Anti-1-amino-3-[18F] fluorocyclobutane-1-carboxylic acid (anti-3-[18F] FACBC): Normal physiology and variant patterns of uptake

Learning Objectives 1. Recognize normal physiological distribution patterns of anti-3-[18F]FACBC. 2. Recognize variants that may simulate disease. 3. Identify incidental uptake which may indicate malignancies other than prostate cancer.

Anti-1-amino-3-[18F]fluorocyclobutane-1-carboxylic acid (FACBC) is a synthetic, non-metabolized, amino acid analog positron emission tomography radiotracer. Though uptake has been described in normal volunteers (J Nucl Med.2007;48(6):1017-20), the majority of patients have been studied in clinical trials involving prostate carcinoma. Normal physiologic background organ uptake patterns are similar to those noted in patients without cancer. Liver and pancreas demonstrate the most intense uptake. Typically on early images (<15 min) pancreatic activity is greater than that of liver, but has faster washout with time. Moderate salivary and pituitary uptake is commonly visualized. Variable mild to moderate bowel activity may also be seen. Moderate red bone marrow and mild muscle activity is present on early images. Marrow activity decreases while muscle activity becomes more intense with time. Brain and lungs demonstrate little to no background uptake. Unlike 18F-FDG, FACBC demonstrates little renal excretion. Mild to moderate activity may accumulate in the bladder with time, but is not of the degree that causes interference with study interpretation. Though there is relatively less inflammatory uptake compared with 18F-FDG, FACBC uptake may also occur from benign processes and these will be highlighted. In addition, uptake due to non-prostatic malignant etiologies may occur and should be further investigated. At the end of this presentation, readers will be able to identify FACBC normal physiological distribution, radiotracer variation patterns that may simulate diseases, and incidental abnormal uptake which may indicate non-prostatic neoplasia.