An evaluation of the errors in cephalometric measurements on scanned cephalometric images and conventional tracings
Department of Orthodontics, Faculty of Dentistry, Yeditepe University, Istanbul, Turkey
Address for correspondence Dr Korkmaz Sayinsu, Department of Orthodontics, Faculty of Dentistry, Yeditepe University, Bagdat cad. No. 238, Goztepe, TR-81006 Istanbul, Turkey, E-mail: drkorkmaz{at}yeditepe.edu.tr
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Summary |
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 Top Summary IntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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The aim of this investigation was to compare the classic method of tracing by hand with a computerized method, where the lateral cephalograms were scanned at 300 dpi and digitized onscreen. The inter- and intra-observer errors were investigated for tracing and digitizing errors.
Thirty lateral cephalograms were scanned into digital format at 300 dpi, displayed on a high-resolution monitor, and processed twice by two operators using Dolphin Imaging Software 9.0. The same radiographs were then traced and measured manually by the same two operators. Intraclass correlation coefficients (ICC) were used for detecting intra- and inter-rater agreement for each cephalometric variable.
The results showed that each operator was consistent in the repeated measurements; all ICC were greater than or equal to 0.90 and none of the 95 per cent confidence limits on these ICC had a lower boundary less than 0.84. Inter-rater agreement also showed correlation coefficients greater than 0.75. The angles, maxillary height, maxillary depth, y-axis, FMA, and nasolabial, and the distance N perpendicular point A had a wider reliability interval and lower correlation than the other parameters tested. The findings demonstrated that the use of computer software for cephalometric analysis carried out on scanned images does not increase the measurement error when compared with hand tracing.
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Introduction |
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TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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In contemporary orthodontics, lateral cephalograms are used for the assessment of treatment changes induced by the appliances used. Therefore, it is important to keep the method error to a minimum in order to see the valid small changes achieved by treatment (Kamoen et al., 2001
). Hence, errors arising from the acquisition of radiographs, tracing, landmark identification, and measurements have been investigated in an effort to minimize related errors (Baumrind and Frantz, 1971a, b; Gravely and Benzies, 1974; Cohen, 1984; Houston et al., 1986; Battagel, 1993; Chen et al., 2000, 2004; Turner and Weerakone, 2001).
Tracing on paper using hand instruments is reported to compare favourably with the results of digitized radiographs and the findings of studies using manual methods could be considered perfectly valid (Richardson, 1981; Sandler, 1988). Manual tracing was found to yield more reproducible results especially for the points articulare and gonion which are constructed on a tracing, but only estimated using the digitizer (Sandler, 1988). Other points were easier to visualize and locate when the outline of the structure could be traced first, such as the apex of the maxillary incisor root (Houston, 1983).
On the other hand, hand measurements are time-consuming and there is a risk of misreading the measuring instruments and registering data to the computer (Sandler, 1988). If digitization is carried out, then the angles and distances are automatically calculated which can eliminate the errors in drawing lines between landmarks and in measurements with a protractor. Moreover, the digital image can be manipulated to process the image and alter its visual appearance which can facilitate landmark identification (Jackson et al., 1985).
Although radiographic film is quite stable and can retain its information for many years, due to its physical nature, it is not always a dependable archive medium (Geelen et al., 1998). Film deterioration has been a major source of information loss in craniofacial biology (Melsen and Baumrind, 1995); therefore, digital archiving of lateral cephalograms is a valuable method for orthodontic clinics.
A previous study revealed that computer-aided cephalometric analysis does not introduce more measurement error when the localization of the landmarks is determined by hand (Gravely and Benzies, 1974). However, other research has shown that there are statistically significant differences in landmark identifications between original and digitized cephalometric radiographs (Chen et al., 2000). More recent research carried out by the same authors concluded that the differences between the measurements derived from the landmarks on original cephalometric radiographs and those identified on their digitized counterparts were statistically significant but clinically acceptable. The inter-observer errors of cephalometric measurements on digitized images were generally comparable with those from original radiographs (Chen et al., 2004).
The aim of this investigation was to compare the classic method of tracing by hand with a computerized method, where the lateral cephalograms were scanned at 300 dpi and digitized onscreen. The inter- and intra-observer errors were investigated for tracing and digitizing errors.
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Materials and methods |
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TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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Thirty lateral cephalograms were randomly selected from the patient files at the Department of Orthodontics, Yeditepe University. These radiographs were scanned into digital format at 300 dpi using an Epson 1680 Pro scanner, with 1600 dpi imaging 40 800 pixels per line and 48-bit colour depth for both film and reflective scanning, and displayed on a 15-inch 1024 x 768 high-pixel resolution Benq FP581 monitor with pixel pitch of 0.297 mm, a contrast ratio of 450:1, and a brightness of 250 cd/m2. All the scanned bitmap images of radiographs were then processed twice by two operators (KS and FI) using Dolphin Imaging Software 9.0 (Los Angeles, California, USA). The same radiographs were then traced twice with a 0.1 mm drawing pen by the same two operators, and measured using a ruler and protractor. There was at least a 3-week interval between the two landmark identification sittings of any radiograph (Figure 1).
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Nine dental, 21 skeletal, and three soft tissue parameters were measured, which consisted of 18 angular measurements, 13 linear measurements, and four ratios (Table 1).
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Intraclass correlation coefficients (ICC) were used to determine intra- and inter-rater agreement for each cephalometric variable. ICC, derived from analysis of variance, assesses rating reliability by comparing the variability of different ratings of the same subject to the total variation across all ratings and all subjects. It is a measure of the homogeneity of elements within clusters and has a maximum value of 1 when there is complete homogeneity (Kish, 1965
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Results |
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TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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The results showed that each operator was consistent in the repeated measurements; all ICC were greater than or equal to 0.90 and that none of the 95 per cent confidence limits on these ICC had a lower boundary that was less than 0.84. ICC of 0.75 or above are usually considered to be good and above 0.9 to be excellent (Table 2). Inter-rater agreement also showed correlation coefficients greater than 0.75 (Table 2). The angles maxillary height, maxillary depth, y-axis, FMA, and nasolabial, and the distance N perpendicular had a wider reliability interval and lower correlation than other parameters tested.
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Discussion |
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TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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In modern orthodontics, quantitative, systematic, and objective measurements based on hard and soft tissue landmarks determined on cephalometric films are used on a daily basis. Precision and reproducibility in data obtained from cephalometrics is important for the orthodontist. Errors in conventional methods arise from radiographic acquisition, landmark identification, and measurement (Houston et al., 1986
; Forsyth et al., 1996a,b). The progress in computer technology in orthodontics has not only resulted in ease of image archiving, image manipulation, transmission, and the possibility of enhancement, but also raised questions on the validity as well as the reproducibility of digital cephalometrics (Forsyth et al., 1996a). ICC calculation was used in the present study in order to determine if the results for two intra- or inter-group measurements presented congruity. t-tests were not used, because these compare the means of two groups, which could have caused mathematical errors in the results. Since a deviation in a few values could affect group means, correlation and agreement was carried out in the assessment of the data. The data in previous similar studies should be evaluated accordingly.
Since there was high agreement between the repeated measurements of each investigator, only one set of measurements were used in the inter-observer agreement evaluation. For both manual and digital measurements, inter-rater agreement indicated a high correlation (Table 2). The angles maxillary height, maxillary depth, y-axis, FMA, and nasolabial, and the distance N perpendicular, showed lower correlation and a relatively wider reliability interval. All these parameters, showing lower correlations, except nasolabial angle, are measurements related to the Frankfort horizontal plane, which passes through porion and orbitale. Porion has also been previously reported to cause problems regarding precision and accuracy (Chen et al., 2000). Nasolabial angle on the other hand, depends on landmarks that are placed on a curve with wide radii which show proportionally greater errors of measurement (Baumrind and Frantz, 1971a). This type of error can be made regardless of the method (digital–manual) used for measurement. Even points articulare and gonion, which were estimated when digitized compared with construction of these points in manual drawing, displayed a very high correlation in intra- and inter-group analyses. Higher errors regarding these parameters, which could exhibit large deviations in a few manual tracings, may arise due to the comparison of means used in t-tests.
An important source of error in landmarks is image quality. Dolphin software allows for enhancement of the cephalogram, which is advantageous especially while precisely marking soft tissue profile landmarks. On the other hand, according to Geelen et al. (1998), image quality is already determined during exposure of analogue films and processing of the image, and little can be done to subsequently improve image quality; authors who share this idea have suggested that analogue has more detail than digital, and even though digital can be enhanced, this would only increase reproducibility and not precision (Macrì and Wenzel, 1993). However, the loss of detail that occurs when an image is compressed into JPEG format does not significantly affect the diagnostic quality of the image when standard compression settings are used (MacMahon et al., 1991; Goldberg et al., 1994). If the film is scanned and transferred to digital format, such as in the present study, the quality of the original film is one of the most important criteria in the validity of the result.
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Conclusion |
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TopSummaryIntroductionMaterials and methodsResultsDiscussionConclusionReferences |
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The validity and reproducibility of the measurements with the Dolphin Imaging Software and with the conventional method are highly correlated. When the advantages of digital imaging such as archiving, transmission, and enhancement are taken into consideration, the digitized method could be preferred in daily use and for research purposes without loss of quality.
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Acknowledgement |
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We would like to express our sincere thanks to Rana Konyalioglu for her kind help with the biostatistics.
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References |
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