Standardized Uptake Value

A semiquantitative method is available to calculate the intensity of FDG uptake within a range of interest on the PET scan. This value is called the Standardized Uptake Value (SUV) and takes
account of such factors as injected activity, patient weight, and time from injection. Simply speaking, the SUV assumes that if there is an even distribution of radioactivity throughout the body the SUV would be measured as 1. Obviously this is not the case, but we can calculate the relative uptake within different parts of the body and relate them to each other. An area with an SUV of 5 means this area has five times the average uptake. Certain modifications can be made to the SUV calculation to take into account, for example, the patient’s body fat (since FDG is not generally taken up into fatty tissue). The SUV allows comparisons to be made between different parts of the body and between different scans on the same patient over a period of time. It must be emphasized that the SUV is only a semiquantitative measurement and can vary considerably with changes in patient’s plasma glucose levels. Many clinicians prefer to avoid numbers and simply use visual interpretation to compare the intensity of one area to another suing the background blood pool as a guide to normality. There is evidence to suggest that both methods are equally accurate. Figures 1.12 and 1.13 demonstrate the change in intensity of an esophageal tumor following chemotherapy
FIGURE 1.12. Pretherapy SUV 15.
FIGURE 1.13. Posttheray SUV 2.
the maximum SUV had decreased from 15 pretherapy to 2 posttherapy. Recent literature would suggest a response of this magnitude correlates with a better prognostic outcome. List of Normal and Variant Uptake See Chapter 9 for a list and illustrations of common patterns of normal uptake and examples of some variant uptake.
NOTE ON ILLUSTRATIONS
Please note that throughout this book the above orientation is used on all axial images. Top left corner is the CT image; bottom left the fused PET/CT and top right is the PET image. There are
however some images that contain a fourth image in the bottom right corner. This appears very similar to the PET image above it. The bottom right image when present is the nonattenuated correction image and is slightly different from the PET image above it (top right) which represents an attenuation corrected PET image, (see Chapter 10 for a more detailed explanation).