Biomedical subjects

H G Gröndahl

Publications and source records attributed to H G Gröndahl.

At least 19 recordsLinked to original sources

PubMed2001

Fractal analyses of osseous healing using tuned aperture computed tomography images.

The aim of this study was to evaluate osseous healing in mandibular defects using fractal analyses on conventional radiographs and tuned aperture computed tomography (TACT; OrthoTACT, Instrumentarium Imaging, Helsinki, Finland) images. Eighty test sites on the inferior margins of rabbit mandibles were subject to lesion induction and treated with one of the following: no treatment (controls); osteoblasts only; polymer matrix only; or osteoblast-polymer matrix (OPM) combination. Images were acquired using conventional radiography and TACT, including unprocessed TACT (TACT-U) and iteratively restored TACT (TACT-IR). Healing was followed up over time and images acquired at 3, 6, 9, and 12 weeks post-surgery. Fractal dimension (FD) was computed within regions of interest in the defects using the TACT workbench. Results were analyzed for effects produced by imaging modality, treatment modality, time after surgery and lesion location. Histomorphometric data were available to assess ground truth. Significant differences (p < 0.0001) were noted based on imaging modality with TACT-IR recording the highest mean fractal dimension (MFD), followed by TACT-U and conventional images, in that order. Sites treated with OPM recorded the highest MFDs among all treatment modalities (p < 0.0001). The highest MFD based on time was recorded at 3 weeks and differed significantly with 12 weeks (p < 0.035). Correlation of FD with results of histomorphometric data was high (r = 0.79; p < 0.001). The FD computed on TACT-IR showed the highest correlation with histomorphometric data, thus establishing the fact TACT is a more efficient and accurate imaging modality for quantification of osseous changes within healing bony defects.

Animals↗

PubMed2001

Detection of artificially induced vertical radicular fractures using tuned aperture computed tomography.

This study compared the accuracy of three imaging modalities for the detection of artificially induced vertical root fractures (VRF) on teeth in cadaver mandibles. Fifty-four single-rooted, endodontically treated mandibular teeth being prepared to carry posts were evaluated using direct digital radiography (DDI) with a Schick sensor, unprocessed Tuned Aperture Computed Tomography (TACT-U) images and iteratively restored TACT (TACT-IR) images. Twenty-eight of these teeth had been subjected to fracture induction using an apically driven force. Nine basis images were used for each TACT image generation. Eight observers used a five-point confidence rating scale to record the confidence with which they considered a fracture to be present or not. Sensitivity and specificity values were computed and receiver operating characteristic (ROC) curves were generated. The areas under the curves (Az) used as an indication of the diagnostic accuracy of the imaging system were as follows: DDI: 0.37; TACT-U: 0.77 and TACT-IR: 0.81. DDI was significantly inferior to the TACT modalities. Differences in detection efficacy based on observers and observation sessions were noted on ANOVA and post-hoc Tukey's tests. This study indicates that TACT is the imaging modality of choice for VRF in endodontically treated teeth.

Analysis of Variance↗

PubMed2001

Three phosphor plate systems and film compared for imaging root canals.

AIM: The aim of this study was to compare three phosphor plate intraoral imaging systems (Digora (DA), Digident (DT), Denoptix (DX)) and E-speed conventional film (CF) for the imaging of root canals. METHODOLOGY: Sixty extracted permanent teeth were exposed using CF, DA, DT and DX. The length of root canal visible from its most apical extent to a line drawn at the level of the cementoenamel junction was measured and this was expressed as a percentage of the distance between the radiographic apex and the cementoenamel line. All images were examined concurrently by two examiners. Films were viewed under standardized conditions and DA, DT and DX images were viewed directly from the monitor screen. The images on the monitor were enhanced to give the subjectively clearest image. RESULTS: The mean percentage of canal visible on CF was 90%, DA 78%, DT 81% and DX 83%. The difference was significant for CF-DA (P < 0.001) and CF-DT (P = 0.001). There was no statistically significant difference for CF-DX or between any of the three phosphor plate imaging systems. CONCLUSIONS: It is concluded that a greater length of root canal was visible on conventional film than on three phosphor plate imaging systems and that this may be of clinical significance.

Analysis of Variance↗

PubMed2001

Signal-to-noise ratios of 6 intraoral digital sensors.

OBJECTIVE: The objective of this study was to compare the signal-to-noise ratios (SNRs) of 6 intraoral direct digital sensors. The sensors were Visualix 1, Visualix 2, DenOptix, Computed Dental Radiography (CDR), CDR APS, and Digora. STUDY DESIGN: The sensors were exposed by using a dental x-ray machine operating at 50 kV, 8 mA and various exposure times. The phantom used was a hole measuring 1 mm in diameter and 1.25 mm in depth, drilled in a 10-mm-thick aluminum block. Digital images were transferred as 8-bit tagged image file format files and analyzed by using a personal computer. RESULTS AND CONCLUSIONS: SNR values increased up to a maximum value at a certain exposure level and then, depending on the system, either decreased or maintained a high level with increased exposure. The Digora system produced the highest SNR values over a large exposure range, whereas the Visualix 2 and DenOptix systems produced the lowest SNR values. The 2 CDR sensors produced rather high SNRs but over a very small exposure range.

Algorithms↗

PubMed2000

Image plate systems differ in physical performance.

OBJECTIVE: The purpose of this study was to compare 2 storage phosphor image plate systems, the Digora and the DenOptix, with respect to physical performance. STUDY DESIGN: The 2 systems were tested both with and without use of their default settings through physical and psychophysical measurements. A homogeneous 10-mm-thick aluminum block, a 10-mm-thick aluminum block with a pattern of holes varying in diameter and depth, and a resolving power target were used as test phantoms. The image plates were exposed at 50 kV and 8 mA with a focus-sensor distance of 30 cm and exposure times ranging from 10 to 3,200 ms. Measurements of large area transfer function, gray level variations, perceptibility, contrast resolution, exposure range, and modulation transfer function were performed. RESULTS: When the two systems were used at their default settings, the DenOptix had a better dose response, a higher contrast index, and a higher modulation transfer function (MTF) than the Digora; however, the DenOptix also had higher noise than the Digora at lower exposures. CONCLUSIONS: When image enhancement algorithms were applied with the Digora system, performance similar to that of the DenOptix could be obtained.

Algorithms↗

PubMed2000

Subjective image quality of solid-state and photostimulable phosphor systems for digital intra-oral radiography.

OBJECTIVES: To compare subjectively the image quality of intra-oral radiographs from six digital systems. METHODS: Two generations of two different solid-state detectors; Visualix-1 and -2 (Gendex Dental Systems, Milan, Italy), Computed Dental Radiography (CDR) and CDR Active Pixel Sensor (APS) (Schick Technologies Inc., Long Island City, NY, USA), and two photostimulable phosphor (PSP) systems; Digora (Soredex, Orion Corporation, Helsinki, Finland) and DenOptix (Gendex Dental Systems, Milan, Italy) were compared. Tooth-containing specimens from different areas of dried mandibles were radiographed at exposures between 91-9400 microGy. Images were transferred to a personal computer, displayed in random order and evaluated in their original form and after applying a histogram equalisation algorithm. Eight observers graded subjective image quality using a 5-point scale. RESULTS: Both CDR systems scored highest for image quality but within the narrowest exposure range. The Visualix images received the lowest scores. The PSP systems produced acceptable image quality at both lower and higher exposures than the solid-state systems. Enhanced images were generally considered to be inferior to the original images, except for those produced by the four solid-state systems at very low exposures. CONCLUSIONS: (i) the PSP systems provided a clinically acceptable image quality over a wide exposure range; (ii) the CDR systems had the best image quality but over the narrowest exposure ranges; (iii) the Visualix systems had the lowest image quality; and (iv) histogram equalisation did not generally improve image quality.

Algorithms↗

PubMed2000

Digitisation and display of intra-oral films.

AIM: To determine the optimal parameters for the digitisation and display of intra-oral radiographs. MATERIALS AND METHODS: Six intra-oral radiographs (EP size 2 dental film, Eastman Kodak Co., Rochester, NY, USA) were digitised using an Arcus II image scanner (Agfa-Gevaert N. V., Mortsel, Belgium). Each film was digitised at 8 bits, with and without a film mask, using three scanner resolutions (200, 400 and 600 p.p.i.), resulting in six versions of each radiograph. Seven experienced observers were asked to evaluate the quality of the resulting images as they were displayed on a Nokia 445Xi monitor (Nokia Display Products, Helsinki, Finland). Monitor settings were varied by changing the colour palette and screen resolution. RESULTS: Digital images of masked films had a statistically significant (t-test with alpha 2 tail < or = 0.05) higher quality than those scanned without a mask. The best image quality was obtained at a resolution of 400 p.p.i. Display options were optimum with 256 colours and a screen size of 1152 x 864 pixels. CONCLUSIONS: Better results were obtained when intra-oral radiographs were digitised with a mask at a resolution of 200 or 400 p.p.i. and displayed using 256 colours and the largest screen size possible. Further studies are needed to extend these results to other makes and models of scanner and monitor.

Algorithms↗

PubMed2000

Computer-based registration for digital subtraction in dental radiology.

OBJECTIVES: (1) To review computerized a posteriori techniques for geometry and contrast registration prior to digital subtraction in dental radiography; (2) to define a uniform notation for their methodological and technical classification and based on this key code; (3) to derive criteria for successful application of computer-based a posteriori registration for routine clinical subtraction. METHODS: All techniques are classified with respect to the (1) dimension of geometry registration; (2) origin; (3) abstraction level, and (4) linkage of features used for registration of geometry; (5) elasticity; (6) domain, and (7) parameter determination of the geometrical transform used; (8) interaction of geometrical registration; as well as (9) origin of features, (10) model of transform, and (11) interaction of procedure for contrast correction. RESULTS: With respect to clinical practicability, superior registration techniques are based on the low level abstraction of intrinsic features for both geometry and contrast registration. By approximately linking the features, a global projective transform should be generated for geometry registration by automatic methods, while automatic contrast correction should be non-parametric. This challenge is met only by one out of 36 published algorithms. Hence, although numerous computer-based techniques have been published, only a few of them are applied more than once in practice. CONCLUSION: The key code proposed in this paper is useful for technical classification of a posteriori registration methods in dental radiography and allows their objective comparison. Further investigations will focus on standardization of practicable procedures to evaluate the robustness of competing methods.

Algorithms↗

PubMed2000

Marginal bone level around implants assessed in digital and film radiographs: in vivo study in the dog.

BACKGROUND: One of the objectives of postoperative radiographic examinations of implants is to evaluate the marginal bone height and its changes over time. PURPOSE: The purpose of this study was to assess the influence of digital image processing on measurements of the marginal bone level around implants. MATERIAL AND METHODS: Implants in beagle dogs, used to study the development of peri-implantitis and subsequent healing following treatment, were monitored with conventional radiography and a digital image plate system. Five observers measured the distance between a reference point and the bone level. Measurements in conventional radiographs were made with the use of an x-ray viewer (2x) and a magnifying lens (7x). For the digital images, the system's built-in measuring function was used together with five image processing techniques: edge enhancement (matrixes set on 5 and 25), inverted grey scale, single color highlight, and color intensity mapping together with the brightness and contrast control. From the time of maximum breakdown and the end of the experiment, histologic values were available. RESULTS: Differences between techniques and observers increased toward the end of the healing period. Measurements made at maximum breakdown did not differ significantly from the histologic value. Measurements made after healing all methods, except that using edge enhancement and a 25 x 25 kernel, differed significantly from the histologic value by underestimating the bone level. CONCLUSIONS: Measurements of bone level around implants from digital radiographs are as accurate and precise as those from film images. In particular cases, the use of specific image processing algorithms may improve both accuracy and precision. After healing, the histologic specimens showed an incomplete bone fill in the crater with a remaining thin layer of connective tissue in contact with the fixture, and in such situations, the morphology of the bone will give a more complicated diagnostic task.

Algorithms↗

PubMed1999

Quality of preimplant low-dose tomography.

OBJECTIVES: The aim of this study was to test the influence of radiation dose on image quality in mandibular preimplant computed tomographic examinations and to compare the quality of computed and conventional spiral tomographic images. STUDY DESIGN: Cross-sectional images were obtained on 17 patients with conventional spiral tomography (Scanora technique) and reformatted computed tomography at 40 and 80 mAs. Observers graded the acceptability of images for implant planning and traced the contour of the mandibular body and canal. RESULTS: Conventional spiral tomographic images scored significantly higher than computed tomographic images whereas mean score differences between computed tomographic techniques were not statistically significant. Anatomic structures, in particular the mandibular canal, were more frequently untraceable in high-dose than in low-dose computed tomography but always traceable in conventional tomograms. CONCLUSION: Conventional spiral tomograms were subjectively preferred over computed tomographic images. For mandibular implant planning, computed tomography examinations can be performed with lower-than-standard mAs. Quantum noise seems to contribute to the visibility of anatomic structures in reformatted computed tomographic images.

Adult↗

PubMed1999

Assessments of the physical performance of 2 generations of 2 direct digital intraoral sensors.

OBJECTIVE: To evaluate the performance of 4 intraoral direct digital sensors regarding their fundamental physical characteristics. The sensors are made by Schick Technologies Inc (Long Island City, NY) and Gendex Dental Systems (Milan, Italy). STUDY DESIGN: The sensors were exposed by using a Prostyle dental x-ray machine (Planmeca Oy, Helsinki, Finland) operating at 50 kV, 8 mA and various exposure times. Three test phantoms were used: a homogeneous 10-mm thick aluminum block, an aluminum block with a pattern of holes of varying sizes, and a resolving power target. Digital images were transferred as 8 bit TIFF files and analyzed by using a personal computer. RESULTS AND CONCLUSIONS: Some improvements could be observed in the physical performance of the new generation of direct digital radiographic sensors when compared with the earlier generation. Smaller pixels and higher quantum efficiency have improved sensor performance.

Artifacts↗

PubMed1998

Film and digital radiography for detection of simulated root resorption cavities.

OBJECTIVES: The purpose of this study was to evaluate observers' ability to detect simulated root resorption cavities in conventional radiographs and digital radiographs from a charge-coupled device system and a storage phosphor system and to determine whether the detectability was influenced by resorption size and exposure. STUDY DESIGN: In teeth from dry mandibular jaw specimens, resorptive defects 1.2 mm in diameter and two different depths (0.6 and 0.9 mm) were prepared in the buccal root surface. Each tooth was radiographed at a number of different exposure settings. Observers were asked to rate their confidence that a resorption was or was not present using a five-graded confidence scale. Receiver operating characteristic analysis was used to evaluate the results. RESULTS AND CONCLUSION: Given optimal exposures, all systems reached what might be considered clinically acceptable Az values (> 0.75). The storage phosphor system reached this value at considerably lower exposures than those required for both the film and charge-coupled device systems. There was a tendency to better detect the deeper lesions and to identify them at lower exposures.

Confidence Intervals↗

PubMed1998

Inter- and intraobserver variability in radiographic bone level assessment at Brånemark fixtures.

The aim was to determine inter- and intraobserver variability in radiographic bone level assessments at Brånemark fixtures and to study the influence of various factors (radiographic density; projection geometry; jaw in which the fixtures were inserted; degree of bone loss; time after fixture loading; and number of radiographs of each fixture) on the variability. Intraoral radiographs from bridge connection and 1- and 3-year check-ups from 15 upper and 15 lower jaws (172 fixtures) were assessed by 6 observers. Measurements were taken from a reference point on the fixture to the marginal bone level, and some were repeated by all observers after 1 months. Results showed a small interobserver variation (0.14 mm) with the intraobserver variation (0.08 mm) as its largest component. The radiographic density and the degree of bone loss showed the strongest influence on the interobserver variation. The only variable with a significant effect on the intraobserver variation was the number of radiographs of each fixture. Calculated confidence values showed that measurement reliability can be improved by letting one observer or preferably more make several, independent readings, allowing for the demonstration of minor differences in bone height over time or between implant systems.

Alveolar Bone Loss↗

PubMed1998

Observer-independent registration of perspective projection prior to subtraction of in vivo radiographs.

OBJECTIVES: To prove that the model of perspective projection allows precise registration of intra-oral radiographs regardless of whether they have been acquired with or without individual adjustment aids and independent of the human observer or computer algorithm marking corresponding landmarks in the images and, based on in vivo radiographs, to introduce and evaluate a model-based registration method. METHODS: Five observers (three experts and two non-experts) were asked to define corresponding points in 24 pairs of in vivo dental radiographs from the same region of the same patient. The landmarks were used to fit the model of perspective projection applying the least squares method. Misplaced landmarks were detected and suppressed by analysing the quality of all subsets of landmarks with respect to the minimal residual (leaving one out method). In addition, local correlation was used to optimize the quality of registration as well as observer independence. RESULTS: Using six or more corresponding landmarks in both radiographs the correlation of the images registered was > 0.95 (S.D. < 0.063) irrespective of the observers' expertise. CONCLUSIONS: Perspective projection is a reliable model for sequentially acquired intra-oral radiographs. The co-ordinates of anatomical landmarks are useful for determining the parameters of perspective projection. Local correlation and leaving one out techniques improve the geometrical adjustment as well as observer independence. Registration is nearly independent of the actual position of the landmarks and hence independent of the observer. Our algorithm will also be useful for registration techniques based on automatically detected landmarks.

Humans↗

PubMed1998

A logistic regression model for analyzing the relation between dentists' attitudes, behavior, and knowledge in oral radiology.

The aim was to study the relation between risk attitude and knowledge in technical, patient-oriented, and organizationally related behavior within oral radiology. A questionnaire was mailed to 2000 randomly selected dentists listed in the register of the Swedish Dental Society, with a response rate of 69.3%. Regression analysis was used for analyzing the effects of the independent variables knowledge, risk attitude, continuing education in oral radiology, counties with specialists in oral radiology, type of practice, work experience, and sex on three categories of dependent variables: 1) technical behaviors: type of film, type of collimator, dose level, frequency of change of chemicals; 2) patient-oriented behaviors: use of patient protection barriers, strict indications for performing full-mouth X-ray examinations and bitewing radiography on new patients and recall patients; and 3) organizationally related behaviors: delegation of X-ray examinations to dental auxiliaries, influence on choice of collimator, influence on choice of film. Knowledge and education had strong direct effects for most of the dependent variables. The technical behaviors were mainly influenced by knowledge, education, and risk attitude, while organizationally related behaviors were influenced by type of practice and sex. The patient-oriented behaviors were influenced by a number of independent variables, such as education, type of practice, work experience, and sex. The present results indicate that both knowledge and the organizational context of dentists influence work.

Adult↗

PubMed1997

The use of tomography for dental implant planning.

OBJECTIVES: To examine the use of tomography for dental implant planning. METHODS: A questionnaire was sent to oral radiology clinics in Sweden and to implantology clinics in different parts of the world with questions on selection criteria and techniques for, and frequency of, pre-implant tomography. Differences between mean values were assessed by t-test. A new method developed by the Swedish Radiation Protection Institute was used to assess radiation absorbed dose from CT. RESULTS: Tomography was used by 93.4% of the clinics, but there was marked variation both between and within different clinical situations. It was performed in all cases by 21% and the majority used it for the evaluation of the maxilla, the posterior mandible and in single implant cases. Small clinics (< 100 patients per year) used tomography frequently and clinics in Sweden significantly more often than those in other countries. The majority had changed their policy recently, using tomography more often. CT was used by 73% of respondents, mainly the small clinics. The majority of the large clinics (> 500 patients per year) used conventional tomography. The mean absorbed dose for CT scanning protocols was 65 mGy. The variation within and between different makes of CT was considerable. CONCLUSIONS: There are large variations in frequency of use of both conventional and computed tomography for dental implant planning by different clinics who also vary in the indications for their choice. A substantial factor influencing the technique chosen was its availability rather than clinical need.

Dental Implantation, Endosseous↗

PubMed1997

Marginal bone level buccal to mandibular molars in digital radiographs from charge-coupled device and storage phosphor systems. An in vitro study.

The aim of this in vitro study was to compare bone loss measurements in the furcation area of mandibular molars in digital radiographs from a CCD-(Sens-A-Ray) and a storage phosphor (Digora) system, 10 1st and 7 2nd mandibular molars, with intact lingual but reduced buccal bone with furcation involvements, were used. Radiographs were first taken with lead markers at the most apical part of the buccal bone and at the cemento-enamel junction. These radiographs were used to establish a radiographically true distance between the CEJ and the buccal bone level. The lead marker at the CEJ served as a reference point for the observers' subsequent estimates of the extent of bone removed, which were made in radiographs without lead markers at the bone level. 1 exposure (400 ms) for the CCD- and 5 (160 ms, 200 ms, 250 ms, 320 ms, 400 ms) for the storage phosphor system were used. Measurements were made in unprocessed (original) and processed images (contrast enhanced and/or high pass filtered). The results showed underestimation of bone loss, but smaller than previously reported for film radiographs. No significant difference was found between the 2 systems when compared at the same exposure. Nor were any significant differences found between unprocessed and processed images or between storage phosphor images from different exposures. We conclude that digital radiographs are comparable to film based radiographs for measurement of buccal bone loss but that lower exposures can be used, especially with the storage phosphor system.

Alveolar Bone Loss↗

PubMed1996

Impact of lossy image compression on accuracy of caries detection in digital images taken with a storage phosphor system.

Image compression may reduce storage needs whether in the lossless (reversible) or lossy (irreversible) form. The aims of the study were to evaluate (1) storage needs, (2) subjective image quality, and (3) accuracy of caries detection in digital radiographs compressed to various levels by a lossy compression method. The material consisted of 116 extracted human premolars and molars. The teeth were mounted three in a line and radiographed by the Digora system (Sorodex Medical Systems, Helsinki, Finland). The images were exported in tagged image file format and compressed with the Lempel-Ziv-Welch reversible and the Joint Photographic Experts Group irreversible compression algorithm on four levels. The total of 580 images were assessed by five observers on a 5-rank confidence scale for caries diagnosis. The observers subjectively judged image quality on an 11-point rank scale. With the reversible compression, images could be compressed to less than 50% of the original storage needs whereas the four irreversible compression factors compressed to 20%, 8%, 5%, and 3%, respectively. For occlusal surfaces, when receiver operating characteristic curve areas were increasingly smaller and the compression rate was higher. The difference between the original and the most compressed images was 14% (p = 0.1). The median quality score was above middle on the 11-point rank scale for all except the most compressed images (median score = 1). In conclusion, for caries diagnosis, compression ratio rates of 1:12 can be justified before accuracy and image quality is significantly affected.

Dental Caries↗