It is well known that many technical and physiologic factors can affect the reliability of the standardized uptake value (SUV) on FDG PET-CT. Another potential problem of which we may be aware but has not been previously discussed is significant SUV overestimation of lesions in the direct neighborhood of large hot sources, namely, areas with high FDG uptake or activity such as a tumor, myocardium, urinary bladder, kidney, or gastrointestinal tract. The magnitude of SUV overestimation of the lesions directly neighboring the large hot sources is varied among the different cases, and it is possibly secondary to “shine-through” effect of the hot sources, which would warrant further systematic investigation such as phantom simulation experiment. If the lesion is in the close territory of the hot source, measured SUV is often overestimated and invalid. Visual interpretation should be used for evaluation of FDG avidity of the lesion. 1. Introduction Positron emission tomography (PET)/computed tomography (CT) with flurorine-18 fluorodeoxyglucose (FDG) has become an established imaging tool in oncology and is now of growing interest in inflammatory/infectious, cardiac, and neurological diseases. FDG PET data are normally assessed visually or by using simple indices such as the standardized uptake value (SUV) for quantification. An SUV is a semiquantitative number that normalizes lesion uptake to injected dose per unit of body mass. More generally, SUV may be normalized to other measure of body habitus such as lean body mass or body surface area. While many alternatives have been proposed, the SUV is generally evaluated at its maximum value as . In practice, lesion SUV is determined by placing the region of interest (ROI) over the lesion and using computer program to automatically calculate the value [1]. SUVs are widely used to measure metabolic activity in lesions. Today, SUV measurements are increasingly being recognized as providing an objective, more accurate, and less observer-dependent measure for prognosis and response monitoring purpose than visual inspection alone [2, 3]. However, many technical and physiologic factors can affect the reliability of SUV, which include the blood glucose level, the time interval between FDG injection and image acquisition, patient’s body composition and habitus, reconstruction technique, selection of region of interest, size of lesion, and the use of contrast agents during CT-attenuation correction. All these are well known to nuclear radiologists and have been discussed extensively in the literature [4–9]. Except for
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