UPSC Prelims 2007 Q123: Science & Technology – Health & Diseases
Which of the following types is used by computed tomography employed for visualization
of the internal structure of human body?
- (a) X - Ray
- (b) South waves
- (c) Magnetic resonance
- (d) Radioisotopes
Answer: (a) X - Ray
Explanation
Computed Tomography (CT) uses X-rays
| Imaging method | What it uses |
|---|---|
| CT scan | X-rays taken from many angles, put together by a computer into cross-section slices |
| MRI | Strong magnetic field + radio waves — no ionising radiation |
| Ultrasound | High-frequency sound waves |
| PET / nuclear scans | Radioisotopes (radioactive tracers) |
CT was developed by Godfrey Hounsfield and Allan Cormack — Nobel Prize in Medicine, 1979.
Answer: (a) X-Ray.
Why each option is right or wrong
- (a) CORRECT. CT builds cross-section images from X-rays.
- (b) Incorrect. Sound waves are used in ultrasound (sonography).
- (c) Incorrect. Magnetic resonance is used in MRI.
- (d) Incorrect. Radioisotopes are used in PET/SPECT nuclear imaging.
Key point
CT = X-rays (Hounsfield & Cormack, Nobel 1979). MRI = magnets + radio waves. Ultrasound = sound. PET = radioisotopes.
Remember
CT scans use X-rays; MRI uses magnets and radio waves.
Common mistakes
- Mixing up CT and MRI — CT uses ionising X-rays; MRI does not.
- Thinking ultrasound uses radiation — it uses sound.
- Forgetting that CT gives higher radiation dose than a plain X-ray.
Exam tip
Match the letter: CT → X-ray (radiation); MRI → Magnet; USG → Sound; PET → Positron (isotope).
Sources
- NCERT Class XII — Physics Part I, Ch 8 (Electromagnetic Waves — X-rays)
- Nobel Prize — Physiology or Medicine 1979