What a difference 30 years makes. Significant advances in veterinary imaging technologies over the last three decades have produced a wide array of diagnostic options for horses. However, with the myriad of modalities that are currently available, it can be difficult to understand why one might be better for a particular problem than another. The following overview of these technologies may assist owners in making informed decisions concerning their horse's medical care.

Digital and computed radiography make images of bone and joint structures using an x-ray machine. Though similar to the radiographs taken with film, digital and computed radiographs have exceptional detail, are frequently used for identifying leg injuries, and are especially useful for most lameness problems involving the bones and joints. The new digital systems provide rapid instantaneous images that can be viewed on a computer or printed on film.

Medical ultrasound uses high frequency sound waves reflected off of tissue planes to generate an image that represents the densities and fluids within soft tissue structures. Many of the newer ultrasound machines are portable and can be brought directly to the patient. Ultrasonography is used on all body systems including the intestines, lungs, eyes, muscle, tendons, joints and heart, as well as cartilage and bone surfaces. It is especially useful for diagnosing tendon and ligament injuries and heart and lung diseases.

Scintigraphy starts with an intravenous injection of a radiopharmaceutical (radioactive isotope) that is linked to a phosphate compound which is actively absorbed into the bones. Once the isotope has circulated to all parts of the horse, a gamma camera is used to detect the radiopharmaceutical uptake that is increased in injured or infected bone areas due to higher metabolic rates. This powerful scanning technique is commonly utilized in horses to locate and diagnose bone, joint and soft tissue problems. Scintigraphy is especially useful for localizing stress fractures, arthritis and infections.

Computed tomography, also known as a CAT Scan, uses three dimensional radiographs to create multiple images as slices of a structure. The large size of the horse limits the parts of the body on which computed tomography can be used. By adapting special tables and gantries, CAT Scans can capture images of a horse's limbs, cranium and neck and are particularly helpful for identifying equine head fractures and dental disease.

Thermography maps the surface temperature of an object by detecting the heat emanating from infrared rays. Because environmental temperatures or focal exposure to the sun can interfere with the mapping process, thermographic equipment must be used in a controlled environment with adequate time for surface temperature equilibration. Thermography is especially useful for diagnosing infection as well as early tendon damage and sites of pressure from a poor fitting saddle.

Magnetic resonance imaging (MRI) provides incredibly sharp and detailed pictures of soft tissues and bone by using radiowaves that are intermittently pulsed into the horse's limb within a strong magnetic field. When energy gained from the radiowaves is released from the tissue, it is detected as a signal and transmitted to a computer. The resulting picture provides clues to the structure as well as the chemical make up of the tissue. As an example, an increased signal shows up with more white than black in a dense tendon or bone indicating abnormal inflammation. MRI is the most powerful veterinary imaging tool available and therefore provides the most detailed images. It is commonly used to diagnose joint, tendon and foot injuries and is especially useful for investigating the depth and location of nail punctures to the hoof.

As the descriptions above demonstrate, medical imaging for horses has never been better and it appears that even more advanced technologies are on the horizon. By working with their veterinarian, owners can utilize the powers of these tools to provide the best healthcare for their horse.

The Marion duPont Scott Equine Medical Center offers an extensive lineup of diagnostic capabilities. To learn more or to schedule a consultation, call 703/771-6800 or visit www.equinemedicalcenter.net.

Dr. White is the Jean Ellen Shehan Professor and Director at Virginia Tech's Marion duPont Scott Equine Medical Center. He can be reached at nawhite2@vt.edu. To view his online profile, visit www.equinemedicalcenter.net.

Virginia Tech's Marion duPont Scott Equine Medical Center is a premier full-service equine hospital located in Leesburg, Va., that offers advanced specialty care, 24-hour emergency treatment and diagnostic services for all ages and breeds of horses. One of three campuses that comprise the Virginia-Maryland Regional College of Veterinary Medicine, the center and its team of equine specialists are committed to providing exceptional treatment to patients, superior service to clients and cutting-edge research to the equine community.