Kristina Hellén-Halme

Effect of ambient light and monitor brightness and contrast settings on the detection of approximal caries in digital radiographs: an in vitro study

OBJECTIVES The aim of this study was to investigate how brightness and contrast settings of the display monitor and ambient light level (illuminance) in the viewing room affect the clinicians ability to diagnose carious lesions in digital radiographs. METHODS Standardized radiographs were taken of 100 extracted teeth. Seven observers evaluated the images for approximal carious lesions twice, once under 50 lux and once under 1000 lux room illumination. Monitor brightness and contrast were varied +/-50% and +/-6%, respectively, to mimic the normal limits of monitor adjustment by an inexperienced user and one optimal setting. This was done by adjusting radiograph brightness and contrast by +/-25%. Thus, five radiographs of each tooth were evaluated. Receiver operating characteristic (ROC) analyses were performed. Histological examinations of the teeth served as the criterion standard. A paired t-test was used to evaluate whether differences in the areas under the ROC curves were significant and kappa was used to evaluate intraobserver agreement. RESULTS When a monitor with optimal brightness and contrast settings was used to detect approximal carious lesions, ambient light levels less than 50 lux were significantly better than levels above 1000 lux (dentin and enamel lesions, P < 0.01; dentin lesions, P < 0.02). Increasing the contrast setting of the monitor by 6% did not change these results; 50 lux was still significantly better than 1000 lux (enamel lesions, P < 0.01; dentin and enamel lesions, P < 0.02) for evaluating radiographs. Intraobserver agreement differed from fair to good. CONCLUSIONS Reducing ambient light to less than 50 lux significantly increased the accuracy of diagnosing approximal carious lesions on a monitor with an optimal brightness setting and an optimal or slightly higher than optimal contrast setting.

How do dentists use CBCT in dental clinics? A Norwegian nationwide survey

Abstract Objectives. Cone beam computed tomography (CBCT) was introduced to Norwegian dental clinics in 2007. The aim of the study was to investigate how dental clinics use this imaging modality, including factors related to workflow and image quality, and to evaluate dentists’ opinions on and experiences of using it. Materials and methods. A web-based 59-item questionnaire regarding the clinical use of CBCT was sent to all 39 CBCT clinics in Norway. Results. Twenty-nine clinics (74%) responded. Most respondents (93%) were from clinics with more than one dentist and 83% had at least one specialist. All clinics had digital intraoral x-ray receptors and all but one had panoramic imaging. The most common indications for CBCT were implant treatment planning (34% of all clinics) and localization of impacted teeth (43% of specialist clinics). Seventy-two per cent of clinics reported an average of four or fewer CBCT examinations each week and 83% of respondents were subjectively satisfied with the image quality. The most commonly used enhancement functions were contrast (97%), brightness (90%) and zoom (86%). Conclusions. The Norwegian CBCT clinics surveyed were fully digitized and had multiple dentists. Periodontists and oral and maxillofacial surgeons were the most frequent specialties represented in the clinics. Clinics with only dental specialists performed more CBCT examinations/week than clinics with general practitioners or both general practitioners and specialists. The most common indications for CBCT examinations were related to treatment planning. This study found some challenges related to image quality and communication within the radiological team.

A phantom for simplified image quality control of dental cone beam computed tomography units

OBJECTIVE The purpose of this work was to develop an inexpensive phantom for simplified image quality assurance (IQA) together with algorithms for objective evaluation of image quality parameters and to integrate these components into an easy-to-use software package. This should help make quality control of dental cone beam computed tomography (CBCT) units accessible, easy, and affordable for any specialist or general practitioner. STUDY DESIGN Our study developed an inexpensive polymethyl methacrylate (Plexiglas) phantom containing objects and structures for objective quantification of the most important image-quality parameters in CBCT imaging. It also paired the phantom with a software package, based on open-source software, for automatic processing and analysis. RESULTS The software produces objectively measured IQA data for low- and high-contrast resolution, uniformity, noise characteristics, and geometric linearity. CONCLUSIONS The authors consider the phantom and methods presented in this article to be a step toward helping clinical dental personnel perform regular quality assurance on CBCT units.

Carious lesions : diagnostic accuracy using pre-calibrated monitor in various ambient light levels : an in vitro study

OBJECTIVES This study investigated the effect of different monitor calibration modes under various ambient lighting conditions on the ability of observers to recognize proximal carious lesions of varying depths. METHODS 7 observers evaluated 100 teeth for proximal carious lesions on standardized digital radiographs using 3 set-ups: (1) pre-calibrated monitor for high ambient light (higher than 1000 lux), (2) pre-calibrated monitor for low ambient light (less than 50 lux) and (3) Barten calibration (Digital Imaging and Communication in Medicine) on the monitor in dimmed ambient light (less than 50 lux). Receiver operating characteristic curves were plotted for all observations. The criterion standard was histological examination of the teeth. The effects of three conditions were compared using a paired t-test. The level of significance was set to p < 0.05. RESULTS No significant difference was found in diagnostic accuracy for the detection of any type of proximal carious lesions between the different calibration modes of the monitor according to different ambient light levels. CONCLUSIONS There is no evidence that any difference between ambient light levels affects the ability to detect carious lesions in digital radiographs as long as the monitor was calibrated in accordance with the surrounding light level.

The Effects on Absorbed Dose Distribution in Intraoral X-ray Imaging When Using Tube Voltages of 60 and 70 kV for Bitewing Imaging.

ABSTRACT Objectives Efforts are made in radiographic examinations to obtain the best image quality with the lowest possible absorbed dose to the patient. In dental radiography, the absorbed dose to patients is very low, but exposures are relatively frequent. It has been suggested that frequent low-dose exposures can pose a risk for development of future cancer. It has previously been reported that there was no significant difference in the diagnostic accuracy of approximal carious lesions in radiographs obtained using tube voltages of 60 and 70 kV. The aim of this study was, therefore, to evaluate the patient dose resulting from exposures at these tube voltages to obtain intraoral bitewing radiographs. Material and Methods The absorbed dose distributions resulting from two bitewing exposures were measured at tube voltages of 60 and 70 kV using Gafchromic® film and an anatomical head phantom. The dose was measured in the occlusal plane, and ± 50 mm cranially and caudally to evaluate the amount of scattered radiation. The same entrance dose to the phantom was used. The absorbed dose was expressed as the ratio of the maximal doses, the mean doses and the integral doses at tube voltages of 70 and 60 kV. Results The patient receives approximately 40 - 50% higher (mean and integral) absorbed dose when a tube voltage of 70 kV is used. Conclusions The results of this study clearly indicate that 60 kV should be used for dental intraoral radiographic examinations for approximal caries detection.

Comparison of the performance of intraoral X-ray sensors using objective image quality assessment

OBJECTIVES The main aim of this study was to evaluate the performance of 10 individual sensors of the same make, using objective measures of key image quality parameters. A further aim was to compare 8 brands of sensors. STUDY DESIGN Ten new sensors of 8 different models from 6 manufacturers (i.e., 80 sensors) were included in the study. All sensors were exposed in a standardized way using an X-ray tube voltage of 60 kVp and different exposure times. Sensor response, noise, low-contrast resolution, spatial resolution and uniformity were measured. RESULTS Individual differences between sensors of the same brand were surprisingly large in some cases. There were clear differences in the characteristics of the different brands of sensors. The largest variations were found for individual sensor response for some of the brands studied. Also, noise level and low contrast resolution showed large variations between brands. CONCLUSIONS Sensors, even of the same brand, vary significantly in their quality. It is thus valuable to establish action levels for the acceptance of newly delivered sensors and to use objective image quality control for commissioning purposes and periodic checks to ensure high performance of individual digital sensors.

The effect of anatomical noise on perception of low contrast in intra-oral radiographs. An in vitro study.

OBJECTIVES Radiographic images suffer from varying amounts of noise. The most studied and discussed of these is random noise. However, recent research has shown that the projected anatomy contributes substantially to noise, especially when detecting low-contrast objects in the images. Our aim, therefore, was to evaluate the extent to which overprojected anatomical noise affects the detection of low-contrast objects in intra-oral images. METHODS Our study used four common sensor models. With each sensor, we took four series of images, three series with and one series without an anatomical phantom present. In each series, we exposed a low-contrast phantom at 18 different exposure times using a standardized method. 4 observers evaluated all 288 images. RESULTS The low-contrast characteristics differed substantially when imaging low contrast on a homogeneous background compared with imaging low contrast when an anatomical phantom was present. For three of the sensors, optimal exposure times for low-contrast imaging were found, while the fourth sensor displayed a completely different behaviour. CONCLUSIONS Calibrating the low-contrast properties of an imaging system using low-contrast objects on a homogeneous background is not recommended. On an anatomical background, low-contrast properties are completely different, and these will mimic the clinical situation much more closely, directing the operator how to best use the system. There is a clear demand for further research on this subject.

Comparison of Swedish and Norwegian Use of Cone-Beam Computed Tomography: a Questionnaire Study.

ABSTRACT Objectives Cone-beam computed tomography in dentistry can be used in some countries by other dentists than specialists in radiology. The frequency of buying cone-beam computed tomography to examine patients is rapidly growing, thus knowledge of how to use it is very important. The aim was to compare the outcome of an investigation on the use of cone-beam computed tomography in Sweden with a previous Norwegian study, regarding specifically technical aspects. Material and Methods The questionnaire contained 45 questions, including 35 comparable questions to Norwegian clinics one year previous. Results were based on inter-comparison of the outcome from each of the two questionnaire studies. Results Responses rate was 71% in Sweden. There, most of cone-beam computed tomography (CBCT) examinations performed by dental nurses, while in Norway by specialists. More than two-thirds of the CBCT units had a scout image function, regularly used in both Sweden (79%) and Norway (75%). In Sweden 4% and in Norway 41% of the respondents did not wait for the report from the radiographic specialist before initiating treatment. Conclusions The bilateral comparison showed an overall similarity between the two countries. The survey gave explicit and important knowledge of the need for education and training of the whole team, since radiation dose to the patient could vary a lot for the same kind of radiographic examination. It is essential to establish quality assurance protocols with defined responsibilities in the team in order to maintain high diagnostic accuracy for all examinations when using cone-beam computed tomography for patient examinations.

Web-based calibration of observers using MRI of the temporomandibular joint

OBJECTIVES Research diagnostic criteria for temporomandibular disorders (RDC/TMDs) were proposed in 1992 with the aim of standardizing and testing methods for diagnosing TMDs. RDC/TMDs have so far been lacking standardized methods for imaging and criteria for imaging diagnosis of disorders of the temporomandibular joint (TMJ). Criteria for disorders of the TMJ have recently been proposed for MRI. The aim of this study was to publish MR images of the TMJ on the web and to test the agreement of five observers using the criteria. METHODS 20 cases of MRI of the TMJ were published on the web together with the criteria. The MR images were taken in closed and open mouth positions, and sagittal and coronal views. Five observers diagnosed disc position, disc shape, joint effusion and loose calcified bodies in the TMJ. RESULTS In all cases except one, three or more observers agreed upon the diagnosis. All agreed on whether a loose calcified body was present or not. The second best agreement was obtained for disc position in the sagittal view, where all observers agreed in 16 of the 20 cases. For disc position in the coronal view and the evaluation of the disc shape, observer agreement was lower. CONCLUSION Criteria were useful in order to standardize and simplify evaluation and thereby probably increase the diagnostic outcome among different observers for MRI of the TMJ. We recommend that the criteria be used internationally to facilitate comparisons between different studies.