Thompson Cancer Survival Center PET Imaging

radiologist looking at computer screens while another radiologist preps a patient for a scan

What is a PET scan?

A PET (Positron Emission Tomography) scan is an imaging test that shows how your tissues and organs are functioning. The PET scanner takes pictures that show the activity in your cells. This exam uses a special tracer that helps your physician identify areas of concern to discuss with you. A PET scan is useful for your doctor because it can detect cancer, see if cancer has spread, verify if a treatment is working, and see if there has been a recurrence. This will help you and your physician make the best treatment decisions possible.

A PET scan vs. a CT scan

PET scan (Positron Emission Tomography) and CT scan (Computed Tomography) are both medical imaging techniques that are used to diagnose and monitor various medical conditions. However, there are some key differences between the two.

A PET scan uses radioactive tracers to detect metabolic activity in cells and tissues, while a CT scan uses X-rays to create detailed images of the inside of the body. PET scans are particularly useful for detecting and monitoring cancer, heart disease, and neurological disorders, as they can show the metabolic activity of cells and tissues. CT scans, on the other hand, are more useful for detecting and diagnosing structural abnormalities such as tumors, bone fractures, and internal bleeding.

How to prepare for your PET scan:

  1. Beginning, 24 hours before your PET appointment, please follow a low-carb diet. (No pasta, bread, rice, potatoes, cereal, sugar, etc.) (*Specific guidance below)
  2. Four hours before your PET appointment, do not eat or drink ANYTHING BUT PLAIN WATER. (No sodas, teas, coffee, gum, candies, breath mints, cough drops, etc.)
  3. If you are diabetic, take insulin and oral medications more than 4 hours before your appointment.
  4. You may take your medications before the test, but only with plain, unflavored water. No regular or decaffeinated tea or coffee.
  5. Please wear comfortable clothes, with an elastic waist if possible. 

Following this preparation ensures that your blood sugar levels are within a range that the PET scan can be completed (50-200 mg/dL).  If your blood sugar is outside this range we will have to reschedule your appointment.

What to expect at your PET Scan appointment:

Please, arrive at your appointment at the requested time and complete your check-in paperwork.

A PET team member will take you to a private room to administer the PET tracer (the substance used in the scan) through your IV.

You will wait in a private room with a recliner for 1 hour to allow the tracer to circulate through your system.

A PET Technologist will take you to the imaging room where you will lay on your back on the PET scan table with your arms above your head. We will place a pillow under your knees for comfort. The scan takes 12 – 24 minutes. We will be able to see and hear you at all times.

After your scan is complete, you are finished and can go about your day normally.

We recommend bringing a snack and drink to have after your scan is finished.

Pre-PET Scan Nutrition Guideline:

A low-carbohydrate diet is important before a PET scan as high-carbohydrate diets can interfere with the accuracy of the scan. 

During a PET scan, a radioactive tracer is used to identify cancer cells, but glucose can also be taken up by cells, affecting the scan’s accuracy. By reducing glucose levels through a low-carbohydrate diet, the tracer is more likely to be taken up by cancer cells, making it easier to detect them. A low-carbohydrate diet can also reduce the risk of false positive results, where non-cancerous cells take up the tracer, leading to a misdiagnosis. 

To optimize the accuracy of the scan, it is recommended that patients follow a low-carbohydrate diet for at least 24-48 hours before the PET scan.

Low Carb Diet Suggestions

Foods to AVOID:

Sugar-sweetened beverages

Fast food

Bread, pasta, Rice Cake, cookies, candy

Foods to Enjoy:

Almonds and walnuts




Meat (chicken, pork, beef, lamb)

Non-starchy vegetables:

(Spinach, asparagus, cucumber, green bell pepper, zucchini, cabbage, salad greens, eggplant)

Low Carb Snack Ideas:

• 3 celery sticks + 1 tablespoon peanut butter
• 5 cherry tomatoes + 1 tablespoon ranch dressing
• 1 cup cucumber slices + 1 tablespoon ranch dressing
• 1 cup salad greens + 1/2 cup diced cucumber + drizzle of vinegar and oil
• 1 hard-boiled egg
• 5 baby carrots
• 1 string cheese stick
• 3/4 cup light popcorn
• 10 goldfish crackers
• 1 cup sugar-free gelatin
• 1 frozen sugar-free popsicle

Thompson PET Imaging Locations

Downtown Knoxville
a department of Fort Sanders Regional
1915 White Avenue
Knoxville, TN 37916

*For GPS to the GARAGE use: 1900 Clinch Ave

West Knoxville
a department of Parkwest Medical Center
9711 Sherrill Boulevard
Knoxville, TN 37932

a department of LeConte Medical Center
710 Middle Creek Road
Sevierville, TN 37862

Questions or Appointment Scheduling

If you have any questions about your PET scan appointment, please call Thompson PET scheduling at 865-331-1492.

Thompson PET Imaging Centers

Downtown Knoxville
a department of Fort Sanders Regional Medical Center
1901 Clinch Avenue
Knoxville, TN 37916

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