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Biomedical subjects

U Welander

Publications and source records attributed to U Welander.

At least 37 records · Page 2Linked to original sources
PubMed1999

Orthodontic application of color image addition to visualize differences between sequential radiographs.

A new technique was developed making it possible to visualize changes that take place after premolar transplantation. Three sequential radiographs from a series of standardized control examinations were digitized and registered to the first radiograph in the series using subtraction technique. The digitized radiographs were then transformed into monochromatic images: red, blue, and green. After correction of gray level and contrast, the three radiographs were superimposed. All details that were common in the radiographs were then displayed in black-and-white. Details that were different appeared in color. Red and blue combines into magenta, blue and green into cyan, and green and red into yellow. A procedure was developed to create color-coded radiographs according to the above. The procedure was applied to cases that had been treated by premolar transplantation. The color coding offers the possibility to identify any radiographic changes that take place over time, eg, growth, apposition or resorption of bone, and progression or regression of pathological processes.

Bicuspid↗
PubMed1999

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.

Alveolar Bone Loss↗
PubMed1999

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.

Humans↗
PubMed1999

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.

Artifacts↗
PubMed1999

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.

Artifacts↗
PubMed1999

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.

Artifacts↗
PubMed1999

An electronic survey of opinions on the compatibility of current X-ray generators with intra-oral digital X-ray systems.

OBJECTIVES: To assess opinions on the compatibility of current X-ray generators with intra-oral digital X-ray systems. METHODS: A questionnaire was posted in both English and in Japanese on oral and maxillofacial radiology electronic bulletin boards. The questionnaire was also mailed to selected researchers and manufacturers in oral and maxillofacial radiology. The replies were evaluated to determine opinion on the current and future status of digital intra-oral imaging with special reference to their compatibility with current X-ray generators. RESULTS: Seventy-one replies were received from 19 countries: 39% from Japan and Korea, 27% from North America, 25% from Europe and 8% from the rest of the world. Eighty per cent of respondents were from academia, 15% from industry and the remainder largely in private practice. Respondents' experience was equally divided between solid state, mainly charge-coupled devices (CCDs) and photostimulable phosphor (IP) technologies. Sixty-eight per cent considered that current X-ray generators are compatible with intra-oral digital systems and many believed this was due to their gray scale flexibility. Twenty-eight per cent believed that existing X-ray generators are inconsistent with low exposure times. Many of the replies suggested that in future pixel size would decrease and bit depth and receptor sensitivity increase. CONCLUSIONS: Most respondents are happy to use existing X-ray generators with digital X-ray systems. However, they also believe that increased sensitivity of receptors could lead to more stringent designs of X-ray generators to ensure more reliable outputs in the low exposure range.

Attitude of Health Personnel↗
PubMed1998

A three-dimensional photographic method for documentation and measurement of dental conditions.

A 3-D photographic technique was developed for the registration of bite conditions. This technique may replace plaster models for archiving purposes. To achieve this, photographic equipment and computer programs should be user friendly, not too expensive, and allow measurements that satisfy scientific demands. This purpose was fulfilled by combining the following elements: a photographic unit with standardized conditions for 3-D photography and a reference object with known coordinates where bite impressions or models are placed during photography. To reconstruct 3-D coordinates from photographs these are placed on a digitizer connected to a computer programmed for reconstructing 3-D coordinates from the digitized 2-D data. The accuracy of the 3-D reconstruction of coordinates, x, y, z, was tested by means of 3-D photographs of a test object with reference points having a precision of +/- 0.5 micron. The mean error for distances of 5 mm and 15 mm varied between -0.17 mm and +0.15 mm. Measurements of 45 degrees and 90 degrees angles had an accuracy that varied from -0.5 degree to +0.9 degree and from -1.2 degrees to +1.5 degrees respectively. An angle between lines and a plane of 54.7 degrees displayed a mean error of +/- 1.6 degrees. The test of the accuracy of the 3-D photographic technique for calculating distances and angles demonstrated that it fulfills demands for scientific applications on clinical material.

Calibration↗
PubMed1998

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.

Absorptiometry, Photon↗
PubMed1997

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.

Analysis of Variance↗
PubMed1995

Absolute measures of image quality for the Sens-A-Ray direct digital intraoral radiography system.

To study the noise characteristics of the Sens-A-Ray (Regam Medical Systems AB, Sundsvall, Sweden) system, 20 radiographs were obtained at each of three different exposure levels at 70 and 90 kVp with a homogeneous x-ray field. Exposures were measured with an ionization chamber. Noise power spectra were calculated over three areas within each radiograph, and ensemble averages were subsequently found from 60 data files at each exposure level. Noise equivalent quanta were calculated with the noise power spectra and modulation transfer function data from previous studies. Finally, the detective quantum efficiency was calculated by dividing the noise equivalent quanta by the estimated incident photon fluence at the different exposures. The system has a maximum detective quantum efficiency of approximately 0.030 at 70 kVp and 0.025 at 90 kVp. A broad maximum exists at approximately 2 cycles/mm, indicating that the signal-to-noise ratio is most favorable at this spatial frequency.

Algorithms↗
PubMed1995

Computerized measurements of the lower third molar related to chronologic age in young adults.

Chronologic age is an utmost important birth record in many industrialized Western countries. When the date of birth is unknown, there is a demand for establishing the chronologic age. Dental methods for age estimations are considered more reliable than most other methods by the majority of researchers and are among the most commonly used means to determine age. Traditionally, these methods have most often been based on subjectively estimated, radiographic stages of tooth development. In the present study metric measurements of the length of the forming root have been used and are compared with one standard method. The formed part of the root of the lower third molar as seen in a panoramic radiograph was digitized. Data were directly stored in a computer for subsequent statistical analysis. The technique of collecting data with the aid of a computer had some statistical advantages. The precision of age estimations was, however, slightly inferior to the standard method.

Adolescent↗
PubMed1994

Color coding of radiographic changes over time by means of image addition.

Differences between sequential radiographs may be displayed in color if the individual radiographs are transformed into monochromatic images and then added. Information in regions where the radiographs are identical is retained whereas differences are emphasized by the color coding that comes about in a quantitative manner from the gray level values in the sequence of radiographs. By using the three additive primary colors, red, blue, and green, two or three radiographs from a sequence may be added. Every possible state of a bone disease, progression, regression, or any combination, will produce a different and specific color code. Different development cycles are described, and the color coding that appears when color image addition is performed is analyzed. The color addition technique should constitute a useful substitute or alternative to subtraction.

Alveolar Bone Loss↗
PubMed1994

Exposure parameters and their effects on diagnostic accuracy.

A new method for analyzing diagnostic accuracy is introduced. A diagnostic accuracy curve may be obtained by plotting receiver operating characteristic analysis data, P(A), as a function of exposure. By means of diagnostic accuracy curves the effects on diagnostic accuracy of tube potential, exposure, and size of carious lesions was studied. It was found that the effect of the tube potential on the accuracy of caries diagnosis is negligible. About 25% of the variation in diagnostic accuracy depends on the exposure and about 80% on lesion depth. With the lesion depth constant, about 75% of the variance in diagnostic accuracy depended on observer performance. The peak of a diagnostic accuracy curve indicates optimum performance. This is found at an exposure that gives a radiographic density of about 1 in enamel and dentin although the tolerable exposure increases with increased lesion depth.

Absorptiometry, Photon↗
PubMed1994

A simple method for measuring MTF in direct digital intraoral radiography. Technical note.

Conventional methods for measuring the modulation transfer function require the exposure of a narrow slit or straight edge followed by computationally intense data analysis. An alternative method applicable to digital systems uses the standard deviation of gray levels within different frequency regions of a bar pattern. To verify that this method gave reliable results, measurements performed for two systems for intraoral radiography with the use of this method have been compared with modulation transfer function values calculated from Fourier transformations of line spread functions measured for the two systems. The almost identical results confirm the consistency of both sets of modulation transfer function measurements and demonstrate the utility of the bar pattern method for performing rapid measurements.

Fourier Analysis↗
PubMed1994

Resolution as defined by line spread and modulation transfer functions for four digital intraoral radiographic systems.

Line spread functions for four commercially available systems for direct digital intraoral radiography were determined from images of a slit of negligible width. From the fitted line spread functions presampling modulation transfer functions were calculated. The four systems were the Sens-A-Ray (Regam Medical System AB, Sundsvall, Sweden), the VIXA/Visualix (Gendex, Chicago Ill.), the RVG (Trophy Radiologic, Paris, France), and the Flash Dent (Villa Sistemi Medicale srd, Buccinasco, Italy). Digital intraoral radiography is in a state of rapid development, and detectors as well as computer hardware and software are continually modified and improved resulting in successively changing system parameters. As this occurs the present work provides a method that may be used to determine comparable data on future systems.

Electronics, Medical↗
PubMed1994

Age estimation with the aid of tooth development: a new method based on objective measurements.

The common methods of age determination with the aid of teeth have been criticized because they rely on subjective estimations of tooth development, as seen in radiographs, and subsequent comparisons with pictures and descriptions in compiled dental charts. The distribution around an estimated age with these methods is usually more than +/- 2 yr between the 10th and 90th percentiles. In an attempt to avoid subjective estimations, objective measurements of developing teeth were correlated with subjects' chronologic ages. The structures measured were crown height, apex width, and root length. With the aid of a multiple regression model, a linear relationship between some of these distances and age was shown. The distances which were best correlated with age differed according to sex and age. This method has a 95% C.I. of about +/- 2 yr around an estimated age. It therefore seems to be more accurate than the earlier methods. Thus, the individual variation in tooth development is of the same order of magnitude, and a better estimation can therefore not be done in children 6-14 yr of age.

Adolescent↗