Veterinary Diagnostic Tools

Have you ever gotten lost in the conversation with your veterinarian when he or she mentions the need to ?do a nuke scan? or ?ultrasound? on your horse’? Incredibly, some owners don’t even ask why a certain diagnostic procedure is needed.

On the flip side of the coin, veterinarians often gloss over diagnostic terms, thinking you already understand them.? You should always ask your vet about anything you’re not sure about, but sometimes you need at least a little knowledge to even ask a question. See How Diagnostic Devices Work.

RADIOGRAPHY.? Out of all the diagnostic modalities, the ?x-ray,? aka radiography, is the most well-known. However, veterinarians rarely use the term ?x-ray? because that term only refers to the radioactive beam taking the picture.? Radiographs refer to the actual photograph of the body part.?

To take a radiograph, the horse must hold still. In many cases, the veterinarian will sedate the horse in order to achieve the level of cooperation needed to take the pictures. By sedating the horse, the veterinarian and expensive equipment are safer, and everyone will be exposed to less radiation because pesky ?retakes? can be avoided. And your pocketbook will benefit, too, as vets charge for each shot.

Veterinarians will commonly take radiographs first when trying to determine lameness.? This is because most equine lameness cases are bone/joint-related, making radiography a handy on-the-farm tool.

Radiology Reality:

? Because many veterinarians get into a routine, they can sometimes forget to ask you if you’re pregnant before taking radiographs.? If you’re pregnant or even could be, speak up and let the veterinarian know!

? Digital radiography is widely considered to be superior to conventional analog films.? With digital radiography, the plate transmits an image to a laptop computer right there on the farm.? Advantages include: Superior image quality and the instant ability to retake a shot if it didn’t turn out well.

? With the advent of digital technology, the price of radiographs has increased significantly. Not much more to say about that. We all just have to grin and bear it.

? When taking radiographs, it’s wise to wear lead shielding if possible (it’s a necessity if you’re pregnant). Examples of protective equipment include aprons, gloves and thyroid shields.? If you aren?t assisting, stand at least 10 feet away while the images are being taken in order to minimize ?scatter? radiation exposure.

? Although radiographs primarily look at bone, they can be used to detect masses in the head as well.

? The ?field units? that veterinarians bring to the farm are only powerful enough to look at legs and feet, the head and neck, and the withers.? Other body parts like the backbone, the thorax (heart and lungs) and the abdomen (liver, kidneys, spleen, etc.) can only be imaged by a powerful wall-mounted unit found in equine hospitals.

? Even wall-mounted units can’t generate a beam powerful enough to penetrate through the hips and pelvis of a standing horse, however.

? Sometimes, to look at the bones in the foot, the horse’s shoe will have to come off. Grin and bear it.

ULTRASOUND. The ultrasound (or ?sonogram?) is the second most common diagnostic tool used in equine practice.? Ultrasound machines are digital and compact?often smaller than a laptop computer! They?re used to look at soft-tissue structures in most instances.? Examples include tendons and ligaments, eyes, the heart, lung surfaces, internal organs, and the ovaries and fetus.

Ultrasound is a dynamic diagnostic modality, as it’s more like a video than a photograph. It can evaluate how the heart beats, and even watch direction of blood flow with technology called ?color doppler.? One of our favorite uses of ultrasound is seeing the heartbeat of a neonatal foal!

Ultrasound Pointers:

? Rectal ultrasound (as performed routinely in breeding practices) comes with risk.? When the veterinarian gently slides his or her arm inside the rectum, there’s a risk of tearing the rectal wall. In most cases, this is fatal to the horse. Again, sedation can help reduce the likelihood of a tear because it will relax the mare and stop her from straining against the veterinarian.

? Ultrasound isn?t as easy as it looks. If the probe isn?t held correctly, it can make the image on the screen look like it is damaged.? With just a slight change in angle, the image can change dramatically.? Therefore, looking at soft-tissue structures from several beam angles is essential to ruling an injury in or out.

? While some ultrasound machines can image soft-tissue structures through hair soaked with rubbing alcohol, superior imagery is achieved when the hair is clipped.

? Diagnostic ultrasound (low-intensity sound waves) is often times confused with therapeutic ultrasound (aka ?acoustic shockwave?), which is a high-intensity wave emission (more on therapeutic ultrasound in an upcoming issue).? The two are quite different.? Diagnostic ultrasound has no therapeutic capabilities whatsoever.

? We commonly use ultrasound to diagnose tendon or ligament injuries in the leg and foot.? Keep in mind that waiting to ultrasound an injury until seven or more days after it occurs may be beneficial in terms of the information that you can gather.? If you have a horse with a swollen leg, the veterinarian will likely have you ice the leg, give the horse NSAIDS, put a wrap on it, and have the horse stand still in a stall until it gets under control.? If the swollen limb is ultrasounded right away, you’re likely to see the injury.? However, if you wait about a week, you’re more likely to have an accurate diagnosis of the severity of the injury.

In other words, a soft-tissue injury can look mild on ultrasound on day 1, but if you come back a week later and look again, it can look much more severe.? This is important because the extent of the injury often will determine the course of treatment.

COMPUTED TOMOGRAPHY. This diagnostic method can be thought of as ?3D Radiographs on Steroids.?? Sometimes known as a ?CT? or ?Cat Scan,? this imaging system looks in high detail at bone. It can be used to assess bone in a three-dimensional aspect, such as with a catastrophic injury to a joint.

CT scanning requires the horse to be unconscious and flat out under general anesthesia. Some equine hospitals use CT guidance when performing intricate procedures such as injecting stem cells into the foot or into a small tendon or ligament.? it’s also used frequently on horses with dental issues.? The CT scan helps veterinarians determine which teeth are involved and the extent of the issue.

CT Bites:

? There is a risk in anesthetizing the horse (albeit a small one).? There are also risks associated with horses waking up from anesthesia (injuries, etc.).

? Sometimes the veterinarians will use a contrast dye to enhance an image. The dyes are either injected into a joint or into the bloodstream. They?re generally safe. (Always check to see if your insurance will cover a CT scan. Some do. See October 2012 issue for more information.)

MAGNETIC RESONANCE IMAGING. This diagnostic tool, frequently termed ?MRI,? provides an incredibly high level of detail when looking at soft tissue and slightly less detail when looking at bone.? It is commonly used to identify soft-tissue injuries inside the hoof capsule.

MRI is performed in a hospital setting, although we’re seeing mobile MRI clinics in the form of a semi-truck and trailer popping up.? MRI can be performed in a heavily sedated standing horse, or in a horse that is under general anesthesia and lying down.

Some controversy exists as to which method and machine is more accurate.? Either way, MRI provides the veterinarian with an incredibly accurate depiction of the body tissue.

MRI Tips:

? It doesn’t involve any radiation like CT scan or radiographs.

? The horse can’t have any metal on or in the body part being examined.? Horses with screws and/or plates in a pastern for instance, can’t have that pastern put into an MRI machine.? Similarly, all shoes must be off.

? In order for an MRI to be accurate, the horse must be completely still. As mentioned, some machines are set up for the horse to be completely knocked out and laying down under general anesthesia.? Other machines allow the horse to stand. But be prepared!? The amount of sedation to get the horse to stand completely still can be significant.

? Sometimes veterinarians will inject the horse with a contrast medium (a dye for lack of a better term) in order to enhance the imaging capabilities of the MRI. Very few adverse reactions in horses have been reported. (Check to see if your insurance will pay for an MRI.)

NUCLEAR SCINTIGRAPHY.? Horses that have lameness coming from multiple locations, or lameness coming from ?who knows where? often end up in front of a Gamma Camera (also known as Nuke/Nuc Scanning).? With this tool, a horse is injected with a radioactive dye.? During exact time intervals, a special gamma camera is then used to take photographs of the horse.

Gamma cameras pick up on gamma radiation that leaves the body after a special radioactive dye is injected into the horse’s bloodstream. The general idea is that inflamed tissue will have a more dramatic or energetic release of gamma radiation due to an increased metabolism that will absorb more radioactive dye from the blood. Areas of inflammation light up as hot spots on the image.

For horses with back and spine pain, or pain coming from the pelvic region, nuclear scanning can be useful. If a horse has poly-arthritis (inflammation in multiple joints), nuclear scanning does a good job at determining which ?wheels are the squeakiest.?

Scintigraphy can be performed with the horse standing, but the horse is heavily sedated in order to achieve stillness.? Scintigraphy is only performed in a hospital setting, and health regulations require that the horse remain in the hospital for a period of time (like 24 hours) after the scan in order to void all of the radioactive dye from its body via urination.

Nuclear Scintigraphy Pointers:

? It can find inflammation only.? We all know that pain is associated with inflammation, so if a nuclear scan finds ?hot spots,? those are likely sources of pain.? But not all pain is due to inflammation.? For instance, nerves can be irritated or impinged with no accompanying inflammation. So, even if the scan comes out clean, it doesn’t necessarily mean your horse is pain-free.

? The radioactive isotope dye is safe to inject. Side effects are rarely reported.

? A lot of horse owners decide to ?go for gusto? and get whole-body nuclear scans performed when their horse may really only be lame in one part of the body.

In most of these cases, the horse is insured, and the insurance is paying for the scan.? OK, but we advise you to think long and hard about ?full body scans? and only do them when necessary.? Reason: If the insurance company gets a full body scan that shows 15 areas of significant inflammation, don’t be surprised if those areas get written out of your renewal contract.? They count as ?pre-existing conditions? whether they are clinically bothering your horse or not.

THERMAL CAMERA. it’s easy to confuse nuclear scintigraphy with a thermal camera, probably because they both help to locate inflammation. The similarities stop there, however.

Scintigraphy is performed in a hospital and involves a highly technical photograph of the horse after he has been injected with radioactive dye.? A thermal camera, on the other hand, can be used right on the farm and doesn’t involve any injected substances.

Animals emit infrared light radiation as a result of normal physiological processes. Because tissue metabolism speeds up in inflamed areas, they show up through the thermal camera as an area that is emitting more light (aka hotter) than others when a horse is being viewed through the camera.? Therefore, a thermal camera can be useful for evaluating inflamed areas.

Thermography Facts:

? As promising as this diagnostic modality sounds, it has many caveats.? For instance, the horse needs to be trotted for about 10 minutes in order for the camera to ?see? inflamed areas more clearly. Also, a thermal image can be heavily influenced by ambient temperature. Therefore, imaging needs to be done in a relatively narrow temperature range.

? There are dozens of thermal imaging systems on the market, at many different price points. However, it’s the interpretation of the results that makes a difference in your horse’s health. This practice shouldn?t be performed without veterinary supervision.

? Thermal cameras give owners a hint about possible problem areas in their horses, but they aren?t a final diagnostic tool.? Rather, they may help to confirm or refute clinical findings in a horse and serve as a precursor to other advanced diagnostics.

Article by Contributing Veterinary Editor Grant Miller, DVM.

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