Radiation Attenuation and Penetration
· Explain the concept of “half-value layer” (HVL) and describe why it is a useful in clinical radiology.
· State the approximate HVL value for a diagnostic x-ray beam in (1) soft tissue, (2) aluminum, (3) lead.
· Describe the procedure in detail for measuring the HVL of an x-ray beam.
· If a 2-mm thickness of material transmits 25% of a mono-energetic beam of photons, calculate the HVL of the beam.
· Describe the relationship of HVL to the linear attenuation coefficient.
· If the linear attenuation coefficient has a value of 0.2 mm, calculate the HVL.
· If the HVL is 1 mm, calculate what thickness of material would be required to reduce the radiation to 10%.
· A narrow beam of 10,000 mono-energetic photons impinges upon a material with a linear attenuation coefficient of 0.05 cm-1. Sketch a plot of number of photons passing through various material thickness.
· Identify three factors that influence the penetrating ability (quality), or HVL, of an x-ray beam.
· Explain the concept of effective energy of an x-ray beam.
· Explain the process of x-ray beam filtration.
· Explain why x-ray beams are filtered.
· Distinguish between inherent and added filtration.
· Identify the materials that are used to filter diagnostic x-ray beams and discuss the specific use of each.
· State the amount of filtration that must be in a diagnostic x-ray beam.
· Describe the process generally used to determine if an x-ray beam contains adequate filtration.
· If an x-ray beam delivers an exposure of one roentgen (1R) to a patient’s body, what will be the approximate scatter exposure in the following directions:
1. Chapter 11. The Physical Principles of Medical Imaging, 2ndEd. Perry Sprawls. Medical Physics Publishing.
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