Appendix C: Genesis of the Signal in MRI

Magnetic resonance imaging (MRI) is a non-invasive imaging technique used to obtain detailed images of the human body, when applied in medicine, or any other 3D complex system, such as soils, rocks, etc. MRI utilizes the interactions between magnetic fields and the proton nuclei present in the system under observation to generate, e.g., anatomical and functional images. In particular, when medicine is concerned, the patient is positioned inside a large static magnet. Radiofrequency coils are used to generate pulses that allow protons of the water molecules in the body to be excited. Then, following relaxation, protons in the various body compartments behave differently. Finally, sophisticated software analysis is able to generate 3D images of the body or a part of it. MRI can provide detailed information about the anatomical structure of tissues and their function as well. For example, through the use of specific contrast agents, it is possible to evaluate perfusion and blood flow in certain tissues. MRI can also be used to detect structural abnormalities, tumours, injuries, inflammation, and other pathological conditions. Thanks to artificial intelligence, it is also possible to improve the speed of image acquisition and image quality. Recent applications are also emerging for studying the chest using fast sequences such as gradient echo and single shot with appropriate weighting. In the near future, thanks to the absence of ionizing radiation, it may be possible to use MRI in the screening of lung cancer and in the study of respiratory conditions related to air pollution.