Ultrasound Exams in Horses: Using the Basics To Go Beyond the Basics

Here's how practitioners can better use ultrasound for musculoskeletal, reproductive and even urinary system imaging.
A veterinary surgeon explains the ultrasonic image to an owner during an ultrasonic examination of her horse's foreleg.  Coombefield Veterinary Hospital, Summerleaze Farm, Axminster, Devon.
Could you be doing more in your practice with your ultrasound equipment? iStock

Many general equine practitioners feel comfortable with their routine use of ultrasound, typically for lameness or reproductive purposes. Some even feel comfortable using ultrasound for thoracic and abdominal scans (e.g., FLASH, fast localized abdominal sonography for horses). Do you ever wonder, though, whether you could be doing more with this powerful imaging modality to diversify the services you offer, provide better medicine and grow your practice?

At the 2021 American Association of Equine Practitioners (AAEP) Convention in December 2021, a group of expert ultrasonographers came together to offer their advice on maximizing the use of ultrasound in the field. They presented information on how practitioners can better use ultrasound for musculoskeletal, reproductive and even urinary system imaging, as well as tricks and tips for imaging both adult and juvenile thoraces and abdomens.

One of those experts, Tracy Norman, VMD, DACVIM, owner of Valley Veterinary Ultrasound, shared her thoughts on “making the most” of thoracic and abdominal ultrasonography in adult horses. Her presentation focused on case selection, patient preparation, equipment requirements and examination technique. Afterwards, Norman kindly spent a few minutes answering additional questions for EquiManagement.

Question: What ultrasound unit best meets the needs of a general equine practitioner, and what probes are most valuable?

Answer: The focus of the practice and the population of horses in the practice will largely dictate the exact type of unit a general practitioner will require; however, there are some generalities that we can make.

For ambulatory practice, it is good to have equipment that isn’t overly bulky or heavy yet is sturdy enough to handle the “rough and tumble” of road life. There are lots of excellent machines out there at all price points, and the ones that are set up in a laptop computer-type format are great for ambulatory practice. A practitioner should look at a variety of machines and see what image looks best to his or her eyes and what platform (the layout of the buttons) makes most logical sense. Another important thing to consider is the service plan that comes with the machine.

In terms of probes, it somewhat depends on the focus of the practice, but for most general practitioners, I feel like the repro/transrectal probe and a tendon probe (high-frequency, linear) are most often used. The large, lower-frequency curvilinear probes are used for internal medicine-type scanning, FLASH scans for colic, and upper-level sports-medicine procedures like sacroiliac joints, backs and necks.

The newer portable (i.e., hand-held/phone-based) ultrasound units continue to become more affordable and readily available. Whether a practitioner should get this type of ultrasound unit or a more traditional machine will depend on the individual practitioner’s preference.

I personally haven’t used the hand-held/phone-based units enough to clearly advise other practitioners one way or another as to whether they are better than a traditional unit or worth the price. That said, the image qualuty I have seen on some of the hand-held units is impressive, and there is definitely a place for this technology in general practice. For example, the Butterfly iQ+, which is a hand-held system compatible wtih iPhone and Android, is capable of imaging all of the body systems.

Question: Are the same basic probes used for reproduction/transrectal purposes and tendon scans useful for transabdominal and thoracic ultrasound examinations?

Answer: The standard transrectal probe used for early and routine pregnancy detection, uterine evaluations and for tracking ovulation cycles is actually great for thoracic scanning, especially in foals.

Indications for thoracic scanning include fever, respiratory signs, inappetence (especially with a recent history of transport), thoracic pain, sternal edema and Horner’s syndrome.

The main things to note are pleural irregularities and pleural fluid. Because of the nature of ultrasound, only the surface of the lung can be evaluated sonographically. For effusions in the thorax, ultrasound is excellent for evaluating the volume and character of the fluid. The heart can be imaged in the ventral fourth intercoastal spaces, and broken ribs can also be diagnosed on ultrasound. In fact, an ultrasound examination can often be more sensitive than radiographs for fractured ribs. In addition to pleuropneumonia, neoplasia, fungal infections and viral pneumonias can cause thoracic abnormalities. And Rhodococcus equi lesions in foals can be detected sonographically.

The tendon probe can also be used to evaluate the lung surface in foals and adults. In adults, however, if there is pathology (e.g., fluid, consolidation), the tendon probe lacks the depth sometimes needed to see the full extent of the pathology. The tendon probe can image to a maximum depth of about 6 cm and has a narrow scan field.

Tendon probes can be used to evaluate foal abdominal structures in a pinch, but a curvilinear probe is more appropriate. The low-frequency curvilinear probes required for advanced abdominal, thoracic and neck/back scanning are different from the “work horses” of general practice.

Question: If general practitioners are interested in puchasing a low-frequency curvilinear probe, what specific types of examinations could they perform?

Answer: The FLASH exam for transabdominal imaging of the acute abdomen uses set window to answer specific questions about potential causes of pain. Generall speaking, it is used by general practitioners in an ambulatory setting to help determine whether a colicky horse should be referred.

Information added to the colic examination by the FLASH exam includes the:

  • presence or absence of excess peritoneal fluid;
  • presence or abscence of fluid distension of the stomach and small intestine;
  • thickness of the small intestine;
  • presence or absense of bowel in the nephrosplenic space; and
  • position of the mesenteric vessels of the right colon.

FLASH can thus help the practitioner determine the likelihood of small intestinal obstruction, small intestinal strangulation, nephrosplenic entrapment, right dorsal displacement, colonic torsion, peritoneal inflammation and rupture of a viscus.

Question: If a practitioner sees enough colic cases and wants to start learning FLASH, is it a good investment to purchase a low-frequency curvilinear probe?

Answer: Absolutely! The FLASH examination adds valuable information to the colic exam. The low-frequency probes can also be used for some sports medicine imaging: sacroiliac injections, necks, backs, examining the pelvis, etc. And if a practice is reproduction oriented, the low-frequency curvilinear probes can also be used for evaluating the fetus later in pregnancy.

Question: When adapting reproductive/transrectal or tendon probes for other purposes, such as the thoraces of foals, do the machine settings need to be altered from what practitioners would typically use for tendons/reproductive/transrectal examinations?

Answer: With any probe, the machine presets/exan type will change when the application changes. This is actually really important; trying to get a good abdominal image with the machine set for musculoskeletal imaging is going to be really frustrating and vice versa. Most, if not all, machines have computer presets that tailor the image processing to the type of image that is being obtained. This is generally designated as “Preset” or “Exam” type.

Question: What key tips do you have for veterinarians to become more adept at using their machines, expanding their repertoire and increasing the number of services they offer to grow their businesses? General practitioners are busy. Even with wet labs, many come home, get lost on their first few ultrasound exams, can’t find what they saw in the labs, get frustrated, then don’t do it anymore! I know you recommend practising as much as possible. Do you have any thoughts on how equine veterinarians can more easily incorporate this “practice” into their practices?

Answer: Again, this very much depends on the focus of practice. The regional and state meetings that have wet labs generally have a wide range of information and are great for folks hoping to get into ultrasound. The more specific groups that focus on, say, lameness diagnosis, tend to have more advanced courses.

If you have access to a low-frequency probe, scan Every. Single. Colic. Don’t charge for the first couple so you don’t feel bad practicing. The clients love to hear that their vets have learned something new and are going to show them for free! I feel that “peeking” in the abdomen or thorax when on a tendon call is tough, and again, I don’t really recommend the tendon probe for adult abdomen at all (“it’s just a recipe for frustration”). But we can take a peek in the thorax for every fever case. I can easily say, “Hey, while we see if this flunixin is going to lower the fever, how about I take a peek in the chest? I learned a new technique at CE and would love to try it out at no charge.”

Concluding Thoughts

“An ultrasound examination involves more than just taking the images at the correct anatomic location,” advised Norman. “Appropriate case selection will also help veterinarians become more adept at maximizing their use of ultrasound. This means that they need to understand the clinical signs that are best illuminated by specific types of ultrasound. Using a FLASH exam for a horse with chronic weight loss, for instance, is not appropriate, whereas a thorough abdominal ultrasound is. In a horse with a fever of unknown origin, even a brief look in the thorax and abdomen for free fluid can be illuminating.”

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