Guide to Equine Diagnostic Imaging

Looking at Your Horse Beneath the Surface

By: Andris J. Kaneps, DVM, PhD, DiplACVS, DiplACVSMR | Updated May 19, 2025

Whether your horse has a subtle lameness or a sudden injury, your veterinarian will take diagnostic steps to figure out the root of the issue. Imaging modalities play a crucial role in helping pinpoint a problem and plan to get your horse feeling their best again.

Today’s equine veterinarians can see more than ever before thanks to incredible advances in imaging modalities over the last 15 years. Continue reading to learn more about types of diagnostic imaging for horses – from stall side technologies to advanced suites at equine hospitals – to make more informed decisions regarding your horse’s care.

Why Diagnostic Imaging is Important

Imaging can provide your veterinarian with detailed views of what’s happening beneath your horse’s skin without invasive procedures, like surgery. These tools can help answer important questions, such as:

• Is there an injury to a tendon, ligament, joint, or bone?
• What treatment options are appropriate?

Choosing the right imaging method is often one of the first steps toward an accurate diagnosis and effective plan for your horse to return to soundness.

Limitations at the Barn vs at the Equine Hospital

Most veterinarians that make farm calls have access to traditional imaging options of radiography and sonography. While portable imaging units provide great imaging quality, higher detail and larger units may only be available at equine hospitals.

Advanced imaging at referral hospitals may include nuclear scintigraphy, magnetic resonance imaging, and computed tomography. Advanced imaging has become so complex that board-certified specialists may conduct and interpret the images. These specialists can be accredited by the American College of Veterinary Radiology (ACVR) or the American College of Veterinary Radiology-Equine Diagnostic Imaging (ACVR-EDI).

Which Scan When?

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Traditional Diagnostic Imaging Options for Horses

Radiography (X-Ray)

Discovered in 1895, x-rays are used to image internal organs and bones. X-rays are created by a generator and form a beam that passes through the area of the horse’s body being examined. As the x-rays pass through, different tissues absorb them at different levels. Dense tissues, like bone, only allow for small amounts of x-rays to pass through, resulting in whiter areas. Soft tissues let more x-rays pass through, which then appear as darker areas. The x-rays that do pass through are recorded by a digital plate called a detector. In the past this would have been done on film, much like taking a picture.

• Safety: X-rays are ionizing radiation which may damage normal tissues if exposed to excessive levels. This is why lead gloves, aprons, and other protective gear are worn to minimize exposure to people taking the images.
• Cost: Prices for x-rays can vary widely depending on your location and veterinarian’s fees. According to a veterinary fee survey shared by the American Association of Equine Practitioners (AAEP), the average set of foot x-rays may cost about $250 while a bundle of pre-purchase exam (PPE) images average $1,120.

How and when x-rays may be useful

Most x-ray exams can be done at the barn and without sedation. The most common use of radiography is to image the legs, hooves, back, and neck, often in cases involving lameness or injury. Here are some examples of when x-ray may be used:

• X-rays of the feet could help your farrier with trimming and shoeing for optimal foot balance (Fig. 2).
• Images of the head and mouth are important for problems involving teeth, sinuses, and bones in that area.
• Abdominal images may be taken in colic cases to rule out enteroliths or sand accumulations.
• The lungs and heart region may be imaged to identify pneumonia, heart enlargement, or fluid in the chest.

Diagnostic Ultrasound

Ultrasound uses sound waves at a higher frequency than humans can hear. Sound waves are directed from a handheld transducer to the site of interest, such as a tendon or ligament. The sound waves are absorbed or reflected off the tissues. The transducer reads the bounced back sound waves, and they are processed by a computer into images [1].

• Safety: There are no negative effects on the body associated with ultrasound. In fact, there is no sensation detected by the horse (or human) to the sound waves.
• Cost: Per the above survey, you may expect to pay an average of $210 for ultrasound of a tendon or ligament. Reproductive ultrasounds of the ovaries and uterus might cost about $80. Prices will vary depending on the area being examined, your provider, and their set up fees.

How and when ultrasound may be useful

Before your vet takes the ultrasound probe out, they (or their technicians) will likely clip the hair and wash the area being examined. Hair and dander trap air, which reduces the image quality. Most ultrasounds are done standing and may require light sedation. Here are some common examples of when a horse may have an ultrasound performed:

• Evaluating a swollen tendon or ligament with a “T-shaped” probe to determine the level of injury.
• Using a curved probe to evaluate abdominal organs in cases of colic. Your veterinarian could see movement of the intestines, gas, the thickness of intestinal walls, and if organs are in the right location or position.
• Used to guide needle placement during joint injections.
• Evaluating heart function (a technique called echocardiography) that visualizes muscle, the valves, and blood flow.
• In reproductive examinations to see the size and stage of ovarian follicles, condition of the uterus, and stage of pregnancy. Testicles of male horses may be evaluated in cases of injury or infection.
• Unusual swellings deep in the skin may be evaluated to determine if its cause is an abscess, soft tissue mass (cancer), or if a foreign body (stick or metal object) is present.

Advanced Diagnostic Imaging Options at Equine Hospitals

Computed Tomography (CT)

CT is an advanced imaging system that uses x-ray combined with computer processing to create cross-sectional images (slices) of the body. Rather than flat images, the images are compiled into a 3D reconstruction using computer processing.

Standing CT machines are most used for imaging the head and neck. Also, some larger systems can scan areas like the pelvis, chest, and stifle. The first reported use of CT in horses was in the late 1980s [3, 4].

• Sedation: There are several types of CT systems where a horse can be either lying down or standing. The horse usually needs to be under general anesthesia and lying on a table which is positioned so that a portion of the horse can move through a large donut-shaped scanner called a gantry.
• Time: As the table moves, the gantry rotates around the horse, capturing multiple images in a short amount of time (distal limbs may only take 10 minutes once positioned appropriately).

How and when CT may be useful

CT is most helpful for imaging complex structures such as the head, neck, and teeth. It has a short imaging time for bone and soft tissue structures. Here are some common examples of its use:

• High detail evaluations of bone that cannot be made using traditional x-ray.
• 3-D reconstruction of complex bone fractures that informs a surgeon and helps them plan the most effective method of surgical repair (Fig. 6).

Magnetic Resonance Imaging (MRI)

MRI relies on a strong magnet, radio wave generator, signal detector, and a computer for image processing. Here’s how MRI images are taken on horses:

1. The strong magnet aligns atoms in the tissue.
2. A pulse of radio waves is aimed at the imaging site which disrupts the normal alignment of atoms.
3. When the radio wave pulse stops, the atoms emit energy as they return to the magnet-induced alignment.
4. The energy signals are recorded by the computer and processed to form an image that is a “slice” of the target area.
5. The slices can be combined to form a 3D image.

The energy atoms emit can vary depending on the type of tissue and its condition. For example, a bruised tendon will look different on MRI compared to a normal tendon. MRI does not emit any radiation, so it does not affect the tissues or body [5].

• Sedation: Low-field magnet systems have excellent image quality and can be done while a horse is standing under sedation. Stronger high-field magnet systems require general anesthesia and are often designed to image larger parts of the body or provide sharper detail.
• Time: An MRI study of the hoof region may require 1-2 hours depending on the number of imaging sequences.

How and when MRI may be useful

MRI is the gold standard for imaging tendons and ligaments of the legs. It produces a higher resolution image of these structures compared to ultrasound or CT.

• Imaging neurologic tissues, such as the brain and spinal cord.
• Certain MRIs may determine if tissue or bone is bruised or contain more fluid than normal.

Nuclear Scintigraphy (Bone Scan)

Nuclear scintigraphy, also referred to as a bone scan, evaluates bones and joints to compare potentially injured and uninjured areas. A bone scan involves an IV injection of a radioactive material. This is usually the radioisotope technetium 99m which travels through the bloodstream and collects in areas of high bone activity. A large camera is then used to detect gamma rays emitted from the body (Fig. 8).

• Time: Imaging can start 10 minutes after the radioisotope injection for soft tissues, and again 2-3 hours after injection to highlight bones and joints. Areas of injured or inflamed soft tissue, bone, or joints will have higher concentrations of gamma rays on the image, called increased radioisotope uptake (RIU) or hot spots. Hot spots may also appear at bony prominences that are only covered by skin, such as the tuber coxae of the pelvis and dorsal spines of the back (Fig. 9). A bone scan is a physiological imaging study as the products used will accumulate in greater quantities at a site that has increased inflammation due to injury [6].
• Safety: Bone scans for horses may require up to 3 days of hospitalization. At the hospital, the horse is kept in a quarantine stall separate from people and other horses for 24 hours after radioisotope injection. This is to allow the radiation levels to reduce to a safe level.

When bone scans may be useful

• If a lameness cannot be localized to a specific area with other techniques.
• When a fracture is suspected.
• On a horse that does not tolerate nerve blocks.
• For subtle or intermittent, undiagnosed lameness.

Positron Emission Tomography (PET scan)

PET is similar to nuclear scintigraphy in that it also images the body’s response to a radioisotope [6, 7]. The isotope injected for PET scans is 18F-sodium fluoride (8F-NaF) which is much more sensitive to bone and soft tissue inflammation than technetium.

The PET scanner captures images in thin slices that are combined into a detailed 3D picture. PET is unique because it can measure how active an area of inflammation is with sharper detail than bone scans. Another advantage of PET is that the images can be joined with x-rays, CT, or MRI to clearly define the area of inflammation.

• Time: About 30 minutes after injection, the horse is scanned while standing. Scanning both front distal limbs (fetlock to hoof) require about 20 minutes.

While not very commonly available, some racetrack hospitals, major equine referral hospitals, and teaching hospitals currently have this technology.

Key Takeaways for Horse Owners

Equine diagnostic imaging is an important step in determining the specific cause and prognosis of an injury. Traditional imaging available on the farm may help answer if a horse’s hooves are properly balanced, tell what stage of gestation a mare is at, and identify swelling of the suspensory ligament. Advanced imaging may initially be costly, but the questions it answers may facilitate the best approach to treatment, ultimately saving money and speeding recovery.

Evidence-Based References

1. Butler, Janet A., et al. Clinical Radiology of the Horse. John Wiley & Sons Inc, 2017.
2. Kidd, Jessica A., et al. Atlas of Equine Ultrasonography. John Wiley & Sons, Inc, 2022.
3. Barbee, David D., et al. “Computed tomography in horses.” Veterinary Radiology, vol. 28, no. 5, Sept. 1987, pp. 144–151, https://doi.org/10.1111/j.1740-8261.1987.tb00043.x.
4. Stewart, Holly L., et al. “Use of cone‐beam computed tomography for advanced imaging of the equine patient.” Equine Veterinary Journal, vol. 53, no. 5, 14 July 2021, pp. 872–885, https://doi.org/10.1111/evj.13473.
5. “Magnetic Resonance Imaging (MRI).” National Institute of Biomedical Imaging and Bioengineering, U.S. Department of Health and Human Services, www.nibib.nih.gov/science-education/science-topics/magnetic-resonance-imaging-mri.
6. Spriet, Mathieu, and Filip Vandenberghe. “Equine Nuclear Medicine in 2024: Use and value of scintigraphy and pet in equine lameness diagnosis.” Animals, vol. 14, no. 17, 28 Aug. 2024, p. 2499, https://doi.org/10.3390/ani14172499.
7. Spriet, Mathieu. “Positron emission tomography: A horse in the musculoskeletal imaging race.” American Journal of Veterinary Research, vol. 83, no. 7, 1 July 2022, https://doi.org/10.2460/ajvr.22.03.0051.