1. Image Quality Q&A

2. RAPHEX Diagnostic Question 2001 D9: The imaging system which is best for visualizing small high contrast objects is: A. Computed tomography B. Film-screen radiography C. Image intensified fluoroscopy D. Magnetic resonance imaging E. Ultrasound

3. RAPHEX Answer to 2001 Question D9 B. Film-screen radiography An example is microcalicifications on mammography

4. RAPHEX Diagnostic Question 2002 D13: The impression of noise in an x-ray image is: A. Increased by increasing the film speed in a screen-film cassette B. Decreased by increasing the film speed in a screen-film cassette C. Increased by decreasing the focal-spot size D. Decreased by decreasing the focal-spot size E. Mainly determined by imperfections in the image receptor

5. RAPHEX Answer for 2002 Question D13 A. Increased by increasing the film speed in a screen-film cassette Increasing the film speed in a screen-film cassette reduces the number of x-ray photons absorbed byt eh screens to produce the same density on the film. Thus, quantum noise increases. Noise is due to the statistics of x-ray detection; it is therefore independent of focal-spot size.

6. RAPHEX Diagnostic Question 2003 D7: Low contrast detectability refers to the ability of a system to distinguish: A. A calcified lung nodule B. A non-calcified lung nodule C. Between overlying and underlying tissues D. The size of a small fracture E. Vessels during the arterial phase of a normal angiogram

7. RAPHEX Answer to 2003 Question D7 B. A non-calcified lung nodule Low contrast detectability represents the ability of a system to reproduce an object whose attenuation coefficient does not vary greatly from the surrounding material

8. RAPHEX Diagnostic Question 2003 D11: Most of the energy tranferred from incident electrons to the target of a diagnostic x-ray tube goes to the production of _____. A. Characteristic radiation B. Bremsstrahlung C. Heat D. Compton Scatter

9. RAPHEX Answer to 2003 Question D11 C. Heat Typically, 99% or more of the energy deposited by the electrons in the target of an x-ray tube is dissipated as heat.

10. RAPHEX Diagnostic Question 2003 A high-ratio grid is used to eliminate a significant portion of the scattered photons. As a result, the radiation dose to the patient will ___ and the radiographic contrast will___. A. increase, decrease B. increase, increase C. decrease, increase D. decrease, decrease E. be unchanged, increase

11. RAPHEX Answer to 2003 Question D21 B. increase, increase Reducing scatter improves contrast. As grid-ratio increases, the patient dose increases, as more radiation is required to replace the radiation absorbed by the grid.

12. RAPHEX Diagnostic Question 2003 D22: A radiographic chest unit with a focused grid produces films with optical densities much lighter towards the edges. A possible cause is: A. Upside-down grid B. Lateral misalignment of the focal spot and the grid center C. Poor film-screen contact D. Patient motion

13. RAPHEX Answer for 2003 Question D22 A. Upside-down grid An upside down grid will produce a film that is dark in the center and almost blank towards the edges. Patient motion produces a blurred image; lateral misalignment produces an overall lighter image; poor screen-film contact produces a spotted image.

14. RAPHEX Diagnostic Question 2002 D18: The main reason a 12:1 grid is never used with portable radiography is: A. There will be too much grid cut-off if the grid is not positioned properly B. The output of portable x-ray units is too low C. It is necessary to keep exposure times under 10 ms. D. The increased scatter makes for wider latitude radiographs which are undesirable for portable chest chest x-rays E. High ratio grids may only be used at high kVp. Portable x-ray units only go up to 90 kVp

15. RAPHEX Answer for 2002 Question D18 A. There will be too much grid cut-off if the grid is not positioned properly The higher the grid ratio, the more sensitive it is to grid cut-off. Slight angulation and/or decentering will cause major density changes on the radiograph.

16. RAPHEX Diagnostic Question 2002 D19: Abdominal radiographs taken at high kVp without a grid can be expected tohave considerable scatter. The ratio (S/P) of scattered photons (S) to unscattered primary photons (P) reaching a screen-film combination without a grid is about_____. A. 0.2 B. 0.5 C. 1.0 D. 4.0 E. 20.0

17. RAPHEX Answer for 2002 Question D19 D. 4.0 Bucky factors of 3 to 6 are expected for grids.

18. RAPHEX Diagnostic Question 2001 D8: Geometric magnification can improve the detection of high contrast objects. The fundamental limitation on useful magnification is: A. Blurring due to focal spot size B. Blurring due to removal of the grid C. H&D curve of the image receptor D. MTF of the image receptor E. Size of the image receptor

19. RAPHEX Answer to 2001 Question D8 A. Blurring due to focal spot size Penumbra, caused by a finite focal spot, increases with magnification. Eventually this dominates the image. The grid, H&D curve, and size have no effect on magnification. The receptor’s MTF becomes less important as magnification increases.