D2 Magnetic resonance imaging (MRI)

Topic

Magnetic resonance imaging (MRI) exploits the magnetic properties of hydrogen protons within the patient's body—particularly those found in water and fat—to generate images with much richer tissue contrast than computed tomography (CT), especially regarding soft tissues.

Unlike CT, which measures tissue electron density, MRI measures two distinct relaxation times of these same hydrogen protons—longitudinal relaxation time and transverse relaxation time. These relaxation times depend on the tissue's molecular composition; tissues with different molecular compositions yield different relaxation times, even if their densities are similar.

This dependence on molecular composition allows MRI to characterize tumor tissue with far more information than density alone provides: it can distinguish the presence of necrosis within the tumor, a fatty component, hemorrhage, fibrosis, or edema in the tissue surrounding the tumor.

Thanks to this ability to characterize tumor tissue in such detail, MRI is the gold-standard imaging technique in oncology for several tumor types: brain tumors such as glioblastoma; prostate tumors (using a variant known as multiparametric MRI); rectal tumors (for local staging); breast cancer (for both local extent assessment and early detection in high-risk patients); bone and soft-tissue tumors; and cervical tumors, where it aids in planning adaptive brachytherapy.

Beyond these applications, functional MRI—which encompasses diffusion-weighted imaging, perfusion imaging, and spectroscopy—provides even further insight into tumor biology, offering information that no other imaging technique can supply. Thus, while computed tomography remains the reference imaging modality for tumor density and general anatomy, magnetic resonance imaging is the imaging modality of choice whenever tumor tissue composition is more important than density.

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