Problems and Objectives for
Learning, Discussion, Review, and Self Assessment
Production and Control of
Resources and References
The Physical Principles of Medical
Visuals for Discussion
- Sketch a cross-section of a
basic x-ray tube and label the components.
- Describe and explain the concept of
the two electrical quantities, KV and
MA, that are associated with x-ray production.
- Describe the events that occur
within an x-ray tube that lead to x-ray production.
- Describe a
focal spot, what is it? where is it?
- Name the material used as the x-ray
tube anode for general x-ray imaging and explain
why it is used.
- Name two materials used as the x-ray
tube anode for mammography
and explain why each is used.
- Lookup in a reference the
atomic number (Z) of the
two anode materials used for mammography and describe the significance of Z with respect to x-ray
- Describe the filament and focusing
cup (i.e., the cathode assembly) of an x-ray tube, including the purpose of
two filaments in some x-ray tubes and the purpose of the focusing cup.
- Name and briefly describe the
process by which electrons are liberated from a heated filament at the cathode
of an x-ray tube.
- Describe the principle factor that determines the
kinetic energy attained by electrons as they strike the x-ray tube anode.
Can it be changed or adjusted?
- Discuss at least two functions of
the x-ray tube housing.
- Describe the process of
bremsstrahlung production and sketch a typical
- Sketch and compare the three
bremsstrahlung spectra for the following factors:
50 kV and 50 mA
100 kV and 50 mA
100 kV and 100 mA
- Describe the production of
characteristic radiation and sketch a typical
- Sketch and compare the
characteristic x-ray spectra for a molybdenum
anode operating at 25 kV and 35 kV.
- Sketch and compare the
characteristic x-ray spectra for a
molybdenum anode and a
rhodium anode both operating at 30 kV.
- Identify the adjustable operating factor(s) that determine(s)
the maximum energy of x-ray photons emitted from an anode.
- Explain why K x-rays
emitted by an
atom have higher energies than L or M x-rays from the same atom.
- Explain why a high Z element
produces some characteristic x-rays with energy greater than that of x-rays
from a lower Z element, even though both elements are bombarded by 100 keV
- Define the expression "efficiency"
of x-ray production and identify the principle factors that affect efficiency , and estimate its
value for a diagnostic x-ray tube.
- Describe how the
efficiency is related
to the electron accelerating voltage (KV).
- Describe the general relationship between x-ray
production efficiency and the atomic number of the anode material.
- Sketch typical graphs and describe
the variation in output (i.e., exposure rate) of
an x-ray tube as a function of: 1. tube voltage (KV) 2. tube current (MA).
What is the type of mathematical relationship for each?
- Estimate the skin entrance exposure
to a 23 cm thick patient for a PA chest radiograph performed at 72 inches
using a technique of 120 kVp and 15 mAs. Use appropriate references as
necessary to obtain typical x-ray tube output data.
- Estimate the increase in x-ray tube
output exposure when the tube potential (KV) is increased from 60 to 75 kVp.
Explain how you arrived at the answer.