Glucose is the source of energy in the brain; hence brain cortex tissue generally has an intense uptake. In the fasting state or NPO, the brain is known to account for as much 20% of total body glucose metabolism. FDG accumulation in the brain is fairly predictable. However, FDG uptake in some parts of the face and neck can be highly variable. Uptake of the salivary glands, including the parotid, submandibular, and sublingual glands this can range from mild to intense. In addition, salivary glands uptake may be symmetric or asymmetric. Asymmetry in the salivary gland can be attributed to the patient’s position or inflammatory changes after surgery or radiotherapy. Also, radiotherapy can decrease uptake on the irradiated side.
Fairly consistent low to moderate FDG uptake occurs in the tonsils and base of the tongue. Uptake in the normal thyroid typically ranges from no accumulation to mild uptake. However, it has been reported that increased uptake in the normal thyroid is seen in approximately 2% of scans of healthy individuals.
Facial Muscles PET / CT Scan
The six muscles that control the movement of the eye like extraocular muscles, the muscles of the oral cavity and the laryngeal muscles reveal varying degrees of FDG uptake. A moderate amount of uptake is usually seen in the anterior part of the floor of the mouth because of the genioglossus muscle, which prevents the tongue from falling back in supine patients. If a patient grinds his or her teeth or chews gum, the muscles of mastication may appear very prominent. Excessive talking after injection can cause prominent FDG uptake with the larynx. Laryngeal uptake in normally very subtle and appears in the form of an inverted V shape.
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| Normal vocal cords (arrows) on (A) CT, (B) PET, |
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| (C) PET/CT fusion images. |
Pet / CT fusion images rather than just PET images have been included to provide anatomic landmarks.
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