Correction of density changes caused by methodological errors in CADIA

Quantitative analysis of errors in alveolar crest level caused by discrepant projection geometry in digital subtraction radiography: An in vivo study

OBJECTIVE

This study compared the difference between 3 intraoral radiographic techniques on digital subtraction radiography (DSR) in vivo that are commonly used in a clinical setting.

STUDY DESIGN

We evaluated and statistically analyzed the errors in the DSR image in 6 regions with 3 radiographic techniques: paralleling technique with a bite block attached to XCP, paralleling technique using XCP, and bisecting-angle technique.

RESULTS

The amount of error using the bisecting-angle technique was too large for DSR, compared to that of the paralleling technique with a bite block attached to XCP. In the mandibular anterior region, the paralleling technique using XCP was not different from paralleling technique with a bite block attached to XCP. The lowest degree of error was present in the anterior region whereas the highest was present in the molar region.

CONCLUSION

Bisecting-angle technique should be avoided, and paralleling technique using XCP can be used in the mandibular anterior region for DSR.

In vitro calibration and validation of a digital subtraction radiography system using scanned images

OBJECTIVES

To calibrate and validate a digital subtraction radiography system using scanned images for quantification of alveolar bone changes by means of computer-assisted densitometric image analysis (CADIA) in vitro.

MATERIALS AND METHODS

Noise levels were determined using 10 standardized periapical radiographs of the same lower molar region in a human dry skull. For validation of the system, radiographs were taken before and after bovine bone particles in measures with increments of 2 mg weighing from 2 to 20 mg were added into each socket of three dry skulls. Radiographs were developed and scanned into a computer with a flatbed scanner. After digitization, the images were subjected to alignment, normalization and subtraction. Appropriate regions of interest (ROIs) were selected and their CADIA values were calculated for the determination of noise levels, and correlations between the CADIA values and the actual bone mass were performed.

RESULTS

When the threshold value was 7, the percentage of pixels deviating from the set threshold value was small (0-11.3%). There were statistically significant correlations between the actual bone mass and the CADIA value for anterior sockets (p<0.001, r2=0.89) and posterior sockets (p<0.001, r2=0.9). For pooled data of both anterior and posterior sockets, the correlation was also statistically significant (p<0.001, r2=0.88).

CONCLUSIONS

A high and statistically significant correlation between the actual bone mass and CADIA value was obtained, which suggests that the system could be suitable for the detection of small alveolar bone changes.

Comparison of 5 protocols based on their abilities to use data extracted from digitized clinical radiographs to discriminate between patients with gingivitis and periodontitis

BACKGROUND

This study was undertaken to compare 5 digital analytic protocols for their abilities to extract data from digital clinical radiographs and discriminate between patients with gingivitis and periodontitis.

METHODS

Five digital-image analysis protocols were compared for their abilities to discriminate between two groups of 24 patients each. One group was diagnosed with healthy gingiva (or gingivitis) and the second with periodontitis. These groups were previously evaluated in published studies that used fractal and morphologic analyses. Pre-existing clinical radiographs for each patient were digitized and regions of interest (ROIs) were placed on interdental bone in mandibular posterior quadrants. The 5 protocols used were: 1) MGB: a median filtration to remove high-frequency noise, a Gaussian filtration to remove low-frequency noise, binarization of the resulting image, and quantification of the black pixels; 2) MGBS: the same protocol as MGB except for a skeletonization of the binary image and a quantification of the skeleton's pixels; 3) GBS: Gaussian filtration, binarization (thresholding on the mean pixel value) of the resulting image, skeletonization, and quantification of the pixels of the skeleton; 4) NS: normalization, skeletonization, and quantification of the skeleton's pixels; and 5) S: a variation of NS, except normalization was not used. The resulting values for the 2 patient groups were compared with Mann-Whitney U tests and effect likelihood-ratio test.

RESULTS

For digitized radiographs, the mean gray-scale value (+/- standard deviation) for gingivitis patients was 183.22 +/- 18.53 and for periodontitis patients 181.26 +/- 17.20. Mann-Whitney U tests resulted in the following P values for these protocols: MGBS <0.01; S <0.01; GBS <0.01; NS <0.01; and MGB <0.83. Effect likelihood-ratio tests indicated that only MGBS and S significantly contributed to models containing the other factors.

CONCLUSIONS

Small variations to protocols affected the strength of the discrimination between the gingivitis and periodontitis groups. While there is potential for morphologic analysis to be used to discriminate between patients with gingivitis and periodontitis, a robust technique was not identified.

Accuracy of quantitative digital subtraction radiography for determining changes in calcium mass in mandibular bone: an in vitro study

The aim of this in vitro study was to determine the accuracy of digital subtraction radiography (DSR) to detect small changes in calcium mass in alveolar bone adjacent to tooth roots. In each of 4 dried porcine mandible segments, one interproximal and one buccal "defect" region was defined adjacent to a premolar root. A series of cortical and cancellous bone slices with a 50 microns--stepwise increasing thickness (0-5000 microns) were attached to the mandible segments covering the respective "defect" region. Standardized radiographs were quantitatively assessed for density changes using DSR. After dissolving each bone slice in hydrochloric acid, its calcium concentration was photometrically determined. For each bone slice, the mean calcium mass covering a single pixel of the subtraction image was calculated. The Wilcoxon signed-rank test and the Mann-Whitney U-test were used for statistical analysis (alpha = 0.05). A strong linear correlation (r2 = 0.86-1.00; p < or = 0.001) was found between the thickness of the bone slices and their calcium mass. Cortical bone showed a 3.5 times higher mean calcium mass/pixel than cancellous bone. Furthermore, a strong linear correlation (r2 = 0.63-1.00; p < or = 0.001) was found between the mean calcium mass per image pixel and the radiographic density changes. Neither the bone type nor the "defect" localization had a significant influence on radiographic density changes caused by changes in calcium mass. A change in mean calcium mass per image pixel of 0.1-0.15 mg was necessary to be detected by DSR. In conclusion, this study revealed a high accuracy of DSR to detect small changes in calcium mass in alveolar cortical and cancellous bone.

Particulate bioglass as a grafting material in the treatment of periodontal intrabony defects

The present clinical trial was designed to evaluate the effects of a bioactive glass, Perioglas, in the treatment of periodontal intrabony defects. 20 patients, 23-55 years of age (44 sites), with intrabony defects completed the 1-year study. Teeth with furcation involvement were excluded. After completion of initial therapy, defects were randomly assigned to either a test or control procedure. Following flap reflection, root planing and removal of chronic inflammatory tissue in both groups, the test defects were restored with the bioactive glass particulate material. Mucoperiosteal flaps were replaced, sutured and a periodontal dressing was used. All the patients received postoperative antibiotics and analgesics and were seen at 1 week for suture removal. Follow-up was then carried out weekly and at 3 months, 6 months, 9 months and 1 year post-surgery. Plaque score, bleeding score, probing pocket depth (PPD), probing attachment level (PAL) and gingival recession were recorded at baseline, 3 months and 1 year. Standardised radiographs for computer-assisted densitometric image analysis (CADIA) were taken at baseline, immediately post-operatively and at 1 year. The CADIA data showed a significant increase (F-ratio: 15.67, p < 0.001) in radiographic density and volume between the defects treated with the Perioglas when compared to those treated with surgical debridement only. PPD and PAL showed significant improvements in both experimental and control sites, with a greater trend to improvement in the experimental sites. It was concluded that this bioactive glass is effective as an adjunct to conventional surgery in the treatment of intrabony defects.

Digital image ratio: a new radiographic method for quantifying changes in alveolar bone. Part II: Clinical application

As reported in a previous paper (1) we have developed a new technique, Digital Image Ratio (DIR), which theoretically avoids some of the drawbacks of quantitative digital substraction radiography. DIR allows the direct computation and visualization of bone-mass-ratio changes. This second paper describes the use of DIR analysis to examine 20 sites in 8 patients undergoing regenerative periodontal therapy. Standardized reproducible radiographs of these 20 sites were taken before and 12 months after surgery. Ten experimental sites were treated with bone graft substitutes (natural coral or natural coral+collagen), and 10 control sites by debridement alone. None of the experimental sites had a density ratio below 1, where 1 indicates no change. The error was +/- 0.07 (0.93-1.07). The experimental sites showed an 18% mean increase in bone density (1.18), which increased to 23% (1.23) for sites filled with natural coral alone. All the control sites had values close to 1.00 (1.00 +/- 0.07) except for 3 sites, which showed a 9-15% loss of bone density. It is thus possible to compare and quantify the changes in experimental and control sites in the same patient using the percentage gain or loss of bone density. This demonstrates that DIR is suitable for clinical applications, and can be used in clinical analysis when bone changes are expected.

Use of an internal standard in subtraction radiography to assess initial periodontal bone changes

OBJECTIVE

To assess the use of an internal reference when performing histogram analyses in digital subtraction images and to determine the ability of the method to detect initial bone lesions.

METHODS

Fifty-one Royal Air Force recruits had standardized vertical bitewing radiographs and clinical assessment of attachment level recorded annually over three years. Subtraction analyses of crestal bone changes at the mesial surface of the upper right first molar were compared with changes at the mesial surface of the same tooth. Changes over the periods from age 17 to 18 years and age 18 to 20 years were monitored using two subtraction procedures.

RESULTS

Reproducibility studies revealed that Pearson correlations between duplicate measurements of the test site alone (16 crest; r = 0.74) were lower than those between duplicate measurements of changes where misalignment was controlled for, either as a difference (16 crest-16 tooth; r = 0.93) or ratio (16 crest/16 tooth; r = 0.93). We used the differences between the mean subtraction density for 16 crest and 16 tooth as our measure of change in bone density. For the duplicate measurements, the standard deviation of these differences was 3.9: a difference of +/- 7.8 was therefore taken as a threshold value for evidence of real change. Bone gain was noted between the ages of 17 and 18 years (16/21 subjects), but some early bone loss was seen between 18 and 20 years (12/21 subjects), with four subjects showing changes significantly greater than the method error. There were no associations between the clinical and radiographic observations.

CONCLUSION

Use of a control site in subtraction radiography improves the reproducibility; such systems can detect small changes in alveolar bone which may assist in early diagnosis of the initial periodontal lesion which may precede observable clinical changes.

Light source-induced error in computer-assisted image analysis with a video-based system

OBJECTIVE

We tested the hypothesis that two different light sources, an alternating current fluorescent viewbox and a direct current halogen viewbox, do not differ with respect to their ability to illuminate reproducibly a radiograph during image capture.

STUDY DESIGN

Two radiographs were taken: one with four hydroxyapatite chips mounted against a dry mandible and one without the chips. They were digitally subtracted with a video-based imaging system. The procedure was repeated at different times.

RESULTS

A statistically significant difference among optical density measurements was found when the alternating current fluorescent viewbox (p < 0.001) was used and was related to light intensity variation. Such effect was not observed with the direct current halogen viewbox (p = 0.873).

CONCLUSION

Study design efficiency was increased by 212% with the use of the direct current halogen viewbox so that to detect a specified treatment effect with a given level of statistical confidence, the sample size has to be 2.12 times greater if the alternating current fluorescent viewbox is used.

Histogram-matching and histogram-flattening contrast correction methods: a comparison

OBJECTIVES

To compare the results or two methods of histogram matching and two methods of histogram flattening for their ability to correct for contrast variations in digital dental images.

METHODS

A custom-built, aluminium stepwedge with 0.1, 0.5 and 1.0 mm steps was placed over Ektaspeed films and exposed for 0.06, 0.12 and 0.25 s, respectively. Radiographs were digitized at 50 microns spatial resolution and 12-bit contrast resolution. Contrast corrections were performed using Rüttimann et al.'s algorithm (1986) for one method of matching (RM) and flattening (RF) and Castleman's algorithm (1979) for the other method of matching (CM) and flattening (CF). Mean pixel grey-scale values were determined for each step. The 0.12 s exposure was considered to be the target image exposure. Absolute differences in pixel grey-scale values between the target images and the modified images were determined.

RESULTS

The median values of the absolute differences in pixel grey-scale values between the target images and the contrast corrected images were: CM = 4.3; RM = 4.1; CF = 70.2 and RF = 70.2.

CONCLUSION

Castleman's and Rüttimann's matching algorithms perform equally well in correcting digital image contrast. Histogram flattening was less effective.

Cell envelope and cell wall immunization of Macaca fascicularis: effect on the progression of ligature-induced periodontitis

The nonhuman primate, Macaca fascicularis, was used to study the role of immunization with selected members of the periodontopathic microbiota in the longitudinal progression of ligature-induced periodontitis. Animals were immunized with cell envelope antigens prepared from Porphyromonas gingivalis and Prevotella intermedia, and a mixture prepared from Fusobacterium nucleatum, Campylobacter rectus, and Actinomyces viscosus. Serum immunoglobulin G (IgG), IgM and IgA isotype antibodies increased significantly in all immunization groups and were specific for each of the immunogens. P. gingivalis and P. intermedia immunization resulted in a stabilization of the proportions of these species throughout most of the experiment. The high P. gingivalis antibody titer resulted in low P. gingivalis numbers being recovered. P. gingivalis immunization, while lowering recoverable viable P. gingivalis, resulted in significantly increased levels of Prevotella loescheii, Prevotella buccae, Bacteroides macacae and Prevotella melaninogenica compared with preligation and preimmunization levels. Actinobacillus actinomycetemcomitans, Capnocytophaga spp. and Eikenella spp. remained at preligation levels postimmunization. Campylobacter spp. increased significantly during the course of the experiment in all groups, whereas the levels of Fusobacterium spp. decreased. Plaque indices and bleeding on probing showed significant increases in all groups following ligation, with the placebo group showing the greatest increase. Pocket depth measurements revealed that , whereas the placebo animals showed an approximate 5% increase, the P. gingivalis- and P. intermedia-immunized groups showed nearly a 20% increase in pocket depth. Attachment level measurements showed significantly greater attachment loss in the P. gingivalis- and P. intermedia-immunized groups, and the F. nucleatum + C. rectus + A. viscosus immunization appeared to prevent significant changes in pocket depth/attachment level loss. Radiographic measurement of bone loss by computer-assisted densitometric image analysis revealed that the placebo group lost bone throughout the experiment. P. gingivalis- and P. intermedia-immunized groups showed an exacerbated loss of bone density and the group immunized with F. nucleatum + C. rectus + A. viscosus exhibited significantly lower amounts of bone loss when analyzed by computer-assisted densitometric image analysis, compared with the other immunized groups. Although immunization with P. gingivalis and P. intermedia cell envelope antigens had an effect on their emergence in the complex microbiota of the developing periodontal pocket, this immunization also resulted in greater bone loss than immunization with F. nucleatum + C. rectus + A. viscosus, suggesting that, whereas selective members of the putative periodontopathic microbiota may play a direct role in periodontal tissue destruction, the complexity of the subgingival microbiota dictates that considerable scrutiny is required to select useful immunogens that can elicit functional protection from periodontal tissue destruction induced by oral microorganisms that already colonize or infect the host.

Bitewing-based alveolar bone densitometry: digital imaging resolution requirements

The resolution requirements were determined for detection of incremental alveolar bone loss from digitized Ektaspeed radiographs. Ten clinical radiographs were examined with a calibrated optical microscope to measure the smallest feature of interest discernible for alveolar bone. Images of trabeculae > 100 microns in diameter could be identified, but smaller ones could not be resolved. The Nyquist Criterion requires sampling with 50 microns (or smaller) pixels to measure such features. Numerous 25 microns Ag aggregates were present. Fifty microns resolution is a practical compromise between noise level and feature resolution. In another example of 10 bitewings digitized at 8 bit grey scale, about half the available range was used for alveolar bone, resulting in uncertainty, over a range of 2 optical density (OD) units, of about 1.42% at the average OD for alveolar bone (1.1). With the same radiographs digitized at 12 bit resolution, over 2000 of 4096 grey scales were used with a corresponding uncertainty of about 0.09%. Twelve-bit precision was also able to resolve smaller increments in an aluminium stepwedge than was 8 bit precision. Twelve-bit grey scale and 50 microns spatial resolution are recommended for alveolar bone densitometry performed with Ektaspeed radiographs.

Healing in periodontal defects treated by decalcified freeze-dried bone allografts in combination with ePTFE membranes. Assessment by computerized densitometric analysis

This study quantitatively assessed radiographic changes in alveolar bone density by computer-assisted densitometric image analysis (CADIA) in periodontal defects that were treated with decalcified freeze dried bone allograft (DFDBA) alone or in combination with interproximal expanded polytetrafluroethylene membranes (ePTFE). The radiographic changes where then analyzed for correlation with the clinically assessed changes. The radiographic changes were evaluated on standardized radiographs of treated sites treated prior to, 1 week after surgery, and 6 months post-operatively. 15 patients with one pair of bilateral interproximal periodontal defects of similar morphology and > or = 6 mm in pocket depth participated. Analysis of the changes 6 months after treatment showed that the increases in density in the defect areas that received the graft were significantly greater than the adjacent areas (p < 0.001). These adjacent areas, in contrast, demonstrated significantly larger loss in radiographic density than the defect area (p < 0.001). The placement of DFDBA into the defects produced in itself significant increases in radiographic density, as illustrated by the results of one week which remained at six months. Utilization of ePTFE addition to DFDBA did not lead to additional radiographic gains in the defect area. While at one week the analysis suggested increased resorption by the combined treatment over grafting alone, such differences did not persist at 6 months post-surgery. Analysis comparing CADIA derived values for change with those of the clinical assessment revealed some associations.(ABSTRACT TRUNCATED AT 250 WORDS)

An in vitro study of the characteristics of a computer-aided radiographic evaluation (CARE) system for longitudinal assessment of density changes

In recent years, several systems for computerized analysis of radiographs have been introduced, most of which use digital conversion of the image followed by subtraction of consecutive images to assess changes. This paper introduces a computer-based qualitative and quantitative radiographic evaluation system based on the CADIA algorithm. Problems associated with computerized radiographic analysis are discussed and evaluation criteria for this type of system are suggested. These criteria include evaluation of system noise and threshold setting, reproducibility, and establishment of the system working curve (validity). The CARE system noise ranged from a -10 to +10 CADIA value and the threshold was set on 13 for all measurements. The reproducibility was high, both for the radiographic technique and for repeated measurements. The working curve was established and showed the system's ability to detect small density changes of 0.048 O.D. which corresponds to 0.27 mm of aluminium thickness or compact bone equivalent. The linear range of the curve was between 0.7 and 1.8 O.D. By controlling the exposure parameters it was possible to work within the linear range of the curve. Based on these evaluation criteria, the CARE system can be used to quantitatively evaluate small density changes on sequential radiographs for early detection of caries and periodontal disease.

Effects of region of interest outline variations on gray-scale frequency distributions for alveolar bone

Normalized cumulative percentage gray-scale distributions from digitized radiographs of dry skulls can be used to evaluate alveolar bone health. With this method, manually defined regions of interest are used to identify the area of the image to be analyzed. The purpose of this study was to determine if variations in the dimensions of the regions of interest affect the gray-scale distributions. Two approaches were used. The effect of region of interest outline variations on (1) the ability to differentiate between various sized bone chips and (2) the ability to distinguish between two groups of skulls with the alveolar bone subjectively rates as normal or diseased were investigated. Four different regions of interest, which consisted of outline and area variations to a basic region, were used. Ninety-one percent of the cumulative histograms that represented chips were sufficiently separated from nonchip plots to be distinguished. Bone health was correctly assessed with a numeric classifier for 37 of 44 quadrants, for an accuracy of 84%, a specificity of 79%, and a sensitivity of 90%. Although ROI size and shape consistency in longitudinal studies are important in radiometric analyses, small variations had minimal impact in this study.

Radiometric classification of alveolar bone health

A radiograph-based classifier for discrimination between normal and diseased alveolar bone was developed. The alveolar bone health of dry mandibles was rated, by consensus of two trained observers, as normal or diseased. Bitewing radiographs of mandibular quadrants were digitized and regions of interest (ROIs) of the alveolar bone between the first and second permanent molars outlined. Gray-scale histograms for the ROIs were computed, and a classifier based on these histograms was developed. Two observers (independently) used only the classifier to rate the bone as being normal or diseased. These ratings were compared with the original ratings of trained observers who viewed and scored the actual alveolar bone. The sensitivity (the ability to detect diseased alveolar bone), specificity (the ability to detect normal alveolar bone), and accuracy were 0.90 or greater, indicating good agreement with subjective visual assessments of dry mandibles. These results suggest that this procedure may be applicable for evaluations of bone health in humans.

Effects of immunization with Porphyromonas gingivalis and Prevotella intermedia on progression of ligature-induced periodontitis in the nonhuman primate Macaca fascicularis

The nonhuman primate (Nhp) has proven to be a useful model of human periodontitis. This study describes the immunological characteristics of this model and the ability of active immunization to interfere with ecological changes in the microbiota and its associated disease symptoms. Nhps were parenterally immunized with whole-cell antigens of Porphyromonas gingivalis and Prevotella intermedia. The immunization elicited an approximate 2-log increase in serum immunoglobulin G (IgG), IgM, and IgA isotype antibody that was highly specific for these immunogens. Postimmunization and postligation, there was minimal change in the levels of specific antibody. P. gingivalis immunization significantly inhibited the emergence of this species during disease progression. In contrast, induction of anti-P. intermedia antibody had a minimal effect on this species within the subgingival plaque. Plaque indices showed few changes that could be attributed to active immunization. Both bleeding on probing and loss of attachment were higher in ligated sites of immunized animals than in the placebo-treated group. A significant increase in bone density loss was observed in the ligated teeth from immunized versus control animals. These findings indicate that active immunization of Nhps can elicit a substantial systemic immune response; however, while this response may effect the emergence of an individual microorganism, it appears that other ecological considerations are critical in disease progression. It is also possible that the induction of a broad-based immune response to multiple bacterial antigens can result in increased disease, potentially associated with hypersensitivity reactions to the bacteria in the subgingival plaque.

Effect of region-of-interest in computerized densitometric analysis of radiographs

The region-of-interest (ROI) in computer-assisted densitometric image analysis (CADIA) is defined by its size and location. This study evaluated the effects of these variables on two quantitative parameters, the change in density and the area with change in density. Pairs of radiographs for these analyses were obtained from sites with "no change" or "known loss" in Cynomolgus monkeys during a study of ligature-induced periodontitis. The size and location of the ROI had clear effects on the two CADIA parameters. To reduce these effects, a corrective procedure hypothesizing a linear relationship between the ROI size and the area with change in density was tested. While this procedure was sufficient to correct for ROI size-dependent differences among "no change" images, it was not effective in images with "known loss". In such images, additional adjustments by increasing threshold levels for the registered change in density were found to reduce but not to eliminate differences between ROIs of different size and location. When densitometric radiographic analysis is used for quantitative comparison of different sites, it is primarily recommended to select ROIs of similar size and location. Application of corrective procedures should follow only after careful evaluation of their effects on sensitivity and specificity.