RADIOGRAPHIC EXPOSURE

Transcription

1 RADIOGRAPHIC EXPOSURE

2 Receptor Exposure Receptor Exposure the that interacts with the receptor. Computed Radiography ( ) requires a. Direct Digital Radiography (DR) requires a.

3 Exposure Indicators Exposure indicators replace the of a too. These indicate the. Exposure indicators may be miscalculated due to:

4 Sensitivity of System A chart is provided by the indicating the ( ). Exposure Index (EI) proportional to amount of radiation striking the receptor. Sensitivity Number (S) proportional to amount of radiation striking the receptor. Relative Exposure Index based on a

5 Overexposure - digital image may be manipulated by adjusting the through. However if it is at of overexposure the computer.

6 Underexposure - digital image, to fix than overexposure.

7 Receptor Exposure Affected by;

8 Controlling factor of Exposure: mas relationship between mas and receptor exposure. mas = ( ) mas =

9 Milliampere ( ) - ( ) traveling through the x-ray tube from the.

10 The greater the tube current (ma) the the number of x-rays produced. Exposure time (seconds or milliseconds) -. Longer time - the number of x- rays.

11 Reciprocity Law - identical mas values at different ma or time settings will Reciprocity Law failure - occurs when.

12 Source Image Distance ( ) - as the distance between the tube and the IR is changed, a. Governed by - The intensity of radiation varies with the because of the of the x-ray beam. Inew = d old 2 Iold 2 d new

13 Intensity is measured with an as the amount of ionization an.

14 Exposure - distance relationship: As SID is increased, the overall exposure is. So must is changed.

15 KV Kilovoltage directly controls but has an influence on. Increase KV - energy - penetration through body. Causes an in receptor exposure. Also the amount of scatter produced

16 KV Wavelength relationship increase KV energy and penetration wavelength. Low KV High KV

17 KV exposure relationship is governed by. A 15% increase in KV causes a.

18 The type of generator also influences the way KV affects the exposure. Types of generators Changing from a single phase to a 3phase 12 pulse (or high frequency) will the exposure by a factor of, so you can the mas by to maintain the same exposure.

19 Types: Grids

20 Grid is a thin flat device made of alternating. Grid is placed between the. Lead in the device is the most effective way to.

21 Grids labeled according to their grid ratio. Grid ratio =

22 Exposure - grid relationship: As grid ratio is increased, Exposure if there is no compensation. Bucky (8 mas) Non bucky (2 mas)

23 Exposure factors must be increased to compensate for: of intensity from scatter radiation reaching the IR. Slight reaching the IR.

24 Moving grid decreases presence When to use a grid:

25 Collimation (Beam Restriction) primary beam, secondary and scatter radiation produced.

26 Cone in more ( collimation)- Exposure, scatter No cone Coned in

27 Photostimulable Phosphor Plate (PSP) Used in CR ( ) When x-rays hit the image plate some energy is. Some energy is and trapped in the.

28 Exposure Image Phosphor plate relationship is; the more radiation captured the.

29 Direct Flat Panel vs Indirect Flat Panel Digital (DR) Indirect flat panel contains that of x-rays so that exposure is needed.

30 Patient Patient factors - tissue ( ) will affect radiographic exposure.

31 Thickness of part depends on: Change in thickness - change

32 Density or Opacity of the part depends on: Change in opacity - change KV

33 Orthopedic Cast when a plaster of Paris cast is applied. Wet Plaster of Paris cast - Dry cast -

34 Types: Contrast Media Positive contrast media - these Density on the image so Exposure factors must be Negative contrast media - these Density on the image so Exposure must be

35 Filtration Filters ( ) some of the radiation. Filters absorb ( wavelengths) so that there is. Total filtration -

36 Types of filtration: Exposure - filtration relationship: Increase amount of filtration - Exposure

37 Anode Heel Effect A of radiation along the. On anode side of tube there is radiation because x-rays are

38 Heel effect more noticeable with:

39 Effects overall uniformity of Exposure. Advantage: Can be used to an advantage when radiographing structures that have a.

40 Exposure Summary INCREASE mas ma Time SID KV Grid ratio WITHOUT COMPENSATION Exposure will Exposure will Exposure will Exposure will Exposure will Exposure will

41 INCREASE Collimation WITHOUT COMPENSATION Exposure will Filtration Exposure will Speed of conversion of Phosphors Exposure will Contrast media Exposure will Patient Thickness Atomic number of structure Exposure will Exposure will Use a cast Anode Heel effect Exposure will Exposure will