In this article, we describe the various causes and patterns of skeletal muscle FDG uptake. Familiarity with these patterns is essential for proper interpretation of clinical FDG PET/CT images.

Bone scintigraphy is a sensitive and popular method for imaging a wide array of benign or malignant skeletal abnormalities. However, the uptake of tracers used for bone scintigraphy may be observed in various extraosseous sites, thereby limiting its specificity. It is difficult to correctly localize such sites of uptake on planar bone scintigraphy alone. The addition of hybrid single-photon emission computed tomography-computed tomography (SPECT-CT) under such circumstances is very useful. The present essay illustrates the commonly encountered extraosseous uptake of 99m Tc-meth-ylene diphosphonate (MDP) and the usefulness of hybrid SPECT-CT in clarifying 99m Tc-MDP uptake. T he ability to assess new bone formation makes bone scintigraphy a popular noninvasive diagnostic technique for imaging the skeletal system. Pathologic entities that commonly demonstrate increased uptake on bone scintigraphy are primary bone tumors, skeletal metasta-ses, infections, and sites of skeletal trauma. Bone-seeking tracers such as 99m Tc-methylene diphosphonate (MDP) and its analogs localize to bone by chemisorption to the surface of hydroxyapatite crystals (1). Sites of new bone formation show increased uptake because of high regional perfusion and increased areas of proliferation. On occasion, certain abnormal processes involving soft tissues can also cause skeletal accumulation of radiotracer (extraosseous uptake) on bone scintigraphy apart from the physiologic excretion of tracer through the urinary tract (2). Probable mechanisms that have been proposed to explain extraosseous uptake of 99m Tc-MDP include a) increased regional vascularity and per-meability; b) tumor necrosis with or without calcification; c) metastatic calcification in renal failure; d) increased tissue calcium concentration; e) serum hypocalcemia of any etiology; f) presence of collagen; and g) improper labeling of the radionuclide (3, 4). Knowledge regarding these potentially confusing entities is important because they may hinder correct interpretation of the disease in question. Identification of such nonosseous uptake becomes particularly difficult if planar scintigraphy is used alone. Additional use of hybrid single-photon emission computed tomography (SPECT)-computed tomography (CT) helps in proper anatomical localization of abnormal uptake noted on bone scintigraphy and improves the quality of interpretation. SPECT-CT increases the sensitivity of bone scintigraphy by detecting additional lesions, and the exclusion of sites of physiological tracer uptake also increases specificity. Attenuation and photon scatter correction of nuclear medicine images by hybrid imaging helps us to obtain more accurate image data. The functional significance of indeterminate bone lesions detected on anatomical imaging studies can also be characterized by SPECT-CT. This pictorial essay reviews a few examples of abnormal processes that may cause extraosseous uptake on bone scintigraphy encountered at our institute and highlights the significance of proper anatomical localizati...

⁶⁸Ga-DOTANOC PET/CT seems to be a promising modality for detecting primary tumor in patients with carcinoma of unknown primary of neuroendocrine origin.

(68)Ga-DOTANOC PET/CT appears to be useful in patients with gastrinoma with negative or equivocal results on CECT, especially the latter group.

Intermediate-risk surgically ablated patients do not need adjuvant RAI therapy and patients who failed to achieve ablation with first dose of (131) I may be dynamically risk stratified as high-risk category and managed aggressively.