1. INSTRUMENTATION

2. ELECTRICAL REQUIREMENTS AND EFFICIENCY  Effective voltage  High frequency inverter technology (over 10,000Hz)  Constant potential output (<13% ripple)  kVp should be set according to machine’s ripple content.

3. Advantages of High- Frequency/Constant Potential Units  Ability to use lower kVp settings  Greater efficiency which results in shorter exposure times  Less patient motion.  Lower x-ray dose to the patient.  Tube will last longer because output is higher.  Less interference from reciprocity law failure.  More compact

4. KV SELECTION  Compton  Photoelectric

5. Technical Factors Defined  kVp – peak kilovolts; measure of the highest energy applied to electrons during the exposure.  mAs- The number of electrons accelerated to the target during a given exposure.  keV – ( kilo-electron volts) The energy received by the electrons.

6. PHOTOELECTRIC EFFECT  Depends on atomic number of substance  Molybdenum (atomic #42) produces characteristic peaks at 17.4-19.6keV.  Glandular tissue (atomic #’s 7,8)  Fatty tissue (atomic # 6)  Calcifications (atomic #’s 15,20)  Low kV beam essential to maximize photoelectric interactions.  25-27kV optimal

7. COMPTON  AVOID COMPTON  Deals with electron densities  No contrast differentiation between fat and glandular tissue with electron density.  Accounts for most interactions within tissues above 28kV

8. Target Material/Filter  Molybdenum – 17-20 keV 25 kVp  Rhodium – 20-23 keV 30 kVp  Tungsten – 15-25 keV 22-26 kVp

9. RECIPROCITY LAW FAILURE  Exposure must be <1sec to avoid this  Grids make it difficult to avoid  Invites client motion  Increases dosage  Capture of excessive scattered radiation on the film  Instead of making exposures beyond the RLF of the film, increase density of film by raising kVp setting.

10. GRIDS  Design  Ratio  Effect on Dose  Effect on Images

11. COMPRESSION  Decreased motion  Decreased geometric unsharpness  Increased contrast  Separates superimposed tissues  Decreased dose  Increased uniform film density

12. COMPRESSION PADDLES  Made of thin Plexiglas  Straight chest wall edge  Sufficient height and angle of chest wall  Squared rather than rounded  Remains parallel when compressed  Vertical alignment between chest wall edge and image receptor  Final compression manually controlled

13. MAGNIFICATION  No grid: causes increase in tube loading, dose and motion due to prolonged exposure time.  Disadvantages of mag:  Increased dose  Decreased sharpness  FSS decreased to improve sharpness: .2mm with 1.5x mag .1mm with 2x mag

14. MAGNIFICATION CONT…. MMMMagnification factors range from 1.4x to 2x 1111.5x mag can see 13 line pairs/mm 2222x only sees 7 line pairs

15. X-RAY TUBE  HVL – amount of AL that when added to the beam, will decrease intensity by 1/2. An indirect measurement of the x-ray beam and expressed in mm-AL.  Includes:  Beryllium window  Moly filter  Mirror  Compression paddle

16. X-RAY TUBE  Heel effect  Electron stream driven by ___  Amount of electrons controlled by ___  When angle of anode is increased:  can withstand larger stream of electrons (greater heat)  results in smaller effective focal spot which provides better resolution  more pronounced heel effect (reduction in intensity of beam from chest to nipple)

17. X-RAY TUBE  Focal Spot Projection  Reference Axis

18. AUTOMATIC EXPOSURE CONTROL  Radiation that is transmitted through an object is converted into an electronic signal, which terminates the exposure when the predetermined level of radiation has been reached.

19. AUTOMATIC EXPOSURE CONTROL  Single Pickup Phototimers  Confined to the center of the chest wall edge  Can move ~3 inches from chest  Difficult to determine adequate placement  Smart Phototimers  A series of photocells  Averages signals of each cell

20. Smart Phototimers  Track from one kVp setting to another  Compensate for differences in breast thickness  Obtain an adequate density for all varying breast densities  Compensate for reciprocity law failure of the film  Provide a kVp and mAs readout  Reproduce accurate densities on each film

21. SINGLE EMULSION FILM  More silver halide and gelatin per emulsion layer than double emulsion  Longer immersion time in developer due to thicker emulsion  More susceptible to artifacts  Anti-halation layer  Base + fog no more than.16-.20

22. H&D CURVE  High contrast films have a steeper average gradient  Fast films respond to lower exposures creating higher optical density with less light exposure.

23. DOUBLE EMUSION FILM  Contrast is less but 60% faster  Less susceptible to processor problems and artifacts

24. CASSETTES/SCREENS  Fluorescent layers either calcium tungstate (blue) or rare earth phosphor (green orthochromatic film)  An increase in screen speed will not cause as much of an increase in quantum mottle (noise) as film would.  The thicker the screen, the greater the blur, but the faster the screen becomes, thus the lower the dose.

25. PROCESSING  Extended processed films remain in developer 47 seconds (as opposed to 23 sec in standard).  Diffusion of developer through the thicker emulsion requires:  Longer immersion in developer  Increase in developer temp  Movement of film through rollers to give developer better access to silver halide

26. EXTENDED PROCESSING  Increased contrast  Increased film speed  Decreased dose  Increased noise

27. STANDARD PROCESSING  Decreased noise  Increased dose