The Bone Scan

      The bone scan is a well established procedure in Nuclear Medicine.  Areas of bone injury or bone destruction are usually associated with ongoing bone repair and consequent increased metabolic activity and calcium turnover.  The radionuclides which mimic the metabolic behavior of calcium will localize in this region of bone repair in increased concentration relative to normal bone.  In the past 85Sr and 18F were the primary radionuclides used.  However, various phosphate compounds labeled with 99mTc are the agents of choice.  The most commonly used radionuclides are Methylene Diphosphonate (MDP) and 99mTc HDP.  The exact mechanism of bone uptake of these radionuclides is not clear. However, current knowledge suggests that it is a combination of bone blood flow and extraction

       Bone imaging studies are useful in a variety of disorders.  These include obscure or switching leg lameness, trauma, negative or ambiguous radiographs, occult fracture, not lame enough to block, flexion tests equivocal, anesthetic blocks are negative, minimal or no change with medication, difficulty visualizing areas of the skeleton radiographically such as the hips, pelvis and parts of the skull. Scintigraphy has been known to be useful in tracking the overall skeletal health of horses in arduous training and also as part of a pre purchase exam.  Studies are helpful in tracking degenerative disease, exercise related trauma, assessment of significant x-ray findings, vascular abnormalities, bone tumors, cysts or abscesses and osteomyelitis.

       The radiation dose to the skeleton and the whole body depends on the rate of clearance of the radionuclides by the kidneys.  In humans the estimated dose to the skeleton with an injected dose of 20 mCi, is 0.7 rads,  to the kidney 0.8 rads, to the bladder with a 2 hour void 2.60 rads and to the whole body is 0.1 rad.

  Three phase Bone Imaging

    A three phase bone imaging study is usually indicated in suspected infection (osteomyelitis and septic arthritis) and in trauma or suspected vascular abnormality.

 Radiopharmaceutical and Dose

     200 mCi 99mTc HDP or other diphosphonate compound is administered intravenously via the jugular vein of the adult horse. The dose for foals and other small animals 3 to 5mCi /  kg is adequate.  Minimum dose is 2 mCi is suggested.


     A large field of view (LFOV) gamma camera with a low energy all purpose collimator. Energy window at 20% centered at 140keV. Nuquest Nuclear Medicine computer.  Alfanuclear data and image processor.


       Once the appropriate area of interest has been established, the collimator is positioned over that area for a dynamic flow study.  The radionuclide is injected as a bolus.  Data is collected soon after the injection with each frame of the dynamic flow set for a duration of 2-5 seconds for approximately 30-60 frames.  It takes approximately 15 seconds for the injected bolus to reach the terminal aorta and 45 seconds to arrive in the distal hind limb of a horse. In the average patient the dynamic flow component of the study could be terminated 30-45 seconds after it appears in the area of interest. Immediately after the flow study, a static image is obtained with about 200-300k counts.  

     One hour to one and a half hours after injection 200mg of furosemide in administered intravenously to facilitate faster renal excretion of the radionuclide and hence better target to non-target ratio.

     The patient returns for the delayed images approximately three hours post injection.  Static images are obtained of the area of interest.  Distal limbs require 100-150k counts, upper limbs and axial skeleton usually require 150-250k counts. Less counts may not be diagnostic. This phase should include regular views, magnified views and additional projections of the area of interest.  Another option is all the images of the upper limb and the axial skeleton are acquired with motion correction applications for 45-60 seconds.

       Care must be taken when acquiring images of the hips, pelvis and sometimes the stifles.  If there is significant amount of activity in the urinary bladder a lead bladder blocker should be placed over the bladder to obscure most of the radioactivity. In some cases this does not help the image quality and the horse must be taken back to the stall until the bladder is emptied and returned later to acquire the needed images.


     A patient history sheet should be completed with pertinent information and relative factors of the study and should be submitted with the images for interpretation.




Large field of view detector is lowered into a pit in the floor to acquire images of the distal limbs.  A shield is placed around the medial aspect of the other leg to prevent visualization.


Acquiring solar views of the foot while standing on the small field of view camera mounted in the floor. A lead "apron" is wrapped around the horsed foot to isolate the foot from the rest of the leg. Additional aprons (not shown) are scattered over the field of view to prevent visualization of the upper body.

Anterior view of the front feet and 
fetlocks. Shielding is needed between the front  and hind limbs.

Posterior view of the hind feet and 
fetlocks. Shielding is needed between the hind limbs and the front limbs.

Transverse view of the pelvis.

A slight caudal tilt is applied to the 
detector realigning the bladder away
from the tuber sacrale and the ilium.

Lateral view of the carpus.

The detector should always be positioned
as close to the patient as possible.




Copyright 2001 University of Pennsylvania School of Veterinary Medicine
Faculty Sponsor: Dr. Michael W. Ross
Technologist: Vivian S. Stacy CNMT
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