A clinical PET scan is a useful tool to aid diagnose many disease states, primarily in oncology, neurology, and cardiology. However, the technique is applicable to all parts of the body for diagnosis, disease staging, and monitoring of therapy. Unlike MRI or CT, PET provides physiologic, anatomic, and biochemical data.
Although PET is more sensitive than gamma SPECT, it is considerably more expensive. The use of FDG imaging with specially equipped gamma cameras has been an alternative to exclusive PET imaging systems. The patient preparation for nuclear medicine use of FDG in gamma SPECT imaging is similar to that for PET imaging of FDG. Because of the physics of 18F, only multiheaded cameras can be used for gamma SPECT acquisitions. Currently, there are certain limitations with gamma SPECT imaging when compared with true PET imaging.
In oncology, FDG-PET has proved useful in several areas, including the diagnosis of pulmonary nodules, the differentiation of pancreatic cancer from mass-forming pancreatitis, and the diagnosis of breast cancer in selected cases of mammography and biopsy failure. PET scanning is used for the initial preoperative staging of cancer involving the lung, liver, colon, breast, head, and neck as well as in melanomas and lymphomas. For example, with lung cancer, PET is useful in determining the degree of operability. With extensive metastasis in the mediastinum, surgery is contraindicated. Staging, detection of recurrence, and response to therapy also can be determined.
In cardiology, PET has demonstrated excellent utility for measuring myocardial blood flow and perfusion and for detecting coronary artery disease. The high-energy photons of PET tracers produce high-quality images even in patients who are obese. In these cases, a PET scan can provide important information for determining which patients will benefit from the more invasive procedures.
In neurology, FDG-PET scanning is a noninvasive aid in predicting prognosis and for surgical planning in epilepsy. By revealing areas of increased and decreased glucose utilization, a PET scan helps surgeons pinpoint the surgical site. A PET scan is used to diagnose a wide variety of dementias, including Alzheimer disease, which shows a distinct pattern of glucose consumption in the temporal and parietal regions of the brain. Also, distinct brain patterns can be seen in the involuntary movement disorders, such as Parkinson disease, Huntington disease, and Tourette syndrome.
Advise the patient that although the actual imaging time required for a single image is 30–45 minutes, the actual time involved may be several hours and occurs before and during radiopharmaceutical injection. Tell the patient that delayed imaging may produce different results than early imaging after injection (after 45 minutes for body tumor and 30 minutes for brain tumor).
Position the patient on a table and then within the scanner. Before administration of the radiopharmaceutical, perform a background transmission scan. In certain procedures, this preliminary scan is optional. A number of positions are assumed, 2–6 minutes at each position.
Administer the radioactive drug intravenously. The patient waits 30–45 minutes in the department.
Patients undergoing PET procedures for colon cancer, suspected pelvic pathology, or kidney studies may require a urinary catheter or furosemide and oral contrast.
Explain that all patients require fasting, and glucose monitoring may be part of the patient preparation before the scan. Elevated glucose results in decreased FDG uptake in cancer cells. Have the patient hydrate before and after FDG injection to minimize bladder uptake.
Combined PET and CT images result in more sensitive, improved images.
See Chapter 1 guidelines for safe, effective, informed intratest care.
Patient preparation for a FDG-PET scan varies among institutions. However, some generalizations can be made.
Pretest Patient Care
Explain test purpose and procedure. Fasting is required for all tests. Sometimes, fasting blood glucose levels are obtained. Caution must be taken if insulin is given because it suppresses glucose tissue uptake. Insulin also suppresses FDG tissue uptake, which affects the quality of the resulting scan. Insulin should not be given within 4 hours of the FDG injection.
Administer the FDG radiopharmaceutical agent intravenously. Monitor blood pressure.
Refer to standard NMI pretest precautions.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed.
Refer to standard NMI posttest precautions.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.