulted in significant patient dose reductions for examinations at all adult default settings.

Quantification of condylar resorption in temporomandibular joint osteoarthritis.

OBJECTIVE: This study was performed to determine the condylar morphologic variation of osteoarthritic (OA) and asymptomatic temporomandibular joints (TMJs) and to determine its correlation with pain intensity and duration. STUDY DESIGN: Three-dimensional surface models of mandibular condyles were constructed from cone-beam computerized tomography images of 29 female patients with TMJ OA (Research Diagnostic Criteria for Temporomandibular Disorders group III) and 36 female asymptomatic subjects. Shape correspondence was used to localize and quantify the condylar morphology. Statistical analysis was performed with multivariate analysis of covariance analysis, using Hotelling T(2) metric based on covariance matrices, and Pearson correlation. RESULTS: The OA condylar morphology was statistically significantly different from the asymptomatic condyles (P < .05). Three-dimensional morphologic variation of the OA condyles was significantly correlated with pain intensity and duration. CONCLUSION: Three-dimensional quantification of condylar morphology revealed profound differences between OA and asymptomatic condyles, and the extent of the resorptive changes paralleled pain severity and duration.

Vaginal delivery compared with elective caesarean section: the views of pregnant women and clinicians.

OBJECTIVE: To quantify the risk of morbidity from vaginal delivery (VD) that pregnant women would be prepared to accept before requesting an elective caesarean section and to compare these views with those of clinicians. DESIGN: Cross-sectional survey. SETTING: Major teaching hospital (nulliparas and midwives) and national samples of medical specialists. SAMPLE: Nulliparas (n = 122), midwives (n = 84), obstetricians (n = 166), urogynaecologists (n = 12) and colorectal surgeons (n = 79). METHODS: Face-to-face interviews (nulliparas) and mailed questionnaire (clinicians). MAIN OUTCOME MEASURES: Maximum level of risk participants would be prepared to accept before opting for an elective caesarean section for each of 17 potential complications of VD. Utility scores for each complication were calculated with higher scores (closer to 1) indicating a greater acceptance of risk. RESULTS: Pregnant women were willing to accept higher risks than clinicians for all 17 potential complications. They were least accepting of the risks of severe anal incontinence (mean utility score 0.32), emergency caesarean section (0.51), moderate anal incontinence (0.56), severe urinary incontinence (0.56), fourth-degree tears (0.59) and third-degree tears (0.72). The views of midwives were closest to those of pregnant women. Urogynaecologists and colorectal surgeons were the most risk averse, with 42 and 41%, respectively, stating that they would request an elective caesarean for themselves or their partners. CONCLUSIONS: Pregnant women were willing to accept significantly higher risks of potential complications of VD than clinicians involved in their care. Pregnant women's views were more closely aligned to midwives than to medical specialists.

Drug abuse and dependency during pregnancy: anaesthetic issues.

Drug abuse is a significant social problem that can lead to serious obstetric complications, some of which may be confused with pregnancy-related disease states. Substance abuse poses a number of challenges with respect to the management of pain and the conduct of anaesthesia in the peripartum period. This review was based on information from a literature search of epidemiological, research and review papers on substance abuse during pregnancy, obtained for the purpose of preparing a background paper for the Ministerial Council on Drug Strategy, Commonwealth Government of Australia. Given that almost 80% of substance-abusing parturients require anaesthetic services in the perinatal period, early antenatal referral for anaesthetic review is recommended. To optimise the care of these vulnerable patients, obstetricians, general practitioners and midwives should attempt to identify substance-abusing parturients and refer them to an anaesthetist. A careful anaesthetic evaluation with non-judgemental questioning is essential, with management tailored to individual patient needs and the urgency of obstetric intervention for vaginal delivery or caesarean section. Opioid-dependent women, in particular, benefit from antenatal pain management planning. Patients recovering from drug addiction should also have a well-documented analgesic strategy. A multidisciplinary approach will involve obstetricians, anaesthetists and staff of the Drug and Alcohol Service. In acute admissions of women by whom antenatal care was not accessed, a high index of suspicion for illicit drug use should arise. Because illicit substance use is so prevalent, if untoward reactions occur during an otherwise uneventful anaesthetic, the possibility of drug abuse should be considered.

Comparison of conventional and cone beam CT synthesized cephalograms.

OBJECTIVES: To compare cephalometric measurements from synthesized cone beam CT (CBCT) lateral cephalograms using orthogonal and perspective projections with those from conventional cephalometric radiographs and dry skulls. METHODS: Ten skulls were imaged using CBCT and conventional cephalometry. CBCT volume data were exported in DICOM format and imported in Dolphin 3D (pre-release version). Orthogonal and perspective lateral cephalometric radiographs were created from 3D virtual models. Nine linear and five angular measurements were made in Dolphin at three different times. Three calliper measures of midsagittal landmarks were made directly onto skulls. Perspective and conventional image measurements were corrected for known magnification. Reproducibility of measurements was assessed using multivariate analysis of variance (MANOVA). Linear and angular measurements were compared between image modalities by measurement using a repeated measures MANOVA model. Differences and absolute value of differences between image measurements and skull measurements were assessed using analysis of variance (ANOVA). RESULTS: Measurements were not different between the imaging modalities (P>0.05), except for the mandibular unit length (P=0.01). Linear midsagittal measurements were significantly greater than skull measurements for perspective CBCT and significantly less than skull measurements for conventional images (P=0.003). Precision of orthogonal CBCT midsagittal linear measurements was significantly better than the other modalities (P=0.007). Orthogonal CBCT projections provided more accurate midsagittal skull measurements than perspective CBCT or conventional cephalometric radiographs. CONCLUSIONS: CBCT can reproduce conventional cephalometric geometry with similar precision and accuracy. Orthogonal CBCT projections provided greater accuracy of measurement for midsagittal plane dimensions than perspective CBCT or conventional cephalometric images.

Quantum chaos and fluctuations in isolated nuclear-spin systems.

Using numerical simulations we investigate dynamical quantum chaos in isolated nuclear spin systems. We determine the structure of quantum states, investigate the validity of the Curie law for magnetic susceptibility and find the spectrum of magnetic noise. The spectrum is the same for positive and negative temperatures. The study is motivated by recent interest in condensed-matter experiments for searches of fundamental parity- and time-reversal-invariance violations. In these experiments nuclear spins are cooled down to microkelvin temperatures and are completely decoupled from their surroundings. A limitation on statistical sensitivity of the experiments arises from the magnetic noise.

Dosimetry of 3 CBCT devices for oral and maxillofacial radiology: CB Mercuray, NewTom 3G and i-CAT.

OBJECTIVES: Cone beam computed tomography (CBCT), which provides a lower dose, lower cost alternative to conventional CT, is being used with increasing frequency in the practice of oral and maxillofacial radiology. This study provides comparative measurements of effective dose for three commercially available, large (12'') field-of-view (FOV), CBCT units: CB Mercuray, NewTom 3G and i-CAT. METHODS: Thermoluminescent dosemeters (TLDs) were placed at 24 sites throughout the layers of the head and neck of a tissue-equivalent human skull RANDO phantom. Depending on availability, the 12'' FOV and smaller FOV scanning modes were used with similar phantom positioning geometry for each CBCT unit. Radiation weighted doses to individual organs were summed using 1990 (E(1990)) and proposed 2005 (E(2005 draft)) ICRP tissue weighting factors to calculate two measures of whole-body effective dose. Dose as a multiple of a representative panoramic radiography dose was also calculated. RESULTS: For repeated runs dosimetry was generally reproducible within 2.5%. Calculated doses in microSv [corrected] (E(1990), E(2005 draft)) were NewTom3G (45, 59), i-CAT (135, 193) and CB Mercuray (477, 558). These are 4 to 42 times greater than comparable panoramic examination doses (6.3 microSv [corrected] 13.3 mSv). Reductions in dose were seen with reduction in field size and mA and kV technique factors. CONCLUSIONS: CBCT dose varies substantially depending on the device, FOV and selected technique factors. Effective dose detriment is several to many times higher than conventional panoramic imaging and an order of magnitude or more less than reported doses for conventional CT.

Accuracy of measurements of mandibular anatomy and prediction of asymmetry in panoramic radiographic images.

OBJECTIVES: Measurements of ideally positioned and systematically mis-positioned skulls were used to evaluate errors in linear measurements and symmetry ratios made with panoramic X-ray images. METHODS: Digital panoramic images of 30 skulls placed in ideal, shifted and rotated positions, were assessed by measuring distances between anatomic points and fiducial references. Differences between photographic measurements (control) and radiographic measurements were compared. Horizontal measurements included a 20 mm wire and the distance from gonion to mental foramen (G-MF). Vertical distances measured included a 40 mm wire, condyle to sigmoid notch length, and condyle to gonion (posterior mandibular height or PMH). A relative symmetry ratio comparing the difference between right and left PMH was also calculated. Distances measured in panoramic images were corrected using the left vertical wire distance or the panoramic unit's stated magnification factor (1.25x). RESULTS: Greatest differences were noted for horizontal measurements and shifted skull positions. Use of an arbitrary magnification correction was consistently less accurate than use of an internal calibration and resulted in general underestimation of actual dimensions. Measures of PMH varied significantly from expected values for each of the three skull positions (P<0.005). Panoramic accuracy for detecting asymmetry was 67% for ideal, 70% for rotated, and 47% for shifted skull positions when an internal reference was used. CONCLUSIONS: Panoramic radiographs should be used with caution in making absolute measurements or relative comparisons. Even when internal fiducial calibration for image distortion of anatomy is used, measurements such as those assessing posterior mandibular facial symmetry may be unreliable.

Speed choice by drivers: the issue of driving too slowly.

Quite correctly, the majority of road safety speeding initiatives focus on drivers travelling at excessive speeds. This study, however, focused on the potential problem of driving too slowly. Six thousand, four hundred and eighty vehicles from around the Perth metropolitan area in Western Australia had their speeds recorded; observations were also made of these vehicles to identify characteristics of the driver and vehicle. In addition, a community survey with 240 members of the public was conducted to examine their attitudes towards slow drivers. As expected, results showed that older drivers drove more slowly than the other age brackets, women drove more slowly than men, and that heavily laden vehicles drove more slowly than other types of vehicles. Additionally, the slowest days were weekdays and the quickest were Saturdays. Community attitudes, generally mirrored the observational findings, and indicated that the public believed that slow driving was sometimes a safety problem causing some accidents. These data are discussed, and some possible countermeasures are briefly introduced to address the problem.

Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and Orthophos Plus DS panoramic unit.

OBJECTIVES: This study provides effective dose measurements for two extraoral direct digital imaging devices, the NewTom 9000 cone beam CT (CBCT) unit and the Orthophos Plus DS panoramic unit. METHODS: Thermoluminescent dosemeters were placed at 20 sites throughout the layers of the head and neck of a tissue-equivalent RANDO phantom. Variations in phantom orientation and beam collimation were used to create three different CBCT examination techniques: a combined maxillary and mandibular scan (Max/Man), a maxillary scan and a mandibular scan. Ten exposures for each technique were used to ensure a reliable measure of radiation from the dosemeters. Average tissue-absorbed dose, weighted equivalent dose and effective dose were calculated for each major anatomical site. Effective doses of individual organs were summed with salivary gland exposures (E(SAL)) and without salivary gland exposures (E(ICRP60)) to calculate two measures of whole-body effective dose. RESULTS: The effective doses for CBCT were: Max/Man scan, E(ICRP60)=36.3 micro Sv, E(SAL)=77.9 micro Sv; maxillary scan, E(ICRP60)=19.9 micro Sv, E(SAL)=41.5 micro Sv; and mandibular scan, E(ICRP60)=34.7 micro Sv, E(SAL)=74.7 micro Sv. Effective doses for the panoramic examination were E(ICRP60)=6.2 micro Sv and E(SAL)=22.0 micro Sv. CONCLUSION: When viewed in the context of potential diagnostic yield, the E(ICRP60) of 36.3 micro Sv for the NewTom compares favourably with published effective doses for conventional CT (314 micro Sv) and film tomography (2-9 micro Sv per image). CBCT examinations resulted in doses that were 3-7 (E(ICRP60)) and 2-4 (E(SAL)) times the panoramic doses observed in this study.

Effect of data compression on proximal caries detection: observer performance with DenOptix photostimulable phosphor images.

OBJECTIVES: To study the effect of lossy image compression on caries detection. Null hypothesis states no difference in caries detection efficacy among observers using original digital images versus images compressed at various rates of compression. METHODS: Digital images of 41 extracted posterior teeth were obtained with a storage phosphor DenOptix (Gendex DenOptix Imaging system) system. Images were exported in Tagged Image File Format (TIFF) and compressed with Joint Photographic Experts Group File Interchange Format (JFIF), as provided by the software of the imaging system. The compressions options JFIF100%, JFIF75% and JFIF50% resulted in reducing the image size to 1:2, 1:11 and 1:16, respectively. Eight observers evaluated the presence or absence of caries on a 5-point confidence scale. The actual caries status of each proximal surface was determined by ground section histology. Responses were evaluated by receiver operating characteristic (ROC) analysis. Areas under the curves (Az) were assessed using analysis of variance (ANOVA). RESULTS: The mean Az scores were 0.85 for original/uncompressed images, and 0.89 for JFIF100%, 0.88 for JFIF75% and 0.88 for JFIF50% images. These differences were not statistically significant (P = 0.26). Differences between observers were also not statistically significant (P = 0.12). CONCLUSIONS: JFIF compression at the level of 1:16 can be used without significant deterioration in diagnostic accuracy for proximal caries detection.

Enhancement of positron-atom annihilation near the positronium formation threshold.

The behavior of the positron- 2 gamma annihilation rate on an atomic target near the positronium (Ps) formation threshold is determined. When the positron energy epsilon approaches the threshold epsilon(thr) from below, the effective number of electrons contributing to the annihilation, Z(eff), grows as Z(eff) approximately A/square root of [epsilon(thr)-epsilon], where A is related to the size of the Ps formation cross section, sigma(Ps) approximately B square root of [epsilon-epsilon(thr)], by A = B square root of [2 epsilon(thr)]/32 pi (in atomic units). Taking account of the finite Ps lifetime eliminates the singularity in Z(eff) and shows that close to threshold the positron annihilation cross section is identical to the para-Ps formation cross section.

Influence of the number of basis images and projection array on caries detection using tuned aperture computed tomography (TACT).

OBJECTIVES: to determine if the number of basis images and spatial distribution of the projection array used for TACT slice generation influence observer performance in caries detection. METHODS: In the first experiment, 2, 4, 8 and 12 basis projections of each of 40 teeth were acquired using a CMOS digital radiography sensor. Projections were distributed radially in space using a 20 degree angular disparity. TACT slices were generated from the four subgroups of images, presented to eight observers, and viewed on a high-resolution monitor. Observers scored the presence/absence of caries using a 5-point confidence scale. Gold standard was histological examination of tooth sections. ROC curves measured observer diagnostic performance. ANOVA tested for significant differences between observers and experimental conditions. In the second experiment, the number of basis projections judged to be satisfactory for TACT slice generation was used. Horizontal and vertical linear arrays of projections were compared to the circular projection array. RESULTS: There was a statistically significant difference between the numbers of basis projections in the detection of both occlusal (P=0.006) and proximal caries (P=0.005). No significant difference was found between projection arrays in the detection of either occlusal (P=0.065) or proximal (P=0.515) caries. CONCLUSIONS: The number of TACT basis projections significantly influences caries detection. Eight or more images should be used. Either linear-vertical, linear-horizontal or circular arrays of basis projections may be used for TACT slice generation in caries detection tasks.