Diagnostic Imaging for Lameness
Today's sophisticated technologies available for diagnosing lameness resemble a Star Wars approach. X rays have taken on a totally new and expanded dimension, MRI is available for equines in many clinics and hospitals, ultrasound plays an everyday role, and scintigraphic scans can reveal lameness secrets that hide from more conventional approaches.
When we talk about diagnostic imaging, the two approaches that come immediately to mind that are advancing with speed are digital radiography and MRI. We'll focus on them and find out where they are today and what they portend for the future in the study and diagnosis of equine lameness.
Cost of Services
One of the basic drawbacks of new and sophisticated technology in many cases is cost, and this true with digital radiography and MRI. It becomes something of a dilemma for horse owners and veterinarians. The veterinarian has to determine how much of an investment in new equipment is justified. The horse owner has to determine how much he or she is willing to pay in the way of increased fees for the new technology.
There are no easy answers to these questions, and there will be broad variance from practice to practice and owner to owner. A large practice that deals with clientele comprised of expensive racehorses or sport horses often will find that its clients demand the best and latest in equipment and technology and are willing to pay the higher fees that might result. On the other hand, for a one-person practice in an area where recreational horses comprise the clientele, such an investment might not be justified from an economic viewpoint.
Digital radiography can be expensive, for instance, but more and more horse owners are demanding its use. Western Bloodstock agency of Fort Worth, Texas is the firm that conducts a series of sales in conjunction with the annual National Cutting Horse Association (NCHA) Cutting Horse Futurity each December in Fort Worth. The agency insists that for one of its prestigious 2-year-old in training sales, all four of a sale candidate's limbs must be X rayed in advance, and it must be done with digital radiography.
A number of veterinary teaching hospitals also have installed digital radiography equipment and are enthused with the results. At The Ohio State University College of Veterinary Medicine, for instance, four digital radiography units have been purchased and are dedicated to equine imaging--three for use in-house and one for ambulatory use--and the results have been "awesome," says Wm Tod Drost, DVM, Dipl. ACVR (radiology), of the radiology section.
There has been a vast improvement in image quality, he says, and digital radiography is much faster than conventional X rays. It is possible to observe an image in as little as four seconds after it is exposed. This compares with 90 seconds to two minutes with the conventional approach; conventional radiographs must be developed before viewing.
In addition, he says, the digital images can be sent simultaneously to other departments in the hospital so that a number of individuals can view them at the same time. Digital files can quickly and easily be transmitted outside the hospital to colleagues for consultation, which is known as teleradiology. Still another advantage, according to Drost, is durability. There is no loss in image quality as can happen with conventional film that is handled multiple times. "With all of the images stored in the computer, imaging studies are not lost and are easy to find, a huge time-saver," he says.
One of the digital radiography units, Drost says, is portable and is used by the school's ambulatory service. Using the conventional method, a veterinarian could only take as many images as the number of cassettes he brought with him on the truck, and to see these images, he had to return to the clinic to develop the film. Taking any additional images required him to return to the farm. But with the portable digital radiography unit, the ambulatory clinician can make as many images as he wants, and he doesn't have to develop images. Images are viewed in the field on a laptop, and while they don't quite have the clarity of the stationary units (which have better monitors for viewing), they can be utilized for a preliminary diagnosis. The veterinarian in the field can later study the images on equipment at the hospital for a final diagnosis.
Digital radiographs are described as high-quality images that are so visually sharp that they can produce an image with more than 16,000 shades of gray compared to only 120 shades with photographic film.
Where Did Digital Radiography Come From?
Much of what is known today about digital radiography is credited to Robin Winsor of Calgary, Alberta. About 10 years ago, Winsor was working in the oilfields around Calgary in the area of research and development. His wife is a veterinarian.
As the story is told, Winsor was helping a geologist download satellite photos one day, showing him how to use the system to find long linear geological features on the earth's surface. Winsor wondered if this technology could be put to use by veterinarians to produce better X rays.
He began researching and developing his idea, using a digital camcorder and an X ray beam in his wife's veterinary clinic. After a year of research, he applied for a patent for a system that would create a high-quality X ray and achieve it in a shorter time than film-based technology or computed radiography, which was already in use at the time in human medicine, and required development of cassettes (more on this in a minute).
He and some of his investor friends established the Imaging Dynamics Company to manufacture and market the product. Today there are many players in the game, with large global corporations developing and marketing their own digital radiography systems. It is technology that is here to stay, and it likely will improve even more in the years to come.
There are two main approaches available in digital radiography--direct digital radiography and computed radiography.
Direct Digital or Computed?
Direct digital radiography is the more sophisticated of the two, but the equipment also is more expensive. In direct digital radiography, the conventional radiographic cassette and film are replaced with a digital imaging sensor. This remains in a cassette tray underneath the X ray table or is carried around by hand to capture X rays of different areas of the horse's body (the imaging sensor resembles a conventional plate). Regardless of the location of the imaging sensor, it is connected to the computer by wires. According to Drost, companies are working on wireless communication between the imaging sensor and computer, but transfer rates are too slow for the technology to be useful at this time.
As is the case with today's digital cameras, there is instant feedback. The veterinarian knows instantly what the X ray has captured. The imaging sensor is exposed by X rays, and almost instantly, an image appears on the computer screen.
Computed radiography, on the other hand, replaces the film, intensifying screen, and cassettes that are used in conventional radiography with an imaging plate. A digital imaging reader is used instead of a wet film processor, which is used in conventional radiography. What this means is the film and chemicals involved in conventional X rays are no longer needed. Instead, once an exposure is made, the imaging plate is placed in an imaging reader. The plate is then exposed to a series of laser lights that read the information on the plate, and a radiograph appears on the monitor. While computed radiography is faster than conventional, it still lags behind direct digital radiography.
Both computed and direct digital radiography images can be manipulated to enhance viewing of different parts of the image. A veterinarian can change the magnification, brightness, and contrast of each image to aid in image interpretation. Another aspect of digital radiography includes integrity of images --certain digital radiographs, if taken using DICOM (Digital Imaging and Communications in Medicine) standards, cannot be altered. These images stand up to legal scrutiny, says Drost.
The Ohio State University decided to switch to digital radiography (Eklin Medical Systems), Drost says, because of speed.
The prime advantage of computed radiography, it seems, is that it is cheaper than direct digital radiography. Mark R. Crootof, DVM, who owns a small animal practice in Saratoga, N.Y., has been researching digital radiography for the past several years, and in the July 2005 issue of Veterinary Practice, he reported on what he had learned.
He gave these cost comparisons for radiographic technologies: purchase of a traditional X ray machine (the equipment that captures the image), $18,000 and up; purchase of a computed radiography system, $35,000 and up, plus X ray machine; purchase of a digital radiography system, $80,000 and up, plus X ray machine.
Crootof was quick to point out that the price range depends upon the manufacturer, the number of additional workstations, and the quality of the monitors. He also pointed out that some manufacturers offer to lease equipment if the practitioner doesn't want to make an outright purchase.
Both types of digital radiography have markedly improved the quality of skull, spine, stifle, and thoracic radiography, says Drost. These large anatomic structures are difficult to image using conventional film/screen radiography.
So, is an investment in digital radiography justified for the average veterinarian? In his article, Crootof quoted a fellow veterinarian as saying that if one installed computed radiography, the break-even point would be about 20 studies per month. With the digital radiography approach, it would be approximately 60 studies per month. The estimates were based on the national average charge for a two-view study.
MRI has proven to be a godsend in the realm of human diagnostics and has quite rapidly found at least a niche in equine veterinary medicine. Its prime drawback is cost. Few veterinarians today can afford the sophisticated equipment, although some practitioners have installed low-field fixed-magnet systems.
Just how does the technology work? There are many explanations available, but perhaps one of the best explanations for the layman was provided by T.S. Mair, BVSc, PhD, DESTS, Dipl. ECEIM, MRCVS, of Bell Equine Veterinary Clinic in Kent, England. He spoke at the 2003 AAEP convention in New Orleans and discussed use of a unit for the standing horse. Here is how he described MRI:
"Magnetic resonance imaging uses the body's natural magnetic properties to produce detailed images of the tissues. The part of the limb being imaged is placed within a strong magnetic field and subjected to radio frequency pulses. A unique radio frequency signal, based on each tissue's magnetic characteristics, is emitted in response to the pulses; these radio frequency pulses are collected to form the image.
"Magnetic resonance signal intensity varies widely in different musculoskeletal tissues because of differences in the proton density and the status of the chemically free versus chemically bound molecular water. Most diseases manifest themselves by an increase in water content and, therefore, MRI is a sensitive test for the detection of disease. The high soft tissue contrast afforded by MRI makes it ideal for assessment of articular cartilage, ligaments, tendons, joint capsules, synovium, and bone marrow."
Among the teaching institutions that have installed MRI units is the George D. Widener Large Hospital for Large Animals at the University of Pennsylvania's New Bolton Center. The unit, says Midge Leitch, VMD, Dipl. ACVS, radiology clinician at the hospital, was installed in August 2005 and has been used extensively since that time. While it has been a valuable piece of diagnostic equipment, it has not been the end-all answer to diagnosing lameness, she says, as all diagnostic equipment should be used in conjunction with a high-quality lameness examination. Magnetic resonance imaging, she says, is a valuable tool in examining for the specific cause of chronic lameness when the particular area of involvement has been determined, after conventional methods haven't revealed the lesion or trauma causing the problem. An example, she says, would be lameness emanating from a problem with the deep digital flexor tendon within the foot itself.
Unfortunately, the equipment is very expensive and its utilization is on the pricey side. Based on information from Leitch and Washington State University, the procedure would be in excess of $1,000 per examination, and it would go up from there, depending on how involved the diagnostic study might be. In addition, most units require that the horse be anesthetized before images are taken, which adds to the cost and risk to the horse. The reason for anesthesia, says Leitch, is that the limb being examined must be totally immobilized in order to achieve clear images of what sometimes is a very small area.
A British company--Hallmarq Veterinary Imaging--manufactures a unit that can be used on the standing horse that has been tranquilized. Some practitioners in this country are using the units, Leitch says. The drawback is that image clarity is compromised if there is any limb movement.
Mair described his experience with an MRI unit at this clinic to his AAEP listeners. He said the results in general were positive and that the approach, with some improvements, might put MRI in the affordable and practical range for many practitioners. "We believe that this system will allow the application of MRI technology in general equine practice, which would be unlikely with higher-field closed magnets because of their inherently higher cost," he said.
The good news is that research continues on these imaging techniques, with the goal being to make them both more efficient and more affordable. Stay tuned.
- A digital image is generated.
- Retrofitting existing radiography equipment is possible.
- Mobile radiography is easily accomplished.
- Excellent image quality is achievable.
- It's less expensive than digital radiography, initially.
- Practitioner still must use an imaging plate.
- There's no real time-saving benefit over traditional radiography.
- Purchase of an imaging reader is required.
DIRECT DIGITAL RADIOGRAPHY
- No processing time is involved and image acquisition is immediate.
- Excellent image quality is achievable.
- It's more expensive than computed radiography.
- It necessitates a wire between computer and imaging sensor, which can be cumbersome with mobile radiography.
- The imaging sensor is more expensive to replace than an imaging plate or cassette.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
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