PET - CT
(Positron Emission Computed Tomography)
Stockton MRI & Molecular Imaging

Information for Patients

• What is PET?
• What is PET-CT?
• What is FDG?
• What information can a PET-CT scan provide to my doctor?
• How do I prepare for my PET-CT scan?
• What should I expect on the day of my PET-CT scan?
• What if I have more questions?

Information for Referring Physicians

• Current Medicare Coverage Guidelines for PET-CT scans
• Patient Preparation for a PET-CT scan
• Post Therapy Considerations Regarding PET-CT
• Alzheimer's Disease and PET-CT
• Myocardial Viability and PET-CT
  

INFORMATION FOR PATIENTS

What is PET?

Positron Emission Tomography, or PET, is a type of medical imaging test that provides your doctor with information about specific physiologic functions within your body. Patients who will undergo a PET scan will first be injected with a small amount of a specific radioactive tracer that emits charged subatomic particles called positrons. The interactions of these positrons in the body are detected by the scanner and allow an image to be recorded and processed in a computer. These images are then interpreted by an experienced physician. The type of radioactive tracer used depends on which physiologic function needs to be evaluated. The most common radiotracer in use today is FDG, which is helpful in evaluating metabolic activity throughout your body.

A normal FDG-PET scan.

What is PET - CT?

PET-CT is the combination of a Positron Emission Tomography (PET) scanner and a Computed Tomography (CT) scanner. A CT scan uses x-rays to create images that provide anatomic structural information about the organs within your body. Combining a CT scan with a PET scan improves overall image quality as well as the accuracy of the test. Stockton MRI & Molecular Imaging uses the GE Discovery ST PET-CT system.

Figure A: the CT image of a PET-CT scan. Figure B: the PET image of a PET-CT scan. Figure C: the fused (combined) PET and CT image.

What is FDG?

FDG is basically a radioactive sugar. FDG refers to Fluorine-18 FluoroDeoxyGlucose, the most common radiotracer used in clinical PET-CT imaging today. An FDG molecule consists of two parts - the radioactive component Fluorine-18, and glucose, the sugar component that is recognized by your body. Fluorine-18 is a radionuclide that emits positrons, and therefore can be detected by a PET-CT scanner. Prior to your PET-CT scan, a small amount of FDG is injected intravenously into your body. Because it is made from a sugar molecule, FDG distributes throughout your body based on the metabolic activity of the various organs and tissues. Fluorine-18 decays quickly, and within a few hours is no longer significantly radioactive. For this same reason, it is very important that you arrive for your scan at your scheduled appointment time.

What information can a PET-CT scan provide to my doctor?

Cancer (Oncology PET-CT)

Evaluation of cancers is the most common use of PET-CT scans today. Using FDG, a PET-CT scan provides information about the distribution of metabolic activity in various parts of your body. Certain cancer tissue (but not all) is known to be more metabolically in comparison to normal body tissue. Ongoing worldwide research has shown PET-CT to be useful in the evaluation of lung cancer, colon cancer, lymphoma, melanoma, breast cancer, esophageal cancer, cervical cancer, and certain thyroid and other neck cancers. For other types of cancer, research is continuing every day to help determine how PET-CT can provide useful information to your doctor.. In most cases (but not all), a PET-CT scan can be used to provide helpful diagnostic information when cancer is not yet certain. More commonly, PET-CT scans are used when cancer is already diagnosed to determine the extent or spread (metastasis) of the cancer (also known as staging the cancer). After a patient has received treatment for the cancer, a PET-CT scan is useful in monitoring response to treatment, or evaluation for possible further progression or recurrence of the cancer over time (also known as re-staging the cancer).

PET-CT scan of a patient with right lung cancer.

Brain (Neurologic PET-CT)

Your brain uses glucose, a sugar, for its energy. Using FDG, which is a radiolabelled glucose, a PET-CT scan can help to identify the regions of your brain that have more or less metabolic activity. In certain patients who have seziures, and surgery or other treatment is being considered, a brain PET-CT scan can be helpful in localizing the parts of the brain involved. Timing of the scan in relation to the seizure activity is important - metabolic activity in the brain will be altered during a seizure and between seizures. Another exciting use of brain PET-CT is in the evaluation of patients with signs or symptoms of dementia (such as changes in memory, language function, personality, or behavior), especially when your doctor is considering Alzheimer's disease as a possible diagnosis. Brain PET-CT scans of patients with certain types of dementias are known to show common patterns of metabolic activity within the cerebral cortex. Evaluation of patients for Alzheimer's diease with a brain PET-CT scan can help to identify which patients may benefit from treatment intended to slow progression of the disease, with the potential to provide benficial cost savings in the long run. [more information]

PET-CT scan of the brain of an elderly patient.

Heart (Cardiac PET-CT)

If you have heart disease and a history of prior myocardial infarction, the injury to the heart muscles can cause the overall function of your heart to decrease. In general, your primary physician, cardiologist, and/or cardiothoracic surgeon always weigh the potential risks versus the expected benefits for any possible therapy being considered for you. In selected cases, information about the metabolic activity of your heart muscles can help your physicians decide if certain therapy, including surgery, has the potential to improve the functionality of your heart. Using FDG, a PET-CT scan can help determine which areas of your heart muscle are viable. [more information]

Images from a FDG-PET scan of the heart.

How do I prepare for my PET-CT scan?

Do NOT eat or drink for at least 6 hours prior to your scheduled appointment. You may drink only water and your medications if they can be tolerated on an empty stomach. Other foods and drinks will affect the distribution of FDG in your body and will decrease the accuracy of your test.

We will contact you prior to the day of your test for further detailed instructions on how to prepare for your scan. These include additional steps you can take in order to make the test more optimal - including following a limited carbohydrate diet 48 hours prior to your test, and avoiding strenuous exercise the day before your test.

Please arrive at your scheduled appointment time. The radiotracer dose (FDG) you will receive will have been ordered in advance and prepared specifically for you hours before you arrive, and will be calibrated to your scheduled appointment time in order to maximize image quality.

What should I expect on the day of my PET - CT scan?

1. Please arrive at your scheduled appointment time. The radiotracer dose (FDG) you will receive will have been prepared specifically for you hours before you arrive, and will be calibrated to your scheduled appointment time in order to maximize image quality.
2. Let the front desk know that you have arrived. We will ask you to provide us with more information about yourself, including your medical and surgical history.
3. You may be given a small medication in the form of a pill (Xanax, or alprazolam). This will help to optimize your scan by helping to temporarily reduce the amount of metabolic activity in various muscles of your body, including in your shoulders.
4. A Nuclear Medicine technologist will meet with you, who will check your blood glucose level. The technologist will then administer a small injection of the radiotracer (FDG) to you intravenously, usually into a vein in your arms.
5. You will then be allowed to relax in a quiet room for about one hour. During this hour the radiotracer is circulating throughout your body and is distributing into your tissues. Relaxation optimizes your scan by reducing the amount of metabolic activity in your muscles. Avoid talking, chewing gum, or any similar activity during this hour.
6. After one hour, the nuclear medicine technologist will take you to the scanner. You will be allowed to use the restroom in order empty your urinary bladder prior to the scan.
7. In the scanner room, you will lie down on a moveable bed which automatically positions you inside of the circular (doughnut-shaped) scanner. The entire procedure, which consists of a quick CT scan followed by a longer PET scan, will take about half an hour. You may be asked to position your arms above your head for the duration of the scan, depending on the images needed. Remain still during the scan in order to increase the quality of the images. The technologist will be monitoring you in an adjacent room at all times.
8. The technologist will inform you when your scan is completed. Once you are free to leave, you may resume your diet as before or as instructed by your doctor.
9. The images from your scan will be interpreted by an experienced physician. Your doctor will be informed of the results typically within 1 to 2 days.

What if I have more questions?

If you have additional questions pertaining to your scheduled PET-CT scan that are not answered here, please call us at 209-466-2000.

INFORMATION FOR REFERRING PHYSICIANS

Current Medicare Coverage Guidelines for PET-CT imaging:

Oncology:

Stockton MRI & Molecular Imaging is now a registered PET facility with the National Oncologic PET Registry (NOPR). The NOPR is a newly-activated nationwide clinical database designed for the Centers for Medicare and Medicaid Services to assess the impact of PET on patient management. What this means to you and your Medicare patients: Our participation with the NOPR allows Medicare coverage of FDG PET-CT scans for a new list of indications which have not previously been covered.

PET-CT oncology indications eligible for entry into the NOPR are listed at http://www.cancerpetregistry.org/indications.htm and include Ovarian, Uterus, Cervical, Prostate, Testicular, Bladder, Renal, Small cell lung, Pancreas, Hepatobiliary, Bone, Connective/ soft tissue, Ocular, Brain, Myeloma, Leukemia, and others including unknown primary malignancies.

• REFERRING PHYSICIANS: The NOPR is essentially a nationwide research database; therefore, additional clinical information is needed. The NOPR requires that the referring physician complete a short pre-PET checkbox questionnaire prior to the scan in order to document how you intend to use the results of the scan in your patient management. This form will be provided to you or can be downloaded at http://www.cancerpetregistry.org/pdf/nopr_prepet_form.pdf to be returned to us via fax (209-466-5097). In addition, a shorter post-PET questionnaire must be submitted within 30 days after the scan, in order to document your assessment of the value of the scan in your patient management. An information sheet is available.
• PATIENTS: The patient's only requirement is to give his or her consent to be included in the registry. Printed informational material (http://www.cancerpetregistry.org/pdf/informational_sheet.pdf) will be provided to the patient, also available in Spanish.
• MORE INFORMATION: More complete NOPR information can be found on the Internet at http:/www.cancerpetregistry.org. For any additional questions, including coverage guidelines, feel free to call us at 209-466-2000.

PET-CT oncology indications already covered by medicare and do not require NOPR submission include diagnosis, staging, and restaging of the following types of cancer: Non-small cell lung cancer, Colorectal, Head & Neck, Esophageal, Melanoma, Lymphoma. For Thyroid cancer, the criteria remains follicular cell, post thyroidectomy and radioiodine ablation, negative recent I-131 whole body scan and thyroglobulin > 10ng. For Cervical cancer, the criteria remains staging for newly diagnosed and locally advanced cervical cancer with no extrapelvic metastasis on CT or MRI.

Breast cancer PET-CT imaging is covered by Medicare in both females and males for staging, restaging, and monitoring tumor response (of locally advanced or metastatic disease) to treatment when a change in therapy is contemplated. However, diagnosis of female breast cancer remains nationally non-covered by Medicare.

Neurologic PET:

Alzheimer's Disease evaluation: in patients diagnosed dementia for over 6 months, for evaluation of Alzheimer's disease versus frontotemporal dementia. [more info] Seizure disorders: for pre-surgical evaluation of refractory seizures.

Coronal view, FDG PET-CT of the brain

Cardiac PET:

• Cardiac Viability: for determination of myocardial viability as a primary or initial diagnostic study prior to revascularization
• see Myocardial Viability and PET-CT

For more information, refer to the Centers for Medicare & Medicaid Services at http://www.cms.hhs.gov .

Patient Preparation for a PET-CT scan

Stress to your patients the need to remain NPO (no food or drink except water, medications) for at least 4-6 hours prior to their scheduled appointment for their PET-CT scan. Prior to scanning, your patient will be injected with FDG, which is a glucose analog. Hyperglycemia in general can reduce the sensitivity of a PET scan. Additionally, the natural postprandial insulin response results in the distribution of FDG prominently to the skeletal muscles and myocardium on imaging. It would be preferable to wait to scan an uncontrolled diabetic patient until better glucose control is established.

Patients must be able to lie still within the PET-CT gantry for approximately 30 minutes, longer for melanoma evaluations.

Refer your patients to this PET-CT page of our website (www.stocktonmri.com) for more information about PET-CT, the procedure, and what to expect. If you or your patients have any further questions, please call us at (209) 466-2000.

Prior to your patient's scheduled appointment, we will contact the patient with further instructions on steps to take to further optimize FDG uptake and imaging, including a low carbohydrate diet and avoidance of strenuous exercise.

Post Therapy Considerations Regarding PET-CT

Ideally, a baseline PET-CT for oncologic indications is preferable prior to initiation of therapy, usually as an initial staging scan. However, this is not always possible, especially if the malignant diagnosis is not known prior to surgery. The following should serve as a guideline of when to schedule a post-therapy PET-CT scan:

• Post surgery: Post operative inflammation can prevent optimal evaluation of local residual neoplastic disease as well as locoregional adenopathy. The general guideline is to delay the PET-CT scan until 6-8 weeks after surgery. However, if evaluation of distant metastasis (i.e. staging) is more of a concern, the PET-CT scan can be scheduled sooner, as long as the referring physician is aware of the limitations of the study within the post operative region and lymph node drainage.
• Post radiation therapy: Post radiation inflammation can prevent optimal evaluation of local and regional neoplastic disease. The general guideline is to delay the PET-CT scan until 8 weeks after radiation therapy, although hypermetabolic post radiation inflammation (e.g. post radiation pneumonitis) has been known to persist for months on PET scans. However, if evaluation of distant metastasis is more of a concern, the PET-CT scan can be scheduled sooner, as long as the referring physician is aware of the limitations of the study in the post radiation therapy region.
• Post chemotherapy / pharmacological therapy: Concurrent chemotherapy and other pharmacological therapies such as corticosteroids can potentially result in false negative studies, especially in the evaluation of metastatic disease without a prior pre-therapy baseline study. For staging studies, the general guideline is to delay the PET-CT scan until 6-8 weeks after chemotherapy. However, more and more PET-CT scans are being utilized in the more immediate post-chemotherapy setting to monitor effectiveness of the type of chemotherapy used. The guidelines for recommended timing of PET-CT scan "chemotherapy monitoring" have yet to be determined, but is being investigated worldwide. In the near future, the Centers for Medicare & Medicaid Services have announced plans for a "Coverage with Evidence Development" category, which will include therapy "monitoring" for most cancers.

Alzheimer's Disease and PET-CT

Indication

	Neurodegenerative disorders (including Alzheimer's disease, frontotemporal dementias, Huntington's disease, etc.) are known to present with common patterns of focal cortical inhomogeneities and regional hypometabolic activity on FDG-PET studies.
	Functional imaging has been shown to assist in diagnosis, particularly in early identification of Alzheimer's disease, in order to facilitate administration of treatment intended to slow progression or delay onset of symptoms (Chang CY, Silverman DH, Expert Rev Mol Diagn. 2004 Jan;4(1):63-9). A multicenter study with comparison to histopathologic diagnoses has shown FDG-PET to have a sensitivity of 94% in the evaluation of Alzheimer's disease, with a specificity of 73% (78% for any neurodegenerative disease) (Silverman DH, Small GW, et.al, JAMA. 2001 Nov 7;286(17):2120-7).		Transaxial images from a brain FDG PET-CT scan demonstrating decreased metabolic activity in the posterior parieto-temporal cerebral cortex bilaterally, a common pattern seen in patients with Alzheimer's disease.
	Evaluating early dementia with the assessment of regional cerebral metabolism using PET has been shown to be associated with a reduced rate of false-postive and false-negative findings compared with conventional clincal criteria, without adding to the overall costs of diagnosis and treatment, with a overall cost savings per correct diagnosis rendered (Silverman DH, Gambhir SS, et al, J Nucl Med. 2002 Feb;43(2):253-66).

	Current Medicare Coverage Guidelines
	The following is summarized from Pub 100-03 Medicare National Coverage Determinations, implemented April 18, 2005:
		"An FDG-PET scan is considered reasonable and necessary in patients with a recent diagnosis of dementia and documented cognitive decline of at least 6 months, who meet diagnostic criteria for both Alzheimer's Disease (AD) and frontotemporal dementia (FTD). These patients have been evaluated for specific alternate neurodegenerative diseases or other causative factors, but the cause of the clinical symptoms remains uncertain." The patient should have had a comprehensive clinical evaluation encompassing a medical history, physical and mental status examination (including formal documentation of cognitive decline occurring over at least 6 months) aided by cognitive scales or neuropsychological testing, laboratory tests, and structural imaging such as magnetic resonance imaging (MRI) or computed tomography (CT). Please ensure that the following information has been collected and is maintained in the beneficiary medical record:
		Date of onset of symptoms; Diagnosis of clinical syndrome (normal aging; mild cognitive impairment or MCI; mild, moderate or severe dementia); Mini mental status exam (MMSE) or similar test score; Presumptive cause (possible, probable, uncertain AD); Any neuropsychological testing performed Results of any structural imaging (MRI or CT) performed Relevant laboratory tests (B12, thyroid hormone) Number and name of prescribed medications	Brain FDG PET-CT scan, sagittal view: metabolic pattern combatible with Alzheimer's disease

Guideline for repeat studies: A repeat FDG-PET brain scan for dementia is considered 'reasonable and necessary' if the results were not conclusive and one year has elapsed, or sooner if the scope and severity of the patient's cognitive deficits have substantially changed.

Patient Preparation

Patient preparation and procedural protocol for a FDG PET-CT dementia evaluation is very similar to an oncology FDG PET-CT study [more info]. A fasting state prior to injection of FDG is optimal. We will provide the patient with a low-stimulation environment for the uptake period (about 1 hour) in between injection and scan. The patient must be able to tolerate lying still, supine, arms down for at least 15 minutes. Because only the brain is scanned, the duration of the scan is shorter than the duration of an oncology study..

Myocardial Viability and PET-CT

see Myocardial Viability and PET-CT

FDG-PET cardiac scan, selected short axis images: the left ventricle myocardial lateral wall is not viable (red arrow).