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RADIOGRAPHIC IMAGING

RADIOGRAPHIC IMAGING. GEOMETRIC PROPERTIES OF IMAGE FORMATION. RECORDED DETAIL. SHARPNESS & ACCURACY OF STRUCTURE LINES RECORDED IN THE IMAGE ALSO CALLED: Spatial resolution – Detail Image sharpness – Definition . UMBRA VS PENUMBRA. UMBRA Image proper PENUMBRA

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RADIOGRAPHIC IMAGING

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  1. RADIOGRAPHIC IMAGING GEOMETRIC PROPERTIES OF IMAGE FORMATION

  2. RECORDED DETAIL • SHARPNESS & ACCURACY OF STRUCTURE LINES RECORDED IN THE IMAGE • ALSO CALLED: • Spatial resolution – Detail • Image sharpness – Definition

  3. UMBRA VS PENUMBRA • UMBRA • Image proper • PENUMBRA • Area of blurriness around object

  4. FACTORS AFFECTING RECORDED DETAIL

  5. CONTROLLING FACTORS • MOTION • Most detrimental to image detail • GEOMETRIC FACTORS • Based on geometric relationship between beam, patient and image receptor • IMAGE RECEPTOR • Film/screen or digital

  6. MOTION VOLUNTARY • DEFINITION/EXAMPLE • INVOLUNTARY • DEFINITION/EXAMPLE • EQUIPMENT • DEFINITION/EXAMPLE

  7. CONTROLLING MOTION • COMMMUNICATION • IMMOBILIZATION DEVICES • SHORT EXPOSURE TIMES

  8. GEOMETRIC FACTORS • OID • SID • FOCAL SPOT SIZE

  9. SID • SOURCE TO IMAGE RECEPTOR DISTANCE • RELATION TO SHARPNESS • Increase SID = increase sharpness • Decrease SID = decrease sharpness • WHY??

  10. OID • OBJECT TO IMAGE RECEPTOR DISTANCE • RELATION TO SHARPNESS • Increase OID = Decrease sharpness • Decrease OID = Increase sharpness • WHY??

  11. FOCAL SPOT SIZE • SIZE OF THE AREA ON THE ANODE WHERE X-RAYS ARE PRODUCED • RELATION TO SHARPNESS • Increase focal spot size = decrease sharpness • Decrease focal spot size = increase sharpness • WHY??

  12. CALCULATING IMAGE BLUR • DETERMINING THE DEGREE OF GEOMETRIC UNSHARPNESS • SOD – SOURCE TO OBJECT DISTANCE Equal to SID minus OID • FORMULA: Focal Spot Size X OID SOD

  13. IMAGE RECEPTOR • FILM SPEED • Faster film = decreased sharpness • Slower film = increased sharpness • WHY?

  14. IMAGE RECEPTOR • SCREEN SPEED • Faster screens = decreased sharpness • Slower screens = increased sharpness • WHY?

  15. IMAGE RECEPTOR • SCREEN / FILM CONTACT • Good screen/film contact = good sharpness • Poor screen/film contact = image blur • WHY?

  16. IMAGE RECEPTORDigital Imaging IMAGE RESOLUTION IS BASED ON THE IMAGE MATRIX Information in the image is displayed in rows and columns • EACH SQUARE (pixel) REPRESENTS A PIECE OF INFORMATION

  17. Digital Imaging • THE MORE PIXELS, THE BETTER THE IMAGE RESOLUTION OR SHARPNESS

  18. DIGITAL IMAGING • BLURRINESS OR PENUMBRA IS EXPRESSED AS: - Point spread function (PSF) • Line spread function (LSF) • Edge spread function (ESF) • THE GREATER THE PSF (etc.) THE MORE BLURRINESS

  19. LINE SPREAD FUNCTION

  20. IMAGE NOISE • ANY FORM OF INTERFERENCE WITH THE IMAGE • OCCURS IN BOTH TYPES OF IMAGING • BACKGROUND INFORMATION THE IMAGE RECEPTOR RECIEVES • QUANTUM MOTTLE – Definition? Cause? • What effect would image noise have on image sharpness?

  21. DISTORTION • DEFINITION • Alteration in the size and/or shape of an object • SIZE DISTORTION • Magnification • SHAPE DISTORTION • Elongation • Foreshortening

  22. DISTORTION DISTORTION

  23. MAGNIFICATION • INCREASE IN SIZE OF THE OBJECT • FACTORS AFFECTING MAGNIFICATION • SID • Increasing SID = decrease in magnification • Decreasing SID = increase in magnification • WHY??? • OID • Increasing OID = increase in magnification • Decreasing OID = decrease in magnification • WHY???

  24. MAGNIFICATION • Why is magnification not a good thing? • Experiment • Which is the worst offender? SID or OID • Experiment • What can be done to minimize magnification when the OID needs to be longer than it should be? • Experiment

  25. CALCULATING MAGNIFICATION Method 1 • MAGNIFICATION FACTOR • Degree of magnification occurring on an image • COMPUTATION OF MF • Image Size 2. SID Object Size SOD • DETERMINING OBJECT SIZE FROM MF Image Size MF

  26. CALCULATING MAGNIFICATION Method 2

  27. SHAPE DISTORTION • SHAPE DISTORTION COMES FROM MISALIGNMENT OF • Central ray • Image receptor • Part

  28. SHAPE DISTORTION • FORESHORTENING • Object appears shorter than it really is • ELONGATION • Object appears longer than it really is

  29. SHAPE DISTORTION • ELONGATION • Occurs when the CR or the IR is improperly aligned • FORESHORTENING • Occurs only when the part is improperly aligned

  30. ALIGNMENT • PROPER ALIGNMENT OCCURS WHEN: • The CR is perpendicular to the IR and the part • The part is parallel to the IR and perpendicular to the CR • The CR is centered to the area of interest

  31. ANGULATION • WHENEVER THE BEAM IS ANGLED, DISTORTION WILL OCCUR • The greater the angulation the greater the distortion • CAN BE ADVANTAGEOUS IN CERTAIN CIRCUMSTANCES • Examples?

  32. ANGULATION - ALIGNMENT • Why is it important to have the CR centered to the area of interest, particularly when looking at fractures or joint spaces? • Experiment

  33. ANGULATION - ALIGNMENT • How does the position of the object in the body affect shape and/or size distortion? • Experiment • Experiment • How does object thickness relate to shape distortion? • Experiment

  34. SUMMARY • TO MINIMIZE SHAPE AND SIZE DISTORTION AND MAXIMIZE DETAIL: • CR perpendicular to IR • Object parallel to IR • CR centered to area of interest • Longest possible SID • Shortest possible OID • Smallest possible focal spot • Highest resolution imaging system • Shortest possible exposure time

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