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June 7, 2004

Of Mice and Men: Vets Make Broad Use of Ultrasound
Vol. 5 No. 12 p. 26

Veterinary ultrasound has literally gone from little gerbil leaps to big Great Dane bounds over the past few years. Introduced to the field in the early ’80s and originally used in veterinary reproductive medicine, ultrasound now helps vets diagnose everything from cardiac and hepatic disease to detached retinas and gastric and intestinal masses.

Robert T. O’Brien, DVM, the head of the imaging center at Michigan Veterinary
Specialists and founder of the International Veterinary Ultrasound Society—an organization that offers veterinary ultrasound certification—says ultrasound imaging is very common at his practice. “At least a third of our patients—here for internal medicine and surgery services—are going to receive an ultrasound scan if they have any signs at all referable to their abdomen—even remotely.”

He says animals as small as lab mice can benefit as much from ultrasound as cows and horses. For example, O’Brien says a 12-megahertz transducer, which is limited in human application to a breast or neck ultrasound, can do a whole-body scan of a gerbil or ferret.

Like a Belly Rub
Animals are rarely sedated for an ultrasound exam. O’Brien says most patients enjoy the massaging effect. “Most of the dogs are happy to lay down, to have someone pet them on the head, and give them some attention. The biggest problem is usually their tail wagging during the course of the study. Cats are much more individualistic and maybe more aloof, and they either just barely tolerate it or may need some form of restraint. But I’d say it’s an unusual cat that we would have to sedate.”

Animals with fine coats, such as Boxers, do not always need shaving before undergoing an ultrasound. “Sometimes we can just douse the area in isopropyl and work through the hair,” says O’Brien. However, northern breed dogs, such as Malamutes or Huskies who have been outside all winter and put on a thick coat, need prepping. “You might as well forget about trying to part their hair. You would need to do a lengthy clip,” says O’Brien.

While ultrasound first entered the veterinary field as a complement to reproductive medicine, its current applications almost mirror those on the human side of medicine. Abdominal, ocular, thoracic, cardiac, and color-flow Doppler ultrasonography are performed at numerous veterinary practices across the country.

“Now, I think it’s the breadth of many things that you would be doing on the human side,” says O’Brien. “We tend to do a little bit less endoscopic ultrasound and interventional work, such as RF [radiofrequency] ablation. We use ultrasound for a lot of biopsies and fine needle aspirates—to drain a lot of things. We have boarded cardiologists who do echocardiography. They use the exact same machines that the top-end cardiologists utilize in their labs.”

O’Brien says there aren’t too many technical differences between human ultrasound and veterinary ultrasound; however, the same cannot be said about the systems used.

Ultrasound With Contrast
“We always made the argument that we have a better machine system than the best U.S. human system. The reason we think so is because we have ultrasound contrast, which is not approved in the United States for abdomen use in humans. The only FDA-approved use is for echocardiography, whereas we can use it off-label. We have software on our top-end machine that the top people in the human hospitals don’t have. We’re more on par with the sonographers and radiologists in Europe and the Far East who can utilize the full breadth of ultrasound technologies,” says O’Brien.

The ultrasound contrast allows vets to determine whether nodules are malignant or benign with a much higher degree of accuracy. “The contrast has been extremely valuable for many of the tumors we have found in dogs that don’t really have a similar corollary in human medicine,” says O’Brien. “One of the most common tumors we see as metastatic tumors in dogs is Hemangiosarcoma. That’s a very rare tumor in humans but a common tumor that shows up in a dog’s spleen, heart, and skin and tends to metastasize to the liver. These nodules are not often seen with grayscale ultrasound, so we use contrast.”

Unique Transducers
Because pregnancy can affect production cows’ and high-priced thoroughbred racehorses’ performance, these animals frequently undergo ultrasound. O’Brien says it is especially important to determine whether or not a horse is carrying twins due to the risk. “If there are twins, one of them needs to be aborted early in the process to avoid a high degree off morbidity to the mare and the foal.”

Most ultrasound on cows and horses is done endorectally because of the difficulties of going transabdominal and because of the advantages already proven by going endovaginal on the human side. “It’s not done with a rigid probe that is inserted into the rectum of a horse or cow—it’s actually taken in with the arm of the vet who is performing the scan,” says O’Brien. “When you take the probe in and you want to look directly down, you can’t have a transducer that needs to be flipped 90° to image straight down—you actually have to have the cable coming off the side of the transducer.”

O’Brien says this cable is called a side cable or side-firing linear transducer. The crystals remain aligned in a linear fashion, but the cable comes off the slender end of the transducer, making the inherent image perpendicular to the long axis of the rectum or colon. “That would be a transducer I don’t think you would ever see in the human field,” he adds.

O’Brien says average human abdomen probes are typically of a frequency, size, and shape inappropriate for animals. “It’s a frequency that is typically too low for us to do the work we need to do. Three and a half megahertz is way under the frequency that I’ll use on almost all of my dogs and cats. We can typically operate in a range of 6 to 7 megahertz for most of our patients—at least on the abdomen side of life—maybe 4 to 5 megahertz on the echocardiographic side. We typically don’t use the probe that would be used for human abdomen transabdominal imaging. Also, the footprint is too big. When we go intercostal or substernal, that’s a very slender area, so that’s a very large footprint on that average. What we tend to use is the probe that you would call a pediatric brain probe. It’s a small footprint, tight curvilinear, higher frequency transducer and that really fits most of our purposes, with the possible exception of the really big dogs, and then there’s a direct 1:1 proportionality to patient size and frequency.”

Pet Insurance
O’Brien says the price of ultrasound ranges from $50 to $500. “If you look across private practice to some of the higher-priced parts of the United States, doing an ultrasound in downtown Manhattan I’m sure is much more expensive than it is on a farm in Iowa or at an academic institution.”

Unfortunately, owners who don’t have pet insurance—which O’Brien says amounts to nearly 99% of the U.S. population—often have to weigh the personal or market value of their animal against the cost of an ultrasound or other specialized procedure.

“Compared to Great Britain, where pet insurance is very very common—I think half the pets or maybe more have pet insurance over there—it’s extremely uncommon here,” says O’Brien. “Most people do not set aside money toward the future of their pets’ healthcare, so it comes as a big financial as well as emotional shock to have to put down anywhere from $1,000 to $3,000 to $5,000 for a major surgery, of which ultrasound would be a part.”

O’Brien says that at his practice (a tertiary referral institution), money is usually no object for owners of small animal pets, which are regarded as a valued part of the family. However, in special cases, the same can be said for large industrial breeds.
“If an animal’s used strictly for industrial purposes, then it’s probably not worth that much as an individual animal. Then again, certain individual animals are worth an awful lot—for example, certain research animals are extremely valuable.”

Racing thoroughbreds, which can be worth millions of dollars, and prized show animals are also exceptions. O’Brien, a sonographer of World Dairy Expo show cows, says that the embryos of cows who win the expo can be worth $1,000 each. “You can get a couple hundred embryos out of cows when you flush them during their cycle, so those owners are willing to spend tons of money.”

Future Applications
O’Brien believes advances in veterinary ultrasound will accelerate as more and more people in the United States acquire pet insurance. “Hopefully, as second-party payment becomes available, our level of sophistication with ultrasound will continue to grow and more clients will be willing to spend extra time, emotion, and money on the patients.” He thinks vets will eventually do more interventional work and even pioneer the use of ultrasound contrast. “I think we’ll eventually leave human U.S. radiologists behind because we’re going to develop [ultrasound contrast], and they won’t have it available,” he says.

For more information about veterinary ultrasound or the International Veterinary Ultrasound Society, visit www.ivuss.org.

— Amy L. Conver is assistant editor of Radiology Today.

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