Positron emission tomography/computed tomography (PET/CT) is a non-invasive diagnostic imaging procedure that is increasingly used in many oncology applications. Patients undergoing PET/CT are injected with a radiotracer, which accumulates in some normal and abnormal structures. Currently, the glucose analogue [18F] Fluoro-2-deoxy-2-D-glucose or [18F-FDG] is the preferred radioactive tracer for PET/CT examinations to diagnose, stage and restage cancer. After the process of phosphorylation of the glucose analogue, FDG-6-phosphate is captured in the cells of the body, thus enabling the imaging of different organs and tissues. Unfortunately, not only do malignant tumors show higher FDG uptake on PET/CT scans, but so do some non-neoplastic and normal physiological conditions; this may obscure or mimic the appearance of malignancies, thus increasing the number of false positive or negative results on FDG PET/CT images (Long & Smith, 2011). Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay One of the physiological conditions that could lead to a false positive or negative result is normal FDG uptake in brown fat and active muscles. According to Long and Smith (2011), brown fat absorption has been clearly recognized in several studies as one of the potential causes of false positive results. It was reported that approximately 3 to 4 out of 100 FDG PET/CT scans would show brown fat uptake; in the mediastinal region, this may be misdiagnosed as nodular metastatic lesions detected around several structures, including the trachea, esophagus, and pericardium, resulting in false-positive results. Brown fat absorption is more common in females and children than in males or adults. The effect of brown fat absorption increases in cold weather and in people with a low BMI. Therefore, it is recommended that during the collection time, the patient's body temperature is maintained with warm blankets and warm room temperature (Long & Smith, 2011). Furthermore, Jadvar and Parker (2005) stated that another potential source of false results commonly observed in FDG studies is the high FDG uptake in working skeletal muscles. Increased activity of working muscles may limit lesion detection, thus increasing the incidence of false-negative results. For example, high absorption in the masticatory muscles (Musculi masticatorii) due to chewing or eating can hide lesions in the head or neck regions. Therefore, patients are advised not to eat and relax after FDG injection. According to Long and Smith (2011) high FDG uptake in inflammatory and infected cells as a result of chemotherapy may be a potential cause of false-positive PET/CT studies for cancer. It has been shown that increased uptake in activated neutrophilic granulocytes and macrophages can mimic the appearance of malignant tumors. Cambiamento et al. (2006) stated that 40% of FDG uptake after therapy is attributed to non-neoplastic tissue. Unfortunately, many cancer patients become vulnerable to infections after undergoing chemotherapy (Long & Smith, 2011). Jadvar and Parker (2005) stated that “active infections such as pneumonia, tuberculosis, histoplasmosis, toxoplasmosis, cryptococcoma, and coccidioidomycosis may demonstrate very high FDG uptake, therapy decreasing the specificity of PET in characterizing lesions” (p. 259) . Another potential cause of the false positive result is normal FDG absorption.