Assessment of external root resorption using digital subtraction radiography.

Digital subtraction radiography was investigated for its capability to detect and quantify experimentally produced external root resorptive defects in teeth. Using a long source to object X-ray technique and E-speed film, serial radiographs of teeth with artificial lesions in a dry human skull (soft tissue simulated) were obtained. Receiver operating characteristic analysis was used to evaluate the diagnostic performance for each imaging system (conventional versus subtraction). To explore the quantitative assessment potential of digital subtraction radiography, images were produced after sequential demineralization by HCl. The acid solution was analyzed for calcium concentration by atomic absorption spectrophotometry. Three-dimensional histogram quantification for each subtracted image was performed. In overall performance for detecting experimentally produced external root resorption, digital subtraction radiography was found to be significantly superior to conventional radiography. In addition, digital subtraction radiography can provide quantification of experimentally produced external root resorptive defects.     

Assessing condylar changes with digital subtraction radiography

Transcranial radiographs of the temporomandibular joint with and without simulated pathology were compared with digital subtracted and histogram equalized images of the same joints. Subtracted images had specificity and sensitivity values of 0.83 and 0.76 respectively, compared with values of 0.42 and 0.54 for conventional radiographs. It was concluded that digital subtraction radiography has the potential to increase the diagnostic yield of transcranial temporomandibular radiography for bony changes to the condylar head.     

Periapical healing after simplified endodontic treatments: A digital subtraction radiography study

AimTo evaluate the 6-month outcome of endodontic treatment of periapical lesions with integrated systems by clinical examination and digital subtraction radiography (DSR).MethodologyEighty-four patients with chronic periapical pathosis were randomly allocated to two groups and received endodontic treatment with Revo-S/One Step Obturator (G1, n = 41) or GTX/GTX Obturator (G2, n = 43). Six months later, clinical examination and DSR analysis were performed. Non-parametric statistical methods were used (p < 0.05).ResultsTotal healing, partial healing and failure occurred in 48.4%, 48.4% and 3.2% of cases in G1, in 50.0%, 43.8% and 6.2% of cases in G2, respectively. No significant difference was detected.ConclusionsThe integrated endodontic techniques allowed for a high 6-month success rate in both groups in accordance with literature data.     

Calibration errors in digital subtraction radiography

Two methods for the measurements of osseous change detected by digital subtraction radiography have been evaluated. Estimates of errors introduced by soft and hard tissues that overlay the region of interest (ROI) or by soft tissue that replaced the bone are made. All estimates are made assuming that the radiation source is a 40 keV monoenergetic beam and the reference standard is equivalent to compact bone. These assumptions facilitate a theoretical analysis of calibration errors on a relative scale. The radiographic image method uses a calibration wedge on each of the two films. The mean gray value of the ROI on each film is converted into an equivalent thickness of bone by matching the ROI mean gray value to a gray value along the wedge. These thickness values are then subtracted to obtain a measurement of the amount of change. The subtraction image method makes use of a wedge on only one of the two films. The image of the subtraction of the two radiographs is used for detection of the area of change and the mean gray value of the ROI is matched to a gray value along the wedge. The thickness of the wedge at this point is the measured change. The errors introduced by inclusion of the cheek over the ROI and the replacement of bone by soft tissue are estimated for the radiographic image method. The influence of unequal beam attenuation between the reference ramp and the ROI is estimated for the subtraction image method. Other factors influencing the accuracy of estimates of osseous change which are nonlinear in their effects are also considered.(ABSTRACT TRUNCATED AT 250 WORDS)     

An observation of the healing process of periapical lesions by digital subtraction radiography

The purpose of this study was to evaluate the efficacy of digital subtraction radiography using a direct digital imaging system in the follow-up study of endodontically treated teeth. The RVG-S was used as a direct digital imaging system. The intraimage variation of the original RVG-S image caused by dark current and sensitivity variations among pixels was corrected by pixel-to-pixel. The interimage variation was further corrected using a copper step-wedge attached to the sensor. Standardized images were obtained from the same geometrical setup during the follow-up. Pixel values at the regions of interest positioned on the periapical lesion increased after the endodontic treatment, and this change continued during the observation period up to 545 days. The subtraction method with direct digital radiography will be a useful tool to evaluate the healing process in endodontic treatments.     

Sources of noise in digital subtraction radiography

In 17 patients, three identical radiographic examinations were performed for the lower premolar-molar region, by two examiners at one visit and by one examiner again approximately 3 months later. Recordings were performed with a newly developed device. The radiographs were converted to digital images in the following way: (1) video camera recording of the radiograph obtained at first visit by the first examiner (A), (2) copying of the numeric image of this radiograph (B), (3) repeated video recording of this radiograph (C), (4) video recording of the radiograph obtained at first visit by the second examiner (D), and (5) video recording of the radiograph obtained after 3 months (E). Subtractions were performed between the images: B - A, C - A, D - A, and E - A. The standard deviation of the histogram for the distribution of gray shades in the subtraction images was used to evaluate noise in the image. The standard deviation was 1.3 between B - A, 2.8 between C - A, 4.0 between D - A, and 4.1 between E - A. Physical noise originating from the video camera and the analog-to-digital conversion process thus constituted the major part of noise seen in subtraction images performed between radiographs recorded with a time interval. This indicates that reproducible recordings could be performed with the present device, which, in combination with a subtraction program able to correct for some geometry and density differences, may aid the use of subtraction radiography in clinical trials.     

Quantitative digital subtraction radiography for the assessment of peri‐implant bone change

The purpose of this study was to develop a digital subtraction technique to assess peri-implant bone change. The method uses subtraction radiography to enhance visualization of the area of change that has occurred between radiographic examinations, and superimposes the area of change on the original radiographs. Furthermore, a reference wedge allows calculation of the mass of the lesion. The method was validated using 21 small bony chips placed on 3 different skulls prior to the first radiograph. The chips were removed, a second radiograph taken, and the images subtracted. A morphologic method was used to isolate the lesion and the change in bone mass calculated. Overall, there was excellent correlation between the calculated lesion mass (mg) and actual lesion mass (r2 > 0.90). The utility of the method was demonstrated using a case that experienced implant failure. These data indicate that quantitative digital subtraction radiography may be of value in measuring peri-implant bone change in root form implants.     

Assessment of simulated internal resorption cavities using digital and digital subtraction radiography: a comparative study

Abstract – Aim: To compare the diagnostic accuracy of digital radiography with that of digital subtraction radiography in the detection of simulated internal resorption cavities. Materials and Methods: Simulated internal resorption cavities of varying sizes were created using round burs in 18 single‐rooted teeth with visible pulp chamber, which had been extracted from dentate dry mandibles and split into two halves in a mesio‐distal direction. Resorption cavities were created in the buccal half of the root in the cervical, middle, and apical third. Digital radiographs were taken from three different horizontal view angles before and after the creation of the cavities. This process was followed by digital subtraction radiography to evaluate their detection. Seven experienced observers and all specialists in endodontics were asked to examine the digital and digital subtraction images for the presence of the cavities. The data were analyzed using SPSS 14. Results: The overall sensitivity of digital subtraction radiography was superior to digital radiography and with statistically better results for all cavities regardless of their location (cervical, middle, apical third) (P < 0.05). The detection of the cavities was affected by the root third in which they were located. Cavities in the apical third were more easily detected compared with those in the middle or cervical third of the root. Small‐sized lesions (0.5 mm, 0.6 mm) in the middle and apical third were more frequent and more easily detected using subtraction imaging. Conclusion: Digital subtraction radiography is superior to digital radiography for the detection and monitoring of the progress of internal root resorption.     

Semiautomated image registration for digital subtraction radiography

Objective. The purpose of this study was to evaluate the semiautomatic alignment and correction of affine geometric discrepancies for digital subtraction radiography.Study design. Algorithms were tested in vitro to determine their ability to semiautomatically select reference points on a second image based on points selected on a first (reference) image. A preserved human mandible was imaged with and without bone-equivalent material chips at varying degrees of angulation. Each chip had a mass of less than 10 mg and was no more than 0.3 mm thick. High levels of specificity and sensitivity for chip detection were achieved with 6 degrees of angular discrepancy or less. The algorithms were then applied to radiographs from six human subjects through use of the bone-chip validation model.Results. Sensitivity was 89% and 100% for the three-point and four-point affine warp algorithms, respectively. Specificity for both algorithms was 100%.Conclusions. The data indicate that semiautomated alignment algorithms may enhance the efficacy of digital subtraction radiography while maintaining diagnostic efficacy in clinical trials.     

A digital subtraction technique for dental radiography

The relative accessibility and stability of the teeth facilitate generation of geometrically identical radiographs over a period of time. When such radiographs are digitized with the aid of a TV camera coupled to an analog to digital converter and a computer, it is possible to conveniently produce subtraction images of high diagnostic value. A digital subtraction technique for longitudinal dental radiography is described; this technique should be applicable to diagnostic situations characterized by a need to detect small changes occurring over a period of time in areas where substantial amounts of structured noise limit their detectability.     

A contrast-correction method for digital subtraction radiography

A contrast correction method for digital subtraction radiography has been developed. Optical density of radiographs was digitized into gray levels using a drum-scanning microdensitometer with high accuracy. Gray levels of one image are converted to be equal to that of the other image using the equation obtained from gray level relations of both images. The reliability of this method was tested using radiographs of a copper step wedge which was exposed and processed under different conditions. The results show that the minimal detectable difference of the optical density was 0.04 for optimal conditions and 0.05 even for the different conditions. These indicate that the digital subtraction with contrast correction using a microdensitometer may be useful for extracting radiographic changes exclusively and it holds the potential for evaluating periodontal therapy quantitatively.     

Extraoral control of geometry for digital subtraction radiography

The use of a cephalostat to stabilize projection geometry for subtraction radiography was investigated. Six replicate repositionings of patients within a cephalostat indicated that the mean angular disparity between repositioning was 0.33 ± 0.10 degrees. Subtraction images produced from films of a phantom with artificial periodontal defects exposed using the cephalostat or stent technique were compared. There was no significant difference in the standard deviations of the gray level histograms obtained using the two methods. However, the ability of 10 investigators to detect the presence or absence of simulated periodontal lesions was superior from subtraction radiographs produced from cephalostat-based images when compared to stent-based images (p < .02). Sets of radiographs taken of 6 patients on the same day or 3 months apart indicate that the cephalometric technique may be used to stabilize projection geometry.     

The use of digital subtraction radiography to evaluate bone healing after surgical removal of radicular cysts

Objective The purpose of this study was to evaluate the bone healing process after surgical removal of radicular cysts by using preoperative and postoperative panoramic radiographs, which were digitized and subtracted using a projective standardization software program (Emago). Methods Seventeen patients with large radicular cysts treated by surgical enucleation were included in the study. All surgical procedures were performed by one of the authors (D.K.). Each patient had a panoramic preoperative radiograph (plain film) and a panoramic postoperative radiograph (plain film), which was taken 6 to 12 months after surgery. All radiographs were taken with the same panoramic unit. The part of the radiograph that included the lesion in the preoperative radiograph was digitized using a CCD digital camera at a standard distance. The postoperative radiograph was also digitized using the same standardized parameters. The preoperative and postoperative images were then manipulated by means of the projective standardization software program Emago to reveal the regenerated area. This area was calculated in pixels, and the percentage of bone healing was determined for each patient. The data were analyzed using Student's t test and the Wilcoxon test for pair differences. Results The percentage of bone healing ranged from 55.14% to 95.68% with a mean of 72.27%. In all cases, the differences were significantly different at P = 0.01. Conclusions Digitizing the part of the panoramic radiograph that included the lesion area and subsequently performing projective standardization is a suitable method for analyzing the healing process by means of subtraction radiography. The projective standardization software program performs the geometric reconstruction and subtraction process. An evaluation of the healing process can be obtained by calculating the regenerated bone area in the subtracted images.     

The performance of projective standardization for digital subtraction radiography

OBJECTIVE: We sought to test the performance and robustness of projective standardization in preserving invariant properties of subtraction images in the presence of irreversible projection errors.Study design Twenty bone chips (1-10 mg each) were placed on dentate dry mandibles. Follow-up images were obtained without the bone chips, and irreversible projection errors of up to 6 degrees were introduced. Digitized image intensities were normalized, and follow-up images were geometrically reconstructed by 2 operators using anatomical and fiduciary landmarks. Subtraction images were analyzed by 3 observers. RESULTS: Regression analysis revealed a linear relationship between radiographic estimates of mineral loss and actual mineral loss (R(2) = 0.99; P <.05). The effect of projection error was not significant (general linear model [GLM]: P >.05). There was no difference between the radiographic estimates from images standardized with anatomical landmarks and those standardized with fiduciary landmarks (Wilcoxon signed rank test: P >.05). Operator variability was low for image analysis alone (R(2) = 0.99; P <.05), as well as for the entire procedure (R(2) = 0.98; P <.05). The predicted detection limit was smaller than 1 mg. CONCLUSIONS: Subtraction images registered by projective standardization yield estimates of osseous change that are invariant to irreversible projection errors of up to 6 degrees. Within these limits, operator precision is high and anatomical landmarks can be used to establish correspondence.     

The effects of beam hardening on digital subtraction radiography

Quantitative assessment of osseous changes attributable to periodontal disease is made possible by digital subtraction radiography. Tissues through which x rays travel to produce dental radiographs essential to this process alter the energy spectrum of the beam such that calibration errors result when densitometry is attempted using a homogeneous calibration standard such as a step wedge. The following controlled in vitro investigation evaluates the extent of such errors caused by these spectral differences, called beam hardening. Simulated osseous lesions of known size were computed densitometrically using selectively filtered radiation to produce the x-ray images. The resulting data confirm the theory and demonstrate with statistically meaningful accuracy that beam hardening can contribute a significant component of variance to absolute estimates of lesion size. They also suggest that other errors (probably attributable to low contrast) may be even more important at high peak kilovoltages.     

The detection of in vitro produced periodontal bone lesions by conventional radiography and photographic subtraction radiography using observers and quantitative digital subtraction radiography

Changes in the periodontium produced by removal of bone cylinders at one interdental site of a dry human mandible, were recorded radiographically. These artificial lesions had diameters of 0.3 mm increasing to 1.4 mm in steps of 0.1 mm. Radiographs were obtained using 3 different X-ray tube potentials and 3 different amounts of radiation. These 9 exposure variables resulted in 9 series of radiographs from the artificial lesions. Observers were asked to determine the presence or absence of these periodontal bone lesions on conventional radiographs and on photographically subtracted images. The images were also evaluated by a quantitative digital subtraction technique. This study showed that the smallest periodontal bone changes were detected with the quantitative digital subtraction technique compared to the other methods using observers. On photographically subtracted images, smaller bone changes were detected by the observers than on conventional radiographs. Only the detection threshold of the quantitative digital subtraction technique was influenced by the 2 exposure factors: kVp and mAs.     

Extraction versus non-extraction: evaluation by digital subtraction radiography

The aim of this study was to investigate the facial profile changes of patients treated with and without extractions of four first premolars using novel computer-based digital subtraction software. The pre- and post-treatment radiographic image pairs of 25 extraction (13 girls and 12 boys, mean age = 12.64 +/- 1.82 years) and 24 non-extraction (12 girls and 12 boys, mean age = 12.48 +/- 1.66 years) Class I patients were subtracted by the software. Student's t-tests were used to determine whether the subtraction values for the linear measurements of radiographic differences registered at various anatomical landmark parameters were statistically different between the groups. To further determine whether any variables related to upper and lower lip changes, regression analyses were performed. The main soft tissue differences between the groups were established at labrale superior, labrale inferior, and sulcus inferior points, with extraction patients showing significantly more retruded upper and lower lips. However, the mean differences between the groups did not exceed 1 mm for these variables. Changes at labrale superior and labrale inferior were associated with sagittal movement of the maxillary (r = 0.549) and mandibular (r = 0.630) incisor midpoints. Changes at sulcus inferior were associated with both sagittal and vertical displacement of mandibular incision point (r = 0.676). Some dentofacial alterations were found but in view of the differences between the groups pretreatment, the inter-group differences reflect different treatment intent rather than differences arising from the extraction and non-extraction modalities.     

根尖片数字减影对牙槽骨微小病损检测能力的评价

目的评价根尖片数字减影处理系统对微小病损检出的准确率。方法于干燥下颌骨牙槽嵴区制作０．２ｍｍ３～１．９ｍｍ３微小病损共７２个，在制作病损前后摄定位根尖片，分别用数字减影方法与直接读片法对这些随机分布的微小病损进行检测。结果对于０．２ｍｍ３～０．５ｍｍ３的微小病损两种方法的检出率均低于５０．０％。对于０．７ｍｍ３病损直接读片法检出率为３８．７％，而ＤＳＲ法为５７．５％（Ｐ＜０．０１），对于０．９ｍｍ３病损，ＤＳＲ法和直接读片法的检测准确率分别为８９．３％和５７．３％（Ｐ＜０．０１）。结论ＤＳＲ系统对微小骨病损的检测能力明显优于直接读片法。