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X-Ray Production_ Intensity _ HVL

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					X-Ray Production, Intensity & HVL

1.   The ratio of electron kinetic energy converted to heat vs. converted to x-ray energy in a typical diagnostic x-ray
     target is about _________.
     A. 1:1000
     B. 1:100
     C. 1:1
     D. 100:1
     E. 1000:1

2-5. For an atom with the following binding energies bombarded by 50 keV electrons, match the energies of possible
     emissions with the types of radiation  Binding energies:        K-shell 30 keV
                                                                     L-shell 4.0 keV
                                                                     M-shell 0.7 keV
     A. Characteristic x-rays only
     B. Bremsstrahlung only
     C. Both
     D. Neither

2.   49.3 keV.
3.   26.0 keV.
4.   54.0 keV.
5.   4.7 keV.

6.   The maximum photon energy in an x-ray spectrum is determined by:
     A. The inherent and added filtration.
     B. The target material.
     C. The kVp.
     D. The maximum mA.
     E. None of the above.

7.   The minimum photon energy in an x-ray spectrum is determined by:
     A. The inherent and added filtration.
     B. The target material.
     C. The kVp.
     D. The maximum mA.
     E. None of the above.

8.   In a typical x-ray beam, the 2nd HVL _______ the 1st HVL.
     A. Is always greater than
     B. Is always less than
     C. Is the same as
     D. Could be greater than or less than

9.   To produce a bremsstrahlung x-ray:
     A. An orbital electron is removed.
     B. An electron is slowed down by the field of the nucleus.
     C. An electron is absorbed by the nucleus.
     D. An electron will change shells, emitting the excess binding energy as an x-ray.
     E. An electron causes the nucleus to jump to a higher energy state, which is then followed by x-ray emission.

10. A monoenergetic photon beam has a half-value layer of 1 cm in lead. After traveling through 1.5 cm of lead, the
    fraction of the intensity remaining is _______%
    A. 100
    B. 70
    C. 50
    D. 35
    E. 20
11. When measuring the HVL of an x-ray beam, a narrow beam must be used because:
    A. The beam must be smaller than the detector.
    B. A broad beam could introduce scattered x-rays, giving a false reading.
    C. The average beam energy would be greater with a broad beam
    D. All of the above are true.

12. A photon beam has a linear attenuation coefficient μ = 0.025/cm in air. The average distance l (i.e., mean free
    path) that an average photon in this beam will travel before interacting is:
    A. 40 cm.
    B. 25 cm.
    C. 2.5 cm.
    D. 4 cm.
    E. 0.025 cm.

13. The average energy of a photon in a diagnostic x-ray beam is approximately ________ of the maximum energy.
    A. 7/8
    B. 3/4
    C. 2/3
    D. 1/3
    E. 1/8

14. The effective photon energy of an x-ray beam can be increased by:
    A. Increasing the tube current.
    B. Decreasing the filtration.
    C. Increasing the mAs.
    D. Increasing the tube voltage.
    E. All of the above.

15. If 1 mm A1 is added to the filtration of an x-ray beam, this would reduce the ________.
    A. Load on the x-ray tube.
    B. Scatter into the detection system.
    C. Maximum field size.
    D. Overall system latitude.
    E. Patient skin dose.

16. In diagnostic x-ray systems, filters are used to “harden” the beam. This process is mainly due to:
    A. Coherent scattering.
    B. Photoelectric effect.
    C. Compton effect.
    D. Pair production.
    E. A, B, and C only.

17-20. Refer to the x-ray output intensity spectra at right, obtained at the same kVp and the mA.
       Answer A for True and B for False.

17. ____ Spectrum I has a lower effective
    energy than spectrum II.

18. ____Two different targets were used to
    produce the two spectra.

19. ____The minimum wavelength is the
    same for both spectra

20. ____Spectrum I and spectrum II are
    produced using a three-phase generator.
21. The characteristic x-rays emitted from a tungsten target when 100 keV electrons are fired at it ________.
    A. Have a continuous spectrum of energies up to 100 kV.
    B. Are about equal in intensity to the bremsstrahlung.
    C. Have energies equal to differences in the electron binding energies of tungsten.
    D. Do not contribute to the imaging process.
    E. None of the above.

22. The effective energy of an x-ray beam ___________.
    A. Linearly increases with the atomic number.
    B. Is proportional to the mAs.
    C. Is not affected by added filtration.
    D. Is equal to the kVp.
    E. Affects subject contrast.

23. X-ray beam quality cannot be characterized just in terms of kVp, because beams of equal kVp may have
    different _________:
    A. Inherent filtration.
    B. Maximum wavelengths
    C. Half-value layers.
    D. Target materials.
    E. All of the above.

24. The second half-value layer (HVL) of a photon beam is approximately the same as the first HVL:
    A. For all x-ray tube generated photon beams.
    B. Only if the energy is below 100 kVp.
    C. Only if the beam is Monoenergetic (e.g., gamma rays).
    D. Never; it is always less.

25. List the following types of x-ray equipment in order of increasing beam half-value layer.
    A. CT, mammography, barium fluoroscopy, skeletal radiography.
    B. Mammography, skeletal radiography, CT, barium fluoroscopy.
    C. Barium fluoroscopy, mammography, skeletal radiography, CT.
    D. Skeletal radiography, barium fluoroscopy, CT, mammography.
    E. Mammography, skeletal radiography, barium fluoroscopy, CT.

26-30. This below compares 3 x-ray tube spectra from the same target material. Answer A for True and B for False.

26. ____ Curve A is a pure, hypothetical x-ray
     spectrum produced in the target without
     attenuation or filtration.

27. ____ Curve C represents a more
     penetrating x-ray beam than beam B.

28. ____Curve B’x maximum energy is about
     33 keV.

29. ____ The energy of characteristic x-rays in
     curve C is higher than that in curve B.

30._____The target material for the three
    spectra could be molybdenum.
31. For a fixed mAs and kVp, increasing the exposure time will significantly affect the __________.
    A. Overall film density.
    B. Overall film latitude.
    C. Speed of film/screen combination.
    D. Motion unsharpness.
    E. Patient exposure.

32. Tungsten has the following binding energies: K=69 keV L =12 keV M=2 keV. Which of these projectile
    electron energies can cause tungsten to emit a 57 keV Kα x-ray?
                      1. 57 keV
                      2. 58 keV
                      3. 57 keV
                      4. 80 keV
    A. 1, 2, 3.
    B. 1, 3.
    C. 2, 4.
    D. 4 only.
    E. All of the above.

33 – 36. For spectra I and II from the same target
    in the diagram at right, choose the most
    appropriate answer from the list below.
    A. Spectrum I.
    B. Spectrum II.
    C. Both.
    D. Neither
    E. Cannot be determined.

33. ____ Low-energy photons have been
    removed by filtration.

34. ____ Minimum photon energy is 50 keV.

35. ____ K characteristic x-rays have been
    removed by filtration.

36. ____ Higher HVL.

37. For a monoenergetic photon beam (such as gamma rays or characteristic x-rays) which of the following is true:
    A. The 2nd HVL is thicker than the 1st.
    B. The 1st HVL is thicker than the 2nd
    C. All HVLs are equal.
    D. The relationship between the 1st and 2nd HVL depends upon beam energy.
    E. The relationship between the 1st and 2nd HVL depends upon filtration.

38. The x-ray spectra at right have the same ____.
                 1. Filtration
                 2. Target material
                 3. HVL
                 4. kVp
    A. 1,2,3,4
    B. 1,3
    C. 2,4
    D. 4 only
39. Regarding an x-ray system used for general radiographic imaging, which of the following is correct?
    A. The predominant mechanism of x-ray production is characteristic emission from the anode.
    B. An increase in kVp will increase the number of x-rays produced.
    C. The Heel Effect results in greater x-ray intensity at the anode end of the x-ray tube anode-cathode axis.
    D. Increase in tube current (mA) will increase the half-value layer (HVL) of the x-ray spectrum
    E. Approximately 99% of the energy consumed by the x-ray tube is converted to x-rays

40. The difference between kVp and keV is the difference between:
    A. Exposure and dose.
    B. Monoenergetic and heterogeneous photon beams.
    C. Potential difference and energy.
    D. Gamma rays and x-rays.
    E. Ionizing and non-ionizing radiation.

41 – 43. For the x-ray intensity spectra shown at
    the right, the different spectra are obtained
    using: (Use A for True and B for False)

41. ____Different target material but same kVp.

42. ____Different kVp and similar tube filtration.

43. ____Similar target material and similar mA.


44. The 1st half-value layer (HVL) for an 80 kVp
    x-ray beam is about equal to:
    A. 20 – 40 mm Al
    B. 2 – 4 cm soft tissue
    C. 2 – 4 mm lead
    D. 2 – 4 cm bone

45. For a typical diagnostic x-ray beam, the HVL is measured in ________.
    A. Mm Pb
    B. Cm W
    C. Mm A1
    D. Cm Cu

46. The energy of characteristic radiation emanating from a tube operating at 100 kVp is determined by:
    A. The elemental composition of the target.
    B. Whether a single phase or three phase, or high-frequency generator is used.
    C. Rectification of the secondary potential.
    D. The tube current.
    E. The space charge compensation circuit.

47. The characteristic x-rays emitted from a tungsten target when 100 keV electrons are fired at it:
    A. Have a continuous spectrum of energies up to 100 kV.
    B. Are about equal in intensity to the bremsstrahlung.
    C. Have energies equal to differences in the electron binding energies.
    D. Do not contribute significantly to the imaging process.

48. Increasing the mAs will _________ the x-ray beam quantity, and will _________ the x-ray beam quality.
    A. Increase , increase
    B. Decrease, increase
    C. Increase, decrease
    D. Decrease, decrease
    E. Increase , not change
49. Most of the energy transferred from incident electrons to an x-ray tube target goes to the production of_______.
    A. Characteristic radiation
    B. Bremsstrahlung
    C. Heat
    D. Compton scatter

50. The effect of adding 0.1 mm Cu filtration to an x-ray beam is:
    A. Lower patient skin exposure.
    B. Increased HVL.
    C. Reduced contrast at the same kVp.
    D. Longer exposure times.
    E. All of the above.

51 – 55. Match the following target and filter materials with the radiographic exam most closely associated with its
    use (use each answer only once.)
    A. Copper, aluminum
    B. Molybdenum
    C. Aluminum
    D. Tin, copper, aluminum
    E. Leaded acrylic shaped wedges

51. ____ Filter used for airway studies

52. ____ Filter used for routine angiography

53. ____Target used for screen-film mammography

54. ____Filter used for chest radiography

55. ____Filter used for scoliosis radiography

56. The maximum wavelength of the photons in an x-ray spectrum is primarily determined by the _____.
    A. KVp
    B. Anode material
    C. Filtration
    D. Anode angle
    E. Ripple

57. Patient entrance exposure increased approximately with _________.
    A. (kVp x mAs)2
    B. kVp2 x mAs
    C. kVp x mA
    D. kVp2 x mA
    E. kVp x mAs
X-Ray Production, Intensity & HVL – Answers
1.     D   X-ray production is inefficient, and steps are needed to dissipate the large amount of heat generated.

2..    B   See answer 5 below

3.     C   See answer 5 below

4.     D   See answer 5 below

5.     B   Bremsstrahlung (“braking radiation”) x-rays are emitted by electrons slowed down by the electrostatic
           field of nucleus, and can have any energy up to that of the incident electron’s kinetic energy. Possible
           characteristic x-rays energies are found by taking the energy differences between electron shells

6.     C   The maximum bremsstrahlung energy in keV is equal to the maximum energy of the incident
           electrons, i.e., to the kVp applied across the tube.

7.     A   The minimum photon energy depends on the inherent and added filtration in the tube assembly.

8..    A   The 1st HVL hardens (increases the average energy) of the beam, making it more penetrating.

9.     B

10.    D   Ix = IO e-μx = IO e-0.693X/HVL = IO e-0.693*3/2 = 0.354 IO. (Note from Lee: for a quick answer, the result
           has to be between 1 HVL (50%) and 2 HVLs (25%). Asnwer D is thus the only possible choice).

11.    B

12.    A   I = 1/μ.

13.    D

14.    D   Increasing the tube current or mAs increases the intensity but does not change the spectrum.
           Decreasing the filtration actually decreases the effective photon energy.

15.    E   Increasing the effective energy by additional filtration increases the penetration and thus reduces the
           skin dose for the same intensity of the exit beam.

16.    B   Removal of lower energy photons by filtration (generally metal filters) is primarily by photoelectric
           effect, which has Z3/E3 dependence of interaction probability. Compton effect may slightly increase
           effective energy. Pair production’s energy threshold is above that of typical diagnostic x-ray units.

17.    A   Spectrum II has more higher-energy photons, hence a higher effective beam energy.

18.    B   Since the characteristic spectra are at the same energy, the target material must be the same.

19..   A   Minimum wavelength corresponds to maximum energy which equals kVp. kVp is the same for both.

20.    B   Different effective energies and total radiation output (area under the curve) indicate that the spectra
           are produced using different phase generators. The higher proportion of lower energies in spectrum I
           suggest it was produced with a single phase generator.

21.    C

22.    E   X-ray beam effective energy is about 1/3 to 1/2 of the kVp, depending on filtration. Added filtration
           increases effective energy. mAs does not affect the bremsstrahlung spectrum.
23.   E

24.   C   Penetrating the 1st HVL hardens polyenergetic x-ray beams, making the 2nd HVL larger than the 1st.

25.   E   HVL increases with kVp and filtration. Mammography is done at very low kVp (HVL ~ 0.3–0.4 mm
          A1); skeletal radiography at 60–70 kVp (HVL ~ 1.5–2.5 mm A1); barium fluoroscopy at 80-110 kVp
          (HVL ~3–5 mm A1); and CT at 120 – 140 kV with added shaped filters (HVL of 6 mm A1 or more).

26.   A   This curve represents a continuous bremsstrahlung spectrum produced by 100 kVp electrons, with no
          hardening (by the target itself or by external filters). Characteristic radiation is not shown.

27.   A   The mean energy beam C is higher than that in beam B, hence it is more penetrating.

28.   B   The maximum energy for both B and C 100 keV, which is equal to the operational kVp.

29.   B   Characteristic x-ray energies are determined by the target material, which is the same for both curves.

30.   B   The target material in question is tungsten, producing characteristic x-rays at a minimum of 59.3 keV.
          The characteristic radiation energy from molybdenum is about 16 and 19 keV.

31.   D   Increasing exposure time increases motion unsharpness. For a fixed kVp and mAs, the film and patient
          exposures, latitude, and speed are unaffected. No change in kVp means no change in system latitude.
          The screen/film system is not significantly affected by exposure time variations.

32.   D   A Ka characteristic x-ray is emitted due to an L-shell electron transition to fill a K-shell vacancy. For
          this to occur, a K-shell electron must be ejected from the atom. The incoming particle must have at
          least as much energy as the binding energy of the K shell (69 keV) to achieve this.

33.   C   Photons below 10 keV have been removed by filtration by both spectra.

34.   D   The minimum photon energy from both spectra is about 10 keV.

35.   D   The K peaks appear on spectrum II, but on spectrum I they are not seen because the kVp is too low.

36.   B

37.   C   Unlike polyenergetic beams produced by an x-ray tube, amnoenergetic beams do not become harder.

38.   C   Their kVp (maximum energy intersection with the x-axis) is the same, and the characteristic peaks
          show that they have the same targets. The different areas under the curves and different minimum
          energies indicate that they have different HVLs and different filtration.

39.   B   Increasing kVp produces more photons. Bremsstrahlung is the predominant x-ray production
          mechanism. The Heel Effect results in greater x-ray intensity toward the cathode end of the tube axis.
          Increasing mA increases the number of photons but does not affect their energy, so it does not affect
          the HVL. Approximately 99% goes into tube heating, and less than 1% is converted into x-rays.

40.   C   KVp (kilovolts peak) is a potential difference; keV (kilo electron volts) is a unit of energy.

41.   B   The x-ray output spectra are for different kVp (60, 80, 100 and 120 kVp) but same tube current (mA),
          exposure time, filtration (same minimum energies) and target material (same characteristic energies).

42.   A   The four spectra have the same minimum energy indicating the same filtration type and thickness.

43.   A   The areas under the spectra follow roughly a kVp 2 dependence (ignoring characteristic x-rays), which
          suggests no change in any factors such as mA (tibe current).
44.        B     The HVL is also approximately 2 to 4 mm aluminum, 2 to 4 cm tissue, and 0.02 to 0.04 mm lead.

45.        C     HVLs are measured with---and requirements are specified in--- mm of aluminum.

46.        A     The characteristic radiation is solely determined by the target material. If the energy of the electrons
                 does not exceed the binding energy of the target electron, characteristic radiation will not be produced.

47.        C

48.        E     Increasing eh mAs increases the number of x-rays, but the shape of the spectrum does not change.

49.        C     Typically, 99% or more of the projectile electron kinetic energy is deposited as heat.

50.        E     Increasing filtration increases HVL by removing more lower energy photons than the more penetrating
                 higher energy photons, which in turn reduces contrast. The more penetrating filtered beam requires
                 less skin exposure for proper receptor exposure. However, since the filter removes photons (both high
                 and low energy) from the beam, exposure time must be increased to compensate. Typically, 99% or
                 more of the energy deposited by the electrons in the target of an x-ray tube is dissipated as heat.

51.        D     High filtration is required to reduce the contrast of the spinal column compared to soft tissue (Note
                 from Lee: I take the answer’s word for it. I personally have never seen such a filter used).

52..       C     A1 filters are used in routine radiography to selectively filter out the lower energy photons.

53.        B     In mammography low-energy photons are required to improve contrast.

54.        A     Filtration is used to increase latitude and reduce patient dose.

55.        E     These shaping filters are attached to the collimators to compensate for intensity differences exiting the
                 patient and reaching the film, thus providing a more uniform exposure over the film image.

56.        C     Maximum wavelength corresponds to be lowest photon energy, which is determined by the filtration.

57.        B     Patient exposure is proportional to x-ray output, which is approximately proportional to kVp2 and to
                 the product of the tube current and exposure time (mAs).



Medical Physics/X-ray Production, Intensity and HVL Physics Exam 2008/pf

				
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