Magnetic Resonance Imaging (MRI) is a medical imaging technique that uses magnetic fields and radio waves to produce detailed pictures of the internal structures of the body. It is a safe and non-invasive procedure that does not use ionising radiation, unlike X-rays or CT scans. MRI scan can help diagnose and monitor various health conditions, such as brain tumours, spinal cord injuries, heart disease, liver diseases and more.
The basic principle of an MRI scan is that the body is composed of water molecules, which contain hydrogen atoms. These atoms have a property called spin, which means they act like tiny magnets. When a patient’s body enters the MRI machine, a powerful magnet creates a strong magnetic field. Under this influence, the hydrogen protons align themselves with the magnetic field. In the next stage, a short burst of radiofrequency (RF) energy is applied. This pulse disrupts the alignment of the hydrogen protons, pushing them out of their equilibrium state.
Once the RF pulse ceases, the protons begin to return to their original alignment, a process known as relaxation. There are two distinct relaxation processes at play - T1 (longitudinal or spin-lattice relaxation) and T2 (transverse or spin-spin relaxation). T1 involves the realignment of protons with the magnetic field, while T2 involves the protons returning to their equilibrium state while interacting with neighbouring protons.
As the protons undergo relaxation, they emit radiofrequency signals. These signals, rich in information about the surrounding tissues, are detected by specialised coils within the MRI machine. The strength and duration of these signals depend on the type of tissue and its composition, providing the necessary data for image formation.
Spatial information is also crucial for creating detailed and accurate images of the internal structures. This is achieved through the use of gradient coils within the MRI machine. These coils generate variations in the magnetic field, allowing the system to encode the location of the emitted signals. The spatial encoding process is vital for determining where in the body the signals originated, enabling the creation of precise images.
The detected signals, along with spatial information, are processed by a sophisticated computer system, which then reconstructs these into high-resolution, cross-sectional images. Different tissues exhibit varying signal intensities, leading to images with remarkable contrast, enabling clinicians to differentiate between structures like muscles, organs, and the brain.
From the alignment of hydrogen protons to the reconstruction of detailed images, each step in the MRI journey contributes to its role as a cornerstone in modern medical diagnostics. As technology advances, the potential applications of MRI continue to expand, promising even greater insights into the mysteries of human anatomy and pathology.