Table 1 Review of main functional and molecular imaging techniques for the evaluation of colorectal cancer
From: Advanced imaging of colorectal cancer: From anatomy to molecular imaging
Imaging technique | Biological basis of imaging technique | Evaluation parameters obtained | Pathophysiological correlation | Advantages | Disadvantages |
|---|---|---|---|---|---|
Dynamic contrast-enhanced MRI (DCE-MRI) | Contrast medium uptake rates Transfer rates Extra-cellular volume Plasma volume fraction | • Qualitative: evaluation of the type of time/signal intensity curve * Semiquantitative evaluation: wash-in; wash-out; time to peak enhancement; etc. * Quantitative analysis (based on mathematical models): Initial area under gadolinium curve (IAUGC); Transfer and rate constants (Ktrans, kep); Leakage space fraction (ve); Fractional plasma volume (vp) | Vessel density Vascular permeability Perfusion Extravascular space Plasma volume | Low toxicity of contrast agents No ionizing radiation Versatility in pulse sequences | Complex biological explanation of many parameters Complex analysis in quantitative models |
Perfusion CT (CTP) | Contrast medium uptake rate in tissues, which is influenced by: • Perfusion & transfer rates • Extra-cellular volume • Plasma volume fraction | • Qualitative evaluation of the type of time/signal intensity curve * Semiquantitative evaluation: Maximum upslope; Peak enhancement; etc. * Quantitative analysis (based on mathematical models): Blood flow; Blood volume; Transit time; Permeability, Ktrans | Vessel density Vascular permeability Perfusion Tissue cell fraction Plasma volume | Availability Low cost | Contrast agent toxicity Low sensitivity to contrast agents Exposure to ionizing radiation |
Imaging techniques based on water diffusion | Diffusivity of water - Monoexponential analysis (DWI) Perfusion component: Intravoxel incoherent motion (IVIM) Structural complexity: Diffusion kurtosis imaging (DKI) Diffusion tensor imaging (DTI) | • Apparent diffusion coefficient (ADC) • Perfusion fraction (f) • Diffusion (D) Non-Gaussian diffusion coefficient (D) and deviations from normal distribution (K) Mean diffusivity, Diffusion anisotropy indices; Fiber orientation mapping | Tissue architecture: cell density & size, extracellular space tortuosity, gland formation, cell membrane integrity, necrosis Microvessel perfusion Quantifying the non-gaussianity of any distribution and may evaluate membrane integrity Anisotropy of tissue structure | Availability No contrast agents No ionizing radiation | Technical complexity of advanced techniques (IVIM, DKI, and DTI) |
MR Spectroscopy Imaging (MRSI) | Contrast medium uptake by macrophages of the lymph nodes | Ratios between metabolites Abnormal Peaks of metabolites Absence of normal metabolites | Analysis of metabolic pathways | Specificity No contrast media | Technical complexity Difficult analysis |
MR-Lymphography (USPIO) | Contrast medium uptake by macrophages of the lymph nodes | • Qualitative evaluation: Change/No change of signal in lymph nodes | Function of the reticuloendothelial system | Specificity | Contrast agent availability Spatial resolution for detecting micrometastases Complexity |
Positron Emission Tomography (PET) | Different metabolic pathways depending on the radiotracer: 1-Energetic Metabolism Fluorodeoxyglucose (FDG) | • SUV = standardized uptake value (ratio between tracer uptake and homogeneous distribution of the tracer within the patient). | Glucose uptake | Emission directly proportional to concentration of contrast agent High sensitivity Whole-body imaging Relative specificity | High cost Low spatial resolution (1–2 mm) No morphological information Radiation exposure Short half-life in many radiotracers -Very short radionuclide agent half-life No evaluation of permeability Technical complexity |
2-Tumour Proliferation Fluorothymidine (FLT) | Activity of thymidine kinase 1 | ||||
3-Hypoxia (F-MISO), (64CuATSM), (F-FAZA) | Uptake is influenced by the O2 level in tissue | ||||
4-Apoptosis (Annexin-V) | Exposure of phosphatidylserine in the cell membrane |