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Image Quality

Image Quality. Part II. Image Quality. Image Quality Photographic Quality Geometric Quality. The films or images have different levels of density – different shades of gray X-rays show different features of the body in various shades of gray.

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Image Quality

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  1. Image Quality Part II

  2. Image Quality • Image Quality • Photographic Quality • Geometric Quality

  3. The films or images have different levels of density – different shades of gray X-rays show different features of the body in various shades of gray. The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass through The images are lighter in dense areas (like bones) that absorb more of the X-rays. Why you see what you see…

  4. Terminology • Density, contrast • Detail • Distortion • Image Sharpness • spatial resolution • Lp/mm • Blur • Motion • SID • OID • Focal spot size • Image receptor • Magnification • Penumbra • Size distortion • Shape distortion • Focal Spot size

  5. Image quality

  6. detail Resolution, ability to distinguish shapes, ability to distinguish lines on image

  7. RECORDED DETAIL • The degree of sharpness in an object’s borders and structural details. • How “clear” the object looks on the radiograph

  8. Recorded detail Image sharpness Spatial resolution Smallest separation of two lines or edges Measured by lp/mm

  9. RESOLUTION TEST TOOLS LINE PAIRS/ MM Depicts how well you can see the differences in structures More lines=more detail

  10. Recorded Detail Factors that affect detail • SID • Focal spot size • OID • Image receptor type • Motion

  11. Focal Spot Geometry Angle of anode size

  12. Focal Spot Geometry Focal spot is not really a single point Dependent on filament size and anode angle.

  13. SID • Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy” -On a radiograph called penumbra • Penumbra (fuzziness) obscures true border • Farther the flashlight from object = sharper borders. Same with radiography.

  14. Recorded Detail: Penumbra and SID

  15. Recorded Detail: Penumbra and Focal Spot Size

  16. Recorded Detail: Penumbra and OID

  17. The position of the structure in the body will influence how magnified it will be seen on the image The farther away – the more magnified

  18. Recorded Detail: OID and Penumbra • The closer the object to the film, the sharper the detail. • OID , penumbra , sharpness  • OID , penumbra , sharpness  • Structures located deep in the body, radiographer must know how to position to get the object closest to the film.

  19. Recorded Detail: Image Receptor Type Film/Screen Imaging excellent spatial resolution-smallest detail that can be detected in an image Computed Radiography (cassettes) Digital Radiography (cassette-less) improved contrast resolution

  20. Motion • Can be voluntary or involuntary • Best controlled by short exposure times • Use of careful instructions to the patient • Suspension of patient respiration • Immobilization devices

  21. Blurring of image due to patient movement during exposure.

  22. distortion Misrepresentation of size or shape of anatomic part; when part is distorted, detail is reduced

  23. Distortion An increase of decrease in the size of an object : magnification or reduction Three types: size, shape, placement of part in body

  24. Types of Distortion FACTOR INFLUENCING DISTORTION • SID-size distortion • OID-size distortion • Beam Angulation-shape distortion • Body Part-Beam alignment-shape distortion

  25. Distortion: SID

  26. 40” SID VS 72” SID Which one is which?

  27. Which one was taken at 72”?

  28. Distortion: OID

  29. Elongation Foreshortened Normal

  30. Which is normal?

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