Computed tomography (CT) imaging technology entered human medical practice in the mid-1970s. About a decade later, the first reports of its use in equine patients were published. Since the birth of veterinary medicine in the 1980s, advances in technology have seen a substantial increase in the use of equine CT to diagnose equine injuries, improving our ability to use this method safely in clinical patients.
What is computed tomography?
Computed tomography is a diagnostic imaging modality that uses the same technology as radiography but produces three-dimensional information. Therefore, CT scans can give us a more detailed look at a horse’s anatomy and any abnormalities present than X-rays can. Unlike magnetic resonance imaging (MRI), CT allows veterinarians to perform scans in minutes, making this modality very attractive for standing patients. This fast and easily accessible modality is also ideal for screening for low-grade pathology (disease or injury), monitoring injuries, and even assessing surgical outcomes in the operating room.
Equine CT Scanner Types
The two main types of CT scanners are fan beam and cone beam. As the name suggests, fan-beam CT is a thin fan-shaped beam of radiation that is rotated around the patient several times to obtain “slices” of the patient’s anatomy, which are then stitched together to create an image. The beam of cone beam CT is wide and cone-shaped. It typically goes around the patient once, capturing a large amount of the anatomy and then reconstructing it to produce the final image.
Fan-beam CT produces images that are generally of higher diagnostic quality than cone-beam CT images and have particularly good soft tissue detail. However, fan-beam CT scanners require a closed system similar to a donut shape through which the horse’s anatomy must pass in order to obtain images. Additionally, cone beam CT scanners can be configured in a variety of ways. This means veterinarians are limited in what anatomical areas of the horse we can safely capture in a fan-beam CT scanner without the need for general anesthesia. Therefore, we rely on a cone beam device to scan the horse’s limbs, which the manufacturer has optimized to image the horse in a standing position. Recently, the emergence of new configurations of fan-beam CT scanners has facilitated their ability to scan equine patients without the need for general anesthesia. These scanners are increasingly used in equine hospitals around the world.
Why do horses need CT scans?
Your veterinarian may recommend a CT scan of your horse for a variety of reasons, from scanning the limbs and neck for bone pathology to investigating the cause of dental or sinus disease. CT scans allow us to quickly capture large amounts of anatomy (such as a horse’s head) and provide excellent detail about the horse’s teeth, head bone structure, nasal passages and sinuses. With the advent of CT systems designed to image the limbs of standing horses, more and more veterinarians are using this modality as part of their lameness examination, especially when they suspect skeletal abnormalities. Some systems can also image the horse’s neck, which is useful for examining the spine for skeletal abnormalities that may be associated with neurological disease. Surgeons can perform CT scans before, during, and/or after complex surgical procedures (such as fracture repair) to assist in the planning and successful execution of these complex procedures. It is also worth noting that owners and veterinarians sometimes choose to send their horses for CT, in part because advanced imaging modalities are most readily available locally, as these types of scans are typically only available at larger equine hospitals.
Latest research on equine CT
We have compiled the following information on the latest research based on the various uses of CT mentioned above.
Neck CT
Some clinics have installed the equipment needed to perform a CT scan of the neck, which can be performed under general anesthesia or immediately. Veterinarians may use it to diagnose and evaluate conditions such as cervical arthritis. They may also use neck CT to assist in diagnosing neurological conditions such as wobbler syndrome (cervical stenotic myelopathy). The condition is difficult to diagnose—historically, it required a combination of X-rays and ruling out other causes of neurological disease. With wobbler syndrome, the spinal cord becomes compressed within the horse’s neck. To try to identify areas of pressure, veterinarians inject a contrast dye-like substance into the space around the spinal cord and take X-rays (a procedure called myelography) that can reveal focal narrowing of that space. Using 2D X-rays, we can only evaluate the dye located above and below the spinal cord, observing possible spinal cord flattening in that plane. However, the rope can also compress from one side to the other; 3D imaging such as CT can detect this type of compression.
skull CT
The skull is a particularly difficult area to successfully image due to the complex anatomy of the facial bones, sinus system, teeth, and soft tissues in this region. With X-rays, again creating a 2D image, these skull components are projected onto a flat surface and superimposed on the resulting image, making it difficult to see exactly what’s going on.
Multiple studies have shown that CT is superior to X-rays in detecting and characterizing disease within the equine skull, including disease of the teeth and sinuses and of sensory tissues such as the inner ear.
In a study published in 2017, Liuti, Smith and Dixon found that X-rays identified only 53 percent of infected teeth in equine patients, while CT identified 100 percent. Sinusitis often accompanies tooth infection and is difficult to locate on X-rays. One sinus compartment, in particular, is difficult to see on X-rays: in one study, veterinarians were able to identify only 17% of conditions involving this sinus on X-rays, compared with 100% on CT (Manso-Diaz et al., 2015). Knowing which sinuses contain infectious material is important to target treatment and, if necessary, plan surgical procedures to treat sinusitis.
Although horses are much less likely to develop cancer than other pet species, the skull is an area where veterinarians often find tumors. The CT characteristics of common growth types in the equine skull, including benign masses such as cysts, have been well described in the literature. This means that while an X-ray may reveal the presence of a mass, a CT can often provide more evidence about the possible type of mass and how it acts in the body, informing possible treatment options and potential outcomes.
Finally, in a 2019 study by Crijns et al. The study found that while X-rays can often detect skull fractures, CT can more accurately show the size and complexity of the fracture, the number of fracture fragments and the extent of associated soft tissue damage. These characteristics may change the way veterinarians treat injuries.
Orthopedic CT
As with skull fractures, CT is sometimes required to fully understand the nature of the extremity fracture and any associated soft tissue damage. This is because radiographs often underestimate the extent of a fracture. CT allows veterinarians to diagnose more subtle bone injuries, such as bone bruises and incomplete or hairline fractures, which are nearly impossible to detect using X-rays alone. For example, in a study published this year by Steel et al. CT has been demonstrated to be superior in assessing some key characteristics of carpal (knee) bone fractures in horses, such as number of fragments and articular surface involvement.
In addition to fracture identification and characterization, veterinarians can use CT before and during surgical fixation of fractures to plan and guide the placement of orthopedic implants designed to stabilize the fracture while it heals. Using CT, surgeons can map the precise trajectory of orthopedic screws, etc., to provide the strongest fixation. In a recent study by Taylor et al. (2022) reviewed the use of CT for surgical planning at a large equine hospital and concluded: “CT plays an important role in surgical planning, adding additional information or significantly The surgical plan was changed.”
Progress of vertical CT
The development of new CT machine configurations has enabled veterinarians to begin using this modality to image previously inaccessible body parts. These include the horse’s elbows, back and pelvis. Recently, a team of veterinarians from the University of Lyon in France and an equine hospital in Belgium successfully placed horses into a fan-beam CT scanner to obtain images of the elbows of 99 equine patients. Based on these images, the team diagnosed conditions such as arthritis, bone cysts and fractures.
Another huge benefit of our increasing ability to perform CT scans on standing patients is the ability to screen high-risk horses for early signs of injury before they develop severe lameness. This is particularly important in racehorses, where the way horses are trained results in specific patterns of bone remodeling. Veterinarians can use CT to visualize these patterns and identify horses at risk for injury, thereby reducing their workload, allowing bone to recover and preventing catastrophic injuries. Some clinics combine these types of CT screening with another emerging technology in the equine field: positron emission tomography (PET). This imaging modality uses radioactive tracers localized to areas of bone remodeling to provide information about the location of “active” lesions. However, PET imaging does not give us good anatomical detail, which is why veterinarians must combine it with another modality, most commonly CT.
The combined use of PET/CT offers great potential for early identification of pathology and reduced injury rates in horses (Spriet, 2022). Veterinarians can also use this combination of imaging modalities not only as a screening tool but also to diagnose various orthopedic conditions in equine athletes. The rapid growth and development of CT technology in the equine field has opened exciting new doors to image horses quickly and safely and generate high-resolution, highly diagnostic images.
refer to
Kryns et al. (2019) Comparison of radiography and computed tomography in the diagnosis of equine skull fractures. Equine Veterinarian. educate. 31(10)543-550.
Klopfenstein-Breger et al. (2019) Cone-beam computed tomography of the head of a standing equid. BMC Vet. beef. 2019 Aug 13;15(1):289.
Liuti, Smith & Dixon (2018) Radiographic, computed tomography, gross pathology, and histological findings in 32 equestrian cheek teeth with suspected apical infection (2012-2015) Equine Veterinary Journal 50, 41–47.
Manso-Diaz et al. (2015) The role of head computed tomography in equestrian practice. Equine Veterinarian. educate. 27(3)136-145.
Riggs (2019) Clinical review: Computed tomography in equine orthopedics – the next giant leap? Equine Veterinarian. educate. 31(3)151-153.
Steel et al. (2023) Comparison of radiographic and computed tomography assessment of third carpal fractures in horses. animal13, 1459.
Stewart (2021) Advanced imaging of equine patients using cone beam computed tomography. Equine Vet J. Sep;53(5):872-885.