Basic Cardiac Magnetic Resonance Physics for Clinicians - a Clinician's Point of View

Lee, Sang Chol

Abstract

Gaining a complete understanding of the physics of magnetic resonance imaging (MRI) is a daunting task. However, as cardiac MRI is being increasingly used in cardiovascular medicine, understanding the basics of MRI physics has become necessary for appropriate assessment of the images and correct interpretation of the findings. MRI is an imaging modality that utilizes the magnetic potential of the body. When the body is placed inside an extremely strong magnetic field, the protons of the water molecules inside the body align along the field, after which, the proton spins are exposed to a radiofrequency pulse with a frequency that matches the precession frequency of the protons in the body. This causes the precession of the protons to resonate and increase in amplitude. Simultaneously, three-dimensional magnetic gradients are applied for targeting specific slices of the body and discriminating the two-dimensional orientation of the organs; this is followed by emission of electromagnetic pulses generated by the resonance with varying frequencies and phases from various parts of the body. As soon as the input pulse has ceased, the machine starts absorbing the electromagnetic pulses that are being emitted by the body. These waves are mathematically converted into images of the internal organs and are visualized through rapid computer processing. To improve the contrast between tissues and abnormal structures, specific pulse sequences and weighting of the images are applied. This review summarizes the principles of MRI physics for clinicians who lack an understanding of fundamental physics.