Colorectal cancer: Parametric evaluation of morphological, functional and molecular tomographic imaging

Table 1 Current limitations of qualitative imaging based on morphological features used for the assessment of colorectal cancer

Diagnostic task	Limits of qualitative imaging
Primary tumor identification	Early stages of CRC hard to detect
	Neoplastic and inflammatory tissue not easily differentiable
Lymph node involvement	Lymph node size criteria often misleading and insufficient
	Shape, border irregularity and structural heterogeneity hard to assess for small lymph nodes
Prediction of early responses to chemotherapy and radiation therapy	Not possible with qualitative evaluation alone
Evaluation of treatment responses and the detection of recurrent disease	Differentiation of residual or recurrent neoplastic tissue from posttreatment induced fibrosis or necrosis is often challenging

CRC: Colorectal cancer.

Table 2 Main quantitative parameters extracted from perfusion imaging of colorectal cancer

Parameter name	Parameter definition	Parameter significance
Regional blood flow	Blood flow per unit volume or mass of tissue, expressed in mL of blood/min/100 mL tissue	It reflects the rate of the delivery of oxygen and nutrients to a certain tissue
Regional blood volume	Volume of capillary blood contained in a certain volume of tissue, expressed in mL blood/100 mL of tissue	It reflects the functional vascular volume
Mean transit time	Mean time needed for blood to pass through the capillary network, expressed in seconds	It reflects the time required for the contrast agent bolus to pass through tissue
Permeability-surface area product (PS)	Flow of molecules through the capillary membranes in a certain volume of tissue, expressed in mL/min/100 mL tissue	It reflects the vascular leakage rate in the microcirculation
Transfer constant (KTrans)	Rate at which the contrast agent transfers from the blood to the interstitium (rate of contrast extraction)	It reflects the balance between capillary permeability and blood flow in a tissue
Tissue interstitial volume (Ve)	Volume of extravascular and extracellular contrast agent in a certain tissue, expressed as a percentage	It is a measure of cell density
Rate constant (Kep)	Rate at which the contrast agent returns from the extravascular-extracellular space to the vascular compartment: Kep = Ktrans/Ve	It reflects the tissue microcirculation and contrast agent permeability