2.3 quality assurance

Question 1

what is meant by the intensity (quantity) of the X-ray beam?

Answer 1

a measure of the number of X-ray photons

Question 2

what is meant by the quality of the X-ray beam?

Answer 2

• a measure of how readily the beam will penetrate any given material
• the beam’s overall energy

Question 3

what defines the intensity of X-rays?

Answer 3

defined by mAs
- milliampere-seconds
- (current x exposure time)

Question 4

mAs defines the number of X-ray photons, how?

Answer 4

the cathode filament (where electrons are produced) is connected to the current, and the current defines the intensity

Question 5

what defines energy of X-rays (quality)?

Answer 5

kVp
- kilovoltage peak
- (potential difference)

Question 6

what is the relationship between the height of the Bremsstrahlung curve and the intensity of the X-ray beam?

Answer 6

the height of the Bremsstrahlung curve will be directly proportional to the intensity of the X-ray beam

Question 7

what is the half-value thickness (HVT) or half-value layer (HVL) of a beam of radiation?

Answer 7

• the amount of a given material (or its thickness) which will attenuate 50% of the intensity of the X-ray beam
• in practice, HVL/HVT measure the penetration power of the beam

Question 8

we express the absorbing power of a material in equivalence of _______

Answer 8

millimeters of aluminum (mm Al)

Question 9

how can attenuation of a beam (change in the number of its photons) passing through a material be described?

Answer 9

N = N0 e^-μx

• N - number of photons
• N0 - original number of photons (before entering the material
• μ - (linear attenuation coefficient), the fraction of photons that interact per unit thickness attenuator
• x - thickness of the material

Question 10

what is the relationship between the quality of an X-ray beam

Question 11

the special thickness that attenuates the beam to 50% is the HVL, which can be described as:

Answer 11

N = N0e^-μx = N02^-x/xh
HVL = xh