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April 2010, Volume 40 Number 4 , p 62 - 63


  • Lora K. Ott MSN, RN


BY THEMSELVES, positron emission tomography (PET) and computed tomography (CT) scans are valuable diagnostic tools, but each has limitations. The PET scan can detect metabolically active tissue such as a malignant tumor but doesn't clearly define underlying structures. The CT scan more clearly defines anatomic structures but doesn't differentiate levels of metabolic activity or provide information about organ function.When CT and PET scans are combined, they complement each other and result in more accurate diagnoses.1 This article describes how the combined PET-CT scan works and how to care for a patient having one. Let's start by looking at the PET scan.Used by itself, PET can help a clinician to visualize areas of increased metabolic activity in the body, including metastatic tissues. These metabolically active tissues use more glucose, and the PET scan can identify areas of the body with increased cellular glucose uptake.For the test, a nuclear marker called FDG (2-F18-fluoro-2-deoxy-D-glucose), which functions similarly to glucose, is injected into the patient.2 After the FDG circulates through the body for 60 to 90 minutes, an image is taken with the PET scan. Malignant cells have an increased level of glucose transporters, which move glucose and FDG across the cell membranes. The scan illuminates areas of active malignant cells, showing a concentration of metabolic activity.The PET scan shows metabolic activity by recording the energy released from the decay (metabolism) of FDG within the cells. The decay process creates positrons, or positively charged electrons. When positrons collide with negatively charged electrons within the cells, the PET scanner detects energy from this interaction and computer reconstruction creates an image.3But without anatomic details, it's difficult to know exactly where the areas of metabolic activity are located within the tissues. That's where a CT scan can help.The CT scan creates the anatomic images, making

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