Browsing by Subject "Subtraction Technique -- Instrumentation"

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    Digital Microradiography: In Vitro Validation of a Novel Imaging Technique
    (2004) Yip, Gary Ka Fai; Roberts, W. Eugene; Everett, Eric; Garetto, Lawrence P.; Hancock, E. Brady; Kowolik, Michael J.; Parks, Edwin T.; Platt, Jeffrey A.; Zunt, Susan L.
    Microradiography has been widely used in mineralized tissue research in determining the mineral content within the specimens being studied. There are considerable limitations of this ageing gold standard such as unavailability of the high-resolution spectroscopic plates and prolonged imaging and processing times. The present study aimed at developing and validating a novel digital microradiographic technique that is not restricted by the limitations of conventional microradiography. Reproducibility of digital microradiography was investigated by studying 4 repeated images of 10 randomly selected sectioned implant-bone specimens acquired by 2 examiners over 2 weeks. The acquired images were analyzed by both manual and automated digital subtractions. Correlation between digital and conventional microradiography was performed by digital subtraction of 23 matching images acquired by both microradiographic techniques. A comparison between manual and automated digital subtraction enabled evaluation of the influence of the digital subtraction protocols on the results of the subtraction. A direct digital microradiographic technique has been developed which does not require analogue recording medium and film processing. The robustness of the digital microradiography was evidenced by the narrow range of means and standard deviations for intra- and inter-examiner reproducibility. The intra-examiner means and standard deviations ranged from 126.54-128.42 and 4.11-5.34 respectively. The inter-examiner means and standard deviations ranged from 126.71-129.87 and 4.68-5.70 respectively. The detection threshold for the digital microradiography was 5 gray scales or 3.9 percent, which was comparable to digital radiography. The high concordance between conventional and digital microradiography was demonstrated by the mean and standard deviation of 8.69 and 1.75 gray scales respectively. There was a statistically significant difference between the results obtained by manual and automated digital subtraction, but the clinical significance is yet to be determined.
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    Use of an Orthodontic Bracket as a Fiduciary Marker for Digital Subtraction Radiography
    (2004) Silverman, Michael J.; Parks, Edwin T.; Roberts, W. Eugene; Hohlt, William F.; Kowolik, Michael; Shanks, James C.
    Radiography is an essential diagnostic technique for the detection of hard tissue changes over time. Digital subtraction radiography allows a significant improvement in the ability to detect subtle changes in hard tissues and has been used for many applications including assessment and monitoring of root resorption, caries, periodontal disease, periapical disease and implants. Subtraction radiography requires two identical images taken at different times. The subtracted image is a composite, representing the changes in density. The ability to accurately detect changes is dependent on the reproducibility of the projection geometry between images and the ability to register or superimpose those images. Historically, this has been difficult to achieve and clinical application of this technique has been limited. Many approaches have been suggested to address this problem. To date, no investigators have used an orthodontic bracket as a fiduciary marker for digital subtraction. The purpose of the study was to investigate the use of an orthodontic bracket with and without additional fiduciary markers for digital subtraction radiography. The hypothesis is that, by virtue of its geometry and stable position, an orthodontic bracket will provide more accurate subtractions than controls using anatomic reference points. This laboratory study examined digital subtraction images obtained from human mandibular incisors with and without brackets. Direct digital images of forty teeth were taken at no angulation and 10 and 15 degrees of labial and lingual tip. The images were reconstructed and subtracted using the Emago/Advanced v3.5 program. The standard deviations of the subtraction histograms were evaluated with an ANO VA model to test the null hypothesis of no significant difference in the accuracy of digital subtractions between groups. An exploratory analysis of the length and width of the reconstructed images was also performed. Ten teeth were randomly selected to have their reconstructions repeated to assess intra and inter operator repeatability with this method. Subtractions performed using the brackets alone or the brackets with additional fiduciary markers were significantly more accurate than those performed with anatomic landmarks (p < 0.05). Reconstruction length of the no bracket group was closer in length to the reference images while length of the bracket groups were closer to the reference image length for labial tipping and closer to the tipped image for lingual tipping. Differences in width between groups were negligible. Improving the accuracy of digital subtraction by using orthodontic brackets as fiduciary markers will assist in research applications of interest to orthodontists, particularly root resorption, and may contribute to the improvement of clinical applications, such as monitoring patients genetically susceptible to root resorption. The use of an orthodontic bracket provides another tool to facilitate the application of digital subtraction radiography.