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Positron-emission tomography (PET) scans give a sharp 3-D image of the spine. A short-acting radioactive dye is injected into the blood stream. After waiting for 30 minutes to two hours, enough of the dye has accumulated in the tissues to scan the body.
Sometimes the dye is called a tracer. It tends to gather at areas where tissue is active and under repair such as an fracture site or area of inflammation. PET scans are often used to look for bone metastases from cancer. They are also widely used to map out the heart or brain.
Research has been done at Harvard Medical School using PET scans to diagnose children with low back pain. An older dye used back in the 1960s (Fluorine-18 sodium fluoride or 18F NaF) was used as the tracer.
The advantages of this dye are that it has smaller particles that cross into the blood vessels faster and easier. The result is that the scan can be started 30 minutes after injection instead of the usual three- to four-hour delay.
This is a definite plus when working with children because they have to hold still for the scan. Any movement (even breathing) can cause what are called artifacts in the image making diagnosis more difficult.
But a PET scan may not be needed if the X-ray is sufficient. The physician also relies on the patient's history and physical exam to suggest when further testing is needed. Nuclear scanning using positron-emission tomography is expensive and not always available, so it's not used routinely.
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