Soft tissue coverage on the segmentation accuracy of the 3D surface-rendered model from cone-beam CT.

OBJECTIVES: The aim of this study is to investigate the effect of soft tissue presence on the segmentation accuracy of the 3D hard tissue models from cone-beam computed tomography (CBCT). MATERIALS AND METHODS: Seven pairs of CBCT Digital Imaging and Communication in Medicine (DICOM) datasets, containing data of human cadaver heads and their respective dry skulls, were used. The effect of the soft tissue presence on the accuracy of the segmented models was evaluated by performing linear and angular measurements and by superimposition and color mapping of the surface discrepancies after splitting the mandible and maxillo-facial complex in the midsagittal plane. RESULTS: The linear and angular measurements showed significant differences for the more posterior transversal measurements on the mandible (p < 0.01). By splitting and superimposing the maxillo-facial complex, the mean root-mean-square error (RMSE) as a measurement of inaccuracy decreased insignificantly from 0.936 to 0.922 mm (p > 0.05). The RMSE value for the mandible, however, significantly decreased from 1.240 to 0.981 mm after splitting (p < 0.01). CONCLUSIONS: The soft tissue presence seems to affect the accuracy of the 3D hard tissue model obtained from a cone-beam CT, below a generally accepted level of clinical significance of 1 mm. However, this level of accuracy may not meet the requirement for applications where high precision is paramount. CLINICAL RELEVANCE: Accuracy of CBCT-based 3D surface-rendered models, especially of the hard tissues, are crucial in several dental and medical applications, such as implant planning and virtual surgical planning on patients undergoing orthognathic and navigational surgeries. When used in applications where high precision is paramount, the effect of soft tissue presence should be taken into consideration during the segmentation process.

Justification and good practice in using handheld portable dental X-ray equipment: a position paper prepared by the European Academy of DentoMaxilloFacial Radiology (EADMFR).

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).

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.

Diagnostic performance of the visual caries classification system ICDAS II versus radiography and micro-computed tomography for proximal caries detection: an in vitro study.

OBJECTIVES: The purpose of this study was: (a) to compare the visual caries classification system ICDAS II with conventional (CR) and digital radiography (DR) for diagnosis of non-cavitated caries on free proximal surfaces, (b) to examine the potential of micro-computed tomography (MCT) to substitute histological examination for the in vitro caries assessment. METHODS: Both proximal surfaces of 20 teeth received classification separately by two examiners by means of the diagnostic modalities examined. The teeth were sectioned and assessed for depth of the lesion. The modalities were compared in terms of degree of inter-examiner agreement, sensitivity, specificity, accuracy, positive and negative predictive value and validity. Two diagnostic thresholds were applied: no caries versus all caries scores (D1), and no dentin caries versus dentin caries (D3). RESULTS: The weighted kappa values for inter-examiner reproducibility for all diagnostic modalities were 0.51-0.81. Visual examination (ICDAS II) reached significant higher sensitivity (0.92-0.96) and negative predictive value (0.9-1) than radiography. Likewise, the radiographic modalities presented significantly higher specificity (0.93-1) and positive predictive values (0.92-1) than the ICDAS II criteria. The overall accuracy performance of radiographic modalities was related to the diagnostic threshold. MCT did not agree with histological validation at each disease severity scale. CONCLUSIONS: The ICDAS II criteria are a promising tool for caries diagnosis on free proximal surfaces. DR and CR radiography present comparable performance. Furthermore, MCT is not capable of constituting a reliable alternative to histological examination for caries research.

Radiographic examination of the temporomandibular joint using cone beam computed tomography.

Cone beam CT (CBCT) is a new technique for maxillofacial imaging. We describe a reconstruction technique for radiographic examination of the temporomandibular joint (TMJ) using CBCT, and we further present four cases where the technique was employed. The technique provides a complete radiographic investigation of the bony components of the TMJ. The reconstructed images are of high diagnostic quality. The examination time is shorter and the patient dose is lower than that with conventional CT. It may therefore be considered as the imaging technique of choice when investigation of bony changes of the TMJ is the task at hand.

Physical properties of a photostimulable phosphor system for intra-oral radiography.

OBJECTIVES: To determine physical properties of the Digora digital intra-oral radiographic system (Soredex Orion Corporation, Helsinki, Finland) for different calibration settings and beam energies. METHODS: The line spread function (LSF) and the modulation transfer function (MTF) were determined from radiographs of a slit. Noise power spectra (NPS) were determined from radiographs exposed to homogeneous radiation fields at 10, 50 and 100% of the calibration exposure for three tube potentials. All calculations were performed using relative values of exposure comprised of gray level, the signal at the photomultiplier tube and the amplified signal in order to confirm agreement between these different approaches. Noise equivalent quanta (NEQ) were calculated from the one-dimensional NPSs and the MTF. Detective quantum efficiencies (DQE) were determined from the NEQs and representative values of the photon fluence. Signal-to-noise ratios (SNR) were calculated for different signal contrasts applying the NEQs. RESULTS: The MTF of the system exhibited typical characteristics and falls to a value close to zero at the Nyquist frequency of about 7 cycles/mm. Noise as expressed by the NPS was found to be relatively low, i.e. about 10(-5) to 10(-6) mm2 depending on exposure and frequency. There was no significant difference between data obtained at different beam energies. The NEQ and hence the DQE were relatively high. DQE decreased with increased exposure. For exposures in the clinical range of the DQE reached a peak value of about 25%. SNRs are favorable. CONCLUSION: The physical properties of the Digora intra-oral system indicate that it is suitable for digital intra-oral radiography.

A simplified method to obtain perceptibility curves for direct dental digital radiography.

OBJECTIVES: To derive and test a simplified method to construct Perceptibility Curves (PCs) for dental digital detectors. METHODS: Mathematical expressions were derived to make it possible to construct PCs from viewer data obtained at two exposures, one low and one high. PCs were constructed applying these expressions and compared with data previously obtained employing the conventional method. RESULTS: PCs constructed according to the simplified method agree extremely well with conventionally obtained data. CONCLUSIONS: Reliable PCs may be constructed according to the simplified method.

Dose response of a storage phosphor system for intraoral radiography.

OBJECTIVES: To determine the dose response function for the Digora(R) (Soredex Orion Corporation, Helsinki, Finland) storage phosphor system for intra-oral radiography. METHODS: Specially designed software provided by the manufacturer was used to register data from the pre-scanning that takes place prior to readout. These data contain information about the signal from the photomultiplier and the amplification that forms the basis for the AD conversion to 8 bit image data. Dose response functions were determined for different calibration settings and also combined into one single function. RESULTS: The dose response function is linear irrespective of calibration. The gray levels of the final radiographs are directly proportional to the amplified signal. The Digora(R) does not fully compensate for exposure differences. Increased exposure results in slightly darker radiographs. CONCLUSIONS: Since the gray levels of the final radiographs are directly proportional to the amplified signal, the gray levels may be used as a relative measure of the exposure in the Digora(R) system provided that they are subtracted from the maximum value of 255.

Physical evaluation of a system for direct digital intra-oral radiography based on a charge-coupled device.

OBJECTIVES: To determine technical properties of a direct digital intra-oral radiographic system, the Dixel(R) (J Morita Corporation, Kyoto, Japan). METHODS: A dose response function and the dark current were calculated from two series of exposures to a homogeneous radiation field. The line spread function (LSF) and the modulation transfer function (MTF) were determined from radiographs of an edge. The noise power spectrum (NPS) was determined at three exposures from radiographs exposed to homogeneous radiation fields. Noise equivalent quanta (NEQ) were calculated from the one-dimensional NPS and the MTF. The detective quantum efficiency (DQE) was determined from the NEQ and a representative value of the photon fluence. Signal-to-noise ratios (SNR) were calculated from the NEQs and different signal contrasts. RESULTS: The dose response function demonstrated a slight curvature. There was no effect of the dark current. NPS ranged from 10-5 - 10-7 mm2 depending on exposure and frequency. At a peak of about 2 cycles/mm the DQE is on an average about 30 per cent. SNRs are favorable. CONCLUSION: The technical properties found in this study indicate that the Dixel(R) system is suitable for intra-oral dental radiography.

Periodontal bone height in professional musicians. Cross-sectional and longitudinal aspects.

Cross-sectional and longitudinal studies of the periodontal bone height were performed on professional musicians playing wind and non-wind instruments. The cross-sectional study population included 244 occupational musicians (186 men and 58 women aged 20-69 years) from three Swedish national orchestras. Eighty-seven were wind instrument musicians. Radiographic full-mouth surveys were performed and the periodontal bone height was measured with a computerized method and expressed as a percentage of the root length. The mean periodontal bone height was 83.4% for the musicians playing wind instruments and 83.6% for those playing non-wind instruments. There was no statistically significant difference in periodontal bone height between the two instrumentalist categories. In addition, the bone height quotients of anterior to posterior teeth were analyzed but no significant differences were found between wind and non-wind instrumentalists. A longitudinal cohort including 92 musicians who had been examined in a corresponding study 10 years earlier was studied. The overall loss of the periodontal bone height over the 10-year period was small, but only wind instrumentalists of the 50-69 year age group exhibited a statistically significant reduction over time. There was no statistically significant difference between musicians as regards instrument played. It is concluded from the cross-sectional and 10-year longitudinal observations that the playing of wind instruments is unlikely to affect periodontal bone height.

Prediction of perceptibility curves of direct digital intraoral radiographic systems.

OBJECTIVES: To derive and test a method to predict Perceptibility Curves (PCs) for direct digital intraoral radiographic systems. METHODS: A test object was used to determine the performance of an average observer with respect to the threshold contrast and internal noise of the human visual system. These data were combined with system parameters to predict PCs mathematically. RESULTS: Data on the performance of an average observer could be defined to obtain values of the effective threshold contrast as a function of background gray level. This function combined with the gamma-value of the system predicted PCs that agreed well with PCs obtained in the conventional way. CONCLUSION: It is possible to predict PCs from a limited number of system parameters together with predetermined data on an average observer.

Comparison of observer reliability in assessing alveolar bone changes from color-coded with subtraction radiographs.

OBJECTIVES: To assess intra- and interobserver agreement on marginal changes in periodontal bone from color-coded compared with subtraction radiographs. METHODS: Sequential radiographs from patients undergoing periodontal treatment were acquired using direct digital intra-oral radiography. Fifty-one pairs of color-coded and subtraction radiographs were produced and evaluated twice by six dentists for changes in marginal bone. Intra- and interobserver agreement were calculated. RESULTS: Intra-observer agreement was significantly higher for the color-coded radiographs (P < 0.05). Interobserver agreement was significantly higher for color-coded radiographs at the second (P < 0.001) but not the first (P = 0.34) evaluation. CONCLUSIONS: Color coding of radiographic differences by means of image addition may be a feasible alternative to the subtraction technique for evaluating periodontal bone changes.

The perceptibility curve test applied to direct digital dental radiography.

OBJECTIVE: To compare the effect of an additional scintillator layer on the psychophysical properties of a CCD detector for digital dental radiography. METHODS: Radiographs of a test object containing ten holes of increasing depth were obtained throughout the exposure range of two CCD detectors at 70 and 90 kVp. One was the original detector for the Sens-A-Ray system (Regam Medical Systems, Sundsvall, Sweden) and the other the same detector covered by a scintillator layer. Ten viewers evaluated the radiographs for the number of perceptible holes. From these data and the dose response functions for the two detectors, the minimum perceptible exposure difference was found. The reciprocal values of this parameter were plotted against the logarithm of exposure to create Perceptibility Curves (PCs). RESULTS: The four PCs had essentially the same shape and height. There was a shift to lower exposures in the PCs for the detector covered by a scintillator. CONCLUSIONS: The two detectors have essentially the same psychophysical properties. Since the detector covered by a scintillator layer is more sensitive, it should be preferred for clinical practice since the dose to the patient is reduced.

A sensitometric comparison of four dental X-ray films and their diagnostic accuracy.

OBJECTIVES: To compare the sensitometric properties and accuracy in the diagnosis of approximal caries of two E-speed (Ektaspeed Plus and EV 57) and two D-speed (Ultra-speed and DV 57) films. METHODS: Speed and contrast for the four films were determined following 30 exposures for each film. Base plus fog density was measured on unexposed films and the increase was studied over a 18-month period. Seventy-five extracted premolars with known pathology were radiographed under standardized conditions and the radiographs assessed by nine observers for approximal caries. Receiver Operating Characteristic (ROC) curve technique was used to analyse the diagnostic accuracy. RESULTS: The sensitometric analysis showed that the Ektaspeed Plus film had the highest speed of the four films. At a density of 1.0 it was 2.28 times faster than Ultra-speed. The contrast of Ektaspeed Plus was comparable with that of the other films and base plus fog density plateaued at 0.4 ten months before expiry date. There were no statistically significant differences in diagnostic accuracy for white spot lesions between the four films. For cavitations there was a significant difference between EV 57 and DV 57 and Ektaspeed Plus (P = 0.005) but not between Ultra-speed and Ektaspeed Plus nor between Ultra-speed and EV 57 and DV 57. CONCLUSION: Ektaspeed Plus film is comparable with D-speed and a conventional E-speed film. Since it is at present the fastest available dental film it should be recommended for general dental practice.