Generation of X-rays Q&A Robert Metzger, Ph.D.

RAPHEX Diagnostic Question 2001 D4-D6: To determine the safe operation condition of portions of the x-ray tube assembly, which of the following charts would be the most appropriate to consult in each of the following situations? Anode cooling chart Housing cooling chart Radiographic ESE chart Radiographic technique chart Single exposure rating chart D4: Number of exposures allowed in 20 minutes D5: Number of exposures allowed in 2 minutes D6: Number of exposures allowed in 0.2 minutes

RAPHEX Answer for 2001 Question D4-D6 D4: B. D5: A. D6: E.

RAPHEX Diagnostic Question 2001 D7: Approximately _____% of the energy carried by electrons which bombard the anode of an x-ray tube is converted into x-ray photons. A. 99 B. 75 C. 50 D. 25 E. 1

RAPHEX Answer for 2001 Question D7 E. Virtually all of the electrical energy goes into heating the anode at diagnostic x-ray energies.

RAPHEX Diagnostic Question 2003 D4: Changing the focal spot from 0.6 mm to 1.0 mm has the following effect: A. Heat loading capacity of the anode is decreased B. Geometric unsharpness of the image is improved C. High contrast spatial resolution of the image is improved D. Available exposure times at a given mA station are increased E. Patient dose is decreased

RAPHEX Answer to 2003 Question D4 D. Available exposure times at a given mA station are increased Increasing the focal spot size increases the area over which the instantaneous heat is distributed. This increases the heat loading capacity of the anode track, and thus the available exposure times for a given mA. Unsharpness and resolution are degraded. The dose remains the same, since the total mAs is unchanged.

RAPHEX Diagnostic Question 2004 G46: The minimum photon energy in an x-ray spectrum is determined by the: A. Inherent and added filtration B. Target material C. kVp D. Maximum mA E. None of the above

RAPHEX Answer for 2004 Question G46 A. The total filtration (combination of the inherent filtration and the added filtration) preferentially removes the lower energy photons. The more the filtration, the higher the minimum energy of x-ray photon.

RAPHEX Diagnostic Question 2004 G39: Regarding x-ray tubes, all of the following are true except: A. The filament emits electrons by thermionic emission. B. Electrons travel from the anode to the cathode. C. The kVp is the peak voltage applied between the anode and the cathode. D. When electrons strike the target, characteristic x-rays and Bremsstrahlung are emitted. E. The target is angled and rotated to increase its heat capacity.

RAPHEX Answer for 2004 Question G39 B. The electrons travel from the cathode (where the filament is located) to the anode (a.k.a. the target).

RAPHEX Diagnostic Question 2004 D6: The energy of the charactieristic 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 a three phase, or a high-frequency generator is used. C. The rectification of the secondary potential. D. The tube current. E. The space charge compensation circuit.

RAPHEX Answer for 2004 Question D6 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 be not be produced. [The binding energies of the target electrons is dependent on the number of protons in the nucleus.]

RAPHEX Diagnostic Question 2002 D16: In the figure below, the factor that was changed to produce the two different x-ray spectra was the: A. Target material B. Filtration C. kVp D. mAs E. Anode angle

RAPHEX Answer for 2002 Question D16 B. Filtration. The maximum photon energy is the same; therefore the kVp is the same. The characteristic x-rays are the same; the target is the same. Changing the mAs would only change the area under the curve. Changing anode angles usually has only a minor effect on the spectrum. The differences in the lower energy cut-off and the average photon energy are indicative of different filtration.