Digital radiography

Deciding whether to purchase not a black-and-white issue for equine practitioners
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Jun 01, 2004


Positioning is still as crucial to digital/computed radiography as it is in conventional X-ray production. Digital radiography can use computer programs to improve film quality and to enhance exposures but positioning technique must still be correct.
The digital revolution has been going on for some time now.

Many veterinary schools and larger private practices have made the jump to digital and computed radiology (CR) systems.

Marketers and manufacturers have shown us all the beautiful images that can be achieved with these devices and veterinarians are being told that they cannot live without this technology.

Many more equine practitioners, however, are still on the fence regarding these new systems and, though interested, are not sure if they are right for their individual practices. There is no debate concerning the technology or the image quality. But, as Dr. Matthew Wright, a consulting veterinary radiologist says, "Digital radiology has nothing (well, very little) to do with the image."

Mitigating factors Digital radiology or CR is a system and its use or non-use and the ultimate decision to incorporate it into your practice depend on a list of factors.

Computed radiology is a digital imaging technology incorporating phosphor plates that capture an image made from conventional exposure to X-rays. The latent image from the phosphor plate is then read by scanning the plate with laser light. This process releases a visible light image that is detected and converted to a digital image that is then transferred to a computer screen. This technology was introduced in human medicine by Fujifilms Medical Systems in the 1980s. It should be remembered that CR is a process or system and not a single product. Since these early beginnings there have been many other systems introduced by many other companies and now both human and veterinary products are available.

Comparing conventional radiology to computed radiology is fairly easy on a technology level. Silver halide film (the standard for traditional radiographs) has a limited response to radiation, which means that it cannot tolerate much variation in latitude. Relatively small degrees of under or overexposure will result in an unacceptable image.

Phosphor plates and the resultant computed radiology image, however, have more exposure latitude and are thus able to produce more shades of gray. These images produce higher contrast and, coupled with the computer's ability to enhance or manage this digital information, computed radiography can be adjusted for exposure variation. This factor is one of the strongest points in favor of CR because it means that even inaccurately exposed films can be salvaged and that computer enhancement may optimize the diagnostic value of images.

Spatial resolution Conventional radiographs have a higher spatial resolution than CR images. Spatial resolution is the number of pixels per unit area. This positive for conventional images does not factor into the discussion however, because much of the increase in standard film resolution is beyond the range of human vision. As technology advances, this resolution difference will prove to be even less of a factor as well. CR, therefore, produces image quality that is as good as traditional films and has the advantage of allowing better contrast in differing areas of the same image through computer manipulation. This explains Wright's comment about CR not being about the image. A well-taken traditional radiograph contains the same information as one taken with CR. The rest of the debate between these two methods of radiology concerns how the images are taken and what can be done with them.

Reduced cost One of the main advantages cited for CR, outside of the technical issue, is reduced cost for radiology. There are no film costs, no processor maintenance including chemical developers to purchase and chemicals to dispose of. There are no film jackets to buy and no need for the space to store films.

These savings are very real but are dependent on going totally filmless and that transition will cost money to achieve. Remember that the image produced by a CR system that you can view will be influenced by the monitor you view it on and any printed image will be dependent on the printer and paper quality. Printers, ink and paper soon replace processors, chemicals and film and the cost/benefits are not as clearly defined.

Storing Digital images must also be stored and this part of the patient's medical record must be protected.

Mary E. Andrews, a licensed human radiology technician and event rider, points out that, "There is a need to input information into the computer prior to taking films so there is a delay in the initial film-taking process." This delay is rarely of concern except in emergency situations but because this initial information is the only means of identifying images it is crucial that it be done consistently and correctly.