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Characteristics of image.pptx

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Characteristics of image.pptx

  1. 1. Image characteristics
  2. 2.  A radiograph that faithfully reproduces structure and tissue is identified as a high quality radiograph.
  3. 3. What is image quality?  Good technique requires considerable skill. It can be.  1)Acquired only by practice and experience..” Factors are time, distance, milli amperage and voltage .  2) Image must have adequate “density (the degree of blackness)  3) “Contrast….. characteristic that permits differentiation between” densities..  4) “Detail( definition)…visual quality that depends upon sharpness and contrast.”
  4. 4. Characteristics of image Noise Contrast Sharpness Resolution
  5. 5. Noise  Noise mean any signal that does not convey useful information of the subject.
  6. 6. Signal to noise ratio  Optimum condition :magnitude of signal > magnitude of noise Signal to noise ratio is low :loss of information
  7. 7.  Scatter radiation-  Un-useful part of x-ray beam, have no use in diagnostic purpose.  scattered radiation reaching to the image receptor also increases noise to radiographic image.  Can be controlled by stationary or moving grid
  8. 8. contrast  The brightness ratio of the lightest to the darkest part of an image or difference in density or luminance  BOUNDRY BETWEEN DARK AND LIGHT AREA APPEAR SHARPLY. TYPES: HIGH CONTRAST. LOW CONTRAST. OPTIMUM CONTRAST.
  9. 9. High contrast; means harsh, with lots of dense blacks and brilliant white
  10. 10. LOW CONTRAST  Contrast level at a minimum  Image appear dull, lacking in any true black and whites
  11. 11. OPTIMUM CONTRAST  Optimum contrast level tends to be neither very high nor very low and is different for different subjects
  12. 12. SHARPNESS Sharpness is concerned with how suddenly blackening changes at the boundary between adjacent part
  13. 13. UNSHARPNESS  THE INABILITY OF FILM SCREEN SYSTEM TO RECORED THE SHARP EDGE.
  14. 14.  IMAGE UNSHARPNESS MAY BE EXPRESS IN FOLLOWINF WAYS;  EDGE SPREAD FUNCTION.  POINT SPREAD FUNCTION.  LINE SPREAD FUNCTION.
  15. 15.  EDGE SPREAD FUNCTION; THE MICRO DENSITOMETER SHOWS VARIATION IN IMAGE DENSITY ACROSS A BOUNDRY IS CALLED EDGE SPREAD FUNCTION
  16. 16. POINT SPREAD FUNCTION  MICRODENSITOMETER SHOWS VARIATION IN IMAGE AT POINT.  POINT STRUCTURE IN AN OBJECT PRODUCE A SHARP IMAGE.
  17. 17. LINE SPREAD FUNCTION  MICRODENSITOMETER TRACE THAT SHOWING VARIATION IN LINE WHICH PRODUCE A LINE IMAGE..
  18. 18. RESOLUTION  It is the ability of the system to demonstrate closely spaced structures in the subject as separate entities in the image  Spatial resolution- ability to image small objects that have high subject contrast.  Ex- bone- soft tissue interface, breast micro- calcification, calcified lung nodule.  Contrast resolution- ability to image anatomic structures of similar subject contrast.  Ex- liver –spleen & gray matter- white matter.
  19. 19.  Lower noise results in a better radiographic image, because it improves contrast resolution.
  20. 20. Modulated transfer function  The object should contain a mesh or grid of closely spaced lines,alternatively radiopaque and radiolucent.  Spacing of the line pairs is expressed as a spatial frequency
  21. 21. Modulated transfer function  Resolution of different imaging system may be compared objectively by reference to the modulated transfer function.  It is charectestic of imaging system that as the detail in the object becomes more finer , the ability of the system to record the detail becomes progressevely reduced
  22. 22. MTF CAN NEVER BE GREATER THAN 1  MFT = information recorded information available
  23. 23. DENSITY CONTRAST RESOLUTION kvp Directly proportional Inversly proportional …… mA Directly proportional Directly proportional directly THICKNESS Inversly proportional inversly inversly FFD inversly inversly inversly FOCAL SPOT SIZE directly inversly inversly
  24. 24.  THANK U

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