What it means
On nuclear medicine and PET images, places where tracer collects stand out, and places with little or none look blank. Photopenic literally means short of light. It describes a spot with less tracer than the tissue around it. This can happen because the tissue there takes up little or no tracer, or because something dense, such as metal, blocks the signal.
When it matters
Many cold spots have simple explanations. Examples are a metal implant, a pacemaker, a fluid-filled cyst or an area treated with radiation. Doctors look more closely when there is no clear cause. A few kinds of bone lesion destroy bone without the repair activity that attracts tracer, so they show as cold. On a thyroid scan, a cold nodule usually leads to an ultrasound, and most turn out to be benign (not cancer).
Questions to ask your doctor
- Is there a clear reason for the cold spot, such as an implant or cyst?
- Does it need a CT, MRI or ultrasound to look at it more closely?
- Was the same area cold on my earlier scans?
