Ultrasound, Magnetic Resonance Imaging and Positron Emission Tomography in the Evaluation of Colon Cancer

Abstract

With the increasing incidence of colorectal cancer (CRC), diagnostic imaging provides an important complementary role to colonoscopy in the management of colorectal pathology. As surgical and oncological therapies have improved, the importance of highly accurate and reproducible imaging has also grown. Further research has gone into the role other modalities may play in patient work-up and management. Transrectal ultrasound and magnetic resonance imaging (MRI) of the rectum provide high-definition imaging of the local spread of rectal tumours, but cannot assess the proximal bowel or more distant metastatic disease. Abdominal ultrasound is used to identify metastatic involvement of the solid abdominal viscera, but cannot evaluate the primary lesion. MR colonography (MRC) depicts all segments of the colon and can identify visceral and nodal metastases. However, staging of the primary lesion, particularly of early tumours, is limited by the resolution of MRC. In CRC PET-CT studies are useful for the initial diagnosis and staging of the cancer by determining the exact location of a tumour, the extent of disease and whether the cancer has metastasised. PET-CT may be used to detect recurrence of disease and to manage ongoing patient care. PET-CT imaging assists treatment planning by selecting the most effective therapy based on the unique molecular properties of the disease and of the patient’s genetic makeup. The evaluation of the effectiveness of treatment may be determined as related to the response to specific drugs and ongoing therapy. Based on changes in cellular activity observed on PET-CT images, treatment regimens may be changed. MR and PET-CT images are presented to illustrate these modalities’ role in CRC management.