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Dental radiology

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Dental radiology
Dental radiology

What is digital dental radiology ?

Classically, dental radiology relies on films. A radiograph is made of shades of gray spanning from black to white, known as continuous tone image. To transform any image into its digital form it has to be minutely examined into individual pieces of information called picture elements (pixels). These pixels have information regarding the light intensity (brightness) and their location (x,y coordinates). Forming a digital image requires a computer to quantify these two parameters: brightness and position.

There are two ways of forming a "digital image": a directly obtained digital image or an image that is transformed from analogic to digital. In the direct way, a digital image receptor is directly attached to the computer, the system being called digital direct radiography (DDR). In the indirect way, a video camera or other digitalizer system captures the information from the radiograph or chassis and displays it from the computer.

The heart of DDR is a charge-coupled device (CCD) array. This CCD is sensitive to X-rays, like a normal video camera to the light. It captures the image in a similar fashion as the film does, but it is instantly stored in the computer memory and diplayed on the monitor. No film processing is needed and the image is available immediately.

Does digital radiology decrease the radiation dose?

Yes, fewer x-ray photons are needed to form an image on a CCD array than on dental film (Dunn et al., 1993). The surface exposed to a DDR is about half the one needed for a single image film. The total amount of radiation depends on the number of images required for the patient, that may require more DDRs than conventional intraoral radiographs

Does digital radiology have more technical quality than films?

No, so far. Everybody agrees that DDR is qualitatively preferred to the standard film (Wenzel et al, 1993). However, technical comparisons, in terms of line-pair detection and modulation transfer function, have shown better results for film than DDR. Reported DDR resolution ranges from 7 to 10 line-pairs per millimeter (lp/mm), varying from 12 to 14 lp/mm for film. This implies that films contain more information than DDR images. This advantage in the image has not been proved to be relevant in diagnostic efficacy. Several studies have shown that DDR and conventional films performed equal in the diagnosis of well-defined lesions within dental enamel (Halse et al, 1994) or for occlusal or approximal caries (Russell et al 1993, Dove et al 1992). Even more, numerous authors have reported the ability of DDR to improve diagnostic performance in detecting approximal dental caries (Grondahl et al, 1982), periapical pathology (Grondhal et al, 1983,1984) and periodontal diseases (Razmus et al, 1994). These results encourage further studies of image processing techniques, suitable for the definitive detection and diagnosis of periapical bone lesions (Mol et al, 1991).

Can a DDR offer several kinds of information?

Yes. A film offers all the information captured by x-ray. For example, if you are interested in the roots and the film has been overexposed in this area, you miss some information. DDR does not show an non-captured area, but can modify the information contained in the image and displayed. The image can be enhanced with changes in gray scale and filters, allowing within the same image to improve different regions of interest. If you want to improve the edges you give "importance" to this area and you decrease some other information (i.e. the pulp), and the reverse.

Can DDR help to control exposure records of the patients?

Yes. Beyond a lower radiation dose, the characteristics (Kv, mAs) of the image may be archived with the patient chart in the stored files. You need a computer or printed log to record the names of the patients. The rest of the information can be found in the computer. 20

Can I get faster images than with films?

Yes. The acquisition of the image is quicker. In fact, several authors use it to visualize the relationship of the osteotomy sit to important anatomic structures, during surgery (Jeffcoat et al, 1993). In addition, you can save a lot of space for archiving. All the images are stored in optical or magneto-optical disks and you can attach the selected images to patients history. And you also save time , in the retrieval process for future comparisons.

Can the stored images be of further usefulness than just being seen?
Yes. The two most common diseases are caries and periodontal bone disease. At the initial presentation bony changes may be minimum. It may be interesting to compare two or more images in order to detect subtle changes. These subtle changes may be concealed for the structural noise (random image features that obscure the signal of interest in a radiographic image). Other limiting factor is that radiograph must be taken in the same position that previous image for comparison. Recently, quantitative methods have been developed for longitudinal comparison of radiographs. Several dental software (Care -University of Texas at San Antonio, U.S.A (Dove et al, 1995), Emago, Department of Oral Radiology, ACTA, The Netherlands (13)) have developed techniques using direct or indirect digital images to compare longitudinal changes in the regions of interest. The aim is to give a quantitative definition of the changes occurred in the images. The images can also be transmitted by telephone for referral and other educational purposes.
What other advantages DDR has?

It has a great environmental advantage as its inferior use of resources. It saves all the devices and chemical wastes used in film processing (Wenzel et al, 1994). And the best of all, the reduced radiation dosages. 20

What about the cost?

From 4000 to 200000 dollars depending on the sophistication of the hardware.
In conclusion

Direct digital radiology, is so far, equally effective in diagnosing dental diseases as classical dental radiology (Scarfe et al, 1995). In the near future, we think that its resolution will be improved. Nowadays, the main advantages are its speed, storage capacity and the reduced exposure to the patient. We think the great value of this technique relies on the possibility of manipulating, enhancing and obtaining quantitative comparison of images throughout time.

Source: Dental radiology

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