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Two Decades of Computerized Information Technologies in Dental RadiographyProfessor and Head, Department of Oral Radiology, Royal Dental College, Faculty of Health Sciences, University of Aarhus, Vennelyst Boulevard, DK-8000 Aarhus C, Denmark; awenzel{at}odont.au.dk
Key Words: radiography • computerized Returning from Tanzania in 1978, where I had served for a year as a volunteer dentist for Danish Church Aid, I enrolled in the PhD program at the Royal Dental College of Aarhus, Denmark. My PhD thesis, defended at the Department of Orthodontics in 1982, was written on an IBM typewriter with magnetic cards for storage, and scientific data-processing relied on punch cards. Soon after, I was employed as a full-time teacher in the Radiology Department. No full-time teacher or researcher was attached to the radiology unit at the time, which was part of the Department of Oral Surgery. Since I was taking over lectures and seminars in radiography and radiology for dental students, new thinking on the educational policy was essential, or I would be up to my ears merely in educational work. This started my life-long enthusiasm for electronic aids, first for the teaching of dental students, later for diagnostic radiography. EARLY EXPERIMENTS WITH ELECTRONIC TEACHING My first experiments on computer-assisted learning were based on early 8-bit microcomputers with very little memory. The authoring language was developed at our dental school in a collaborative work with major industry and was years ahead of its time. I developed computer-assisted instruction programs for dental students in various disciplines, e.g., radiographic recording techniques and radiation physics and biology. Such self-instruction programs soon covered about 20% of all teaching hours in the radiology curriculum (Wenzel and Gotfredsen, 1985, 1987), and tele-experiments were initiated in radiography education for dental assistants in remote areas (Wenzel and Frovin, 1988). This was quite a new approach to teaching in my part of the world and was favored by the media. Today, newer developments of these early programs are still in use for student education in dental radiography (Wenzel and Gotfredsen, 1997). Computer-based learning can offer all students the same information, resulting in more creditable and standardized skills and building a common platform from which more academic discussions can take place. Today, we also take advantage of the Internet, and educational materials available for students in radiology include images and questions and answers to previous exams (www.odont.au.dk/radstud). The lectures that my co-workers and I give can be seen as pdf files the day after the lecture and thus be reviewed by students at any time (the material is all in Danish). The new DOS-based computers that appeared on the market in the middle of the 1980s awakened my interest in diagnostic radiography with the radiograph in digital form (Wenzel, 1988). My first computer bought for research cost more than $10,000 and had 64 kbyte of RAM. It was equipped with a frame-grabber card and connected to a black-and-white CCD-camera and a black-and-white monitor, through which a conventional film radiograph could be digitized. The resolution was limited, 512x512 pixels, which was in accordance with its limited storage capacity. Indirect digital images are obtained today mainly by digitizing the film in a scanner, and the image resolution is optional, depending on the quality of the scanner. EVALUATION OF CHANGES OVER TIME BY SUBTRACTING TWO IMAGES When I started digitizing dental films, this was nothing new. At the National Institute of Dental Research, an ingenious researcher, Richard Webber, was one of the first to digitize dental radiographs to determine if more information could be extracted from a subtraction radiograph, which was created by subtracting the information in a digitized film recorded after the removal of small volumes of alveolar bone from that in a film recorded before the bone changes were made, than from comparing these two radiographs in the traditional way (Webber et al., 1982). His pioneer work included mathematical corrections of distortions in the images to be subtracted caused by differences in shape and position of the film relative to the x-ray beam (Webber et al., 1984). Webber’s work on the implementation of digital subtraction into dentistry encouraged me and others to further investigate the possibilities of this technique. When two radiographs are recorded with controlled projection angles and thereafter subtracted, theoretically all unchanged background anatomical structures are canceled, and these areas can be displayed in a neutral grey shade in the subtraction image, while regions that have changed between the radiographic examinations are displayed in darker or lighter shades of grey. Efficient use of subtraction radiography required controlled projection geometry but, in addition, highly qualified programming if unavoidable projection distortions were to be compensated for by mathematical algorithms. Positioning of reference points in the two images to be subtracted provided subtraction images superior to the traditional manual superimpositioning of the images (Wenzel, 1989). A great many laboratory studies were conducted in the 1980s comparing subtraction with conventional radiographs for the detection of small changes in marginal bone, and concurrent views are that subtraction is more accurate for the detection of bone changes than comparing two radiographs conventionally (for reviews, see Hausmann et al., 1988; Reddy and Jeffcoat, 1993; Wenzel, 1999). In clinical trials, the method has been particularly useful for evaluating the effects of guided bone regeneration procedures (Wenzel et al., 1992; Christgau et al., 1997, 1998; Eickholz and Hausmann, 1998), and has also been implemented in the evaluation of the progression of caries lesions (Wenzel et al., 2000). Recently, subtraction was emphasized in the final Consensus Statements from the International Workshop on Clinical Caries Trials this year as one of the future methods that might provide more quantitative information from radiographs on caries lesion behavior. These statements will soon be published in Advances in Dental Research. An excellent review on the history of subtraction radiography was published in a previous "Discovery!" (Hausmann, 1999). THREE-DIMENSIONAL IMAGE DISPLAY OF DENTAL STRUCTURES A subtraction image is still a two-dimensional display, and the changes in brightness (density) do not reflect absolute thickness measures, because these are dependent on several factors, e.g., the circumscribing region. In 1985, Webber already predicted the future of three-dimensional radiography in a scenario on computer-based diagnostic imaging devices (Webber, 1985). Here for the first time, a model with dental examples using the principle of tomosynthesis was revealed. With a total of eight projections, clinical information on tooth structure was extracted and expressed in three dimensions. Webber’s vision was that such new technologies would find their way into clinical dental practice within a decade. Indeed, about 10 years later, Webber and co-workers announced the refined development of the tomosynthesis principle, now known as Tuned-Aperture Computed Tomography®, or TACT® (Webber et al., 1996). Numerous subsequent studies have demonstrated that TACT’s capability of displaying structures in three dimensions increases the accuracy of detecting dental pathology (Tyndall et al., 1997; Webber et al., 1997; Webber and Messura, 1999; Nair et al., 2000, 2001). While most of these studies have been performed in vitro, without doubt the technique is one of the most promising developments in dental radiographic diagnostics for the coming years. For his contributions in the field of dental imaging, Dick Webber was awarded the degree Doctor of Odontology honoris causa from Göteborg University in 2001. DIRECT DIGITAL IMAGE CAPTURE FOR THE DENTIST At the first European meeting of dental and maxillofacial radiology held in Geneva in 1987, Francis Mouyen, a French dentist and inventor, demonstrated the first direct digital intra-oral radiography system for dentistry, which was to be known as RadioVisioGraphy (Mouyen et al., 1989), from Trophy Radiologie. (I remember introducing myself to Francis with the words: "I am probably not the right age or sex, but I would like to perform experiments with this new digital receptor.") Some months later, Francis installed an RVG unit in my department, and one of the first diagnostic papers evaluating the performance of the new CCD system compared with film was published (Wenzel et al., 1991). The same year, my doctoral (DrOdont) thesis was defended, which included a review of the history of indirect digital radiography (Wenzel, 1991). The introduction of new receptors was the starting signal for my interest in the utility of digital radiography in dentistry. The first RVG consisted of an exchangeable scintillation screen, fibre optics, and a miniature charged-coupled device (CCD). Monitor resolution in personal computers was still low in the 1980s, and only a limited number of grey shades could be supported at a time (VGA graphic card). The RVG unit therefore utilized a black-and-white, TV-quality stand-alone monitor for image display. As soon as S-VGA graphic cards were available, the digital image could be displayed on the computer monitor, showing 64 of its 256 shades of grey at a time, and many new CCD sensors were brought out simultaneously with the explosion of developments in computer technology (Nelvig et al., 1992; Molteni, 1993). The introduction of Microsoft WindowsTM loosened the tight relationship between monitor display and software. This broadened the utility of programs for enhancement of the image in real-time, leading to the well-known contrast, brightness, and gamma curve functions that facilitate the use of the digital image (Gotfredsen et al., 1996). Initiated by Allan G. Farman, Francis Mouyen received the degree of Doctor of Sciences honoris causa from the University of Louisville in 2000 for his contribution to science. In 1994, the first stimulable storage phosphor system, Digora® was launched for dental imaging based on technology known for years from medical radiography (Gröndahl et al., 1996). The storage phosphor plate looks like film and must be read out in a scanner after exposure. The many advantages of the new digital receptors have been evaluated in numerous reviews over the years (Wenzel and Gröndahl, 1995; Wenzel, 1998, 1999), and current manufacturers of digital dental systems can be seen on our Web page: http://www.odont.au.dk/rad/digitalx.htm. Diagnostic accuracy is just as high with digital receptors as with film for most tasks in dentistry (for review, see Wenzel, 1999), though there are exceptions (Hintze and Wenzel, 2002). The use of digital radiography systems in general dental practitioners’ offices is still limited. The first national survey was performed in Norway by my colleague Anne Møystad and me (Wenzel and Møystad, 2001a,b), in which we estimated that approximately 15% of dentists have exchanged their conventional film with digital receptors, and that most dentists prefer a storage phosphor to a CCD system. The number of "digital" dentists is steadily increasing, and our findings have recently been confirmed by a study from the Netherlands (Berkhout et al., 2002). Both digital concepts have their advantages. Ideally, more than one system should be available in a dental office, and particularly in big radiology departments, if the patient is to be offered the best and most convenient examination for a given diagnostic task. A real challenge for me, therefore, was to develop a radiology department wherein several digital units could work together independent of the fact that they all store their images in different file formats. With the considerable skill of my programer, Erik Gotfredsen, our goal was accomplished by developing software that communicates images from all digital sources and displays these in the individual patient’s record (Gotfredsen and Wenzel, 1999). This has paved the way for the introduction of digital imaging in our dental school as one of the first in the world. AUTOMATED COMPUTER DIAGNOSIS However advanced the new digital imaging receptors and displays, there is still the diagnostic task to be performed by the human observer. It is well-known in radiography that the accuracy of diagnosis depends on the skills of the observers, and that great variation exists among these, particularly for caries diagnosis. It would be fortunate if more automated detection systems with high reproducibility and accuracy were available for the dental practitioner. In Hong Kong, a bright young scientist, Nigel Pitts, was one of the first to evaluate the efficacy of an automated analysis system in dental radiography. In the early 1980s, Pitts published several studies showing promising results that computer analysis was as accurate as human observers for the detection of caries lesions with even higher sensitivities (Pitts, 1984, 1987). More recently, others have developed programs that have performed equally well (Heaven et al., 1994; Firestone et al., 1998), but none of these is available for general dentists. Unfortunately, the one system for automated caries detection that dentists can purchase lacks accuracy and consistency (Wenzel, 2001; Wenzel et al., 2002). Obviously, dentists will benefit from computer-based decision support programs in the future, just as general medical practitioners have benefited from, e.g., automated ECG analysis. An excellent survey on decision-support systems in dentistry has been published by White (1996). Looking back on my first 20 years of building a radiology department in continuous progress, I acknowledge that the true milestones in the field of electronic dental radiography were reached by several innovative scientists, a few of whom are mentioned above. I myself only followed in their footsteps. I would like to close with the words of the Danish philosopher, the father of existentialism, Søren Kierkegaard: "There are people who treat the ideas they pick up from others so frivolously and disgracefully that they ought to be prosecuted for illegal traffic in lost and found property."
— Søren Kierkegaard’s Journals and Papers, Received for publication June 4, 2002. Accepted for publication June 13, 2002. REFERENCES
Journal of Dental Research, Vol. 81, No. 9,
590-593 (2002) This article has been cited by other articles:
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