• Ultrasound of the abdomen and, if indicated, within the rectum. Endorectal ultrasonography can accurately
  show tumor invasion and enlarged lymph nodes outside the rectum, but cannot indicate if enlarged lymph
  nodes actually contain metastatic tumor.
• Abdominal CT and MRI scans to identify distant metastases before surgery.
• Chest x-ray may reveal lung metastases. 
• PET (positron emission tomography) scanning, if available (experimental) can help assess the early response
  of liver metastases to chemotherapy by showing changes in sugar metabolism.
• Radioimaging body scan before surgery with CYT-103 monoclonal radiolabeled indium antibodies may help
  detect hidden metastatic disease in about 12 percent of cases. This experimental method can complement CT
  scans, increasing their diagnostic sensitivity for finding hidden metastatic sites in the pelvis and other areas
  outside the liver. Other monoclonal antibody and imaging tests are being developed. Current monoclonal
  antibody scans are not completely reliable in the detection of liver metastases.
      Studies with anti-CEA monoclonal antibodies have shown a high accuracy in detecting tumors smaller than
  1/2 in. (1 cm). This may be helpful to the surgeon. The usefulness of these radioisotope scans is not yet
  certain.

Endoscopy and Biopsy 
• Examination of the entire colon with a colonoscope (colonoscopy), or the lower part of the colon and rectum
  with a flexible tube (proctosigmoidoscopy) and biopsy of any mass found.