PET/CT Scan

Information for Referring Physicians

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What is Positron Emission Tomography?

Positron emission tomography (PET) is a noninvasive diagnostic imaging procedure that assesses the level of metabolic activity and blood flow in various organ systems of the human body. A special camera called a PET scanner is used to produce cross-sectional or tomographic images, which are obtained from positron-emitting radioactive substances (radiopharmaceuticals or tracers) such as 2-[F-18] Fluoro-D-Glucose (FDG), that are administered intravenously to the patient.

Why is PET different?

PET is different from other types of imaging modalities such as X-ray, CT, MRI and ultrasound because PET detects metabolic or 'functional' changes in the body while the other modalities primarily see anatomic or 'structural' changes.

This is important because disease always causes metabolic changes prior to anatomic changes and this can contribute to possible earlier detection.

Many manufactures are now making combined PET and CT scanners (known as PET/CT) like we have here at Lahey Clinic. This hybrid technology allows the acquisition of functional and structural data to be obtained in one scan.

What are some common uses for PET?

PET is considered particularly effective in identifying whether cancer is present or not (diagnosis), if it has spread (staging) if it is responding to treatment, and if a person is cancer free after treatment (restaging). PET is also used to assist in the initial treatment planning and to monitor treatment effectiveness.

Cancers for which PET is considered particularly effective include: lung; head and neck; colorectal; esophageal; lymphoma; melanoma; breast; thyroid; cervical; pancreatic; and brain as well as other less-frequently occurring cancers.

PET is also used in assessing cardiovascular disease and evaluating neurological conditions such as dementia and Alzheimer's disease, epilepsy and motor disorders such as Parkinson's disease.

What can I expect?

Patients undergoing a PET/CT scan will first have the procedure explained to them, followed by a series of screening questions that the technologist will ask.

An IV will be placed in a vein in the arm and an injection of FDG will be administered. There are no side effects to the injection. The patient will be asked to wait from 60 to 90 minutes for the F-18 FDG to distribute in the body. Movement, reading, and talking may be restricted during this time, as this will affect the pattern of F-18 FDG uptake. The patient will be asked to void prior to the start of the scan.

During a PET/CT scan the patient will be required to lay on his or her back, remain still and breathe normally during the scan.

First, two brief CT scans (1 minute each) will be taken with the CT part of the scanner. During these scans the table will move quickly in and out of the scanner.

Next, a 20 to 30 minute scan will be taken with the PET part of the scanner. The table moves slowly during this scan.

Per your physician's request, a more elaborate CT scan may also be performed to provide more extensive diagnostic information.

The technologist will then have the physician review the images to determine if further scanning is needed.

Do I need to do anything to prepare?

• Because the uptake of the FDG relies on normal blood glucose levels, preparation for a PET/CT scan requires that you do not eat or drink for at least four (4) hours before your scan, except for water only. Also, you must avoid gum, sucking on hard candy or putting anything in your mouth containing sugar for at least four (4) hours prior to your scan.
  
• You may be asked to follow a special diet before your scan.
  
  
• Please inform us ahead of time if you are diabetic, and we will discuss further preparation with you.
  
  
• You will be asked to refrain from exercise for 48 hours prior to your scan as exercise interferes with the uptake of the FDG.
  
  
• You may take all prescribed medications on the day of your exam, unless instructed otherwise by the ordering physician.
  
  
• Drink 48 to 64 oz. of water the day before the exam, and 16 to 24 oz. the day of the exam to ensure hydration.
  
  
• Please wear comfortable clothing with no zippers or snaps.
  
  
• Also, please let us know if you might be pregnant or are currently breastfeeding.
  
  
• If you are having a cardiac PET/CT you must not ingest anything containing caffeine for at least twelve (12) hours prior to your scan (i.e. regular coffee, decaf coffee, tea, soda, chocolate).
  
  
• Also, you must not take any medications containing theophylline for at least twenty- four (24) hours prior to your scan. Please call your physician if you are not sure.
  
  
• Your Lahey health care provider will discuss your preparation with you in detail and will answer any questions that you may have.
  
  

Is it Safe?

Yes. Most of the radioactivity from the injection passes out of the body in the urine and stool.

Your Lahey health care provider will talk to you in detail about what you can expect before, during and after your PET/CT scan and will answer any other questions that you may have.

Click here to see Sample PET/CT Images