Radiation Attenuation and Penetration

Learning Objectives

References and Resources

Mind Map Summary

Learning Objectives

 ·        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. back toward x-ray tube                 
  2.  forward toward receptor 
  3.  out the side

References and Resources

1.  Chapter 11. The Physical Principles of Medical Imaging, 2ndEd. Perry Sprawls.  Medical Physics Publishing.

Resources on the Web



Mind Map