Large animal radiography
I) Introduction: The most radiographed large animal is the horse, x
rays of horses are
commonly taken of the lower leg to diagnose lameness. Often a series of films is taken
(at various angles) to discern the small change
s causing lameness, especially in complex
structures like the hock and knee (carpus).
Cattle and other livestock are radiographed less than horses because their economic value
is usually less than the horse.
In the field, portable x
ray machines have to b
e used, but at large animal clinics mobile
and stationary units are also available. These more powerful units enable the use of
techniques similar to those in small animal medicine. Even with the extremely powerful
stationary units at some facilities, film
s of the thorax and abdomen are done on small
sized patients (foals) usually.
Since most students will spend at least sometime riding with a larger animal veterinarian
the emphasis of this unit will be on farm call “field” techniques, which are very differ
from those in small animal practice.
II) Special considerations:
A) The patients: Horses (and cattle) are obviously much bigger and stronger than small
animals, when a horse kicks or “spooks” personnel and/or equipment can be injured and
can be a real challenge to get large animal patients in position and standing
perfectly still for x
rays. Tranquilization, twitches or other techniques (holding the
opposite leg up) may be needed to keep the patient still for the long exposures needed.
member patience and calmness is especially important with horses.
B) The equipment: Portable machines are used for farm calls; they are relatively
lightweight and use the electrical outlets in barns. The machines are less powerful than
the stationary mac
hines used in small animal, usually having a maximum Ma of 20.
Consequently, to get MaS levels high enough to penetrate the heavy bones of adult horses
very long exposure times are needed. For example comparing a small animal machine
with a portable larg
e animal machine:
300 Ma x 1/30second = 10 MaS
20Ma x ½ second = 10 MaS
It takes 15 times longer to achieve the same density using the portable machine.
In the past, machines were “hand held” now many ar
e suspended from a tripod to
decrease movement and increase safety.
Because the patient is not on a stationary table the focal film distance is not exact.
Although measurements are taken between the tube and the cassette, it is easy to have
ent of the cassette and some variation in focal film distance. Small cassettes
(8 x10) are used for most films and should be held by a special holder to (not by hand, as
in the past).
Another potential problem is collimation. It maybe impossible to accurat
ely collimate due
to the light in the barn. Also, unlike the high voltage designated electrical lines supplying
ray machine in the clinic the voltage may not be constant from farm to farm.
And finally, there are not “dark rooms” in the mobile vete
rinary units used by large
animal practitioners, so the films have to be developed later in a clinic.
It probably seems that with all these obstacles large animal radiography would be hit and
miss at best! But, that is not the case, most large animal pra
ctitioners have perfected their
techniques and take diagnostic radiographs safely and consistently.
III) Patient preparation: As with small animal radiography the patient should be clean and
dry. In addition, if films of the hoof are to be taken the shoe
s have to be removed and the
bottom of the hoof cleaned and packed with a radiolucent material. This prevents air
IV) Positioning devices: Because of the unusual angles that the equine hoof is filmed at
special positioning devices for the hoof
and cassette have been made. Below are photos
of some older wooden devices.
V) Views (equine)
A) Distal phalanx
2) Distal phalanx
DorsoP (palmar or plantar)
3) Distal phalanx
1) DP & oblique view
C) Proximal phalanges
2) Proximal phalanges
oblique (dorsal and medial)
1) DP view
oblique (lateral and medial)
L) Pelvis (under anesthesia) VD
2) Guttural pouch
N) Teeth (oblique views)
O) Cervical spine
Questions from text:
1) Why should large animal patients be “introduced
” to the x
2) What is the KVP (maximum) for most of the portable machines?
3) How powerful (Ma) are the large stationary units seen at veterinary colleges/referral
4) What is the main disadvantage of a mobile unit?
5) Describe a casse
6) During the lateral exposure of the distal phalanx, why must the foot be as near to the
edge (back) of the block as possible?
7) How is the skyline view different from most other views? (hence the name “skyline”)
8) Why is the stifle joint di
fficult to radiograph?
9) Why are cheek teeth hard to see on radiograph?
10) How many cassettes are usually needed for thoracic radiographs in the horse?