In 2000, a study was conducted to compare the imaging efficiency of 18F-fluorodeoxyglucose (18F-FDG; t1/2: 109.8 min) PET, the “gold standard” of clinical cancer imaging (Gambhir et al. 2001), with CEA-Scan SPECT in colorectal cancer patients (Willkomm et al. 2000). This evidence concerns the gene CEACAM5 and colorectal cancer.