XRAY EMISSION

1
X-RAY EMISSION

• Factors that effect x-ray emission
• Quantity
• Quality

2
X-RAY QUANTITY

• The number of x-rays in the useful beam

3
FACTORS EFFECTING X-RAY QUANTITY

• mAs
• Primary controlling factor for quantity
• mAs is directly proportional to the x-ray
  quantity
• Expressed mathematically as
• I1mAs1
• I2 mAs 2

4
Factors effecting X-ray Quantity

• kVp
• Quantity is proportional to kVp2
• Expressed mathematically
• I1(kVp 1)2
• I2(kVp 2)2

5
15 rule

• A change in kVp by 15 will have the same effect
  on optical density as changing the mAs by 50
• Increase kVp, half mAs to maintain density
• Decrease kVp 15 , double mAs to maintain density.

6
TYPES OF FILTRATION

• Inherent filtration
• Due to the tube construction, the glass window
  provides a means of filtering out some low energy
  x-ray photons
• Added Filtration
• Adding a thin sheet of aluminum or comparable
  material between the useful beam and the patient
• Compensating filtration
• A type of added filtration in which the thickness
  of the compensating filter coincides with the
  body part to be radiograph

7
Factors effecting X-ray Quantity

• Distance
• Quantity varies inversely with the square of the
  distance from the x-ray tube target
• Mathematically expressed
• I1 (D1)2
• I2 (D2)2

8
Factors effecting X-ray Quantity

• Filtration
• Filters out low energy x-ray beams and hardens
  the x-ray beam
• Reduces patient dose to low-energy, non
  informative
• x-rays

9
X-RAY QUALITY

• Refers to the penetrating ability of the beam
• Hard x-rays
• Have high penetrability and high quality
• Soft x-rays
• Have low penetrability and low quality

10
FACTORS AFFECTING QUALITY

• kVp
• Chief controlling factor of quality
• Increasing kVp increases the quality of the x-ray
  beam

11
Factors affecting QualityHalf-value Layer

• The thickness of absorbing material necessary to
  reduce the x-ray intensity to half of its
  original value

12
FACTORS AFFECTING QUALITY

• FILTRATION
• Adding filtration increases the quality of the
  x-ray beam by selectively removing low-energy
  x-rays.

13
Types of Compensating Filters

• Wedge Shaped
• Used for body parts that are thick at one end and
  thin at the other
• Trough shaped
• Used mainly for the chest medistinum
• Bow tie shaped
• Used in CT to compensate for head or body shape
• Conical filters
• Used in Digital fluoroscopy

14
THE END