Digital Radiography - What You Need to Know Before Going Digital

Digital Radiography - What You Need to Know Before Going Digital

With the recent advent of digital imaging in medicine, and subsequently dentistry, many practitioners are considering making the conversion to digital-based systems. Multiple factors play into this important decision, including: the quality of image available, transfer of images to other practitioners or insurance companies, ease of use for staff, patient radiation dosages, and cost.

The main advantage of digital radiography over traditional film is that digital images are available immediately. This saves time in treatment requiring progress films or if a shot needs to be retaken. It should be noted that charge-coupled device (CCD) systems offer immediate images, while photostimulable phosphor plate (PSP) systems do not. When using traditional films, waiting for an image to develop is not only time consuming, there are also discontinuity of the procedure and chain of infection issues to be considered.

Image storage is more palatable with digital, since micro-storage technology allows us to store large volumes of data on drives that use very little space; conventional films produce cumbersome charts that can be lost or difficult to find. Other advantages with digital include avoiding the inconsistency of chemical processing and the associated disposal of hazardous wastes and lead foil. Also, images can easily be transferred to other dentists who have the necessary computer technology, or printed on photo paper for those who do not. Lastly, studies have shown a reduction in patient radiation of 70% or greater with digital radiography.

Patient education is improved by an image displayed immediately on a chairside monitor, rather than making the patient leave the chair to squint into a viewbox at a miniscule shadow. The ability to enhance an image, particularly by increasing brightness or contrast, is a tremendous benefit to the practitioner because often a film is not viewed until after the patient has left the office.

Conversion to digital imaging carries certain disadvantages that should be weighed. The armamentaria are expensive, fast evolving, and relatively new, so there is a risk of the technology becoming obsolete quickly or the manufacturers failing to survive. Dr. Gordon Christensen has estimated the cost of converting to digital radiography to be $11,000 to $15,000 for a wired system, and $20,000 to $22,000 for a wireless system. Additionally, some of the sensors are somewhat fragile and small and can easily be damaged or lost; the cost to replace a sensor varies from $6,000 to $12,000, depending on the system used. Finally, there is the cost in man-hours of converting old records to digital; scanning and saving each radiograph could be a monumental task for a busy practice.

In choosing a system to purchase, first consider CCD versus PSP. The CCD is the most common device used today. Its sensor is about the same size as a #2 intra-oral film and is connected to the computer by an optic fiber wire in most cases. Microwave technology has been used with CCDs, eliminating the need for the wire tether, but requires additional electronic components. The CCD consists of a silicon chip with an active array of rows and columns called pixels (picture elements). These pixels are analogous to silver crystals in conventional films but are 80% more sensitive to radiation, thus the reduction in radiation dose to patients. Smaller pixel sizes mean more pixels fit onto the sensor, which decreases the size of the receptor but increases the cost. CCDs are available in large enough sizes to accommodate panoramic films, and manufacturers have made CCDs that can be retrofitted to existing units to ease the cost of equipment conversion. With cephalometric imaging, a CCD large enough to capture an entire skull is too expensive to manufacture and sell, so a different technology has been employed that involves a CCD array and a scan lasting several seconds.

PSP technology uses photostimulable phosphor plates as the image receptors. Essentially, the storage plates store latent electronic images trapped in phosphor crystals. When a laser beam stimulates the phosphor crystals, trapped electrons are released and light is emitted in proportion to the amount of radiation absorbed by the phosphor crystals. The light is converted into pixel values and the image is formed in a semi-direct fashion. Although the latent image is available for several days, it is best to read the storage phosphors within a few minutes of exposure, since a small amount of decay occurs. The phosphors may then be flooded with light and reused.

The main advantages of CCDs over PSPs are the immediate availability of the image and the lack of an intermediate step. The primary disadvantages are a bulkier receptor with a smaller active area, and with most CCD detectors, a fiber optic wire connected to the computer. So with CCD systems, unless multiple operatories are equipped with sensors (an expensive undertaking), radiographs can only be taken in one operatory at a time. Also, the patient must be positioned close to the computer (as wireless technology improves, this problem will be alleviated). Cost varies with the system purchased and depends greatly on the replacement frequency of the receptors.

When contemplating the plunge into the exciting realm of digital radiography, there are many financial and technologic aspects to consider. It’s a daunting choice, but keep in mind that the digital revolution is upon us. Insurance companies accept digital images, and the immediacy of transmission often leads to faster reimbursement. The ease of communication with colleagues and laboratories is practice-enhancing to say the least. When talking to manufacturers and distributors, know that their claims in regard to performance and durability are often optimistic. A better gauge of performance is a trusted colleague who has used the technology—a visit to his or her office is akin to test-driving an expensive vehicle prior to making the purchase. In closing, do your research, close your eyes, and jump in!

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