Ultrasound? ...Ultra
Practical!
By Karen
Berk
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Ultrasound,
as a diagnostic tool in Equine management and health care, has become staple of
our industry. While the Racing and Show World utilizes ultrasound to scope
everything from lungs to limbs, it is the reproductive aspects we will address
here.
Ultrasound technologies and their use have been with us since the
late 1950s. Given it's recognized benefits and efficacy for medical diagnosis,
it is also one of the clinically safest procedures available for both
technician and patient.
Let us begin with how ultrasound works. The
machine itself, by way of a transducer sends out beams of sound for very short
periods of time, and then listens for echos. Perhaps the best example would be;
Place yourself in a large, empty room. You shout and then listen. An echo is
heard as sound bounces off the walls. The further away you stand from the wall,
the longer it takes for the echo to return to you. You have now sent out a
sound beam, and your ears are picking up the returned echo. Your brain
translates this into a picture, or recognition.
The ultrasound machine
is simulating this by using what it hears, to create a picture on a screen.
Every time it hears an echo from the sound beam it has sent out, translates it
onto a monitor. The location of each dot depends on how long it takes the echo
to reach the machine. Gray shades are determined by how strong, or loud, the
machine perceives the echo to be. An echo from a hard smooth surface will be
louder then a soft bumpy surface. A strong echo comes from deeper, and is
perceived and viewed as a whiter image. While a weak or soft echo, being either
closer proximity or fluid, will be grey to black. The ultrasound machine sends
out thousands of beams a minute in order to create the image we see on the
screen. It then takes a trained technician, (vet) to read the images.
Tissues vary in their echocentricity, or ability to reflect sound waves. Air
and dense tissue reflect most sound waves, whereas fluids propagate them.
Reflected sound waves are received by the transducer and converted to
electronic impulses in the machine, and displayed on the monitor.
The
equipment consists of these three primary parts:
- The
TRANSDUCER is the component held in the examining hand of the person
performing the ultrasound. Within it is a crystal that emits the ultrasonic
beam, or high frequency sound wave, and then "listens" for the echoes. The
echoes produce images of soft tissues and organs. The examiner moves the
transducer within the area to be examined, aiming it at specific structures
such as the ovaries or uterus.
- The MONITOR
is simply a TV screen that receives and displays the images created. Often it
has a stop / freeze capacity, and an attached Polaroid camera for capturing the
images.
- The MACHINE
contains the computer and power to transform the echoes the trasducer hears, to
the picture you and the examiner see on the monitor. It also has a control
panel and can measure structures, such as follicles.
There are currently
two methods of performing reproductive ultrasounds, trans- abdominal and
trans-vaginal.
The trans-abdominal method is frowned upon in equines,
due to the density of the body, and conflicting organs. There are commercially
available units, used by breeders to identify early pregnancies. These do not
have capability or accuracy in pregnancies past 14 days, and do not detect
ovulation or additional reproductive applications.
Trans-vaginal
ultrasound is the form breeders are familiar with. After carefully removing
feces from the rectal tract, an ordinary rectal palpation is done. Next, a well
lubricated transducer is introduced into the rectum of the mare, and as with
palpation, the organs are identified and scanned, in a systematic manner. Care
is taken that no air or fecal matter is caught between the transducer and the
tissue or organ of interest. It is also preferable to advance the transducer
over the cervix and body of the uterus until the bifurcation of the uterus is
visualized. The transducer is then moved slowly over the horn to the tip, to
image the ovary. Pre-ovulatory follicles are seen as black spheres, as they are
an-echoic, or fluid filled. Ovulating follicles have a pear shape or are losing
their cylindrical shape. Post ovulation, the follicle becomes a corpus luteum,
or yellow body, losing it's fluid content, and are viewed as a light grey or
white sphere.
Diagnostic ultrasonography is used in the broodmare
for:
- Evaluation of
ovarian activity; Gauging stages of estrus cycle, identifying estrus, diestrus,
anestrus, prediction of ovulation, "silent heat" mares.
- Detection and
evaluation of pregnancy; With a high quality ultrasound unit, equipped with a 5
MHz trans-rectal transducer, embryonic vesicles can be detected as early as
9-10 days post ovulation, also twins, and estimation of conceptus age.
Additionally, gender can also be determined, by identifying the position of the
genital tubercle, at 60 to 70 days post ovulation.
- Diagnosis of changes
and problems in the reproductive tract; These can include, but are not limited
to, uterine endometrial cysts, fluid accumulations, abscesses and masses.
Although not a common
procedure, ultrasonography in the stallion is a excellent tool for diagnostics
of what otherwise would be inaccessible. It permits non invasive evaluation of
the testes. This would be for both fertility problems and to estimate daily
sperm output. Rectally in the stallion, it allows access to the accessory
genital glands, and abdominal / inguinal exploration for
chryptorchids.
In the growing field of Frozen Semen, success greatly
hinges on the use of ultrasound. Frozen spermatazoa, post thaw, have a very
short life span. Unlike fresh chilled or live cover, whom can have a 48 hour
viability post ejaculation, thawed cell have a 6 to 8 hour viability. Thus
timing the insemination, 8 hours prior, or 6 hours post ovulation, must be
strictly adhered to. Ultrasound checks are numerous when ovulation approaches,
and can admittedly be quite costly. Additionally, since there is a higher
occurrence of uterine inflammatory response with frozen semen, one must check
to make certain the uterus has evacuated efficiently. Often this is with the
aid of Oxytocin and post insemination flushes. Uterine fluid will show up as
black, since they are an-echoic, in an ultrasound exam.
There will
repeatedly be the controversy of cost versus chance, in taking advantage of the
ultrasound technology. I seem to always have the same response. Horse shows are
very costly, as are trainers, advertising. trucks, trailers, show clothes,
barns, stud fees, shipping, feed, and on and on. Why start short changing now.
Success in a breeding program is money saved. Foals on the ground, with the
least amount of effort, makes for a monitarily successful, and professional,
breeding business. Certainly not all breeding endeavors require ultrasound.
Yet, please consider, it can be one of the most time, labor, and overall cost
saving tools you can employ.
Many thanks to Dr. Bob Smith, of Palm West
Veterinary Hospital, Wellington Florida, for his patience, photos, and
ultrasound information and expertise. Also, thanks to Lassergut Farms, USA for
sharing their experience and use of their mares and facility.
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