Tc99m HDP may accidentally
be injected or leak into the perivascular space surrounding the jugular vein. A well
seated needle and an adequate amount of time invested in holding off the area after
withdraw of the needle usually prevents this artifact. In some instances the horse
may retract from the initial stick leaving a puncture wound in the jugular vein. If
a reattempt is made to soon and the wound is not sealed from the initial stick, isotope
could leak from this area even though careful efforts were made to seal the area of the
second injection site. Isotope in the perivascular space has been known to trickle
down to the proximal humeral area eliciting an artifact and potential false positive
reading if an anterior posterior view is not acquired. Uptake of isotope by the lymph
nodes is also known to create intense focal artifacts in the region.
Significant Tc99m remaining in the perivascular space alters the target to background
ratio in neck and shoulder images and may be non diagnostic.