Radiographs (X-Rays)
There has been a major shift in equine radiography in the last few years with the introduction of digital radiographic systems. The old x-ray film technology was inefficient and difficult for veterinarians to provide at the highest level, particularly 'in the field'. With digital radiography, image quality is improved and ability to manipulate images after obtaining them provides even more flexibility and potential for increased diagnostic accuracy. Problems obtaining optimal medical images of animal patients are greatly reduced with this exciting new technology. Immediately after an image is 'made' it is available for assessment. This is particularly useful 'in the field' where, if necessary additional images can be made at the time, rather than having to return at a later date after films have been developed. The digital format of these images also makes it easy to send the images for a second opinion.
While radiographs are an excellent screening tool to evaluate bones, they provide minimal information about the important soft tissue structures (ligaments, muscles and tendons) that support these structures and this is a major disadvantage of this modality. However, radiographs of the site of lameness are relatively inexpensive and still provide significant information about the status of the osseous structures.
Computed Tomography
Computed tomography, or CT scanning, is becoming more available in private veterinary practices. In this technology, thin 'slice' x-ray images are generated. These 'slice' images make interpretation of complex 3-dimensional anatomy like a horse's head much easier. CT scanning has revolutionized the diagnosis of many musculoskeletal, thoracic and abdominal problems in cats and dogs but because of its relatively poor soft tissue contrast resolution, it has limited used in the evaluation of soft tissue injuries of the horse limb. It is however, very useful in the evaluation of nasal, sinus and dental disorders in horses and in assessing complex joint fractures in preparation for surgery. Horses undergoing a CT scan require general anesthesia and a special table is required to support the horse which 'piggybacks' the couch on a standard human CT.
Magnetic Resonance Imaging
Magnetic resonance imaging, MRI, is an exciting technology that is becoming more available in veterinary medicine. Magnetic resonance images, produced by the interaction of a very strong magnetic field with the body's hydrogen atoms, are characterized by exquisite ability to differentiate between normal and abnormal tissues at a level not possible with any other imaging modality. The main indications in horses are the assessment of chronic lameness that have proved difficult to diagnose or is unresponsive to symptomatic treatment.
Diagnostic Ultrasound
Diagnostic Ultrasound uses high frequency sound waves to generate a sectional images and like radiology, is used extensively as one of the first imaging modalities in the assessment many chest, abdominal disorders and lamenesses. Many practices have in-house access to this technology. Ultrasound is commonly used in the diagnosis of diseases of ligaments, tendons and joints, and is often used after the lameness has been localized to a given region. Ultrasound is also commonly used to guide injection of therapeutic agents, for example in treatment of arthritis of the neck, or sacroiliac disease.
Scintigraphy or 'Bone Scan'
Scintigraphy (bone scan) is an imaging modality commonly used as part of a lameness evaluation. Other imaging modalities evaluate the normal or abnormal anatomy of a structure, but scintigraphy measures more the bone function and response to injury, such as the increased blood flow that might occur as a result of a fracture, or inflammation and remodeling associated with ligament injury, arthritis or laminitis.