AIIMS 2006 Physics MRI Assertion Reason Question

Explanation of the Question

Assertion: Magnetic Resonance Imaging (MRI) is a useful diagnostic tool for producing images of various parts of the human body.
Reason: Protons of various tissues of the human body play a role in MRI.

Correct Answer: A) A is true, R is true, and R is the correct explanation of A.

Why the Correct Answer is Right

1. Understanding MRI:

   • MRI is a non-invasive imaging technique that uses strong magnetic fields and radio waves to generate detailed images of the organs and tissues within the body. It is particularly effective for imaging soft tissues, making it invaluable in medical diagnostics.

2. Role of Protons:

   • The primary mechanism behind MRI is the interaction of the magnetic field with hydrogen protons, which are abundant in water and fat—two major components of biological tissues. When placed in a magnetic field, these protons align themselves with the direction of the field.
   • When a radiofrequency pulse is applied, it disturbs this alignment, causing the protons to absorb energy and move to a higher energy state. Once the pulse is turned off, the protons return to their original alignment, releasing energy in the process. This released energy is what is detected and transformed into images.

3. Conclusion:

   • Since protons are indeed crucial for the functioning of MRI, the assertion (A) is true, the reason (R) is also true, and R provides a correct explanation for why A is true. Thus, option A is the correct answer.

Why Other Options are Incorrect

• Option B: A is true, R is true but R is not the correct explanation of A.

  • This option cannot be correct because the role of protons is fundamentally what enables MRI to produce images. The reason directly explains the assertion, making this option invalid.

• Option C: A is true, R is false.

  • This option is incorrect because both the assertion and the reason are true. MRI is useful, and protons do play a significant role in its operation.

• Option D: Both A and R are false.

  • This option is clearly incorrect as we have established that both the assertion and the reason are true.

Relevant Concepts

• Magnetic Field: The magnetic field used in MRI is typically around 1.5 to 3.0 Tesla, which is significantly stronger than the Earth's magnetic field.
• Hydrogen Protons: The abundance of hydrogen in the human body (about 60% water) makes it an ideal target for MRI imaging.
• Relaxation Times: The time it takes for protons to return to their original state after being disturbed is characterized by two key processes known as T1 (longitudinal relaxation) and T2 (transverse relaxation) times. These times vary between different tissues, providing contrast in the images.

In summary, the correct answer (A) is justified through the direct relationship between the technology (MRI) and its operating principle (the role of protons in generating images), reinforcing the understanding of how MRI works in medical physics.