Home › Forums › Radiology and Imaging › DIGITAL SUBSTRACTION RADIOGRAPHY
Welcome Dear Guest
To create a new topic please register on the forums. For help contact : discussdentistry@hotmail.com
- This topic has 2 replies, 3 voices, and was last updated 12/06/2011 at 8:34 am by drmittal.
-
AuthorPosts
-
10/06/2011 at 4:56 am #12129AnonymousOnlineTopics: 0Replies: 1150Has thanked: 0 timesBeen thanked: 1 time
They are used to diagnosis of subtle changes in bone. Eg; it can be used to assess bone levels before and after periodontal therapy, study of periapical region, study of the superior surface of the condyle. The basic advantages includes overall contrast is improved and the structures are more closely visualized in the processed image, the trabecular fine marrow spaces are excellently visualized, low density as well as high density structures are equally enhanced and better visualized. The diagnostic problem in a radiographic examination lies primarily in the identification of image features, caused by a pathologic process, buried in a background of normal anatomical structures. During interpretation, the desired part has to be separated from the irrelevant distribution of other structures. The other structures which do not contain diagnostic information of interest have been termed as “noise.” Here the reference radiograph is digitized and converted into its positive image by the computer. The subsequent radiograph is then displayed on the same server and aligned to the reference image and then digitized. Substraction of the gray levels between the two images is then performed. Any change that has occurred between the original radiograph and the subsequent radiograph shows up as light or dark areas. Loss of bone is seen as dark areas and gain of bone as light areas. To compensate for variations in film response, oral hard tissue measurements with film are sometimes made with the aid of an intraoral stepwedge. Correct placement of the wedge is a problem, however, because it is difficult to match the cheek thickness and scattered radiation intensity without superimposing the step wedge image on the teeth, bone, film-positioning device, or occlusal registration material. Subtraction radiography with film is improved by contrast and exposure corrections. The process is tedious and is of questionable validity for detection of generalized bone loss (osteopenia). Loss of a substantial amount of bone would violate a fundamental assumption by changing the histogram and would therefore reduce the apparent bone loss or gain if histogram-based correction is used. ,No one has yet shown how to distinguish among changes in the histogram that are due to changes in bone mass, film, exposure, and processing. Indeed, an unambiguous distinction may not be possible from image histograms alone. If contrast corrections and the use of intraoral stepwedges are fraught with difficulties, then a better, more reproducible method of measuring x-ray attenuation is needed.
12/06/2011 at 6:56 am #1730512/06/2011 at 8:34 am #17308drmittalOfflineRegistered On: 06/11/2011Topics: 39Replies: 68Has thanked: 0 timesBeen thanked: 0 timesDigital subtraction radiography (DSR) is a technique used to determine qualitative changes that occur between two images taken at different points in time. The first image is the baseline image and the second image shows the changes that have occurred since the time the first image was taken. DSR involves subtracting the pixel values from the first image from the pixel values of the second image. The result of the subtraction process is visualization of the changes only because everything unchanged has been removed. In order for images to be subtracted, they need to have the same image projection geometry, receptor placement and file size so that the subtracted image provides the desired information. Reconstruction software has become available to correct placement and image projection geometry to make DSR more feasible for use by clinicians. Also, digital images have standard file sizes and number of pixels in each image, which facilitates the operation.Subtracted images may reveal a continued disease process or demonstrate the effectiveness of a particular treatment. In 1998, Parsell et al. studied various methods to detect oral cancellous bone lesions and found that digital subtraction radiography with or without enhancement improved the likelihood of a correct cancellous defect diagnosis. In another study by Danesh et al., DSR was used to compare radiographic crestal alveolar bone mass and change in clinical periodontal attachment level following guided tissue regeneration. The investigators found strong agreement between digital subtraction radiographic assessment of crestal alveolar bone mass and clinical attachment level. These and other studies suggest that digital subtraction radiography will prove to be a useful tool in the diagnosis and treatment of dental disease.
-
AuthorPosts
- You must be logged in to reply to this topic.