Biomedical subjects

H-G Gröndahl

Publications and source records attributed to H-G Gröndahl.

9 recordsLinked to original sources

PubMed2006

Degradation of storage phosphor images due to scanning delay.

OBJECTIVE: To evaluate the degradation of storage phosphor images relative to scanning delay. METHODS: A series of exposures of an aluminium step-wedge with five 2 mm incremental steps were made using blue Digora storage phosphor plates (SPPs). After the first exposure the plates were immediately scanned. After the second the plates were scanned after a half hour delay, after the third after a 1 h delay and so on until a final delay of 8 h. Mean grey values (MGVs) of each step of the wedge and its background were compared using repeated measures analysis of variance (ANOVA). Difference between group means was assessed using Bonferroni/Dunn multiple comparison test (P<0.05). RESULTS: MGVs increased with the increase in scan delay. Repeated measures ANOVA revealed that MGVs of the background and each step of the wedge were significantly different from each other for all scan delays (P<0.0001). Bonferroni/Dunn test showed that MGVs from plates scanned half an hour after exposure were not significantly different from those scanned immediately (P>0.05). Longer delays gave rise to significant differences in MGVs (P<0.05). CONCLUSION: Digora SPPs show statistically significant degradation of grey level values and contrast in plates scanned half an hour or longer after exposure.

Aluminum↗

PubMed2004

Quality of film-based and digital panoramic radiography.

OBJECTIVES: To compare the image quality of panoramic radiographs obtained with storage phosphor plate and screen-film systems. METHODS: Panoramic radiographs were taken in 60 patients both with film and with a storage phosphor plate system (30 with DenOptix (Dentsply/Gendex) and 30 with Digora PCT). The images were obtained with either the Cranex Tome or the Scanora multimodal X-ray unit. The screen-film combination was Lanex medium/Curix Ortho HT-G. The digital images were displayed as 8-bit images with a 300 dpi resolution on a 19" monitor and the film images were placed on a light box adjacent to the screen. Ten observers evaluated diagnostic image quality by means of visual grading analysis of different anatomical structures. The structures were scored as being visualized much better (5), better (4), equal (3), worse (2) or much worse (1) in the digital images than in the film images. The mean number of patients receiving the different scores was calculated. Statistical methods used were Wilcoxon sign rank test and Mann-Whitney test. RESULTS: On average, visualization was equal in 19 of the 30 patients imaged using Digora PCT; in 10 it was worse. The corresponding values for DenOptix were 20 and 9. The difference between the film-based and the digital images was small but statistically significant (P<0.0001). The difference between the two image plate systems was not statistically significant (P>/=0.17). CONCLUSIONS: It was concluded that digital panoramic radiographs are equivalent to film-based images for most purposes.

Adult↗

PubMed2004

A digital subtraction radiography scheme based on automatic multiresolution registration.

OBJECTIVES: To establish a digital subtraction radiography scheme for aligning clinical in vivo radiographs based on the implementations of an automatic geometric registration method and a contrast correction technique. METHODS: Thirty-five pairs of in vivo dental radiographs from four clinical studies were used in this work. First, each image pair was automatically aligned by applying a multiresolution registration strategy using the affine transformation followed by the implementation of the projective transformation at full resolution. Then, a contrast correction technique was applied in order to produce subtraction radiographs and fused images for further clinical evaluation. The performance of the proposed registration method was assessed against a manual method based on the projective transformation. RESULTS: The qualitative assessment of the experiments based on visual inspection has shown advantageous performance of the proposed automatic registration method against the manual method. Furthermore, the quantitative analysis showed statistical difference in terms of the root mean square (RMS) error estimated over the whole images and specific regions of interest. CONCLUSIONS: The proposed automatic geometric registration method is capable of aligning radiographs acquired with or without rigorous a priori standardization. The methodology is pixel-based and does not require the application of any segmentation process prior to alignment. The employed projective transformation provides a reliable model for registering intraoral radiographs. The implemented contrast correction technique sequentially applied provides subtraction radiographs and fused images for clinical evaluation regarding the evolution of a disease or the response to a therapeutic scheme.

Algorithms↗

PubMed2004

Effective and organ doses from scanography and zonography: a comparison with periapical radiography.

OBJECTIVES: To compare absorbed and effective doses from scanographic and zonographic examinations performed in the Scanora unit with intraoral periapical radiography. METHODS: Absorbed dose measurements were made on an anthropomorphic phantom head with LiF thermoluminescent dosemeters in the regions of the pituitary gland, eye lenses, parotid glands, submandibular glands, thyroid gland and skin. Energy imparted was calculated from the measurements of air collision kerma and effective doses by using the quotient 24 mSv J-1 between energy imparted and effective dose. The upper and lower third molar region was examined with intraoral radiographs and with ramus scanograms, dental scanograms and dental zonograms. Radiation dose measurements were also performed for Scanora panoramic radiography (jaw and dental). RESULTS: The effective doses for the ramus and dental scanograms were 0.01 mSv, similar or lower than for intraoral radiography. Zonography yielded the highest effective dose (0.03 mSv). Except for the skin doses, the salivary glands received the highest doses. Salivary gland doses were slightly higher from narrow beam than from intraoral radiography. CONCLUSIONS: Detail narrow beam radiography with the Scanora is an alternative to periapical radiography and is preferred, from a radiation dose point of view, over zonography.

Humans↗

PubMed2003

Quality of digital pre-implant tomography: comparison of film-screen images with storage phosphor images at normal and low dose.

OBJECTIVES: The aim of this pilot study was to compare the image quality of a storage phosphor system with that of conventional film-screen in pre-implant conventional tomography, and to test the influence of radiation dose on image quality in the storage phosphor system. METHODS: Cross-sectional conventional tomographic images (Scanora) technique) were obtained on 11 patients with film-screen and with storage phosphor image plates (Digora) PCT) at normal and low doses. Ten observers graded the visibility of anatomical structures of importance for implant planning. A three-step rating scale was used, where -1 =worse, 0=equal and 1=better than the reference image. RESULTS: Although image quality was graded as equally good in the majority (59%) of images, the storage phosphor system scored significantly lower than film-screen (-0.37 vs 0.00, respectively) for all the images. Low dose storage phosphor images were rated significantly lower (-0.21) than normal dose images (0.00). CONCLUSIONS: In the majority of patients, anatomic structures of importance for implant planning are visualized equally well on storage phosphor and film-screen images. However, where differences do exist, storage phosphor images score lower than film-screen images. Dose reduction in the storage phosphor system had a negative influence on image quality.

Adult↗

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↗

PubMed2002

Caries development in a young population managed by a restrictive attitude to radiography and operative intervention: II. A study at the surface level.

OBJECTIVES: To longitudinally assess the distribution of fillings and carious lesions in permanent posterior tooth surfaces, caries states fillings were made, and survival time of proximal lesions in different states in a young population managed by minimal operative treatment and a restrictive attitude to radiography. METHODS: Bitewing radiographs from age 6-20 in 285 patients were analysed. Proximal and occlusal surfaces were coded for caries depth and fillings. Start and end dates for different caries states in proximal surfaces were assigned and survival times in these states calculated by means of survival statistics. RESULTS: The frequency of carious/filled occlusal surfaces in the population increased from 6 to 19% and that of proximal surfaces from 1 to 26%. At age 19, 86% of the occlusal and 7% of the proximal surfaces affected by caries were filled. An overwhelming majority of unfilled carious proximal surfaces had enamel lesions only. Of all fillings, 81% were placed in surfaces with dentine lesions. The occlusal and proximal surfaces of the first molar and the distal surface of the second premolar accounted for most lesions and fillings among the 19-year-olds. The average survival time of lesions in the enamel was 8.0 years and in the outer half of the dentine 3.4 years when right-censored data were taken into account. CONCLUSION: In a young population exposed to optimal levels of fluoride with a caries preventive programme, a restrictive attitude towards operative treatment can be combined with longer average intervals between radiographic examinations than those prescribed by current guidelines.

Adolescent↗

PubMed2002

Caries development in a young population managed by a restrictive attitude to radiography and operative intervention: I. A study at the patient level.

OBJECTIVES: To assess, in a young population (age 6-19) managed by a restrictive attitude to radiography and operative intervention, prevalence of patients with posterior caries and/or fillings, probabilities of new proximal dentine lesions given different caries experience, correlation between radiographic intervals and caries experience, and prevalence of endodontic treatment. METHODS: Bitewing radiographs, taken between age 6 through 19 in 285 patients, were analysed in succession. Occlusal and proximal surfaces were coded for caries depth (0-4) and presence of fillings (5). Simple regression analysis was used to determine relations between radiographic intervals and caries experience. Significance testings of probability estimates were made with chi(2)- and t-tests, when applicable adjusted by the Bonferroni-Holm correction for mass-significance. RESULTS: The prevalence of patients with >/ or =1 fillings/dentine lesions in occlusal surfaces increased from 6-78% and in proximal ones from 1-38%. The probability of developing new proximal dentine lesions/fillings over different time periods was significantly lower among caries-free patients than among those with enamel or dentine lesions. There was a poor correlation between radiographic intervals (mean=16 months, range=6-33) and accumulated caries experience. Endodontic treatment had been made in a total of six teeth in six patients. CONCLUSIONS: A restrictive attitude both to the frequency with which radiographs are taken and to operative treatment of proximal caries seems to be possible in young populations with low caries prevalence.

Adolescent↗

PubMed2002

Accuracy of tuned aperture computed tomography in the diagnosis of radicular fractures in non-restored maxillary anterior teeth--an in vitro study.

OBJECTIVES: This study compared the accuracy of three radiographic imaging modalities for the detection of artificially induced radicular fractures on maxillary anterior teeth. METHODS: Fractures were induced in 28 of 54 maxillary incisors in 15 cadaver specimens using a distally directed force. Radiographs evaluated included conventional two-dimensional direct digital radiographs (DDI), unprocessed Tuned Aperture Computed Tomography (TACT-U) and iteratively restored TACT (TACT-IR). Eight observers recorded their findings using a five-point confidence-rating scale. Receiver Operating Characteristic (ROC) analyses were done, followed by ANOVA to test for significant effects of observers, imaging modality and fracture location. Post hoc tests were carried out in instances where ANOVA indicated significance. RESULTS: The areas under the ROC-curves (A(z)) were, respectively: DDI: 0.53; TACT-U: 0.83 and TACT-IR: 0.97. TACT-IR and TACT-U performed significantly better than DDI (P < 0.001) with TACT-IR providing a higher detection accuracy than TACT-U (P < 0.033). A difference in detection accuracy was also noted based on fracture location (P < 0.001). Tukey's post hoc analyses revealed that fractures extending beyond the middle third of the root were more accurately detected. Inter-observer agreement was 0.68, and intra-examiner agreement, 0.87 (kappa analysis). CONCLUSIONS: TACT performed significantly better than direct digital images in detecting trauma-induced radicular fractures in unrestored, maxillary anterior teeth.

Analysis of Variance↗