When your horse needs medical attention, it is helpful if your veterinarian can visualize the problem internally. Veterinary medicine has made significant advances over the last 20 years in providing tools for this purpose. Ultrasound was first introduced in the 1970s for reproductive imaging to monitor the mare's reproductive tract and to optimize the time for breeding. Tendon imaging began in the early 1980s and primarily involved imaging "core lesions" (tears of the superficial digital flexor tendon i.e., bowed tendons) in Thoroughbred racehorses.

Since that time, ultrasound has expanded considerably, now allowing veterinarians to image just about any structure in the horse: heart, lungs, abdominal organs (kidney, liver, spleen, intestine, etc.), eyes, tongue, esophagus, etc. Basic tendon and ligament ultrasonography has also expanded to include the soft tissue structures of joints including stifles, hocks, elbows, shoulders, fetlocks and knees (carpi). For example, in the equine stifle (equivalent of the human knee), veterinarians can diagnose injuries such as meniscal tears and collateral ligament damage. Veterinarians can use ultrasound to identify the presence of foreign bodies with penetrating wounds and chronic draining tracts. Traditional radiography cannot detect wood or other nonmetallic foreign bodies whereas ultrasound has proven useful for this purpose. Ultrasound can also determine if external wounds reach the joints and tendon sheaths.

In addition, ultrasound also can be used to view bone surfaces for the presence of fractures and infected bone. For example, pelvic fractures are difficult to radiograph in the standing horse because of the horse's large size. Ultrasound, however, can be used to detect incongruities in the bony surfaces which may indicate injury and/or fractures.

Veterinarians still use ultrasound regularly for reproduction, but its use has also expanded to monitor fetal well-being in high risk pregnant mares and to identify the sex of the fetus.

An ultrasound examination provides an image of internal structures produced by sound waves transmitted into the body. Scanning the tendon results in an image that can reveal damage as a black space in the middle of the tendon as shown above (arrows).

How Ultrasound Works

An ultrasound machine works by emitting a beam of sound waves from an ultrasound transducer into the body tissues. In general, the ultrasound waves can penetrate to a maximum depth of 40 cm (15 inches). The ultrasound waves interact with the various tissue types in different ways: the waves can be reflected, scattered, refracted or attenuated. The reflected waves are transmitted back to the ultrasound transducer. This information is interpreted by the ultrasound machine which produces a two dimensional black and white image called a sonogram.

VMTH Diagnostic Ultrasound

At the UC Davis Veterinary Medical Teaching Hospital (VMTH), Dr. Mary Beth Whitcomb and her associates frequently use ultrasound to diagnose tendon and ligament injuries and to monitor their healing. Ultrasound enables veterinarians to quantify and document the extent of damage sustained in a "bowed tendon" or "pulled suspensory ligament." During the initial ultrasonographic examination, detailed measurements are taken. Then, during the rehabilitation period, the degree of healing can be assessed by comparing the initial measurements to the current scan at each recheck. This information enables the veterinarian to design a tailored exercise program to the individual horse based on the progression of healing. Regular rechecks also allow early detection of reinjury necessitating a decreased exercise level to prevent severe reinjury.

Ultrasound is used during a performance evaluation on the treadmill to evaluate heart function.

At UC Davis, veterinarians often use ultrasound in conjunction with other medical diagnostic procedures to assess respiratory disease and abdominal organ dysfunction. Ultrasound facilitates a more accurate evaluation of the amount of fluid within the chest of a horse suffering from pleuropneumonia. Diseases of the kidney, liver, spleen and other internal organs can be diagnosed more readily using ultrasound than with other more traditional methods. Ultrasound also provides an accurate guide to obtain biopsies from affected organs (e.g., liver, kidney, spleen, etc.) and avoids the risk of damaging nearby vital structures. Veterinarians also use ultrasound to evaluate possible causes of colic such as small intestinal strangulation, masses, abscesses, etc.

When evaluating the equine heart, ultrasound has become an extremely valuable tool. The heart's anatomical structure and function can be readily determined as well as abnormalities in heart size, wall thickness or defective cardiac valve function. These findings are often useful in determining the cause of poor athletic performance as well as for treating the clinically abnormal equine patient. The ultrasound examination of the heart, (echocardiogram) is now considered an integral part of any complete cardiovascular evaluation in all species.

When evaluating the equine eye, ultrasound can be helpful in assessing damage to the retina or other structures in the back of the eye. Ultrasound is particularly useful when visualizing the back of the eye is precluded by cataracts, cloudy fluid in the eye, masses, etc. At the VMTH, an equine ophthalmological examination often includes ultrasound. In short, the use of ultrasound within the UC Davis VMTH has become one of the most useful tools in the diagnosis and treatment of equine medical problems. Its use will undoubtedly increase as researchers continue to develop new techniques and as the technical instrumentation also advances.

Next Step in Equine Diagnostic Ultrasound

Ultrasound image of a normal eye.

Ultrasound image of a cataract.

Ultrasound has developed considerably over the last decade and has become a valuable diagnostic tool for a variety of ailments; therefore, it is imperative that equine practitioners receive general training in its use. To meet this need, the UC Davis School of Veterinary Medicine has offered an equine ultrasound course since 1997 to junior year veterinary students. As equine ultrasonography (diagnostic techniques) is a relatively new field, many of today's practicing veterinarians did not receive ultrasound training during their primary veterinary education. Therefore, veterinarians with specialty training in this field are in demand to instruct and assist other practicing veterinarians in the newest ultrasonographic diagnostic techniques.

To meet the need for advanced training for equine practitioners, Dr. Whitcomb organized a two day musculoskeletal ultrasound course with lecture and labs in April 2000. Due to the demand and success of the course, she plans to make this an annual continuing education event in the early spring. Interested veterinarians can contact Dr. Mary Beth Whitcomb at (530) 752-0290.

Scanning the eye is easily accomplished through the closed eyelid.

In addition to general training, it is important to develop more specialists in equine diagnostic ultrasound. There is only one formal postgraduate training program available in large animal ultrasound which is offered by New Bolton Center at the University of Pennsylvania. UC Davis is taking an active role in creating more individuals with specialty training in equine ultrasonography; therefore, starting in the summer of 2000, the UC Davis School of Veterinary Medicine plans to offer a one year ultrasound fellowship to veterinarians with at least one year of practice experience.

Technologically speaking, the next step in equine ultrasound is the use of high frequency transducers to improve imaging of superficial structures. High frequency transducers (16 - 50 MHz) only penetrate about one to four cm., but provide exceptional detail. These transducers will allow veterinarians to detect tendon and ligament damage at an earlier stage than what is currently possible. Also, diagnostic images can be obtained of smaller ligaments (joints) that were not clearly visible in the past. This would open up a whole new area of diagnosing joint lameness. These transducers would also be helpful in evaluating any superficial structure, including the equine eye.

As veterinary medicine continues to advance, veterinarians will have more tools to utilize in the complex process of diagnosing abnormalities/injuries. As the ultrasound equipment improves and as more veterinarians become specialized in diagnostic ultrasound, the veterinary care and treatment of all horses will continue to improve.

The UC Davis School of Veterinary Medicine will remain on the cutting edge of the expanding field of diagnostic ultrasound. The UC Davis Veterinary Medical Teaching Hospital (VMTH) has a comprehensive ultrasound service open to the public. The VMTH also offers therapeutic ultrasound through the new Equine Physical Therapy Service. For more information or to schedule an appointment, contact the VMTH Large Animal Clinic at (530) 752-0290.

HELPFUL TIPS

When to Use Diagnostic Ultrasound

Musculoskeletal

• Swelling, heat or sensitivity of any tendon or ligament.
• Joint swelling without radiographic explanation.
• Lameness localized to specific region.
• Monitor tendon and ligament healing throughout rehabilitation program.

Abdomen

• Acute colic - diagnostic aid for small intestinal surgical lesions.
• Chronic colic - multiple causes, e.g., thickened colon, tumors, abscesses.
• Evidence of organ disease:
• Kidneys/bladder - blood in urine, abnormal blood or urine tests.
• Liver - elevated liver enzymes, abnormal blood tests.
• Fever of unknown origin - possibly caused by abdominal abscesses or tumors.

Thorax

• Any lower respiratory tract disease.
• Fluid in the lungs.
• Pneumonia - determine extent. (Most practitioners do not have radiographic equipment to perform thoracic radiographs in adult horses.)
• Fever of unknown origin.
• Tumors.

Cardiac

• Evaluation of murmurs or arrhythmias (abnormal heart rhythm).
• Recent onset of poor performance in racehorses.

Ocular

• Critical to visualize retina and posterior structures when the eye is cloudy (inflammation) or obscured by cataracts.
• Abnormal "bulging" of the eye for masses.

Swellings/draining tracts

• Determine presence and number of foreign bodies.
• Determine nature of swelling (i.e., abscess or hematoma or tumor).

Pregnant Mares

• High risk mares (i.e., mares that have undergone surgery, etc.) - evaluation of fetal well-being.
• Transabdominal ultrasound allows detection of placentitis and/or placental separation.
• Fetal sexing.

Shock Wave Therapy to Stimulate Healing

A new type of therapeutic tool is currently being tested at the UC Davis Veterinary Medical Teaching Hospital through the large animal ultrasound service: extracorporeal shock wave therapy (ESWT). Since October 1999, 100 - 120 horses have been treated. Early results from these treatments indicate that the technique may be useful for certain orthopedic disorders.

• ESWT delivers high pressure pulses of acoustic wave energy to injured tendons, ligaments and bones to stimulate healing and provide pain relief. This technology was originally developed in human medicine to break up kidney stones without surgery (lithotripsy).
  
  
• The VMTH's Storz equipment is the only shock wave machine available with ultrasound guidance capabilities which allows veterinarians to treat the precise location of injured area.
  
  
• General anesthesia is not required for treatment, only mild sedation, and the horses tolerate the treatment very well while standing. Other shock wave equipment requires general anesthesia which involves the inherent risk of recovery.