Radiology

Filmless Radiology -- Now and In the Future

Dr. Hadley will present "Quality Intraoral and Extraoral Radiographs" at the ADA Annual Session on Sunday, Oct. 25 from 8:30 am - 11:00 am, and repeating from 1:30 pm - 3:30 pm in the Executive Conference Room at the University of the Pacific School of Dentistry.

Many changes have occurred in the technology used to acquire dental images. Most of the research has been directed to reducing radiation to the patient while maintaining excellent diagnostic quality. With the introduction of computer technology and monitors, the patient is exposed to less radiation while diagnostic capabilities for the dental practitioner are enhanced. When this exciting, emerging technology is more fully utilized in practice, there will be great benefits to the patient and the dental profession alike.

Dental radiology has seen many changes over the past 10 years, leading to new technologies that have had a profound effect on the practice of dentistry. As we move into the next century, dentists will see the results of the advances being made now, and will most likely benefit from easier, more accurate diagnoses and increased patient satisfaction with their overall treatment. Following is a review of some of the recent developments in dental radiology that will make a difference in the future of dentistry.

Xerography

Dental xerography was first introduced about 20 years ago. Xerography is a method of imaging by utilizing a charged selenium alloy plate in a lightproof cassette, about the size of a #2 film. It is placed into the mouth and held with a device and exposed to radiation, at 50% dose reduction relative to D-speed film. This exposure creates a latent image of charge carbon particles. The particles are then transferred between a sheet of transparent polyester and mylar; thus, a hard copy picture is produced. It is viewed conventionally or by reflected light.

There are advantages and disadvantages with this system. Advantages include good diagnostic utility showing the presence of proximal caries and periapical diseases. In assessing periodontal disease, this system shows excellent images of bone trabeculation, lamina dura, calculus and furcation bone loss. There could be up to 80 percent less radiation when compared to D-speed film using rectangular collimation. It is less expensive than other automatic film processing systems, such as gender-GXP or the PerioPro. Xerography single film production takes less than two minutes to create a hard copy, and is better suited for single film production than for full mouth exposures.

Major disadvantages include high-edge enhancement, which creates radiolucent artifacts around densities such as fillings, which give false indications of caries. Another disadvantage is that xerographic equipment is less reliable than other film processing equipment, and sometimes the cassette is uncomfortable in the patent's mouth. The system has not gained popularity because of the high initial capital expense of the processing unit.1

Digital Scanning System

A small corporation, Digiray, is conducting ongoing research in digital radiography. This research emloys a unique reverse collimation of the scanning source of x-ray while directed at an object. The x-ray beam is collimated to the size of a 1mm crystal receptor and changed into light, which goes to a photo multiplier, creating an electrical signal processed by a computer for viewing on a monitor. This reverse collimation is the only type known at this time. It reduces radiation to the object to only 1/10 of the amount of a single D-speed film. Because of many reasons, such as high expense and lack of funding, this concept has not been well utilized.

In 1991, The Department of Radiology at the University of the Pacific School of Dentistry in San Francisco began reducing the number of films in a full mouth from 28 to 20, which reduced radiation exposure to the patient. At the same time the rectangular collimator was introduced along with the Rinn XCP device, which helps to position the rectangular collimator correctly for the right angle paralleling x-ray technique. By using the rectangular collimator, the amount of radiation to the patient is reduced by another third. Kodak Ektaspeed-plus film is used for all intraoral exposures, which reduces the amount of radiation by 50 percent for each film while maintaining excellent diagnostic quality. However, in 1995, only 20 percent of dental offices in the United States and Canada were using Ektaspeed-plus film and only 3 percent of offices were using rectangular collimation to reduce radiation to patients.3

Storage Phosphor System

Storage phosphor systems are charged plates which are about the same size as conventional film sizes. They can be exposed a multitude of times, are thin and smooth-edged, and can be used in most holding devices. After having been exposed, the plates are placed into a scanner. (There are several kinds: Digora, Dent-X, and Dentsply.) When the plates are scanned, images appear on the monitors to be viewed and they are digitally manipulated.

In a recent study by Wenzel, it was suggested that the storage phosphor system may not use less radiation than E-speed film, especially even when there is collimator size reduction.11 Another investigator found that these devices are better than film when measuring periapical lesions. Although these systems give images similar to film, it was concluded that there is a higher image quality with a wider exposure range compared to film and other digital systems.12

Storage phosphor systems show improved detection of caries when compared to enhanced computer images and Ektaspeed-plus film. Also, images from these plates showed favorable contrast differentiation and gave good diagnostic quality at even 53% reduction of radiation compared to E speed film.13

Digital Imaging

Digital imaging uses intraoral sensors, which is said to reduce the amount of radiation to the patient by 90 percent. Due to the relatively high cost to purchase a digital system, the benefits of utilization have not, as yet, had widespread acceptance. But there are pervasive benefits for the dental practitioner and certainly for the patient. Instantaneous digitized computer images have many wonderful qualities: obviously there is no film5 and the radiation reduction is as much as 70 percent compared to film.6 It is a fast way to obtain images over a wide range of (KVP) settings.7

With inherent benefits from these current technologies, there has been a tremendous amount of in-depth research to gain information about how to use this diagnostic tool and how treatment may be impacted. Still in debate are questions such as whether the patient is really exposed to less radiation, the cost effectiveness of this method, and if the immediate image on the computer monitor provides better diagnostic information than the digitized information from a scanned storage phosphor plate.

Digital radiology can be efficient in clinical use. There is a great capability to store digital information, exchange radiographic material and perhaps improve diagnostic quality and accuracy with automated image analysis.8 Clinically, images are larger than film because of monitor resolution and digital image size.

A word of caution is that dentists cannot detect altered diagnostic contents of images that have been manipulated. Therefore, digital images must have greater data protection.9 Investigators who compared film with digital imaging concluded that both film and digital imaging are diagnostically acceptable for detection of proximal caries and periapical lesions.10 Some professionals feel that more studies need to be conducted to determine if digital imaging is better than film, but as yet little evidence reveals that digital enhancements change interpretation, working practices, or treatment decisions.11,12,13

Although there have been many studies done with digital and storage phosphor systems, one researcher who surveyed dental students found that many want digital radiology introduced into the curriculum, at least as an elective course. Although the benefits of such a class would include fewer misconceptions about digital radiography and an understanding of how digital radiology will play a role in the future, it was felt that teaching methods and the content of such courses would need careful consideration.14

Conclusion

Most assuredly there have been great changes in digital radiology in the past 10 years. There are many ways now to reduce the amount of ionizing radiation to the patient. This has come about with the help of film companies developing film requiring less radiation while maintaining excellent diagnostic qualities. Computer technology has not only demonstrated the capability for less radiation, but also allows the clinician to view the images in different ways, which will provide data that can be stored and shared, resulting in accurate diagnoses and timely treatments.

As dentists become more knowledgeable about digital radiology and want more information, the industry will comply. Reduced capital expenses will go hand in hand with the demand. There will be more studies to reduce the bulkiness of the sensors to make them patient- friendly. Monitors with a wider range of small pixel sizes will result in better resolution and more accurate diagnosis. The clinician will be able to retrieve diagnostic information more quickly and will be able to more clearly discuss with the patient issues about teeth, the surrounding bone, and others parts of the mouth. The patient will be able to see images--acquired with less radiation--on a computer monitor, helping him or her to understand and accept treatment more easily.

Author

Dr. Jack Hadley is a professor in radiology and director of the emergency clinic at the University of the Pacific School of Dentistry in San Francisco.

References

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4. Wenzel A, Digital radiography and caries diagnosis. Dento Maxillo Facial Radiology 27(1):3-11, 1998.
5. Borg E. Granaahl HG, On the dynamic range of different w-ray photon defectors in intraoral radiography. Dento Maxillo Facial Radiology 25(2), 82-88, April 1996.
6. Lim KF, Loh EE, Hong YH, Intra-oral computed radiography - an in-vitro evaluation. J of Dent 24(5):359-64, 1996.
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8. Saxe MJ, West DJ Jr., Incorporating digital imaging into dental hygiene practice. J Dent Hygiene 71(2):71-5, 1997.
9. Farman TT, Farman AG et al, Charged - coupled devices panoramic radiography effect of beam energy on radiation exposure. Dent Maxillo Facial Rad 27(1):36-40, 1998.
10. Hayakawa Y, Farman AG et al, Optimum exposure ranges for computed dental radiography. Dent Maxillo Facial Rad 25(2):71-5, 1996.
11. Versteeg CH, Sanderink GC, Efficacy of digital intraoral radiography in clinical dentistry, J of Dent 25(3-4):215-224, 1997.
12. Visser H, Kruger W, Can dentists recognize manipulated digital radiographs? Dento Maxillo Facial Radiology 26(1):67-9, 1997.
13. Kullendorf B, Nelsson MR, Diagnostic accuracy of direct digital radiology. O Surg, O Med, O Path, O Radio & Endo 82(3):344-50, 1996.
14. Scarfe WC, Potter BJ, Farman AG, Effects of instruction and the knowledge, attitudes and beliefs of dental students towards digital radiography. Dento Maxillo Facial Rad 25(2):103-8, 1996.

To request a printed copy of this article, please contact/ Jack Hadley, DDS, UOP School of Dentistry, Department of Radiology, 2155 Webster Street, San Francisco, CA 94115.