Digital Dental Radiology
Departments of Radiology. (1) Hospital La Fe (2) Hospital Dr. Peset. Valencia. Spain
Index
Introduction
What is digital radiology ?
Does digital radiology decrease the radiation dose?
Does digital radiology have more technical quality than films?
Can a DDR offer several kinds of information?
Can DDR help to control exposure records of the patients?
Can I get faster images than with films?
Can the stored images be of further usefulness than just being seen?
What other advantages DDR has?
What about the cost?
Conclusion
Bibliography
Return
Introduction
Reviewing current advances in dentistry is difficult due to the lack of scientific publications in professional
journals. Most of the information comes from nonreferred sources and manufactures.
Conventional dental radiography is being surpassed by digital radiography, but does digital dental
radiography (DDR) have only advantages ?
In this paper, we intend to summarize the main goals of this technique.
What is digital 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.
Bibliography
- Anonymous. Impact of Digital Radiology. The advantages of the Emago(r)
software package. http://rad1.acta.nl/radiology/emago/emago.html. (8/1/96).
- Dove SB, McDavid WD (1992). A comparison of conventional intra-oral radiography and computer
imaging techniques for the detection of proximal surface dental caries. Dento-Maxillo-Facial Radiology 21:127-34.
- Dove, SB. "Digital Imaging in dentistry". http://ddsdx.uthscsa.edu/dig/digimage.html (8/12/95).
- Dunn SM, Kantor ML (1993). Digital radiology facts and fictions. J Am Dent Assoc 124:39-47.
- Grondahl, H.G., Grondahl, K., Okano, T.,Webber, R.L (1982). Statistical contrast enhancement of subtraction
images for radiographic caries diagnosis. Oral Surgery,.Oral Medicine,.Oral Pathology. 53:219-223, . 20
- Grondahl K, Grondahl HG, Webber RL (1984).
Influence of variations in projection geometry on the detectability of periodontal bone lesions. A comparison
between subtraction radiography and conventional radiographic technique. Journal of Clinical Periodontology 11:411-20.
- Grondahl HG, Grondahl K (1983). Subtraction radiography for the diagnosis of periodontal bone lesions. Oral Surgery,
Oral Medicine, Oral Pathology 55:208-13.
- Halse A, Espelid I, Tveit AB, White SC (1994). Detection of mineral loss in approximal enamel by
subtraction radiography. Oral Surgery, Oral Medicine, Oral Pathology 77:177-82.
- Jeffcoat MK (1993). Application of digital radiography to implantology. Journal of Dental Symposia 1:30-3.
- Mol A, van der Stelt PF (1991). Application of digital image analysis in dental radiography for the description of periapical bone lesions: a preliminary study. IEEE Transactions on Biomedical Engineering 38:357-9.
- Wenzel A, Hintze H (1993). Perception of image quality in direct digital radiography after application of various im
age treatment filters for detectability of dental disease. Dento-Maxillo-Facial Radiology 22:131-4.
- Razmus TF (1994). Caries, periodontal disease, and periapical changes. Dental Clinics of North America 38:13-31.
- Russell M, Pitts NB (1993). Radiovisiographic diagnosis of dental caries: initial comparison of
basic mode videoprints with bitewing radiography. Caries Research 27:65-70.
- Scarfe WC, Fana CR, Jr., Farman AG (1995). Radiographic detection of accessory/lateral canals: use
of RadioVisioGraphy and Hypaque. Journal of Endodontics 21:185-90.
- Wenzel A, Grondahl HG (1995). Direct digital radiography in the dental office. International Dental Journal 45:27-34.
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Received March 1996
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