Nuclear Imaging: SPECT Scans and PET Scans

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Single Photon Emission Computed Tomography or SPECT Scan is a sensitive diagnostic test that may be performed to detect a stress fracture in the spine, spondylosis (spinal osteoarthritis), infection (eg, discitis), tumor in a vertebral body. The test results provide information about blood flow to tissue or an organ.

First, the patient is comfortably positioned on the table. Next, a small amount of radioactive dye called a tracer is injected intravenously. During the test, the SPECT machine's camera rotates about the patient and simultaneously sends pictures to the system's computer. The pictures are converted into 3D images.

Nuclear MedicineThe SPECT machine's camera simultaneously sends pictures to the system's computer. The pictures are converted into 3D images. Photo Source: 123RF.com.Healthy cells and tissues absorb the tracer at a different rate than those that are injured or diseased. A deviation (change) from normal rate of absorption may reveal abnormal metabolic activity that indicates structural changes (eg, vertebral bone tumor growth).

While x-rays, CT scans and MR images (MRI) are helpful in most cases to confirm a diagnosis, these tests only image the structure, not how that structure is functioning on a cellular basis.

PET Scans

Many physicians in fields including cardiology, neurology, and oncology use PET Scanning. A PET image can map the biological function of an organ, can detect subtle metabolic changes, determine if a disease is active or dormant, may be used to determine if a tumor is benign or malignant (malignant tumors have classic metabolic patterns), and may be used to stage certain types of cancer.

A PET Scan is an expensive test. PET facilities require sophisticated computer equipment, a cyclotron, and highly trained specialists. A cyclotron is a machine - an accelerator that propels charged particles (eg, protons) using alternating voltage in a magnetic field.

The test begins with the injection of a radionuclide (tracer) specific to the function/metabolism to be investigated. Within a short period of time, the tracer collects in the specific body area. The patient lies comfortably on the scanning table, while a ring-shaped machine is properly positioned over the target body part. Detectors in the 350-degree ring pick up gamma rays emitted from internal body tissues. The computer analyzes this data to produce cross-sectional images on film and/or a video monitor. The images are often color coded according to the concentration of the tracer.


Women who are pregnant are not able to undergo PET or SPECT Scanning because of the radioactive isotopes used. The amount of radioactive material injected is minimal. It is quickly broken down by the body and passed within 48 hours. Temporarily increasing fluid intake for a day or two following the test can help facilitate elimination of the tracing substance.

Commentary by Rick C. Sasso, MD

Imaging studies are simply a tool for your doctor to use in helping to define the cause of your problem. Rarely will the study by itself make the diagnosis. It must be viewed in the context of the history and physical examination of the patient.

Updated on: 08/06/19
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Rick C. Sasso, MD
Orthopaedic Surgeon
Indiana Spine Group
Carmel, IN
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