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Biomedical subjects

N L Frederiksen

Publications and source records attributed to N L Frederiksen.

At least 19 recordsLinked to original sources
PubMed1999

Influence of the digital image display monitor on observer performance.

OBJECTIVE: To assess the influence of the display monitor on observer performance. MATERIAL AND METHODS: Artificial enamel lesions were created in 40 extracted teeth at random using 1/4 and 1/2 round burs. Teeth were mounted in dental stone blocks to simulate a hemidentition. Approximate exposures were recorded at 70 kVp using a Digota (Soredex, Orion Corp, Helsinki, Finland) digital imaging system, calibrated to achieve optimum density. Six dentists rated each image on a five-point scale for the presence or absence of a lesion. Radiographic images were viewed on the following monitors: (1) AlphaScan 711 (Sampo Corp.); (2) Multiscan 17 Se II (Sony Electronics Inc.); (3) DS 2000 (Clinton Electronics Corp.) and (4) Latitude CP Laptop (Dell Computer Corp.). Raters were allowed to magnify and to adjust density and contrast of each image at will. Receiver Operating Characteristic (ROC) analysis was performed and curves were plotted for each image. Data was subjected to repeated measures analysis of variance and ordinal logistic regression to test for significance between variables and to determine odds ratios. RESULTS: Mean ROC curve areas ranged from 0.8728 for the Sampo monitor to 0.8395 for the Sony. Repeated measures analysis of variance showed significant differences between observers (P < 0.0001), lesion size (P < 0.0001), examiner/monitor interaction (P < 0.033) and examiner/block interaction (P < 0.013). However, no significant difference was found between monitors. CONCLUSION: This study suggests that observer performance is independent of the visual characteristics of the display monitor.

Analysis of Variance↗
PubMed1998

Endodontic working length assessment. Comparison of storage phosphor digital imaging and radiographic film.

OBJECTIVE: This study compared the difference in interpretation of the position of endodontic file tips between two imaging systems: photostimulable storage phosphor luminescence imaging versus radiographic film. STUDY DESIGN: Thirteen patients were selected at random. Preoperative and trial file length radiographs were made with a dual image receptor composed of a Digora Digital Imaging Plate and a piece of Ektaspeed Plus film. Exposure techniques for E-speed film were used. Root length and file length measurements were made from digital images with the Digora system's measuring tools. Measurements were also made on radiographic film with a 7 x measuring magnifier. Root length, file length, and their difference were compared for both film and digital images. RESULTS: Differences were found to be less in digital than in film images. Photostimulable storage phosphor luminescence imaging performed similarly to Ektaspeed Plus film for measuring root lengths, but file tip positions (especially of small file sizes) were difficult to visualize with E-speed film. CONCLUSIONS: The smaller difference between file tip and root apex found with digital imaging suggests that this technique is more accurate to assess trial file length. This imaging modality for assessing file positions during root canal treatment may be beneficial to the practitioner.

Bicuspid↗
PubMed1998

A reliability comparison of submentovertex and zonographic methods of horizontal condylar angle estimation.

OBJECTIVE: The objectives of this retrospective clinical study were, first, to compare submentovertex radiography and zonographic temporomandibular joint orientation programs that use the Scanora imaging system with respect to the reproducibility with which the angulation of the horizontal condylar axis may be determined and, second, to assess the level of agreement between the 2 methods. STUDY DESIGN: Submentovertex radiographs and zonographic projections of 16 joints (8 patients) were evaluated. Two raters independently determined the horizontal angulation of each condyle 3 times using each method. Horizontal condylar angle measurements differing by no more than 5 degrees were considered to be in agreement. Statistical analyses were performed with a repeated-measures analysis of variance, sign tests, and Wilcoxon signed rank test. RESULTS: No significant difference was found in the 3 measurements between the 2 raters (P = .9122) or between the raters adjusted for method (P = .5093). A significant difference was found between methods (P = .0001). Intrarater agreement values were 81% and 88% for the submentovertex method and 75% for each rater for the zonographic method. Interrater agreement was 94% for each method. Intermethod agreement was 50% for one rater and 81% for the other. CONCLUSIONS: The submentovertex and zonographic methods of determining the horizontal condylar angulation demonstrated consistency and reliability both within and between the raters. However, the zonographic method did not agree with the submentovertex method. This findings does not imply that the zonographic is not a clinically acceptable technique for the determination of the horizontal condylar angulation when subsequent tomographic projections are made on the same unit with the same head-positioning device.

Analysis of Variance↗
PubMed1998

Effect of different background lighting conditions on diagnostic performance of digital and film images.

OBJECTIVE: To compare the performance of a photostimulable phosphor (PSP) imaging system with radiographic film for the detection of approximal lesions under two background lighting conditions. METHODS: Bitewing exposures were made of the extracted human teeth with artificial approximal lesions using D-speed and E-speed radiographic film and a PSP imaging plate. Eight dentists rated 12 approximal surfaces in each image on a 5-point scale. Images were viewed with overhead fluorescent room lighting on and off. ROC curves were generated for each image receptor and lighting condition. Repeated measures analysis of variance ANOVA tested differences between observers, lesion size, image receptor, lighting condition. RESULTS: Mean ROC curve areas for D-speed film viewed in full ambient light scored highest (0.8030) followed by E-speed film using dark conditions (0.7386). The lowest mean curve area was found when PSP (enhanced mode) images were viewed in a dark room (0.6726). Significant differences were found between observers, lesion size, image receptor and image receptor-lesion size interaction. No significant difference was found with background lighting. CONCLUSIONS: Background lighting does not appear to effect the ability to detect artificial approximal lesions.

Analysis of Variance↗
PubMed1997

Effect of the geometry of the intraoral position-indicating device on effective dose.

OBJECTIVE: The objective of this study was to calculate and compare the effective dose and to estimate risk from the use of intraoral position-indicating devices of differing geometries. STUDY DESIGN: Thermoluminescent dosimeters were placed at selected sites in the upper portion of a tissue-equivalent human phantom to record the equivalent dose to weighted tissues and organs. The phantom was exposed to simulated complete mouth surveys with either a long (29.8 cm) or short (19.6 cm) round open-end position-indicating device, a long (35.3 cm) or short (23.3 cm) rectangular open-end position-indicating device, or a pointed (29.6 cm) closed-end position-indicating device. RESULTS: The effective dose was calculated as the sum of the equivalent doses to each organ or tissue multiplied by that organ or tissue's weighting factor. The salivary glands were included as part of the remainder. The effective dose ranged from 362 micro Sv for the pointed position-indicating device, to 63 micro Sv for both the long and the short rectangular position-indicating devices. CONCLUSIONS: These effective doses were calculated to represent a probability for stochastic effects that range in magnitude from 26 x 10(-6) to 4.6 x 10(-6).

Equipment Design↗
PubMed1996

Effective dose and risk assessment from detailed narrow beam radiography.

Studies of the effectiveness of commonly used imaging techniques have shown that they are less than optimal in revealing oral disease. The diagnostic accuracy of detailed narrow beam radiography (scanography) has been reported to be significantly better than intraoral periapical radiography for the observation of periodontal pathoses and at least as good as periapical radiography for detecting periapical lesions. The purpose of this study was to calculate and compare the effective doses and risk estimates from the use of detailed narrow beam radiography and intraoral radiography. With the use of a tissue equivalent human phantom and thermoluminescent dosimetry, the effective dose from detailed narrow beam radiography was found to vary from 5 to 35 microSv depending on the anatomic location of the image layer and intraoral radiography from 9 to 150 microSv depending on the type of survey. Effective doses of these magnitudes represent 0.6 to 18.8 days of equivalent natural radiation exposure and a probability for stochastic effects on the order of 0.37 to 10.95 x 10(-6).

Humans↗
PubMed1995

A sensitometric comparison of Fuji Super HR-G and Kodak T-mat G panoramic films.

Film contrast, relative speed, and resolution of Fuji Super HR-G panoramic film were determined according to specifications of the American National Standards Institute and compared with those of Kodak T-mat G panoramic film. The films were simultaneously exposed by Kodak Lanex regular intensifying screens with time-scale sensitometry. Optical density was read with a digital densitometer, and characteristic curves were plotted and analyzed by polynomial and linear regression. The average gradients of the linear regression curves between 0.25 and 2.00 optical density units above base plus fog were taken as contrast (HR-G: 1.831, T-mat G: 1.712). Relative speed, when exposed with Lanex regular intensifying screens and calculated at 1.00 optical density unit above base plus fog, was 412 for HR-G. A speed of 400 was chosen for T-mat G to match Kodak consumer information. Resolution for both films was similar. These findings suggest that Fuji Super HR-G panoramic film develops similar contrast, speed, and resolution to Kodak T-mat G panoramic film.

Linear Models↗
PubMed1995

Diagnostic imaging in dental implantology.

A success rate for osseointegrated implants approaching 100% has been reported. This rate of success has been made possible in part by a comprehensive appraisal of the morphologic features of the proposed implantation site: the quality and quantity of available bone, the presence of pathoses, the inclination of the alveolar process, and the relative location of anatomic structures to the site of implantation. Radiography has been found to be invaluable for the assessment of the proposed fixture site and for the evaluation of the fixture in time after implantation. The question of which radiographic technique to apply, intraoral or extraoral, plain film or digital radiography, remains for the clinician to answer after careful consideration of all variables.

Cephalometry↗
PubMed1995

Effective dose and risk assessment from computed tomography of the maxillofacial complex.

The effective dose from computed tomography of the maxillofacial complex has been estimated and used for an assessment of risk. For each scan sequence 64 TLDs were placed in 27 selected sites in the upper portion of a tissue-equivalent human phantom to record the equivalent dose in radiosensitive organs/tissues. Equivalent doses ranged from 0.11 mSv (bone marrow, maxillary scan) to 20 mSv (salivary glands, mandibular scan). By the use of a calculation that included the salivary glands as part of the remainder, two contiguous 1 cm axial slices of the maxilla were found to result in an effective dose of 0.1 mSv, and four contiguous 1 cm axial slices of the mandible in an effective dose of 0.76 mSv. Effective doses of this magnitude represent a probability of stochastic effects of the order of 8 X 10(-6) and 56 X 10(-6) respectively.

Absorption↗
PubMed1994

Grid versus air gap. A comparison of cephalometric techniques.

This study compares two cephalometric radiography techniques: one that uses a grid, the other an air gap, both of which increase image contrast by reduction of scatter radiation to the film. A 12.0 cm water phantom was used with a modified cephalometric radiography unit operating at 71 kVp. Air gaps (patient-to-film distances) of 0.0, 7.5, 12.5, 17.5, 25.5 cm were compared with a 10:1 ratio stationary focused grid at 0.0 cm. Comparisons were made from the measured patient surface exposure, the calculated contrast improvement factor, nominal magnification, and image resolution at each distance. Radiation exposure to the patient was 2.52 times greater with the grid than without. Using regression formulas, the contrast improvement factor of the grid was calculated to equate to an air gap of 9.5 cm. The 9.5 cm air gap would reduce patient exposure by 59.6% with similar image contrast and resolution as compared with the grid. Overall magnification was increased by 6.6% with the 9.5 cm air gap.

Air↗
PubMed1994

Effective dose and risk assessment from film tomography used for dental implant diagnostics.

There are no data relating complex film tomography with effective dose that may be used to estimate the relative risk associated with dental implant diagnostics. The purpose of this study was to calculate the effective dose and estimate risk from the use of the Scanora multimodal imaging system. With the use of a tissue equivalent human phantom and thermoluminescent dosimetry, panoramic radiography was found to result in an effective dose of 26 microSv, while complex film tomography resulted in an effective dose of < 1 microSv to 30 microSv depending on the anatomical location of the imaging plane and the collimation option. An effective dose of this magnitude for panoramic radiography was estimated to represent a probability for stochastic effects on the order of 1.9 x 10(-6). Similarly, the effective dose associated with film tomography may be estimated to be equal to a probability for stochastic effects in the range of << 1 x 10(-6) to 2.2 x 10(-6).

Bicuspid↗
PubMed1992

Localization of a displaced root fragment by stereoscopy and pluridirecitonal tomography.

The case reported describes two methods used with the Scanora integrated imaging system to locate a root fragment thought to be displaced into the maxillary sinus--rotational narrow beam stereoscopic scanning and wide angle cross-sectional pluridirectional tomography. While the stereo scans located the fragment within the sinus, a more accurate determination of its site, in relation to an object of known position, was obtained from the tomograms.

Foreign Bodies↗
PubMed1990

Parameters affecting radiographic contrast.

Kilovoltage, in most cases a variable readily controlled by the operator, and half-value layer have come to be regarded as factors defining image contrast. This has led to the assumption that comparable levels of image contrast may be obtained using X-ray units operated at the same kilovoltage and with the same half-value layer. To ascertain the validity of this view X-ray beams generated by seven X-ray units were compared with each other and with those from a Gendex Model 1000 operated at the same kilovoltage. The basis for comparison was the level of image contrast the X-ray beams were capable of producing after passage through selected thicknesses of aluminium absorber. While results showed no correlation between the nominal (stated) operating kilovoltage of any X-ray generator studied and the level of image contrast produced, a correlation (-0.98) was found between the measured half-value layer and image contrast when the units tested were compared with the Model 1000. This information should significantly affect the criteria used for the selection and/or operation of X-ray generators.

Bone Density↗