Quizbank/Under construction/Basic Physics of Digital Radiography

The first quiz to be converted tyo quizbank form has been lifted from Wikibooks:Basic Physics of Digital Radiography/The Quiz

{In soft tissue, Compton scattering becomes the most important interaction process above:} - 5 keV. + 25 keV. - 50 keV. - 75 keV.

{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).

{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.

{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%.

{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.

{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.

{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.

{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.

{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.

{The Compton scattering probability per electron is approximately:} + Independent of Z. - Proportional to Z. - Proportional to Z2. - Proportional to 1/Z2.

{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.

{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.

{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.

{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.

{The finite size of the X-ray tube focal spot gives rise to:} - Pseudo-linear transformation. - Quantum mottle. + Penumbra. - Magnification.

{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?

{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%.

{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.

{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.

{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.

{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.

{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.

{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.

{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.

{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.

{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.

{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.

{The Compton absorption probability per electron is approximately:} + Independent of Z. - Proportional to Z. - Proportional to Z2. - Proportional to 1/Z2.

{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.

{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.

{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.