X-ray, ultrasound & co: diagnostic imaging methods for horses

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We’ve all been there: the horse is lame, and nobody knows why. That’s where it gets expensive, the first step before therapy is to diagnose the problem. Next question is which tool is most suited to reach an appropriate diagnosis?

The options are varied, but not always entirely favourable. If anaesthesia is necessary, the diagnostics are not always without risk for the horse. For the horse owner to understand the outcome of each diagnostic tool that is available to them to assess the possible cause of lameness, knowledge regarding different methods and their prices ranges will help in making an informed decision for the next steps. This next step is important to reach the best chance of diagnostic, there is nothing more frustrating than spending thousands of pounds on the wrong method, as we are all trying to help our horses to lead a healthy and happy life.

Here is an overview of the diagnostic methods currently in use,. Not every vet can offer each and every one. Some require a specialist who has the equipment and experience to interpret the results. Others can only be carried out in specialised hospitals, which then involves transporting the horse and possibly an overnight stay in the hospital which involves further costs.

X-ray and ultrasound – the mobile solution for a quick look

The most common methods are X-rays and ultrasound or sonography. The vet usually has mobile equipment, which can initially be used to try and identify the cause of the lameness or swelling. These small devices are generally not as powerful as stationary devices in a veterinary hospital, but the examination can be carried out remotely, which minimises stress and costs for horse and owner.

During an X-ray, radioactive radiation is sent through the body and absorbed differently by tissue, bones, and organs. The residual radiation then hits an X-ray film opposite, which is exposed to varying degrees. The result is a two-dimensional black and white image of the part of the body being examined. Bone absorbs significantly more radiation than soft tissue (cartilage, tendons, ligaments, muscles, etc.). While the latter can only be seen as outlines on the X-ray image, bone structures can be visualised in great detail. X-rays are therefore generally used to examine bones in horses. This includes fractures (breaks), fissures (hairline fractures), changes in density (e.g. the navicular bone in hoof roll inflammation or subchondral bone cysts) and the position (e.g. of the coffin bone after laminitis or of fragments that have broken off after fractures).

In ultrasound, also known as sonography, directed sound waves are sent through the tissue to be examined instead of X-rays. These are reflected differently by different tissues due to their different water content and the reflection is picked up again by the ultrasound probe and displayed as a black and white image. This enables the examiner to pick up tendon damage or tissue scarring, for example. The mobile vet will use ultrasound primarily for tendon and ligament damage as well as for gynaecological examinations. The stationary devices based at the Equine hospital are more suitable to examine internal organs such as the lungs or heart. If you need a heart ultrasound for a sport horse, you must take the horse to a hospital specialising in this.

Ultrasound and X-rays can be carried out in the stable with a mobile unit by your vet who has the appropriate equipment with him. X-rays are used for suspected bone damage, ultrasound for suspected soft tissue damage. The costs vary (depending on the number of images, degree of difficulty of interpretation and other factors), but are within an affordable range, therefore these methods are frequently used when there is an indication towards a symptom to provide a clear result.

Computed tomography (CT) – the 3D X-ray

If the X-ray examination does not provide a clear diagnosis, although there is a strong suspicion of bone damage, it is possible to examine the horse using computertomography. In principle, this is similar to X-rays, as X-rays are also sent through the tissue to be examined. In contrast to X-rays, however, the result is not two-dimensional. With CT, several images are taken in different levels, which are then combined on the computer to create a three-dimensional image. This enables a much more precise visualisation and interpretation of the examined structures.

In horses, this method is currently only possible for the legs and the head/neck area; there are not (yet) any CT scanners large enough to examine a complete horse. The examination can be carried out standing or lying down. Only a light sedation is necessary when the horse is standing up, same as in dental treatment. A CT scan is only resorted to if the conventional X-ray did not provide a clear diagnosis, e.g. in the case of small fissures in the bone that cannot be seen on a conventional X-ray. An overlooked fissure can turn into a fracture, depending on its location, it may no longer be possible to treat it otherwise. The disadvantage of computertomography is that the horse will have to be transported to the hospital and sedated, an approximate estimate for such procedure is around 800 pounds.

Magnetic resonance imaging (MRI) – the gold standard

If neither a CT scan nor an ultrasound scan can detect anything, there is also the option of having an MRI (magnetic resonance imaging or magnetic resonance tomography). Again, it is only possible to look at the legs and the head/neck area, as there are not (yet) any MRI machines large enough for a complete horse. Which areas of the horse can be examined and whether the horse is examined in a standing or lying position depends on the respective device for both CT and MRI, it should therefore be decided upfront in which hospital which examination can take place.

MRI produces a three-dimensional image of all tissues using magnetic fields and radio waves, making it a combination of CT and ultrasound. This allows a high level of informative value, as all tissues are included, and the quality of the images is excellent. Almost all structures of the body can be visualised, i.e. tendons, bones, and the surrounding tissue. This enables an accurate diagnosis of soft tissue in areas where several structures overlap and therefore ultrasound does not provide a clear result. Not many veterinary hospitals have such a device. Transport and, sedation charges also apply here, there are estimated around 1,200.00 pounds.

Scintigraphy – for the detection of inflammation

The lameness cannot always be clearly localised. Many of us will have experienced this, the horse isn’t ‘quite right’ there is on and off lameness often appearing on different legs on different days and it’s almost impossible to pinpoint where it’s coming from. This can occur when the problem is located somewhere in the body, the trunk area, or if several structures in the musculoskeletal system are affected. For problems of such nature in the musculoskeletal system, scintigraphy is often used in horses. While sonography is ideal for examining specific, delimited areas of tissue, scintigraphy allows the whole horse to be examined in order to narrow down the causes of the problem.

For this examination method, the horses are administered an intravenous infusion containing radioactive substances. These radioactive substances accumulate particularly in parts of the body that are affected by inflammatory processes. The radioactive radiation is then absorbed and the areas where inflammation is present become visible as dark spots on the image.

Scintigraphy is primarily used for problems with bones, but ligaments, joints and tendons can also be examined. No matter which tissue is inflamed: there is always an accumulation of radioactivity in this area. Light sedation is also necessary for this type of examination, but the examination is carried out in a standing position, which significantly reduces the risk compared to a full anaesthetic. The horse must remain in quarantine, i.e. in the hospital, for one to three days for the radiation from the radioactive substances administered, to wear off.

As the accumulation of radioactivity is scanned with a so-called gamma camera, the accumulations can be visualised throughout the horse’s body. This has the advantage that structures that cannot be visualised with other examination methods can also be detected. This can be particularly helpful when the lameness comes ‘from above’, where access for examination is difficult to reach, with this method the sacroiliac joint, the pelvis, the stifle, or the lumbar spine can be viewed. The disadvantage is that due to the close proximity of structures, it is often not possible to make an exact diagnosis, i.e. to differentiate whether the tendon, ligament, joint capsule, muscle, bone or any combination of these is affected in the area. Afterwards further investigations are usually necessary to get more precise diagnostic. Transport costs to the hospital and the overnight stay one to three days applies, estimated at around 800 pounds.

Thermography – diagnostics via infrared radiation

Thermography is used in a very similar way to scintigraphy. Here too, the body is scanned, but only with a thermal imaging camera for infrared radiation. This measures the heat emitted by the horse and is very good at detecting circulatory disorders, inflammation, and overloaded structures. Thermography is therefore just as suitable as X-rays or ultrasound for an initial clarification of the problem and can even be used preventively in the case of overloaded structures, i.e. to avoid an injury, if the horse compensates certain body parts while overloading of the healthy body parts occurs in order take pressure of the area of discomfort.

The advantage of thermography over scintigraphy is that no radioactive substances must be administered to the horse. Most thermographers are also mobile and come to the stable for the examination. For this examination to be successful some points must be taken into consideration. For example, the horse shouldn’t be exposed to sunlight prior to examination, the location, where the horse is being examined must be enclosed and shut off from draughts, otherwise the data produced is in jeopardy. Thermography is not able conclude on the exact ins and outs of an ‘injured’ area so further diagnostic clarifications are usually necessary, for example using X-rays or ultrasound. The method does however narrows down the area of the body in which there are inflammatory processes that are probably the cause of the visible lameness. Thermography is usually carried out by non-veterinarians, which is why prices vary even more than for veterinary services. A fully trained thermographer and a complete thermography of the horse, including a professional evaluation, would be expected around 200 pounds.

What, when and for which problems?

If a horse shows lameness issues, the vet will perform a conventional lameness work up, by watching the horse closely in all three gaits on a straight line and usually also a circle, this process is used to narrow down where the lameness is coming from. The next step would be to further inspect, palpate the area or perform flexion test if necessary. In case of hoof pain, the hoof tongs can be used to further establish the exact area, in case of laminitis the toe can be palpated gently to see if there is a reaction, same procedure can be applied to suspected navicular disease. An experience vet can quickly differentiate between the two conditions. The initial examinations usually can indicate what direction the work up will take, if there is visible swelling or the horse stands in a certain position to elevate discomfort or shows extreme sensitivity at certain areas. Depending on the localisation, a decision is then made on the next step, i.e. ultrasound or X-ray, which can be carried out in the stable.

If the lameness cannot be clearly assigned to one leg or if you must assume that the cause is not in the lower (distal) section of the limb, but somewhere higher up (e.g. stifle) or perhaps comes from the spine, then an initial assessment can be made with thermography. Depending on the results, a decision will then be made as to whether the horse needs to be taken to an Equine hospital for further examination in order to localise the cause using scintigraphy, computer tomography (CT), magnetic resonance imaging (MRI) or arthroscopy (joint endoscopy).

Only a proper diagnosis enables targeted therapy in the next step. Saving on diagnostics is saving at the wrong end. Because treatment ‘on guessing’ can – if the diagnosis is wrong – cause more damage and end up being more expensive than if a proper diagnosis had been made from the outset.

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