Structural Magnetic Resonance Imaging (MRI) is a non-radioactive and non-invasive technique whose main objective is the anatomical study of body structures. Through this technique it is possible to make the diagnosis and prognosis of pathologies that affect the organs. Most frequently used to assess the anatomical brain structure, as it allows physicians to view soft tissues with greater definition. This technique has excellent spatial resolution and contrast. The technological advancement of MRI has enabled the development of new techniques such as Functional Magnetic Resonance (fMRI), spectroscopy and Imaging Tensor Diffusion (DTI), techniques that allow obtaining physiological data on brain activity.
The physical principles of MRI mainly involve the magnetic properties of the MRI machine and radiofrequency (RF) radio waves. Thus, it becomes possible to form spatial images of soft tissues through the acquired data.
The magnetic resonance device works as a large magnet generating a magnetic field 30 thousand times greater than the earth's field. Currently, there are 3 types of MRI devices based on the power of the electromagnetic field, they are the 1.5 T, 3T and 7T devices. The magnetic field is generated by an electric current applied in liquid helium at a temperature of -269 C, which starts to act as a superconductor.
Normally, H atoms perform random movements when subjected to the earth's magnetic field. Thus, the total magnetization of H atoms is zero. Therefore, when subjected to the powerful magnetic field of the MRI, the H atoms are displaced and aligned in a parallel way inside the human body. When the magnetic field is applied, the atoms start to rotate around their own axis and align in an antiparallel way.
Then, RF pulses are emitted that excite and misalign the H atoms, generating the precession movement (relaxation period). Therefore, upon receiving the RF pulses, the atoms leave the initial position and form angles (90 and 180) and then return, a phenomenon known as resonance or relaxation. Thus, the H atoms emit a new radiofrequency wave that can be calculated by the Lamor Frequency, called the Free Induction Signal (SIL). This signal is sent to the computer and decoded, making it possible to identify the position and intensity. The data is stored in the form of matrices and concatenated to form gray scale pixels. The stored pixels of the slices of the transversal, longitudinal and coronal sections form the voxels of the three-dimensional image.
Thus, with this technology it is possible to form images of the anatomical brain structure and other body structures. Therefore, its applications are numerous and its contribution to the advancement of medicine and neuroscience is unquestionable. Being an important tool to aid in the diagnosis of tumors and brain injuries.
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