Absorption, Attentuation, and Grids Flashcards
What is known as the total reduction in the x-ray number in the beam after penetrating tissues?
Attenuation
What dictates attenuation?
atomic Z and X-photon’s energy
What is exponential attenuation?
There is no fixed number for X-rays being absorbed while passing through a different medium
What is the Half-Value Layer (HVL)?
- X-rays of any given energy( from 10 keV to 150 keV) are more penetrating in the material of low Z than in the material with high Z
- characteristic of the useful X-ray beam
What is the HVL of an X-ray beam?
-the thickness of the absorbing material necessary to reduce the X-ray intensity by 50% of its original value
Does added filtration attenuate low or high energy x-photons more?
-Low energy x-photons
What are the 3 types of filtering?
1) tungsten anode absorbs low energy
2) glass housing and dielectric oil
3) metal of different thickness
What are compensating filters used for?
When needed to expose body parts of unequal thickness
What is the 10th value layer?
attenuates the primary beam by 90% or the primary beam will be reduced to 1/10 of its intensity
What are grids used for?
reduce scatter noise and improve image contrast resolution
What 3 things does scatter intensity depend on?
- kVp
- Beam field size
- patient’s thickness
Where are grids placed?
In the Bucky between the patient and image receptor
When are grids used?
- kVp = 60+
- tissue thickness = >10cm
What is composed of a grid?
- lead strips
- aluminum and plastic interspacing
How much of scatter can grids remove?
-up to 80%
