Positron Emission Tomography (PET)

Uses for PET in brain imaging

• Brain tumor imaging
• Detection of Alzheimer's disease
• Determination of epileptic focus
• Assessment of viable areas for experimental tissue transplantation in Parkinson's disease and Huntington's disease
• Determination of normal from abnormal areas of brain metabolism
• Determination of normal from abnormal areas of brain perfusion

How are neurological P.E.T. studies performed?

A brain scan is done to aid in the diagnoses of seizures, dementia and tumor versus radiation damage from treatment. If the scan is required for the location of a seizure focus, the patient must be seizure free for 12 hours. The technologist will give a small, safe quantity of a radioactive form of glucose by IV injection. The brain uses glucose as its only metabolic fuel. Since this is a radioactive form of glucose, brain cells actively collect or take up the glucose. The patient reclines on a bed for the IV injection and "uptake" time. PET scanning begins approximately 40 minutes after injection. The patient lies on the imaging bed and the patient's head is positioned comfortably for scanning. The distribution of the radiotracer is read by a nuclear medicine physician. Results will be made available to the patient's referring physician.

What the patient needs to know

• Nothing by mouth for 4 hours before appointment except water with medications
• Patient will need IV
• Scanning time is 1-2 hours
• Total time in PET Imaging Center is 2-3 hours
• No after effects from injection or imaging
• May return to normal activity immediately after PET scan is completed
• PET nurse will call patient the day before the scan to answer questions concerning procedure

Uses for PET in evaluation of myocardial viability

• Determine the extent of heart muscle metabolism
• Evaluate the matching of metabolism and flow in the myocardium

How are myocardial viability PET studies performed?

PET can determine the extent of heart muscle metabolism. The technologist will give a small, safe quantity of a radiotracer by IV injection. Since the heart muscle or myocardium will utilize glucose (or sugar), the PET study is used to locate areas of viable myocardium. The patient is comfortably positioned on the imaging bed in the PET scanner approximately 40 minutes after injection. The scan typically takes between 30-40 minutes, to acquire, but can vary between individual patients.

What the patient needs to know

• Nothing by mouth for 4 hours before appointment except water with medication
• Patient will need IV
• Scanning time is 1-2 hours
• Total time in PET Imaging Center is 2-3 hours
• No after effects from injection or imaging
• May return to normal activity immediately after PET scan is completed
• PET nurse will call patient the day before the scan to answer questions concerning procedure
• Diabetic patients need special preparation prior to imaging. Ideal blood glucose is less than 150 mg/dl. on arrival in PET Imaging Center.

Patient considerations, including when PET is used for cancer studies

Upon arrival to the PET Imaging Center the patient is interviewed for pertinent medical history and discussion of the PET procedure. Dates of last surgery or biopsy, last radiation date, last chemotherapy and previous PET scans are attached to the dictation packet.

Any relevant medical history is brought to the attention of the Nuclear Medicine Physician. Any possibility of pregnancy and/or breast feeding must be ruled out prior to administration of the radiopharmaceutical. In rare circumstances, a PET study may be contemplated for a pregnant patient, but the benefit to the patient must outweigh the potential risk to the fetus. The justification for any radiopharmaceutical administration to a pregnant woman must be thoroughly documented in the patient's medical record. A breast-feeding woman is educated with respect to potential risks to her infant and advised on the amount of time she should abstain from breastfeeding. This physician/patient interaction will be documented in the medical record.

The patient voids if not catheterized. Allergies and history of diabetes or elevated blood sugar are discussed. The patient's level of pain is evaluated.

A PET staff nurse measures height, weight and blood glucose via Accucheck. This information is recorded in the nurses' notes and on the Physician Order for Radiologic/Nuclear Medicine Consulation/Request for Procedure Form, referred to as the "requisition." The Nuclear Medicine physician is notified when the blood glucose value exceeds 150 mg/dl. The study is cancelled or will proceed according to the decision made by the Nuclear Medicine physician.

Patients arriving for PET Imaging with blood glucose levels between 150mg/dl and 200 mg/dl may be given Regular Insulin IV at least one hour before injection of 18F-FDG per order of Nuclear Medicine Physician The recommended dose of Regular Insulin is .05 units/kg. This dose may need to be adjusted depending on the patient's diabetic medication history (Insulin, glyberide, etc.), food intake, and/or weight. The blood glucose level should drop below 150 mg/dl before injection of the 18F-FDG. The PET schedule must permit making this adjustment.

An intravenous (IV) catheter is placed in an upper extremity vein preferably the antecubital vein for continuity. In patients with a high likelihood of axillary node involvement (e.g., breast cancer, melanoma, lymphoma), all 18F-FDG injections will be made via a catheter in the contra-lateral arm to the primary cancer. If bilateral disease is present and the patient is not a diabetic, the injection will be made via a foot or ankle vein. In all cases where the injection site is questioned, the Nuclear Medicine physician will be consulted prior to injection.

An indwelling or previously placed line such as a Hickman line is not routinely used unless access to peripheral sights is not possible. On some occasions, a small cannula butterfly is used for 18F-FDG injections.

Drainage of radioactivity from the bladder, in most cases, is necessary when the pelvis is imaged. A Foley catheter is placed by a Registered Nurse.

The PET technologist reviews the study with the patient. A careful explanation is given to the patient. All female patients are questioned if there is any possibility they are pregnant or if they are presently lactating. The patients are all given time to ask questions concerning the study before the radiopharmaceutical is administered. The study instruction will include:

• The patient is instructed to lie quietly for at least the first twenty minutes following the injection. During this period as much as 95% of the FDG dose is taken up into metabolically active tissues. The patient should refrain from excessive moving, to limit swallowing, and even avoid talking. Seemingly, inconsequential movements of the jaw and tongue may influence the outcome of the study. The total waiting time before imaging starts is 90 minutes.
• The PET/CT scan involves a CT scout image and a regular CT scan this is followed by the PET study. Depending on the area of interest, total imaging time (barring unforeseen technical difficulties) is less than 30 minutes. The patient should be finished with imaging in about 2 hours from time of injection.

The IV catheter is not removed until after the study and will remain in if there are other studies pending following PET. The catheter is left in place for pain medication or sedation if needed during imaging. The 3-way stopcock may be a sight where activity is trapped during administration; it is removed following administration and replaced with a reflux valve. The activity present in the syringe, the 3-way stopcock, and IV tubing are assayed and any residual activity detected is used to determine the actual administered activity. If infiltration of the dose is suspected the injection site is surveyed with an ion chamber to get an estimate of the amount not administered

Patients are informed of their ability to communicate with a Nuclear Medicine Technologist by speaking inside the camera. Microphones inside the camera will convey the patient needs to P.E.T. personnel

After the study is acquired

• A careful check of the data is made to assure that the study is complete.
• The IV is removed if no further studies following PET require IV access.
• Any markings put on the patient's skin are taken off.
• The catheter placed for bladder irrigation is removed
• The patient is removed from the Biograph scanner

Post-study policies and instructions

• Patient is offered juice or water before exiting the imaging room
• The patient is escorted to the restroom.
• The patient is instructed to hydrate well and void frequently for the next few hours.
• Home care instructions for patients who have had a Foley catheter are reviewed and signed by the patient and by the RN giving the information.
• Sedated patients are evaluated by an RN and will meet discharge criteria follwing UIHC Sedation Guidelines.

Last Reviewed 2005

Source: University of Iowa Department of Radiology

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.