Preoperative evaluation of colorectal cancer using CT colonography, MRI, and PET/CT

Table 1 Benefits and limitations of imaging techniques

	CT colonography	MRI	PET/CT (colonography)	Recommendations
T staging	Wall deformities are associated with a specific T stage. Wall deformities are classified by degree, and the overall accuracy for T stage is 73%-83%	MRI with a pelvic phased array coil is a well-established modality. High-resolution T2-weighted imaging is the key sequence. Evaluation of the circumferential resection margin is important	SUVmax is more significantly related to tumor size than to T staging. PET/CT colonography is useful for obstructing colorectal cancers that cannot be traversed colonoscopically.	MRI = CT Colonography > PET/CT
N staging	Metastatic lymph nodes tend to be more than 1cm in diameter, and have a circular shape, irregular border, central necrosis, and calcifications. The overall accuracy of identifying metastatic lymph nodes on contrast CT colonography images is 59%-71%	Sensitivity 80%-85% and specificity 97%-98% by using border irregularity and mixed intensity signal intensity of lymph nodes instead of size criteria. Ultra-small particles of iron oxide-enhanced MRI is a promising modality	Sensitivity of 42.9% and specificity of 87.9% for the detection of preoperative lymph node involvement	MRI > PET/CT > CT
M staging	CT colonography demonstrates liver metastases, pulmonary metastases and other sites of disease. The sensitivity of liver metastases detected by CT is 85% and the specificity is 97%	Gd-EOB-DTPA-enhanced MRI has become a first-line imaging modality to identify liver metastases	The role of PET/CT for the detection of liver metastases is not well-defined	Liver metastases: MRI >> PET/CT > CT For other distant metastases: PET/CT > CT > MRI
Limitations	Radiation exposure (Model-based iterative reconstruction provides low dose and high quality images)	Expensive and time consuming. Motion artifact. Difficulty in differentiating fibrosis from tumor infiltration, which compromises the ability to distinguish early stage T3 tumors from stage T2 tumors	Expensive and time consuming. Physiological fluorodeoxyglucose gastrointestinal uptake may lead to misinterpretation
Benefits	Easily available. Three-dimensional CT provides a great deal of information regarding vascular anatomy, which can assist in planning laparoscopic resections	Established imaging modality for T staging, chemoradiation therapy evaluation and the identification of liver metastases	Valuable for the evaluation of distant metastases

CT: Computed tomography; MRI: Magnetic resonance imaging; PET: Positron emission tomography; SUV: Standardized uptake value; Gd-EOB-DTPA: Gadolinium ethoxybenzyl diethlenetriamine pentaacetic acid.