PET/CT

What is PET/CT and How Does It Work?

PET is an acronym for positron emission tomography, and CT is an acronym for computed tomography. PET scans work by using a special form of sugar called 18-FDG, or fluorodeoxyglucose. 18-FDG is a radioactive form of sugar that can be detected by a PET scanner. The administered levels of radioactivity are minimal and safe. The tracer stays in your body for only a short period of time and has no known side effects.

When cells are involved with tumor or other inflammatory processes, they tend to use more glucose than normal tissue. The PET scanner can detect where the 18-FDG localizes to tissue. When we combine a PET scan and a CT scan at the same time, we can be more precise in localizing exactly where the 18-FDG accumulates. We can also use the CT scan to determine if an abnormality tends to collect unusual amounts of FDG.

The purpose of the study is to determine whether abnormal tissue represents tumor or a benign, nonmalignant process. If you have already been diagnosed with cancer and have undergone therapy for the tumor, PET/CT can determine how the tumor is responding to the therapy, as well as whether the tumor has recurred.

Why Am I Getting a PET/CT Scan?

PET scans have found many applications in the medical field, including use in patients with cancer, neurologic disorders, and cardiovascular disease. A PET scan has been shown to be particularly useful in oncology patients because of its capability to detect and stage primary cancers, as well as metastatic disease.

PET can help physicians differentiate between benign and malignant lesions, especially when patients have nodules in their lungs. In patients who have already undergone therapy such as surgery or radiation treatment, PET can help distinguish between changes from these therapies versus tumor recurrence.

PET is also being used to evaluate a patient's response to current treatment. Changes in the PET scan reflect changes on a molecular level, and can tell your doctor how effective your therapy is working - even before changes would be seen on conventional imaging studies such as x-ray or CT scans.

What Does PET/CT Equipment Look Like?

If you have had a CT scan, you will find that a PET/CT scanner looks very similar. Patients are placed on a flat table that moves through a doughnut-shaped machine, which acquires both sets of images. Note that the opening for a PET/CT scanner is not as long as those used for MRIs, and patients seldom have any troubles if they suffer from claustrophobia.

How Can I Prepare for the Exam?

You need to inform us of several important issues prior to arriving for your PET scan, as these can affect your study. Please inform us if any of these conditions apply to you:

• You are diabetic. High serum blood-sugar levels (>200) will diminish the accuracy of your PET scan.
• You have had recent surgery.
• You may be pregnant or if you are currently nursing.
• You cannot lie still on a table for approximately 30 minutes.
• If you have difficult veins and have a port that can be accessed.

Your diet is also important prior to the exam. We recommend that you follow a low-carbohydrate, high-protein, high-fat diet 12 hours before arriving for your PET scan.

You should fast at least six hours before the exam. This includes no hard candies, no coffee with cream and sugar, and no gum. Being well hydrated helps with finding a vein for the injection so patient's with difficult veins should drink water before coming to their appointment.

You should also avoid any strenuous exercise, such as running, the day before the exam.

Jewelry is not recommended because it will have to be removed

What Can I Expect the Day of the Exam?

You should allow about three hours total for your PET/CT scan to be performed. It is important to arrive on time due to the FDG injection at the scheduled time for the optimal scan. It is also very important that you have fasted at least six hours before the exam. This includes any candies, gum, sugar or cream in coffee, as eating these may adversely affect your scan. You should take all your prescribed medications with water unless told otherwise.

Wear warm, comfortable clothing, such as a sweat suit on the day of the exam, and avoid any clothing that may contain metal, such as zippers or snaps. You will be able to wear your glasses or dentures.

When you come to the PET/CT suite for your exam, you will register and then be asked some important questions regarding your medical history prior to undergoing the scan. It is important that you provide accurate information on the following procedures:

• Have you had any biopsies recently? If so, what part of your body was biopsied?
• Have you undergone any recent surgeries? If so, what kind of surgery and when was it performed?
• Are you receiving chemotherapy? When was your last administration?
• Have you undergone radiation therapy? What part of your body was treated and when?
• Have you had any recent infections?
• Do you have any copies of previous CT, MRI, or PET scans? If so, it is important that you bring them with you so comparisons may be made.

You will then have an IV placed in your arm for the administration of the 18-FDG. Your blood glucose level will also be checked.

The 18-FDG is radioactive, and because of this, we want to minimize the exposure to others around you. Family members cannot be with you from the time the 18-FDG has been administered until after the exam.

After the 18-FDG has been injected, you will be placed in a quiet room until it is time for your exam. This is typically 45 minutes to 1 ½ hours. It is very important during this time that you rest quietly and do nothing strenuous, including no talking, gum chewing, or even reading.

Once you are ready for your PET/CT scan, you will lie on your back on a table with your arms above your head. The table will slowly move through the gantry while the data for the images is collected. You will be on the table for approximately 30 minutes for the standard exam. Additional views, if needed, take about 15 minutes.

After the exam, the data is processed and the images are interpreted by a radiologist. A report is dictated, which is then sent to your referring physician.

What Happens After the Exam?

After the exam is completed, you may resume your normal routine, including diet and medications. The dose of radiation you received for the exam requires no special precautions.