Biomedical subjects

P F van der Stelt

Publications and source records attributed to P F van der Stelt.

At least 19 recordsLinked to original sources

PubMed2006

Automated osteoporosis risk assessment by dentists: a new pathway to diagnosis.

General dental practitioners use a vast amount of panoramic radiography in their routine clinical work, but valuable information about patients' osteoporotic status is not collected. There are many reasons for this, but one of the prime reasons must be the disruption involved in clinical routine with lengthy manual radiographic assessment. We have developed computer software, based on active shape modeling that will automatically detect the mandibular cortex on panoramic radiographs, and then measure its width. Automatic or semi-automatic measurement of the cortical width will indicate the osteoporotic risk of the patient. The aim of our work was to assess the computer search technique's ability to measure the mandibular cortical width and to assess its potential for detection of osteoporosis of the hip, spine and femoral neck. Mandibular cortical width was measured using the manually initialized (semi-automatic) method and, when assessed for diagnosing osteoporosis at one of the three measurement sites, gave an area under the ROC curve (A(z))=0.816 (95% CI=0.784 to 0.845) and for the automatically initialized searches, A(z)=0.759 (95% CI=0.724 to 0.791). The difference between areas=0.057 (95% Confidence interval=0.025 to 0.089), p<0.0001. For diagnosing osteoporosis at the femoral neck, mandibular cortical width derived from the manually initialized fit gave an area under the ROC curve (A(z))=0.835 (95% CI=0.805 to 0.863) and for the automatically initialized searches A(z)=0.805 (95% CI=0.773 to 0.835). The difference in A(z) values between active shape modeling search methods=0.030 (95% CI=-0.010 to 0.070), and this was not significant, p=0.138. We concluded that measurement of mandibular cortical width using active shape modeling is capable of diagnosing skeletal osteoporosis with good diagnostic ability and repeatability.

Absorptiometry, Photon↗

PubMed2006

Accuracy in osteoporosis diagnosis of a combination of mandibular cortical width measurement on dental panoramic radiographs and a clinical risk index (OSIRIS): the OSTEODENT project.

Clinical questionnaires and dental radiographic findings have both been suggested as methods of identifying women at risk of having osteoporosis and who might benefit from bone densitometry. The aim of this study was to measure the diagnostic accuracy of a combination of mandibular cortical width (MCW) measured from dental panoramic radiographs (DPRs) and the osteoporosis index of risk (OSIRIS) in the diagnosis of osteoporosis. 653 women (age range 45-70 years, mean age 54.95 years) in four European centres underwent standardised dual X-ray energy absorptiometry (DXA) to provide reference data on osteoporosis status. Each subject was interviewed to derive OSIRIS scores and underwent DPR examination. MCW was measured directly by five observers. Receiver Operating Characteristic (ROC) curve analysis was used to calculate sensitivities and specificities of the clinical and radiographic tests for the diagnosis of osteoporosis. 512 (78.4%) of the study population were classified as having normal BMD and 141 (21.6%) as having osteoporosis. Using ROC analysis, OSIRIS gave a ROC curve area (A(z)) of 0.838, with a sensitivity of 70.9% and a specificity of 79.5% at a diagnostic threshold of <or=+1. MCW on DPRs gave Az values for the five observers ranging from 0.71 to 0.78, providing sensitivities between 41.0% and 59.6% and specificities of between 81.8% and 90.3% at a diagnostic threshold of a 3 mm MCW and sensitivities between 94.2% and 99.3% and specificities of between 9.8% and 23.7% at a diagnostic threshold of a 4.5 mm MCW. Inter-observer repeatability was less than 2.15 mm for 95% of subjects. Combining clinical and radiographic tests had the effect of improving specificity at the expense of a fall in sensitivity. Diagnostic thresholds for MCW and OSIRIS can be chosen to provide the sensitivity and specificity combination that best suits locally determined needs. However, the addition of OSIRIS as a stepwise 'follow-up' test to radiographic assessment of MCW should only be performed if the aim is to have a test for which the highest achievable specificity is desired.

Absorptiometry, Photon↗

PubMed2006

A sensitive method for measuring spatial orientation in bone structures.

OBJECTIVES: This article introduces the newly developed line frequency deviation (LFD) method for measuring the orientation of the trabecular structure and shows that it is more sensitive than the mean intercept length (MIL) method that is commonly used. METHODS: The LFD method, which has been developed to measure the orientation of bone on two-dimensional X-ray images, was expanded to handle three-dimensional shapes. For the purpose of comparison, both the LFD and the MIL methods were applied to micro CT scans of 24 trabecular bone samples as well as to 24 simple synthetic samples. LFD and MIL values were calculated in various directions and collected in polar plots. Next, the anisotropy was quantified by calculating the coefficient of variation as well as by fitting ellipsoids through the plots. RESULTS: The MIL method yielded smooth rather spherical ellipsoidal polar plots with almost no sensitivity for changes in structure. The LFD method yielded more slender polar plots and more sensitivity for geometrical changes. The LFD method yielded significantly more anistropy and larger variation in anisotropy. CONCLUSIONS: The LFD method is a more sensitive descriptor of spatial orientation of bone structures than the MIL method.

Anisotropy↗

PubMed2006

End-user survey for digital sensor characteristics: a pilot questionnaire study.

OBJECTIVE: To survey end-user opinions on dental digital sensor characteristics for the design of a new X-ray imaging sensor. MATERIALS AND METHODS: 100 questionnaires were sent out to dentists and dental radiologists. The questionnaire consisted of six parts related to dental sensors. A: Details about the respondent; B: Prioritization of most important aspects of digital sensors; C: Rating advantages and D: disadvantages of digital sensors; F: Dental features that need to be enhanced by digital sensors; G: End-user comments. RESULTS: Fifty-six questionnaires were returned. Contrast resolution and imaging time were assessed as the most and the least important aspects, respectively. Aspects considered as advantages by approximately 80% of respondents were: optimal contrast resolution, increased specificity, increased discrimination between diseased and healthy tissue, increased sensitivity, lower dose to the patient by more than 20%; as a disadvantage, increased patient dose was given. Dental features considered important by over 80% of the respondents were for intraoral radiographs: the visibility of caries, periapical, periodontal, and bone lesions; for panoramic radiographs: reduction of ghost images, image sharpness and bone. Bone and soft tissues on cephalograms and bone on temporomandibular joint (TMJ) tomograms were mentioned by over 70%. CONCLUSION: The most desired characteristic for a new sensor is contrast resolution. Dose saving is not considered as important unless it is more than 20%. Examination time is not a major issue. Caries, periapical and periodontal, and bone lesions for intraoral radiographs, reduction of ghost images, image sharpness and bone for panoramic radiographs were the most frequently mentioned dental features that should be enhanced by digital sensors.

Artifacts↗

PubMed2005

[Research methods in dentistry. 8. Methods for longitudinally detecting differences in bone density: digital subtraction radiography].

Subtraction radiography has been developed in 1934 by the Dutch radiologist B. Ziedses des Plantes. The technique is based on the subtraction of two radiographic images. As a result, only the differences remain visible, and structures which have been unaltered in between both exposures, are suppressed. The technique was introduced also in dental radiology in the eighties in the last century. Since then, many studies have been performed showing the benefit of this technique in dental diagnosis. A requirement for reliable results is that the two radiographs which are used for the subtraction have equal brightness and contrast, as well as a completely identical projective geometry. Since radiographic images can be acquired digitally, methods have been developed to make density and contrast equal for both images used for the subtraction process even after the images have been taken, using dedicated software programs. The projection geometry of two images can be made identical in this way as well. Because of this, the technique can also be applied in general dental practice.

Bone Density↗

PubMed2004

Minimum number of basis projections for caries detection with local CT.

OBJECTIVES: To investigate the relationship between the number of basis projections for local computed tomography (CT) and the detection of proximal caries and to find a minimum number of projections needed to maintain diagnostic accuracy. METHODS: We presented observers (n = 12) with stacks of both axial and vertical CT slices of 23 extracted teeth placed in a dry human mandible. The slices were prepared with 14, 20, 33 and 100 basis projections. The observers scored the proximal surfaces for the presence of caries on a 1-5 confidence scale. The performance of the varying number of projections was compared with conventional digital radiographs. RESULTS: The performance of all four CT modalities was significantly better than conventional radiographs (P = 0.005 to P = 0.021) and showed a consistent increase with the number of projections. Diagnostic performance depended significantly on lesion depth (P = 0.00), but not on observer. CONCLUSIONS: We conclude that the number of CT projections used can be reduced at least to 20 with the diagnostic performance still markedly better than that of conventional film, provided that the observer can make use of both axial and vertical stacks of CT slices.

Dental Caries↗

PubMed2004

Effect of number of projections on image quality of local CT.

OBJECTIVES: To determine the image quality of the local CT imaging procedure, in terms of resolution, contrast, and noise as a function of the number of projections. METHODS: The contrast and resolution of the images was determined with a phantom object consisting of three rods of different materials, as well as a phantom human head embedded in soft tissue equivalent material. In addition, slices reconstructed from computed sinograms were used for comparison. RESULTS: Sharpness, contrast and noise were determined as a function of the number of projections. The number of projections was found to affect the contrast and the noise most, and had much less influence on resolution. CONCLUSIONS: Judging from the images of the phantom head and the numerical data, it seems that the minimum number of projections needed to obtain images of useful quality in the geometry used is about 33. Improved image quality (at any number of projections) can best be achieved through noise suppression.

Artifacts↗

PubMed2004

The dynamic range of digital radiographic systems: dose reduction or risk of overexposure?

OBJECTIVES: To investigate the range of diagnostically acceptable digital radiographs and film as a function of exposure time, as well as the relationship to dose reduction and consequences for dental practice. METHODS: Five systems for intraoral radiography were used to take a series of radiographs, with increasing exposure times, of five different dry bone specimens. Seven observers evaluated the 25 series of radiographs. The observers had to determine which radiographs of each series were acceptable for dental diagnostics and which radiograph of each series they preferred. RESULTS: For Ektaspeed Plus film, the exposure time for the preferred radiograph was 0.52 s, with a range of diagnostically acceptable radiographs from 0.23-1.02 s. The preferred radiograph of the solid-state systems required less radiation than film (Sirona, 0.13 s; MPDx 0.35 s). The exposure range of these systems is narrow. In contrast, the exposure range of the phosphor plate systems is very wide. The preferred radiograph of the phosphor plate systems required high exposure (Digora, 1.21 s; Gendex DenOptix, 1.16 s). CONCLUSIONS: All digital systems require less exposure than film for diagnostically acceptable radiographs, but this is less obvious for preferred radiographs. Solid-state systems alert the dentist when a too long exposure time is used by a lack of image quality; phosphor plate systems, however, produce good quality radiographs even at high exposure times, which may result in an unnecessarily high dose.

Analysis of Variance↗

PubMed2003

Feasibility of local CT of dental tissues.

OBJECTIVES: To prove the feasibility of a local CT system as a method of CT suitable for use in dentistry. METHODS: Using an experimental set-up consisting of an X-ray source, a turntable and a charge-coupled device (CCD) detector connected to a PC, CT scans were made of a single molar and a dry mandible. Slices were reconstructed using filtered backprojection. An experimental comparison was made between a full CT geometry and a local CT geometry. RESULTS: Horizontal and vertical slices through the mandible were obtained showing the internal structure of a molar and the surrounding bone. The slices show good contrast and details. A computer experiment gave visual evidence that slices obtained by local CT are not substantially different from slices obtained from a full CT set-up with respect to resolution. CONCLUSIONS: Based on the results obtained so far, local CT of dental structures appears to be a promising diagnostic instrument.

Feasibility Studies↗

PubMed2003

Comparison of standard and task-specific enhancement of Digora storage phosphor images for approximal caries diagnosis.

OBJECTIVES: To compare approximal caries detection on Digora storage phosphor images pre-enhanced with the automatic "caries-specific Oslo enhancement procedure" ("Oslo-enhanced" method) and storage phosphor images individually enhanced by observers particularly experienced in digital imaging using standard brightness and contrast functions of the Digora system ("Digora-enhanced" method). METHODS: Seven staff members from four oral radiology departments rated 240 approximal surfaces for caries with regard to lesion depth in the inner and outer half of the enamel and dentine, using a 5-point confidence scale. The observations were validated histologically. A receiver operating characteristic (ROC) analysis and an analysis of variance with three dependent variables (observer confidence, observer signed error and observer absolute error) were performed. RESULTS: The most evident difference between the methods as elucidated by the ROC analysis was the highly significant smaller interobserver and intraobserver variance with the Oslo-enhanced method for all but one observer. The methods were not different with regard to average diagnostic accuracy (A(z) values) as tested with paired t-tests, and there was no correlation between A(z) across methods. The method and lesion main effects, as well as the lesion by method interaction effect, were multivariately significant (P<0.001) in favour of the Oslo-enhanced method. On a univariate level, the method main effect was not significant for the absolute observer error (P=0.330). All other univariate effects were significant (P<0.001). CONCLUSIONS: The accuracy of approximal caries detection with Digora storage phosphor images pre-enhanced and images individually enhanced was similar, but interobserver and intraobserver variability improved with the Oslo-enhanced method. Since image manipulation is not performed with the Oslo-enhanced method, the increased speed of the diagnostic procedure combined with the improved observer variability would probably be even more pronounced for the general dental practitioner.

Analysis of Variance↗

PubMed2003

Detection of caries with local CT.

OBJECTIVES: An in vitro observer study of the detection of interproximal caries by local CT. METHODS: Detection of caries by means of conventional two-dimensional (2D) digital radiography and by two CT modalities was compared. Ground truth was obtained from histological examination of the sectioned teeth. Twenty-three extracted teeth (46 surfaces) were placed in groups of six in two dry mandibles. The observers (n=10) scored the proximal surfaces for the presence of caries on a 1-5 confidence scale. Data analysis used analysis of variance (a General Linear Model). Observer and method were entered into the model as within-subject variables and lesion depth was entered as a between-subjects variable. RESULTS: The analysis showed observer, method and lesion depth effects as well as several interaction effects to be significant. Observers performed significantly better with the vertically reformatted CT slices than with conventional radiographs (P=0.025). Furthermore, there were significant differences between observers, and several interactions were found to be significant. This means that although the reformatted slices performed best overall, this performance differed significantly depending on observer and on lesion depth. CONCLUSIONS: Vertically reformatted CT slices obtained with local CT performed significantly better than conventional 2D digital radiographs in visually detecting caries. Axial slices did not perform better than conventional radiographs. When vertically reformatted slices are used, local CT is a promising tool for the detection of interproximal caries.

Analysis of Variance↗

PubMed2002

A comparison of two compression algorithms and the detection of caries.

OBJECTIVES: To assess the effect of two compression algorithms (JPEG and wavelet) on the detection of approximal caries. METHODS: Fifteen bitewing radiographs were generated using 100 posterior teeth mounted in blocks. The images were produced on conventional films (Ektaspeed Plus) and scanned at 300 d.p.i. Digital images were then compressed 9:1 with JPEG and wavelet methods. Nine observers detected the presence and depth of approximal caries recorded on a 5-point confidence scale and a 4-point depth scale from images viewed in random order. Histological examination provided the true depth of the lesions. Data were analysed by means of ANOVA. The null hypothesis was that there is no significant difference between the two compression algorithms and the original uncompressed images. RESULTS: JPEG performed significantly worse than the original and the wavelet algorithm (P<0.001) for the detection of dentinal lesions. However, no significant differences were found for the detection of sound surfaces, enamel lesions, and lesions up to the DEJ between JPEG-compressed images and each of the other two modalities. There was also no significant difference between the wavelet-compressed images and the original for all lesion depths. CONCLUSIONS: At a compression ratio of 9:1, there were no significant differences among the original images, JPEG and wavelet compressed images for the detection of enamel caries. JPEG-compressed images performed inferiorly to the original and wavelet-compressed images for the detection of dentinal lesions. Wavelet compression is a better choice than JPEG at the compression ratio investigated in this study.

Algorithms↗

PubMed2001

Machine classification of dental images with visual search.

RATIONALE AND OBJECTIVES: The authors performed this study to assess the performance of a computer-based classification system that uses gaze locations of observers to define the subspace for machine learning. MATERIALS AND METHODS: Thirty-two dental radiographs were classified by an expert viewer into four categories of disease of the periapical region: no disease (normal tooth), mild disease (widened periodontal ligament space), moderate disease (destruction of the lamina dura), and severe disease (resorption of bone in the periapical area). There were eight images in each category. Six observers independently viewed the images while their eye gaze position was recorded. They then classified the images into one of the four categories. A sample of image space was used as input to a machine learning routine to develop a machine classifier. Sample space was determined with three techniques: visual gaze, random selection, and constrained random selection. K analyses were used to compare classification accuracies with the three sampling techniques. RESULTS: With use of the expert classification as a standard of reference, observers classified images with 57% accuracy, and the machine classified images with 84% accuracy by using the same gaze-selected features and image space. Results of kappa analyses revealed mean values of 0.78 for gaze-selected sampling, 0.69 for random sampling, 0.68 for constrained random selection, and 0.44 for observers. The use of sample space selected with the visual gaze technique was superior to that selected with both random-selection techniques and by the observers. CONCLUSION: Machine classification of dental images improves the accuracy of individual observers using gaze-selected image space.

Artificial Intelligence↗

PubMed2001

Scanning resolution and the detection of approximal caries.

OBJECTIVE: To determine a proper scanning resolution for digitizing bitewing radiographs in the detection of approximal caries. METHODS: Fifty-two premolars and 48 molars were mounted in blocks and imaged on conventional film (Ektaspeed Plus, Eastman-Kodak, Rochester, NY USA) simulating a bitewing projection. The 15 bitewing radiographs were then scanned with a flatbed scanner at three resolutions 150, 300 and 600 d.p.i. The digitized images were displayed in random order on a high-resolution cathode ray tube monitor. Ten observers assessed the caries status of 200 approximal surfaces. They scored lesion presence on a 5-point confidence scale and depth on a 3-point scale. The observer's scores were compared with the results from a histological examination. Data were analysed using analysis of variance, by calculating signed observer error, absolute observer error and observer confidence. RESULTS: Lesion depth had a significant effect on confidence of lesion recognition. The main effect of resolution and the interaction between resolution and lesion depth were significant. Pair-wise comparison showed a significant difference between resolutions in case of sound surfaces and surfaces with dentinal lesions for absolute error. The confidence increased as the resolution increased but no significant difference was found between 300 and 600 d.p.i. The best score for depth estimation was obtained at the 300 d.p.i. scanning resolution. CONCLUSIONS: When bitewing radiographs are scanned with a flatbed scanner, a resolution of 300 d.p.i. seems the best choice. At this resolution the digital file size is manageable without significant loss of the information necessary for caries diagnosis.

Absorptiometry, Photon↗

PubMed2001

Detection of simulated internal tooth resorption using conventional radiography and subtraction imaging.

OBJECTIVES: To compare the diagnostic accuracy of conventional radiography with digital subtraction imaging in the detection of simulated internal resorption. METHODS: Simulated resorption cavities were created by the sequential use of progressively larger round burs (ISO size range 006-016) in the labial wall of the coronal or apical thirds of the pulp chamber of the maxillary incisors of two cadavers. Five viewers examined 120 pairs of radiographs, one of each pair being baseline (no lesion) and the other with or without a lesion. The process was then repeated with subtraction images of the pairs of radiographs. Receiver Operating Characteristic (ROC) analysis was used to compare the diagnostic accuracy of the two imaging modalities. RESULTS: Using conventional radiography, the minimum lesion size detectable coronally was in the 'medium' range (ISO size 010 and 012 round burs), but only 'large' lesions (ISO size 014 and 016) could be detected in the apical region. The overall diagnostic accuracy of subtraction imaging was superior to conventional radiography but only significant (P<0.05) for coronal lesions. CONCLUSION: Subtraction radiography may be a useful tool for detecting and monitoring the progress of internal root resorption.

Cadaver↗

PubMed2001

Comparative dose measurements by spiral tomography for preimplant diagnosis: the Scanora machine versus the Cranex Tome radiography unit.

Objective. The purpose of this study was to determine the dose profile of the Cranex Tome radiography unit and compare it with that of the Scanora machine. Study design. The radiation dose delivered by the Cranex Tome radiography unit during the cross-sectional mode was determined. Single tooth gaps in regions 3 (16) and 30 (46) were simulated. Dosimetry was carried out with 2 phantoms, a head and neck phantom and a full-body phantom loaded with 142 thermoluminescent dosimeters (TLD) and 280 TLD, respectively; all locations corresponded to radiosensitive organs or tissues. The recorded local mean organ doses were compared with those measured in another study evaluating the Scanora machine.Results. Generally, dose values from the Cranex Tome radiography unit reached only 50% to 60% of the values measured for the Scanora machine. The effective dose was calculated as 0.061 mSv and 0.04 mSv for tooth regions 3 (16) and 30 (46), respectively. Corresponding values for the Scanora machine were 0.117 mSv and 0.084 mSv.Conclusion. Cross-sectional imaging in the molar region of the upper and the lower jaw can be performed with the Cranex Tome unit, which delivers only approximately half of the dose that the Scanora machine delivers.

Anatomy, Cross-Sectional↗

PubMed2000

Interaction between noise and file compression and its effect on the recognition of caries in digital imaging.

OBJECTIVES: To determine the interaction between image noise and file compression, with special emphasis on the accuracy of caries diagnosis. METHODS: Fifty-nine bitewing radiographs of patients were taken simultaneously with Ektaspeed Plus (Eastman-Kodak, Rochester, NY, USA) film without lead foil and the Digora storage phosphor system (Soredex, Helsinki, Finland). Three different levels of Gaussian noise were added to the original digital images which were then compressed with JPEG 53. Seven observers evaluated the presence and depth of caries lesions on selected approximal surfaces on a 5-point scale. The results of JPEG 27 compression from a previous study were also included. ROC analysis was used together with multivariate analysis of variance (MANOVA). RESULTS: JPEG 27 and 53 reduced the file size down to 7% and 4.6% of the original respectively. ROC curve analysis showed no significant difference between image conditions (original, JPEG 27, and JPEG 53) at the same noise level. JPEG 27 and 53 had larger Az scores than their original counterparts at the same noise level. However, MANOVA showed that for depth estimation of enamel lesions JPEG 53 resulted in a higher observer error. CONCLUSIONS: Both JPEG 53 and 27 could reduce some of the adverse effect of noise from the image by removing high spatial frequencies. JPEG 53, resulting in a compression ratio of 1:21, does not compromise the diagnostic performance in general. JPEG 53 compression may however affect the ability to detect enamel lesions.

Artifacts↗

PubMed2000

Fractal properties of bone.

OBJECTIVE: To introduce the applications of fractal analysis of bone in medical imaging in general and dental radiographs in particular. RESULTS: Various methods for measuring fractal dimension have been used to compare normal with osteoporotic bone with contradictory results. This disparity may be attributed to differences in the anatomical sites studied and differences in methods used to obtain the 2D images. However, differences in methods used to measure fractal dimension can also be responsible. CONCLUSION: When fractal dimension is used to study bone it must be remembered that all stages in the analytical chain have an impact on the results. Thus, to obtain more conclusive results, studies on the fractal dimension of bone should be carefully designed and individual methods thoroughly evaluated.

Algorithms↗