We are lucky at Kilmore Equine Clinic to have a number of referral facilities close by, giving our clients access to some incredible imaging technology and teams of knowledgeable specialists for those tricky lameness cases! This article will give you an understanding of how some of these advanced imaging technologies work and which cases they might be useful for.
CT- Computed Tomography
What is CT and how does it work?
The term “computed tomography”, or CT, refers to a computerized x-ray imaging procedure in which a narrow beam of x-rays is aimed at the patient and quickly rotated around the area (usually the head or leg), producing signals that are processed by the machine’s computer to generate cross-sectional “slices” of the area. These slices are called tomographic images and contain more detailed information than conventional x-rays. Once a number of successive slices are collected by the machine’s computer, they can be digitally “stacked” together to form a three-dimensional image of the patient that allows for easier identification and location of basic structures as well as possible abnormalities. CT can help with both diagnosis and treatment planning.
In horses we can use CT to look at the head and neck and lower limbs. CT imaging of the head may be able to be done in standing, sedated horses, avoiding the need for a general anaesthetic.
What is it used for?
CT is the ideal technique for imaging the head and evaluating animals for diseases of the teeth, sinuses and nasal cavity but is also extremely useful for assessing bone and soft tissue injuries in the lower limbs
As CT allows for 3D visualisation of the anatomy it can be used to identify a wide variety of pathology and it is extremely useful for planning prior to surgery. Due to the extra information obtainable using a CT it may also be used in theatre during surgeries to assist surgeons with difficult procedures such as fracture repairs.
Nuclear Scintigraphy/ Bone Scan
What is nuclear scintigraphy and how does it work?
Nuclear scintigraphy (sometimes known as "bone scanning") can be an invaluable diagnostic tool in complicated lameness cases.
The procedure involves injecting the horse into the vein with a radioactive isotope / "dye" (technetium 99), which emits gamma radiation. It then passes around the horse’s circulation and is taken up by the bones of the skeleton. If an area of bone has increased activity (like the site of a fracture), then more radioactive isotope will be taken up by this area. Shortly after the injection a special camera called a gamma camera is used to detect the radioactivity emitted and provide detailed images of the skeleton with abnormal areas seen as “hot spots”.
Although it is well known to be a safe procedure, after injection and imaging the horse is kept in controlled conditions for twenty-four hours to comply with radiation safety regulation requirements. Horses are generally allowed to leave the hospital the day after imaging, but sometimes the technique identifies problems which require further investigation. This must be done the following day to avoid unnecessary handling when the radioactivity levels are still relatively high.
What is it used for?
Nuclear scintigraphy can be useful in cases where nerve blocks have not revealed the source of the lameness, when other imaging techniques have not shown any abnormalities, in cases of multi-limb lameness and in difficult to image areas when we have diagnosed pain in the pelvis, neck or back. It is mainly used for imaging bones, although vascular and soft tissue phases are also possible.
It is particularly useful to identify either subtle or very early bony damage before it is visible on an x-ray. For this reason, bone scanning is useful for identifying stress fractures. It is also used to look for abnormal stress modelling of bone and to monitor fracture healing.
MRI- Magnetic Resonance Imaging
What is MRI and how does it work?
MRI is a non-invasive imaging technology that produces three-dimensional, detailed anatomical images of soft tissues and bone. MRI does not use the ionizing radiation of x-rays like CT (computed tomography), making it a safe, efficient and effective modality. Instead MRIs employ powerful magnets to generate an image.
These magnets produce a strong magnetic field that forces protons in the body to align with that field. When a radiofrequency current is then pulsed through the patient, the protons are stimulated, and pull against the magnetic field. When the radiofrequency field is turned off, the MRI sensors can detect the energy released as the protons realign with the magnetic field. The time it takes for the protons to realign with the magnetic field, as well as the amount of energy released. The images are produced based on the differing magnetic properties between various types of tissues.
The magnetic field of the MRI extends beyond the machine and exerts very powerful forces on objects of iron, steels, and other magnetizable objects, for this reason horses will have their shoes removed before the procedure.
MRI previously had to be done with the horse lying down under a general anaesthetic but there are now standing MRI machines that only require a sedative to help prevent the horse from moving throughout the procedure.
What is it used for?
MRI scanners are particularly well suited to image the soft tissues of the lower limb. The ligaments, tendons and other soft tissue structures are seen much more clearly with MRI than with regular x-rays and CT. It is often used in lameness cases for diagnosis and treatment monitoring where other imaging modalities have not been able to assist in diagnosing the problem.