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Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
Exposure factors2
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Exposure factors2

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  • 1. EXPOSURE FACTORS DR Hussein Ahmed Hassan
  • 2.  Exposure factors are factors that control density (blackening) and contrast of radiographic image. They are some of the tools that technologists use to create high-quality radiographs
  • 3. Exposure Factors Controlled by the Operator  kVp  mA times Exposure Time = mAs  Determines the quality and quantity of the exposure  FFD (SID), Focal Spot and Filtration are secondary factors
  • 4. 1- EXPOSURE FACTORS:  KVP. :  It controls the quality of the beam, i.e. PENETRATION.  It influences : a: penetration power, i.e. beam quality; kVp. α penetration power. b: Radiographic contrast; kVp. α 1/radiographic contrast.    c: Radiation dose to patient.
  • 5. KVP  kVp controls radiographic contrast.  kVp determines the ability for the beam to penetrate the tissue.  kVp has more ef fect than any other factor on image receptor exposure because it af fects beam quality.
  • 6. KVP  To a lesser extent it also influences the beam quantity.  As we increase kVp, more of the beam penetrates the tissue with higher energy so they interact more by the Compton ef fect.  This produces more scatter radiation which increases image noise and reduces contrast.
  • 7. KVP  50 kV 79% is photoelectric, 21% Compton, < 1% no interaction  80 kVp 46% is photoelectric, 52% Compton 2% no interaction  110 kVp 23% photoelectric, 70% Compton, 7% no interaction  As no interaction increases, less exposure is needed to produce the image so patient exposure is decreased.
  • 8. High kVp. low radiographic contrast Low kVp. High radiographic contrast
  • 9.  MA.: 1 Ampere = 1 C/s = 6.3 x 1018 electrons/ second.  The mA selected for the exposure determines the number of x-rays produced.  The number of x-rays are directly proportional to the mA assuming a fixed exposure time.  100 mA produced half the x-ray that 200 mA would produce.
  • 10. MA  Patient dose is also directly proportional to the mA with a fixed exposure time.  A change in mA does not af fect kinetic energy of the electrons therefore only the quantity is changed.
  • 11. MA  Many x-ray machines are identified by the maximum mA or mAs available.  A MP 500 has a maximum mAs of 500 mAs.  A Universal 325 has a maximum mA of 300 and maximum kVp of 125
  • 12.  MA  More expensive three phase machines will have a higher maximum mA.  A General Electric MST 1050 would have 1000 mA and 150 kVp.
  • 13.  EXPOSURE TIME  The exposure time is generally always kept as short as possible.  This is not to reduce patient exposure but to minimize motion blur resulting from patient movement.  This is a much greater problem with weight bearing radiography.
  • 14. EXPOSURE TIME  Older machine express time as a fraction.  Newer machines express exposure time as milliseconds (ms)  It is easy to identify the type of high voltage generation by looking at the shortest exposure time.
  • 15. EXPOSURE TIME  Single phase half wave rectified fasted exposure time is 1/60 second 17 ms.  Single phase full wave rectified fastest exposure time is 1/120 second or 8 ms  Three phase and high frequency can provide exposure time down to 1 ms.
  • 16. (4) MAS. :  It af fect the total number of x-ray produced by the tube during exposure, i.e. QUANTITY.  It is the product of two quantities; mA. the tube current; s. the exposure time;
  • 17. MAS  mA and exposure time is usually combined and used as one factor expressed as mAs.  mAs controls radiation quantity, optical density and patient dose.  mAs determine the number of xrays in the beam and therefore radiation quantity.  mAs does not influence radiation quality.
  • 18. MAS  Any combination of mA and time that will give the same mAs should provide the same optical density on the film. This is referred to as the reciprocity law.  As noted earlier for screen film radiography, 1 ms exposure and exposure longer than 1 seconds do not follow this rule.
  • 19. MAS  On many modern machines, only mAs can be selected. The machine automatically gives the operator the highest mA and shortest exposure time.  The operator may be able to select mA by what is referred to as Power level.
  • 20. MAS  mAs is one way to measure electrostatic charge. It determines the total number of electrons.  Only the quantity of the photons are af fected by changes in the mAs.  Patient dose is therefore a function of mAs.
  • 21. Ampere is 1 coulomb (C) of electrostatic charge flowing each second. 1A = 1C/s = 6.3 X 10 18 electron/s 20 mAs = 0.2 Amperes. This charge releases this No. of electrons: 6.3 X 10 18 X 0.2 = 1.26 X 10 18 electron/s 20 mA. mAs 40 mA. mAs 80 mA. 200 mA. X 1.0 s = 20 X 0.5 s = 20 X X 0.25 s 0.1 s = 20 mAs = 20
  • 22. (5) Focal spot:  Most x-ray tubes of fer two focal spot sizes: a. Fine focus: b. Broad focus:
  • 23. a/ Fine focus: (0.3 – 0.6 mm 2 )  It records fine details.  It can not withstand too much heat.  Its usage may require long exposure time.  Used whenever geometric factors are more (long subject-film distance, short FFD ... etc).
  • 24. a/ Broad focus: (0.6 – 1.2 mm 2 )  It can withstand too much heat.  Always used in combination with short (s) and fast film/screen system.  Used whenever voluntary or involuntary motion is highly expected.  Used when radiosensitive organ is within exposed area or 10 cm from
  • 25. Two focal spot
  • 26. FOCAL SPOT SIZE  The focal spot size limits the tube’s capacity to produce xrays. The electrons and resulting heat are placed on a smaller portion of the x-ray tube.  The mA is therefore limited for the small focal spot. This
  • 27. FOCAL SPOT SIZE  If the mA is properly calibrated, the focal spot will have no impact on the quantity or quality of the beam.
  • 28. (6) F.F.D. :  The intensity of x-ray beam reduces with increased FFD.  It follows the Inverse Square Law ( I.S.L.) . I α 1/d 2 .
  • 29. DISTANCE  Distance af fects the intensity of the x-ray beam at the film but has no ef fect on radiation quality.  Distance af fects the exposure of the image receptor according to the inverse square law.
  • 30. INVERSE SQUARE LAW  mAs (second exposure) SID2 2nd exposure  ---------------------------- = ----------------------- mAs (first exposure) exposure SID2 1st
  • 31. DISTANCE  The most common source to image distances are 40” (100 cm) and 72”(182 cm)  Since SID does not impact the quality of the beam, adjustments to the technical factors are made with the mAs.  To go from 40” to 72” increase the mAs 3.5 time.
  • 32. DISTANCE  Increasing the distance will impact the geometric properties of the beam.  Increased SID reduces magnification distortion and focal spot blur.  With the need to increase the mAs 3.5 times for the 72” SID, tube loading becomes a concern.
  • 33. DISTANCE  72” SID is used for Chest radiography and the lateral cervical spine to reduce magnification.  72” SID used for the full spine to get a 36” beam.
  • 34. (7) FILTERATION:  Thin sheet of Al (aluminum) 1mm or 2mm thick added to the pathway of radiation to filter the low energy radiation.  Increasing filtration will increase the quality and reduce the quantity of the beam.  It removes low energy radiation:  Reduce skin dose;  Harden the beam;
  • 35. FILTRATION  All x-ray beams are af fected by the filtration of the tube. The tube housing provides about 0.5 mm of filtration.  Additional filtration is added in the collimator to meet the 2.5 mm of aluminum minimum filtration required by law.  2.5 mm is required for 70 kVp.
  • 36. FILTRATION  3.0 mm is required for at 100 kVp.  3.2 mm is required for operations at 120 kVp.  Most machines now are capable of over 100 kVp operation.  We have no control on these filters.
  • 37. FILTRATION  3.0 mm is required for at 100 kVp.  3.2 mm is required for operations at 120 kVp.  Most machines now are capable of over 100 kVp operation.  We have no control on these filters.
  • 38.  FILTRATION  CHIROPRACTIC RADIOGRAPHY IS A LEADER IN THE USE OF COMPENSATING FILTERS. WE HAVE TOTAL CONTROL OVER COMPENSATING FILTRATION.  IN AREAS OF THE BODY WITH HIGH SUBJECT CONTRAST OR WIDE DIFFERENCES IN DENSITY, COMPENSATING FILMS IMPROVE IMAGE QUALITY AND REDUCE PATIENT EXPOSURE.
  • 39. THE END

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