| 1. |
- Economopoulos, TL, et al.
(författare)
-
A contrast correction method for dental images based on histogram registration
- 2010
-
Ingår i: Dentomaxillofacial Radiology. - : British Institute of Radiology. - 0250-832X .- 1476-542X. ; 39:5, s. 300-313
-
Tidskriftsartikel (refereegranskat)abstract
- Contrast correction is often required in digital subtraction radiography when comparing medical data acquired over different time periods owing to dissimilarities in the acquisition process. This paper focuses on dental radiographs and introduces a novel approach for correcting the contrast in dental image pairs. The proposed method modifies the subject images by applying typical registration techniques on their histograms. The proposed histogram registration method reshapes the histograms of the two subject images in such a way that these images are matched in terms of their contrast deviation. The method was extensively tested over 4 sets of dental images, consisting of 72 registered dental image pairs with unknown contrast differences as well as 20 dental pairs with known contrast differences. The proposed method was directly compared against the well-known histogram-based contrast correction method. The two methods were qualitatively and quantitatively evaluated for all 92 available dental image pairs. The two methods were compared in terms of the contrast root mean square difference between the reference image and the corrected image in each case. The obtained results were also verified statistically using appropriate t-tests in each set. The proposed method exhibited superior performance compared with the well-established method, in terms of the contrast root mean square difference between the reference and the corrected images. After suitable statistical analysis, it was deduced that the performance advantage of the proposed approach was statistically significant.
|
|
| 2. |
- Economopoulos, T, et al.
(författare)
-
Automatic correspondence using the enhanced hexagonal center-based inner search algorithm for point-based dental image registration
- 2006
-
Ingår i: Conf Proc IEEE Eng Med Biol Soc. ; 1, s. 1421-1424
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper a modified version of the center-based inner search algorithm, the enhanced hexagonal center-based inner search algorithm, for automatic point correspondence is proposed towards dental registration. The modified algorithm is incorporated within a general registration scheme which is based on extracting a set of candidate points on the reference image, finding their corresponding points in the other image (float image) using the proposed algorithm and applying an affine geometrical transformation towards automatic registration. The performance of the proposed algorithm is evaluated against a well-known method for automatic correspondence, in terms of the registration accuracy. Qualitative and quantitative results on registering 24 dental pairs showed that the proposed algorithm outperforms the other method for automatic correspondence.
|
|
| 3. |
- Economopoulos, T, et al.
(författare)
-
Automatic correspondence using the enhanced hexagonal centre-based inner search algorithm for point-based dental image registration
- 2008
-
Ingår i: Dentomaxillofacial Radiology. - : British Institute of Radiology. - 0250-832X .- 1476-542X. ; 37, s. 185-204
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives: In this paper, the enhanced hexagonal centre-based inner search (EHCBIS) algorithm, for automatic point correspondence, is proposed for dental image registration. Methods: The presented algorithm is incorporated within a general registration scheme, which is based on extracting a set of candidate points on the reference image, finding their corresponding points in the image to be transformed (float image) using the proposed algorithm and applying a suitable geometrical transformation towards automatic registration. The performance of the proposed algorithm is evaluated against three well-known methods for automatic correspondence, the self-organizing maps, the automatic extraction of corresponding points and the trimmed iterative closest point method, in terms of registration accuracy. Results: Qualitative and quantitative results on registering 123 dental pairs show that the proposed algorithm outperforms the other methods for automatic correspondence with or without the presence of noise. Conclusions: The EHCBIS method is capable of defining automatically corresponding points in dental image pairs. It can be incorporated within a general scheme for point-based registration of dental radiographs acquired with or without rigorous a priori standardization. The applied projective transformation provides a reliable model for registering intraoral radiographs. The methodology does not require any segmentation prior to alignment providing subtraction radiographs and fused images for clinical evaluation regarding the evolution of a disease or the response to a therapeutic scheme.
|
|
| 4. |
- Ekestubbe, Annika, 1953, et al.
(författare)
-
Low-dose tomographic techniques for dental implant planning.
- 1996
-
Ingår i: The International journal of oral & maxillofacial implants. - 0882-2786. ; 11:5, s. 650-9
-
Tidskriftsartikel (refereegranskat)abstract
- Image quality in preimplant computerized tomography (CT) examinations made with different radiation doses (40 to 280 mAs) and scanning modes (standard and helical axial, 15-degree angled, and frontal) and in conventional spiral tomography (Scanora) was compared. Mandibular canal and alveolar bone crest visibility was evaluated in images from mandibular jaw segments. Visibility was unaffected by radiation dose in CT examinations except in frontal scanning, where a small actual difference was statistically significant. Differences among CT scanning modes and between CT and conventional spiral tomography were highly significant. Low-dose mandibular preimplant tomography can be performed with CT using lower-than-normal radiation doses or with conventional spiral tomography.
|
|
| 5. |
- Ekestubbe, Annika, 1953, et al.
(författare)
-
Oral radiologi
- 2005
-
Bok (övrigt vetenskapligt/konstnärligt)
|
|
| 6. |
- Ekestubbe, Annika, 1953, et al.
(författare)
-
Quality of preimplant low-dose tomography.
- 1999
-
Ingår i: Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics. - 1079-2104. ; 88:6, s. 738-44
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 7. |
- Ekestubbe, Annika, 1953, et al.
(författare)
-
The use of tomography for dental implant planning.
- 1997
-
Ingår i: Dento maxillo facial radiology. - : British Institute of Radiology. - 0250-832X. ; 26:4, s. 206-13
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 8. |
- Fransson, Christer, 1956, et al.
(författare)
-
Severity and pattern of peri-implantitis-associated bone loss.
- 2010
-
Ingår i: Journal of clinical periodontology. - 1600-051X. ; 37:5, s. 442-8
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: The purpose of the present study was to describe the severity and pattern of peri-implantitis-associated bone loss. Material and Methods: Intra-oral radiographs from 182 subjects were analysed. Bone-level measurements were performed in 419 implants with a history of bone loss. All radiographs obtained in the interval from the 1-year follow-up to the end-point examination (5–23 years) were analysed. The amount of bone loss that occurred from 1 year after prosthesis insertion was assessed and the pattern of bone loss was evaluated. Results: The average bone loss after the first year of function was 1.68 mm and 32% of the implants demonstrated bone loss geqslant R: gt-or-equal, slanted2 mm. The multilevel model revealed that the bone loss showed a non-linear pattern and that the rate of bone loss increased over time. The model also revealed that the pattern of peri-implantitis associated bone loss was similar within the same subject. Conclusion: It is suggested that peri-implantitis-associated bone loss varies between subjects and is, in most cases, characterized by a non-linear progression, with the rate of loss increasing over time. One of the main goals in implant therapy is to preserve tissue integration and thereby maintain bone support. Marginal bone loss is thus considered a critical outcome variable in the evaluation of implant therapy. It has been suggested that data on bone loss during the first year of function should be distinguished from that occurring during the subsequent period of service. According to the suggested success criteria for implants (Albrektsson et al. 1986, Albrektsson & Zarb 1993), marginal bone loss should not exceed 1.5 mm during the first year in function and should be <0.2 mm/year thereafter. A modification to these criteria that indicated a maximum bone loss of 2 mm between prosthesis installation and 5 years of follow-up was presented in a consensus report from the European Workshop on Periodontology in 1999 (Wennström & Palmer 1999). Whether certain amounts of bone loss around implants should be acceptable or not requires an understanding of the mechanisms involved in the process of bone resorption. Although the question on the aetiology of marginal bone loss around implants still has to be completely unravelled, previous studies have demonstrated the association between progressive bone loss during function and clinical signs of inflammation in peri-implant tissues (Roos-Jansåker et al. 2006, Fransson et al. 2008). We have previously reported on the prevalence and extent of peri-implantitis-associated bone loss (Fransson et al. 2005, 2009). From the analysis of radiographs obtained from 662 subjects treated with implant-supported prosthesis, it was documented that 184 (27.8%) of the subjects had geqslant R: gt-or-equal, slanted1 implant with peri-implantitis-associated bone loss (Fransson et al. 2005, 2008). Within this group of subjects, about 40% of the implants were affected (Fransson et al. 2009). Using this subject sample, the purpose of the present study was to describe the severity and pattern of peri-implantitis-associated bone loss.
|
|
| 9. |
|
|
| 10. |
- Gröndahl, Hans-Göran, 1940, et al.
(författare)
-
Radiographic examination of the implant patient
- 2008
-
Ingår i: In: Lindhe J, Lang NP, Karring T (eds.). Clinical Periodontology and Implant Dentistry (vol 2), fifth edition. PA: Wiley-Blackwell.
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
|
|
