Understanding the science behind magnetic resonance imaging

  • May 7, 2024
  • Posted by: OptimizeIAS Team
  • Category: DPN Topics
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Understanding the science behind magnetic resonance imaging

Subject: Science and tech

Sec: Health

Context:

  • Magnetic resonance imaging (MRI) is a critical non-invasive tool for examining the internal structures of the human body.
  • The foundational techniques of MRI were developed in the early 1970s, with significant advancements made later that decade by Paul Lauterbur and Peter Mansfield, who refined the technology for commercial application.
  • Their contributions were recognized with the Nobel Prize in Medicine in 2003, underscoring the importance of MRI in contemporary medical diagnostics.

What is Magnetic resonance imaging (MRI)?

  • MRI is a non-invasive diagnostic tool that uses strong magnetic fields to create detailed images of soft tissues within the body, such as the brain, cardiovascular system, spinal cord, joints, muscles, liver, and arteries.
  • It is particularly useful for observing and treating certain cancers like prostate and rectal cancer, as well as monitoring neurological conditions such as Alzheimer’s, dementia, epilepsy, and stroke.
  • Functional MRI (fMRI) is a variation used to study brain activity by measuring changes in blood flow.
  • However, the use of strong magnetic fields means that individuals with metallic implants or embedded metallic objects, like shrapnel or pacemakers, may not be able to undergo MRI scans due to safety concerns. Additionally, these magnetic fields can demagnetize credit cards if carried close to the scanner.

Working of MRI:

  • MRI works by using the natural abundance of hydrogen atoms found in fat and water throughout the body to generate detailed images.
  • The procedure involves four key components within an MRI machine.
    1. Superconducting Magnet: This is the primary component that creates a powerful and stable magnetic field around the body part being examined. It aligns the spinning hydrogen atoms in the body, such that their spin axes point along the direction of the magnetic field.
    2. Radiofrequency Pulse Emitter: This device emits pulses that specifically target a small population of ‘excess’ hydrogen atoms (those whose alignment is slightly off due to natural variances among approximately a million atoms). These excess atoms absorb the radiofrequency energy and become excited.
    3. Detector: When the radiofrequency pulse is turned off, the excited hydrogen atoms release the absorbed energy as they return to their lower energy state. This released energy is detected as emissions.
    4. Computer System: The emissions collected by the detector are converted into signals that a computer processes to construct two- or three-dimensional images of the scanned body part.
  • The entire process is non-invasive and particularly useful for imaging soft tissues in the human body. 
  • The strength of the magnetic field and the nature of the tissue influence the specific radiofrequency (known as the Larmor frequency) needed to excite the hydrogen atoms.
Pros of MRICons of MRI
Precision and Flexibility:

  • MRIs can focus on very specific areas of the body, down to just a few millimeters in width.
  • MRI can scan different body parts in fine detail without requiring the patient to move.

Comprehensive Imaging:

  • MRI can image the body from virtually all useful directions and in small increments, which is crucial for detailed diagnostics.

Tissue Differentiation:

  • MRI utilizes the T1 relaxation time, the period it takes for ‘excess’ hydrogen atoms to return to their lower energy states after excitation.
  • This time varies among tissues, allowing MRIs to differentiate between types of tissue by displaying them in different shades of grey.
  • Contrast agents, often gadolinium-based, can be used to further enhance tissue visibility by altering the T1 relaxation time.

Safety:

  • They pose no long-term health risks to patients.
  • The body’s atoms return to the normal state post-scan without any residual effects.
  • However, the effects on pregnant women are less understood, leading some facilities to avoid scanning during pregnancy.
High Cost:

  • MRI machines are expensive to purchase and maintain.
  • In turn, it becomes expensive for patients as well.

Patient Discomfort:

  • During an MRI scan, patients are required to lie still inside the machine. Any movement can distort the images, potentially requiring a rescan.
  • This can be challenging for claustrophobic patients, although some open-bore MRI designs may alleviate this issue.

Energy Intensity:

  • Operating an MRI machine involves generating a strong magnetic field, typically around 1 tesla or more, using superconducting coils cooled by liquid helium.
  • Although superconducting materialsdo not lose energy as heat, maintaining such a setup is still energy-intensive and costly.

Noise:

  • The operation of MRI machines involves switching heavy currents through gradient coils, which produces loud noises.

Source: TH

Larmor frequency Magnetic resonance imaging (MRI) Science and tech Understanding the science behind magnetic resonance imaging