1. ALARA Principle ☢️
As Low As Reasonably Achievable - The golden rule of radiation safety!
TIME
Less time in radiation field = Less dose
DISTANCE
Inverse Square Law: Double distance = 1/4 dose
SHIELDING
Lead aprons, thyroid shields, gonadal shields
2. X-ray Production ⚛️
High-speed electrons hit the anode target, producing X-rays through two mechanisms:
Bremsstrahlung Radiation (Braking Radiation)
Electrons decelerate near nucleus → X-rays with continuous spectrum (most X-rays produced this way)
Characteristic Radiation
Electrons knock out inner shell electrons → Discrete energy peaks (specific to target material)
3. X-ray Tube Components 🔌
CATHODE (Negative)
- Filament (tungsten coil) - electron source
- Focusing cup - directs electrons
- Thermionic emission
ANODE (Positive)
- Target (tungsten or rhenium-tungsten)
- Focal spot - where electrons hit
- Rotating anode for heat dissipation
4. Exposure Factors (mAs and kVp) ⚡
mAs (Milliampere-seconds)
Controls QUANTITY of X-rays (number of photons)
Directly proportional to patient dose
mAs = mA × time
kVp (Kilovoltage Peak)
Controls QUALITY of X-rays (penetrating power)
Higher kVp = More penetrating, lower contrast
15% Rule: ↑15% kVp = Double exposure
5. Image Quality Factors 📸
Density (Optical Density)
Overall darkness of image. Controlled by mAs.
Contrast
Difference between light and dark areas. Controlled by kVp.
Spatial Resolution
Sharpness/detail. Affected by focal spot size, motion, geometry.
💡 Pro Tips for the Board Exam
- ✓ Remember: mAs controls QUANTITY, kVp controls QUALITY
- ✓ Inverse Square Law: I1/I2 = (D2)²/(D1)²
- ✓ Line Focus Principle: Actual focal spot > Effective focal spot