Basic Physics of Digital Radiography/The Quiz

A quiz on X-ray production & their interactions with matter is available below for those who wish to test their knowledge and understanding of these topics.

Additional quizzes are also available on:

• Radiation Biology & Dosimetry
• Technology of Radiographic Imaging

X-Ray Production & Interactions with Matter

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Points for an incorrect answer:
Ignore the questions' coefficients:

1 In soft tissue, Compton scattering becomes the most important interaction process above:

	5 keV.
	25 keV.
	50 keV.
	75 keV.

2 The intensity of an X-ray beam increases and the subject contrast remains unchanged by:

	Increasing the kVp.
	Decreasing the filtration in the beam.
	Changing from a single phase generator to a three phase one.
	Increasing the exposure (mAs).

3 As the kV is increased, the contrast between soft tissue and bone seen in a radiographic image:

	Decreases up to 69.5 kV but thereafter increases due to tungsten K-radiation.
	Increases up to 69.5 kV but then remains constant.
	Increases above 80 kVp, especially in Computed Radiography.
	Decreases regardless of the choice of image receptor.

4 If an aluminium filter 5 mm thick transmits 25% of a monoenergetic X-ray beam, then 10 mm will transmit:

	0%.
	2%.
	5%.
	6.25%.

5 Increasing filtration reduces the intensity of the X-ray spectrum:

	Equally at all photon energies.
	Only at the lower photon energies.
	Mostly at the lower photon energies.
	Mostly at the higher photon energies.

6 In comparison with a single phase HV generator of the same kVp, the effective energy of the X-rays from a medium frequency generator is:

	Higher.
	Lower.
	The same.
	Twice.

7 The anode of a diagnostic X-ray tube is angled to give:

	Proper reflection of the electron beam.
	A smaller actual focal spot.
	A smaller effective focal spot.
	Higher beam homogeneity.

8 Unlike the energy of a X-ray photon, that of a photoelectron is initially lost:

	In a single interaction.
	As heat.
	As a result of multiple ionizations.
	By conversion into photons of energy 511 keV.

9 For fixed kVp and filtration which will produce a beam with the largest Half Value Layer (HVL):

	Constant potential generator.
	Single phase generator.
	Mobile capacitor discharge unit.
	The HVL would be the same for all three.

10 The Compton scattering probability per electron is approximately:

	Independent of Z.
	Proportional to Z.
	Proportional to Z2.
	Proportional to 1/Z2.

11 The design of an intensifying screen is a compromise between the twin desires of low patient dose and low quantum mottle. Which of the options below best satisfies this compromise:

	High detection efficiency (DE) and high conversion efficiency (CE).
	High DE and low CE.
	Low DE and high CE.
	Low DE and low CE.

12 A modulation transfer function equal to 1.0 at a particular spatial frequency (f) means:

	The high voltage ripple transmitted from mains fluctuations is 1%.
	The energy transferred to tissue is equal to that of the incident radiation.
	The electronic circuit utilised with automatic brightness control is set to perfect linearity.
	The diagnostic image perfectly reproduces contrast variations in the object radiographed at that spatial frequency.

13 The scattered radiation during a diagnostic X-ray examination arises mainly as a result of the:

	Compton effect.
	Photoelectric absorption.
	Coherent scattering.
	All of these.

14 Electrons striking the tungsten anode of an X-ray tube with 80 keV energy can produce:

	Bremsstrahlung X-rays of maximum energy 80 keV.
	Bremsstrahlung X-rays of average energy of 80 keV.
	Characteristic X-rays of 80 keV.
	No characteristic X-rays whatsoever.

15 The finite size of the X-ray tube focal spot gives rise to:

	Pseudo-linear transformation.
	Quantum mottle.
	Penumbra.
	Magnification.

16 The X-ray tube current (mA) influences which ONE of the following parameters:

	Maximum X-ray energy?
	Number of X-ray photons?
	Mean energy (quality) of the X-rays?
	Patient penetration?

17 The proportion of the energy of an electron beam incident on the X-ray tube anode that is converted into X-rays is about:

	0.2%.
	2.0%.
	4.0%.
	20%.

18 The X-ray tube current is dictated by:

	The anode speed of rotation.
	The size of the focal spot.
	The filament current.
	The filament current and the kilovoltage.

19 For the photoelectric effect, the absorption per unit mass of the absorber depends approximately on the atomic number (Z) of the absorber according to:

	1/Z.
	Z.
	Z3.
	Z for kV less than 50 and Z2 for kV greater than 50.

20 To reduce image noise by a factor 10 the number of information carriers (i.e. X-rays photons) must ideally be increased by a factor of :

	3.1.
	10.
	20.
	100.

21 Which ONE of the following statements is false?

	The LSF stands for line spread function.
	Veiling Glare reduces the width of the LSF.
	The LSF is obtained from an analysis of a radiograph of a slit.
	The MTF can be obtained from a Fourier transformation of the LSF.

22 When a filter is used to harden a diagnostic energy X-ray beam, it does so mainly by:

	Compton effect.
	Photoelectric absorption.
	Unaltered scatter.
	Coherent scattering.

23 An X-ray beam with a high HVL is:

	Said to be more penetrating.
	Likely to result in a larger skin absorbed dose.
	Said to be soft.
	Less likely to produce scatter.

24 A radiograph is taken of a kidney using a SID of 100 cm with the kidney 50 cm from the plane of the image receptor. The kidney shadow is 24 cm long. The length of the kidney is approximately:

	12 cm.
	24 cm.
	36 cm.
	48 cm.

25 The term photon was coined to apply to:

	A small wave packet or bundle of electromagnetic radiation.
	An accelerated electron (in the diagnostic range).
	Any electron emitted from the photo-sensitive surface of an image intensifier tube.
	The collimated X-ray beam.

26 The type of X-ray interaction with matter in which all of the energy of the incident photon is expended in dislodging a bound electron is called:

	Photoelectric effect.
	Compton effect.
	Pair.
	None of above.

27 The inverse square law relationship between radiation intensity and distance from a point source of radiation (e.g. XRT focal spot) is due to:

	Chance.
	Scatter in air.
	Absorption in air.
	Divergence of the X-ray beam.

28 The Compton absorption probability per electron is approximately:

	Independent of Z.
	Proportional to Z.
	Proportional to Z2.
	Proportional to 1/Z2.

29 The effect on the X-ray spectrum of reducing the anode angle is similar to that of:

	Increasing filtration.
	Increasing kV.
	Decreasing kV.
	Increasing mAs.

30 In Compton scattering:

	The energy is shared between a recoil electron and an emitted photon.
	All excess energy is given to an ejected electron.
	The energy is shared between a scattered photon and a recoil electron.
	The photon is re-emitted with the same energy but at another angle.

31 For bone, X-ray attenuation is predominantly due to:

	Photoelectric effect, at energies than 75 keV.
	Photoelectric effect, at energies greater than 50 keV.
	Compton scatter, at energies greater than 25 keV.
	Compton scatter, at energies greater than 50 keV.