Know what magnetic resonance imaging is


Posted: Date Posted – 11:35 PM, Wed – 18 May 22

By Dr. Modala Mallesh
Subject matter expert
Palem, Nakrekal, Nalgonde

This article is a continuation of previous articles that help you understand what constitutes the biological sciences and its various branches/concepts. Today we will be discussing the second part of biomedical technology with a focus on Magnetic Resonance Imaging (MRI).

Magnetic Resonance Imaging (MRI)

  • An MRI (magnetic resonance imaging) is a diagnostic radiology technique that uses magnetism, radio waves and a computer to produce images of body components.
  • It is important to note that MRI does not use ionizing radiation, as X-rays do, and is generally a safe procedure.
  • MRI is a non-invasive medical imaging technique that helps doctors diagnose certain anatomic abnormalities/pathological conditions.
  • This technique uses proton nuclear magnetic resonance to generate proton density images of body parts.
  • MRI uses a powerful magnetic field, radio frequency pulses and a computer to produce detailed images of organs, soft tissues, bones and virtually all other internal body structures.

To note: IRMM provides good contrast between the different soft tissues of the body, which makes it particularly useful for imaging the brain, muscle, heart and cancerous tissue compared to other medical imaging techniques such as computed tomography (CT)/X-rays.

MRI scanner and procedure:

  • The MRI scanner is a giant circular magnetic tube.
  • A patient is placed on a mobile bed which is inserted into the magnet.
  • The human body is mostly made up of water molecules which each contain two hydrogen nuclei/protons.
  • The magnet creates a strong magnetic field which aligns the protons with the direction of the magnetic field (protons are not aligned under normal conditions).
  • A second radio frequency electromagnetic field is then activated for a brief period. Protons absorb some of the energy of these radio waves.
  • When this second radio frequency emission field is turned off, the protons release energy at a radio frequency that can be detected by the MRI scanner. (Protons return to their steady state from the energized state at different relaxation rates).
  • Different tissue types emit different “quanta” of energy (in the form of different wavelengths and at different rates)
  • Abnormal tissues, such as tumors, can be detected because protons in different tissue types return to their steady state at different rates.
  • Tissues such as bone containing less water (therefore fewer protons) look different on an MRI image.
  • As a result, there is a contrast between the images of different tissues depending on their water content.
  • Even in the case of the same tissue, healthy normal cells and diseased cells emit different energy waves – hence the difference in images of different cell types.
  • The information received is processed by a computer and an image is generated.
  • The image and resolution produced by MRI is quite detailed and can detect minute structural changes in the body.
  • For some procedures, radiocontrast agents, such as gadolinium, are used to increase image accuracy/resolution.
  • After scanning is complete, computer-generated images (tomographs – images of thin slices of body parts) can be transferred to film (hard copy).
  • A radiologist interprets the images of the body parts and gives his diagnostic opinion.

To note:

  • MRI is used to distinguish pathological tissue (such as brain tumors) from normal tissue.
  • MRI can even show hairline fractures in the pelvis and hip that may not be detected by traditional X-ray/CT scans.
  • Bloating of blood vessels called aneurysms can be detected using MRI (aneurysms can occur when a tear begins in the layers of the walls of the aorta, arteries, veins/part of the heart).
  • Also, MRI is preferred over CT scans because CT scan involves effects of ionizing radiation whereas MRI does not have ionizing radiation.

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