by Leif Kullman
Advantages with Digital Imaging
Earlier I have tried to explain what a digital image is and in my October message I promised to tell you a little more about different advantages with these images. There are many advantages that can be straight listed, but I should try to report on these by telling you about some of the lectures and abstracts in the symposium of DIGITAL IMAGING IN DENTAL RADIOLOGY that recently was held in Amsterdam, The Netherlands.
It was the 4th Symposium on Digital Imaging in Dental Radiology and a continuation of the meetings in 1990,1992 and 1994. In the scope of the symposium it was stressed that the development of digital radiology has made tremendous progress recently. Many systems for the acquisition of digital images are today available. Programs to improve the diagnostic yield of digital imaging have grown more sophisticated . Therefore one of the goals of the symposium was to obtain a comprehensive overview of the state today in this field.
The discussed topics included
computer aided image interpretation
communication and teleradiology
image reconstruction and 3D representation
diagnostic quality of digital systems
impact of digital radiology on clinical dentistry
digital panoramic radiology
Professor Richard Webber from U.S.A spoke the first day on Tuned-Aperture Computed Tomography in dentistry: Theory and Applications'. He presented a new method for creating three-dimensional radiographic displays based on optical aperture theory known as tuned-aperture computed tomography (TACT). This method has advantages over conventional plain film and tomographic methods including an ability to accommodate patient motion between the exposures and a potential for interactive sampling of 3-D data. Also an ability to synthesize projections suitable for digital subtraction without mechanical stabilization of projection geometry and the ability to produce 3-D displays from any number of projections. The method has a lot of potential, future applications in dentistry.
Digital panoramic radiography systems
Several manufacturers are now presenting digital panoramic radiography systems. One of them is Siemens and such a system (Orthophos) had been tested by researchers from Germany with good results. A similar system with the same advantages, creating a dental office completely free from photographic film and chemical processing in the future, was presented by Planmeca, Finland. Their panoramic system is like many others complemented with a transversal slicing system, enabling for example preimplant transversal investigations in the jaws. Some other researchers reported about the dose reduction in digital panoramic radiography. With different intraoral systems it has been proven that a dose reduction with 60-90% is possible. With the new panoramic equipements a reduction with at least 30% have been indicated.
Digital subtraction
A major advantage with digital radiographs is a possibility to perform digital subtraction. With this application it is possible to follow for example the healing of an apical radioluscens or a marginal bone retraction or the proceeding of a caries decay. Two digital images must be available from the same area (but exposed at different times). The different greyscale levels in one of the pictures are subtracted from the greyscale levels in the same positions in the other picture (the last taken picture). Areas where something have happened (i.e. bone apposition) will be seen in the new"subtraction" picture while the greyscale level will be zero in areas with status quo. Subtraction methods have a great diagnostic capacity being even very sensitive. However a great problem has been that the radiographs must be taken with almost identical projections. Researchers are now working on programs eliminating this limitation and some German and Swedish researchers (Lehmann; Gröndahl et al.) presented a suitable technique for alignment of both standardized as well as free-hand taken radiographs.
Some other researchers from Sweden (B. Svensson et al.) had studied caries diagnosis using Sens-A-Ray digital radiography and reported that the diagnostic accuracy is equal to that of film radiographs for this system.
Future trends
During the last day Professor Lambrecht from Switzerland gave a presentation of a "A Computer tomography-based 3D Model Technology for Computer Aided Surgery". CT-based computer aided surgery (CAS) will in the future play an important role. Two systems were presented and their advantages and disadvantages in the planning and performance of computer aided surgery procedures in oral and maxillofacial surgery were discussed.
Next month I will present some interesting case or cases (including radiographs and anamnestic records).
Leif Kullman
