Aspirant Academy

Science and Technology

Medical Diagnostics

Physics: Motion, Work/Power/Energy, Gravitation, Light, Heat, Electricity, Magnetism, Sound, EM Waves, Medical Diagnostics, Nuclear Fission/Fusion, Radiation Safety

Paper II · Unit 2 Section 8 of 13 0 PYQs 31 min
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Medical Diagnostics

7.1 Imaging Technologies

X-ray Radiography (1895, Wilhelm Röntgen — first Nobel Prize Physics 1901)

  • X-rays (0.01–10 nm wavelength) pass through soft tissue but are absorbed by calcium-rich bones.
  • Applications: bone fractures, lung diseases (TB, pneumonia), dental cavities, chest screening.

CT Scan (Computed Tomography / CAT Scan)

  • Multiple X-ray beams rotate around the patient; detector arrays measure attenuation from each angle.
  • Computer reconstructs cross-sectional (tomographic) images — can show 3D internal anatomy.
  • Applications: stroke detection, cancer staging, internal injuries, organ assessment.
  • Limitation: higher radiation dose than plain X-ray; not suitable for pregnant women.

MRI (Magnetic Resonance Imaging)

  • Uses a strong magnetic field (1.5–3 Tesla, ~30,000× Earth's field) and radiofrequency pulses.
  • Hydrogen atoms (in water and fat) align with field, then emit radio waves when RF pulse ends.
  • These emissions are detected and computed into high-resolution images.
  • Advantage: No ionising radiation; excellent soft-tissue contrast (brain, spinal cord, muscles, ligaments).
  • Applications: brain tumours, MS, spinal disc herniation, ACL tears, cardiac structure.

PET Scan (Positron Emission Tomography)

  • Patient receives F-18 fluorodeoxyglucose (FDG) intravenously — a radioactive glucose analogue.
  • Cancer cells' high metabolic rate = high glucose uptake = high FDG concentration = "hot spots."
  • F-18 decays emitting positrons; positron annihilates with electron → two gamma photons at 180° — detected and back-projected to give metabolic map.
  • Also used for Alzheimer's diagnosis (brain glucose metabolism), cardiac viability assessment.

Ultrasound (Sonography)

  • High-frequency sound waves (2–15 MHz) directed into body; reflections from interfaces (organ boundaries) create images.
  • Completely safe (no ionising radiation) — standard for foetal monitoring in pregnancy.
  • Applications: obstetrics (foetal development), abdominal organs (liver, gallbladder, kidneys), echocardiography (heart function), Doppler ultrasound (blood flow velocity).

7.2 Electrophysiology

ECG (Electrocardiogram):

  • Records electrical activity of the heart from surface electrodes.
  • P wave: atrial depolarisation; QRS complex: ventricular depolarisation; T wave: ventricular repolarisation.
  • Detects arrhythmias, heart attacks (ST elevation in MI), conduction defects.

EEG (Electroencephalogram):

  • Records brain's electrical activity (10–100 µV, 1–30 Hz) via scalp electrodes.
  • Used for epilepsy diagnosis, sleep disorders, brain death assessment.