Nebraska Health Imaging

PET INTRODUCTION
Positron Emission Tomography (or P.E.T. scan as it is commonly referred) is an imaging technique that relies on changes in tissue biochemistry. Most well known conventional medical imaging techniques, such as X ray, ultrasound, CT and MRI, depend on changes in the anatomy or structure of organs. P.E.T. is able to image changes in cells and tissues often before there are changes in anatomy. Biologically active natural compounds such as oxygen, carbon and glucose labeled with radioactive isotopes are given intravenously and react in the body identically to their non radioactive counterparts. The normal and abnormal activity (distribution) can be imaged with a P.E.T. scanner. The tracer amounts used do not have a pharmacological effect and there are no known biological or radiation hazards associated with P.E.T. imaging.

The most commonly used radiopharmaceutical in P.E.T. imaging is 18F-fluorodeoxy-glucose, or simply FDG. This compound is radioactive sugar. Glucose is metabolized in cancer tissues to a greater extent than in normal tissues; consequently cancerous tissues can be seen on the FDG-P.E.T. scan. This unique information can have a profound impact on treatment decisions (e.g., Is that new mass cancerous and has it spread?).Most FDG-P.E.T. imaging today is done to evaluate cancer patients. Through the efforts of a number of nuclear medicine societies, the FDA has approved FDG-P.E.T imaging for several cancer related problems. A partial list of these cancer-related problems are presented below:

evaluation of solitary lung nodules for the presence of cancer.
preoperative staging and re-staging of some lung cancers.
staging and re-staging of lymphomas.
staging and re-staging of malignant melanomas (skin cancers) prior to surgery.
staging and re-staging of colon cancer.
staging and re-staging of breast cancer.staging of cervical cancer staging and restaging of esophageal cancer staging and restaging of head and neck cancer staging and restaging thyroid cancer Other cancers, such as liver, pancreas, and soft tissue sarcomas, can be detected and followed with FDG-P.E.T.

A number of cost effectiveness analyses have shown that thousands of dollars can be saved without loss of life expectancy when P.E.T. is used in the evaluation of cancer patients. P.E.T. may result in the earlier diagnosis of cancer. Unnecessary procedures and surgeries may be avoided if the patient is found to have more extensive disease than expected. Treatment that is more appropriate or even life saving may be offered to the patient shown to have disease that is less advanced than expected. Costly batteries of tests ordinarily required for staging might be reduced to a single P.E.T. scan.

How is a PET Scan Performed?
PET scans can be done on an outpatient basis. It is also possible that some hospital inpatients may undergo a PET examination for certain conditions. Although each PET center may have specific protocols in place, LifeScan Chicago uses the following procedure:

In What Conditions are PET Scans Helpful?
Oncology (Tumors): The largest growth area of PET is in the area of tumor evaluation. The information PET provides on the active status of tumors has proven extremely helpful for determining methods of therapy or surgery. Scans performed after treatment will demonstrate the effectiveness of that treatment on the tumor.

Neurology: Many patients with epilepsy do not respond well to drug therapy. When surgical intervention is required, PET can be helpful in locating the exact area of the brain causing the seizures. Imaging the brain with radioactive glucose has also been found useful in diagnosing Alzheimer's Disease and other conditions that may cause memory loss or mental deterioration.
Cardiology: PET is very helpful in determining whether coronary bypass surgery will be beneficial. The information is important in selecting those patients who are considered good candidates for this type of surgery.

How PET Differs From CT/MRI
P.E.T. is extremely sensitive and effective in detecting recurrent cancer, especially in patients with positive and rising tumor markers who are otherwise asymptomatic. This information is very practical and enables the physician and patient to make cost effective treatment decisions, such as avoiding unnecessary surgery, directing more complete surgery, or allowing surgery when it had seemed contraindicated.

In patients who have received chemotherapy, it is difficult to demonstrate early shrinkage of the cancer when using CT or MRI to monitor tumor response, even when the treatment is effective in controlling or stopping tumor growth. In contrast, P.E.T. can often show decreased or even absent tumor metabolism after only one or two cycles of chemotherapy. P.E.T. can determine ineffective therapy early on, saving money on expensive treatments and morbidity, but can also save precious time otherwise wasted while waiting for the desired response. With this information, early modification of treatment and selection of a new therapeutic regimen can occur. A P.E.T. scan�s ability to detect treatment response cannot be matched by CT or MRI.

CT, MRI and P.E.T. imaging all provide a non invasive way to see the inner workings of the UNMC Physiciansn body. P.E.T. however, does not have to wait for changes in the anatomical structure of the patient to determine staging, recurrence, therapy response and differentiation of scar and residual disease.

P.E.T. can determine the nature of solitary pulmonary nodules that are smaller than 4 cm in size and this is very useful for preoperative staging. CT will show a lesion but will not determine whether it is benign or malignant. CT is also less accurate in finding metastases, and cannot differentiate malignancy from scar or other tissue in checking recurrence of colon cancer (P.E.T. sensitivity is 96% vs. CT sensitivity of 53%.)

In determining the extent of malignant melanoma (staging), P.E.T. is more sensitive and accurate than CT (P.E.T. 96% vs. CT 55%). P.E.T. is also more sensitive and specific than CT for staging lymphoma. CT cannot always differentiate benign from malignant tissue in re-staging and surveillance of lymphoma patients. In initial staging of breast cancer, P.E.T. evaluation of the axilla has a sensitivity and specificity of 81% and 100% in an area where CT is not very useful in differentiating between benign and malignant tissue. In re-staging ovarian cancer after chemotherapy treatment, P.E.T. sensitivity is 94% vs. CT 73%, and the specificity of P.E.T. is 100% vs. CT 38%.

The preparation for the test will vary depending on the reason for the P.E.T. scan. Patients are asked to fast from food for 4-6 hours before their exam. Patients need to be well hydrated, drinking plenty of water before their exam. Patients may take medications unless otherwise instructed by their physician. Patients should wear comfortable clothing.

Diabetic patients must follow these additional instructions prior to the exam to ensure an acceptable blood sugar level (blood sugar must be under 200 to proceed with the exam):

Diabetic patient--controlled by diet:

Exam should be scheduled first thing in the morning
Patient must begin fasting the night before-please contact Nebraska Health Imaging for instructions

Diabetic patient--controlled by oral medication (Glucophage or Glucovance):

Patient may take oral medications as scheduled
Patient must fast the night before except for water

Diabetic patient--controlled by insulin:

Patient may take insulin with a light meal
Patient must be scheduled at least 4 hours after their insulin injection

If you have any questions regarding these instructions, please don't hesitate to contact Nebraska Health Imaging prior to your exam time to ensure that rescheduling your appointment won't be necessary.

Your doctor has referred you for a PET scan and there are several guidelines you will be asked to follow. You will be asked to not eat or drink anything expect water and medications for six hours prior your scan. Other instructions include:

Please plan to be on time for your scan appointment.
Please allow 3 hours for the PET examination.
It must be 3 ~ 6 weeks since your radiation and/or surgery.
Women who are pregnant must not be scanned, and nursing mothers should ask for specific instructions.
Diabetics should ask for specific instructions.
You should wear comfortable clothing.
You should drink at least 8 glasses of water the day before the scan.

Before the scan, a small IV will be placed in a vein that will be used to check your blood sugar level and to inject the radioactive substance (FDG) for the test. This line remains in place until the scan is completed.

After the radioactive dose (FDG) injection, up to an hour will elapse before the scan begins. It is important to lie quietly without talking or moving during this period. You will also be asked to lie still during the scan, which usually lasts about 60 minutes. If you are having more than one scan to evaluate different areas of your body, the procedure may take up to two hours to complete. You should plan to be at the Center for about 3 hours overall for the entire process.

Most of the FDG collects in your bladder, so it is important that you urinate shortly after the scan is completed. Drink plenty of extra fluids for the rest of the day and urinate frequently to help eliminate the substance from your system as quickly as possible. The radioactive substance used in the study has a very short half life, and most of it is gone within the first four to eight hours after the injection.

Following the scan, the information is processed and filmed by a technologist and then interpreted by a trained, board certified nuclear medicine physician. A report is then prepared and sent directly to the physician who ordered the test, who will discuss the results with you.

FREQUENTLY ASKED QUESTIONS
Why do I need this exam?
The information provided by your PET scan can have a major impact on how your physician treats your disease. For example, a PET scan can show whether or not a tumor is malignant and whether it has spread. This information will help your physician decide the best approach to treatment. A PET scan can also monitor your progress so that if you are not responding as well as expected, your treatment can be changed to one that is more aggressive or effective.

How accurate is a PET scan?
PET is very accurate in detecting the presence of many different types of cancer cells. It can show whether or not a tumor is malignant and if it has spread to other areas in the body. It has been shown to be highly accurate in evaluating lymphoma, melanoma, ovarian cancer, and brain cancer, esophageal cancer, cancers of the head and neck, and recurrent breast cancer. It is also the most accurate way currently available to detect the spread of colon and lung cancer.

How long is the procedure?
A PET scan takes approximately 2 ~ 3 hours from start to finish. The actual length of time varies according to the patient's diagnosis.

What does the PET scanner look like?
The equipment looks very similar to a CT scanner: a donut shaped machine that is open on both ends. When you are ready for scanning, you will lie down on your back on a comfortable table that moves slowly through the opening. The camera is very quiet as it acquires the information it needs to generate the images. You will be asked to lie still while the images are being taken.

What if I am claustrophobic?
Most patients find the PET scanner very tolerable, even if they are claustrophobic. If this is still a concern for you, you are welcome to ask your referring physician for an anti anxiety prescription to take prior to having the scan performed.

May I bring a family member or friend with me to the test?
Yes. However, because you will be radioactive for a short while after your injection, family members and friends will not be allowed to be with you during that time. They are more than welcome to wait in our waiting area or they may leave and come back once your test is finished. Because the radioactive tracer has such a short half life, it doesn�t stay in your system for very long, and it will be safe to interact with other people once your test is finished.

What are the risks associated with PET?
A PET scan is similar to other imaging modalities such as CT, MRI, and other nuclear medicine procedures. Although the type of radiation is different, the amount a patient receives is roughly equivalent to a couple of chest X rays.

Is there anything I need to do after the scan?
You may leave as soon as your scan is complete and, unless otherwise instructed by your physician, you may eat and drink immediately. In fact, you will be urged to drink more than normal amounts of water to increase urination that will help flush your system of the radioactive substance injected for the scan.

How-and When-do I find out the results?
A complete report will be prepared by the technologist and interpreted by a board certified nuclear medicine physician. This will be sent as soon as possible to your physician, who will then review the results with you and answer any questions you may have.

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