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Digital Radiology

Overview

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Digital radiography is becoming an increasingly popular method of producing radiographs in both dentistry and medicine because it offers numerous advantages over conventional film and film processing. Radiographs can be produced in real-time; thus eliminating the wait for processing. Radiation exposure is reduced by as much as 90% from conventional film taking. The cost, labor and record-keeping necessary to maintain a chemical processor and darkroom are eliminated. The costs of purchasing and disposing of film and environmentally hazardous chemicals also become unnecessary.

With recent advances in technology making digital images comparable to or better than film, the disadvantages of digital radiography are now mostly associated with the initial cost of the hardware, software and network cabling necessary to implement such a system. Another cost that is harder to quantify but worthy of consideration is the learning curve associated with new techniques and skills for producing the radiographic images as well as sharing, storing and retrieving the images over a computer network within your office. Office morale can be affected positively or negatively depending upon how the new technology is introduced and how the staff is trained.

CCD Sensors

The digital process of taking dental radiographs is an outgrowth of the aerospace industry’s need for real-time inspection of the structural integrity of components and assemblies. Most digital radiography systems use a charge-coupled device (CCD) that is attached by a thin cable to a computer. The sensor has a thin layer of silicon crystals spread on its surface. Covalent bonds between adjacent silicon atoms are broken by incoming photons (radiation). The breakage of these bonds forms an electron-hole pair and a latent electronic image distributed as a pattern of electrical charges in the matrix of silicon crystals. The CCD collects and integrates these charges and the software program imports this data as an image that is labeled and made part of the patient’s file. This image can then be adjusted for darkness and contrast, enlarged and otherwise manipulated to produce diagnostic information.

Drawbacks of the CCD systems are that sensor placement must be learned, and some adjustment of conventional techniques is necessary when using a rigid sensor that has a cable coming off of it. The cost of sensors is substantial, and equipping multiple operatories can be extremely expensive. One can share sensors between operatories, but this can be cumbersome, and Murphy’s Law will dictate that when sharing a sensor, the need for it will arise simultaneously among those sharing it.

The biggest advantage of the CCD systems is that the image is available within seconds. The need for tube head or sensor placement adjustment can be recognized before the patient, sensor or tube head have moved and can be adjusted accordingly. Traffic in the hallway to and from the processor is eliminated.

Storage Phosphors

Storage phosphors are essentially a type of reusable film with an outward appearance resembling intensifying screens used in extraoral (such as panoramic) radiography. The storage phosphors, however, actually store the adsorbed x-radiation energy in a “halogenide” layer. A laser that releases the energy and records it in digital form then scans the latent image held by this stored energy. Storage phosphor plates theoretically last indefinitely, but they need occasional replacement because of mechanical wear caused by movement intraorally and in the processing unit. The DenOptix (Dentsply/Gendex) and DIGORA (Soredex/Orion) are two intraoral storage phosphor systems. The DenOptix system also has a panoramic and a cephalometric option.

The storage phosphors have the advantage of utilizing similar film placement and exposure techniques as conventional radiography, but this is also one of its drawbacks. The time needed to bring the sensor film packets to the processor, which must be in a low-light environment, could be used for other more productive purposes. Additional time is also needed to “refresh” the film packets in brighter light, such as a view box, prior to their next use. The laser processing itself takes one to two minutes for a periapical or bitewing image, and about five minutes for a panoramic film.

Hardware Requirements

Most offices already have the x-ray equipment needed for the radiation source in digital intraoral (bitewing and periapical) radiography. Digital systems utilize conventional tube heads with the exposure time turned down significantly. If the timer of your tube head cannot be set low enough, which might be the case on some older models, a filter can usually be installed to bring the radiation exposure low enough.

Extraoral digital radiography is not nearly as flexible in its radiography hardware requirements. Many digital panoramic systems are compatible only with the panoramic x-ray machine made by that same company. The DenOptix system has the advantage of being compatible with virtually any panoramic cassette, although processing time is as long or longer than for conventional film. The Schick Technologies panoramic system is compatible with most recently manufactured panoramic machines that have a flat rigid cassette. Older machines with a rigid curved cassette are not supported by the Schick panoramic system. The Schick system offers a real-time image with CCD technology and does not require the handling and processing of a phosphor screen.

The computer hardware requirements for digital radiography are easily satisfied by virtually any computer system currently on the market. The cost of the computers has become a secondary issue with the dramatic price decreases in seen in the past year. The digital hardware and software remains expensive, however, although these prices continue to decline even as the technology improves.

Repair needs shift from traditional dental suppliers to computer hardware and software technicians and consultants. This is a critical issue to have arranged before an emergency arises. As one becomes more dependent on electronic storage media, data backup also becomes more critical. Multiple levels of backup are best, with nightly backups from one hard drive to another within the office network as well as a full backup stored off-site being a good foundation. It is important to test your backup to confirm that you are backing up what you think you are backing up and that data replacement can actually be done from your backup media.

Digital radiography should be evaluated first with regard to one’s practice needs and utilization patterns. Digital x-ray images may be integrated with one’s practice management software, although this is not a requirement and many practitioners use the digital radiography software as a free-standing program independent of their main practice software. Image quality, ease of placement of the sensor or phosphor plate, ease of learning and intuitiveness of the software for working with, storing and retrieving the radiographic images, and cost should all be evaluated. One must make the decision to implement this technology if and when it fits into individual practice philosophies and goals.

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