Nuclear scintigraphy uses radioactive isotopes injected into the horse's bloodstream to identify areas of bone with increased metabolic activity. The isotopes accumulate in actively healing bone and damaged soft tissues, emitting gamma rays detected by a camera to create images. It is a sensitive way to diagnose subtle or complex lameness issues, monitor fracture healing, and examine areas like the pelvis or back inaccessible to other modalities. The horse is hospitalized after the scan for 48 hours as the isotope decays to ensure handler safety. Scintigraphy highlights injury locations but may require other tests to characterize findings fully.

2. What Is Nuclear Scintigraphy?
n Musculoskeletal system
imaging modality
n Aids in diagnosing
subtle to severe and
complex lameness
n Can be used to monitor
the healing of fractures
n Pre-purchase exams
n Referred to as nuclear
medicine, bone scan,
and scintigraphy

3. n Horse is injected with a radioactive isotope (Tc99m) that has an
affinity to localize in bone.
n Areas of osteoblastic activity or accelerated metabolism of the bone
will result in a “hot spot”.
n Gamma radiation is emitted by the horse and detected by the
camera creating an image.
How It Works

4. Phases of a Bone Scan…
n Vascular Phase
¨ Not used readily in horses unless
a lack of blood supply is
suspected. Ie. iliac thrombosis
n Soft Tissue or Pooling Phase
¨ Allows us to examine the soft
tissue structures of the lower limbs
(ie. tendons/suspensory)
n Bone Phase
¨ Performed 2-3 hours after
injection to ensure the isotope has
been well distributed into the
bone.

5. n Hospitalized for a
minimum of 48 hours
after injection.
n Patients are confined to
a stall to allow for the
radioactive isotope to
decay.
n Ensures both patient
and handler safety.
Horse Handling and Management

6. Why Scintigraphy?
n Scintigraphy is an excellent
way to identify lameness
issues that are difficult to
diagnose.
¨ Pelvic, shoulder and back imaging
are all possible. These areas may
be inaccessible to other modalities
(x-ray or ultrasound).
n Aids to rule out suspected
fractures or isolate the main
cause of a lameness if a “multi
focal” lameness is present.

7. n Highly sensitive but non-specific
¨ It is extremely good at isolating an area of increased metabolic
activity (fractures, inflammation etc) but may not characterize the
nature of the injury specfically. (bone bruising vs. a chip vs.
fracture).
n Radiography / ultrasound or regional anesthesia can
then be used to characterize the highlighted areas of
interest.
n Many “hot spots” are completely diagnostic in that there
are breed and occupational characteristics that make
them definitive

8. When would you consider
Scintigraphy?
n A sudden onset lameness.
n Failure to localize the
lameness by blocking.
n Lameness involving one or
multiple limbs.
n Persistent / intermittent
lameness.
n History of poor performance.
n Monitor the healing of an injury
or fracture.
TIBIAL STRESS FRACTURE
AFTER 4 MONTHS STRICT STALL REST

9. n Front end, hind end,
or full body
n With or without soft
tissue phase
n It is important to
always compare left
and right sides of the
horse. Some “hot
spots” are normal for
certain breeds
BONE SCAN OF A FOAL –
NORMAL INCREASE UPTAKE
IN GROWTH PLATES
BONE SCAN OF A
WARMBLOOD – WITH
INCREASED UPTAKE
OF THE DORSAL P1

10. ORGIN OF SUSPENSORY
(Avulsion Fracture)

11. HUMERAL STRESS FRACTURE

12. Bilateral Pelvic Fractures

13. MULTI FOCAL KNEE
PATHOLOGY

14. MULTI FOCAL KNEE
PATHOLOGY

15. Osseous Cysts
LF - Normal
RF - Cyst

16. EXERTIONAL
RHABDOMYOLYSIS – TYING UP
n Muscle
damage
due to a
breakdown
of striated
muscle
fibers. Note
the “brush
stroke”
uptake of
isotope.

17. Case 6: “Mood”
n 2 Year Old Thoroughbred Racing Filly
n Presented with acute right hind lameness
n Suspected to have an injury to the
proximal right hind limb / pelvis
n Scintigraphy elected

18. n Giving – Pelvic Fracture