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IMAGE QUALITY REVIEW

IMAGE QUALITY REVIEW. Dr Mohamed El Safwany , MD. Intended learning outcome. The student should learn at the end of this lecture radiological image quality review. What affects DENSITY on the radiographic image?. Factors Affecting mAs & Density. Patient factors:

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IMAGE QUALITY REVIEW

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  1. IMAGE QUALITY REVIEW Dr Mohamed El Safwany, MD.

  2. Intended learning outcome The student should learn at the end of this lecture radiological image quality review .

  3. What affects DENSITYon the radiographic image?

  4. Factors Affecting mAs & Density • Patient factors: • size of pt., density / pathology of tissue • kVp • Collimation • Distance • Grids • Film/Screen Combinations • Processing

  5. Influences technique & density on image Patient’s Body Habitus (size)

  6. Scatter Creates fog Lowers contrast (more grays) Increases as kV increases Field size increases Thickness of part increases Creating the Image

  7. Effects of collimation on scatter

  8. Collimate to area of interest -reduces scatter and radiation dose to the patient

  9. Grids • A device with lead strips that is placed between the patient and the cassette • Used on larger body parts to reduce the number of scattering photons from reaching the image

  10. Grid is placedbetween patient (behind table or upright bucky) & cassetteIf placed BACWARDS CAN CAUSE GRID ERRORS

  11. GRIDS CAN LEAVE LINES ON THE IMAGE

  12. Recorded Detail • The degree of sharpness in an object’s borders and structural details. • Other names: -sharpness of detail -definition -resolution -degree of noise

  13. 2 principal characteristics of any image are Spatial & Contrast Resolution • Spatial resolution • Resolution is the ability to image two separate objects and visually distinguish one from the other • Spatial resolution is the ability to image small objects that have high subject contrast (eg. bone-soft tissue interface, calcified lung nodules)

  14. 2 principal characteristics of any image areSpatial & Contrast Resolution • Spatial resolution • Determined by focal-spot size and other factors that contribute to blur • Diagnostic x-ray has excellent spatial resolution. It is measured in line pairs per mm. (CT measured in cm)

  15. Factors that affect the detail of an image

  16. Main Factors Affecting Recorded Detail • kVp & mAs • Motion • Object Unsharpness • Focal Spot Size • SID (Source to Image Distance) • OID (Object to Image Distance) • Material Unsharpness

  17. GEOMETRIC QUALITIES • DETAIL • DISTORTION • MAGNIFICATION

  18. POOR DETAIL GOOD DETAIL

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

  20. Decrease Motion Unsharpness • Instruct patient not to move or breath • Use Immobilization devices • Use Short exposure times • Lock equipment in place

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

  22. SID Source to Image Distance • The greater the distance between the source of the x-ray (tube) and the image receptor (cassette), the greater the image sharpness. • Standard distance = 40 in. most exams • Exception = Chest radiography 72 in. *See page 74 in your book

  23. OIDObject to Image Distance • 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. *See page 74 in your book

  24. Focal spot size – determined by filament in cathode & surface area used at anode

  25. Distortion • Misrepresentation of the true size or shape of an object -MAGNIFICATION (size distortion) -TRUE DISTORTION (shape distortion)

  26. MAGNIFICATION • TUBE CLOSE TO THE PART (SID) • PART FAR FROM THE CASSETTE (OID)

  27. 40” SID VS 72” SID

  28. Size Distortion & OID • If source is kept constant, OID will affect magnification • As OID , magnification  • The farther the object is from the film, the more magnification

  29. A = goodB & C = shape distortion (elongation of part)

  30. D & E = shape distortion (foreshortening of part)

  31. Shape Distortion • Misrepresentation of the shape of an object • Controlled by alignment of the beam, part (object), & image receptor • Influences: Central ray angulation & body part rotation

  32. Image Distortion • When the part to be imaged – does not lay parallel with the IR (cassette) • If the Central Ray is not perpendicular to the part

  33. Elongation Foreshortened Normal

  34. Distortion (x-ray beam not centered over object & film) Distortion (object & film not parallel)

  35. Central Ray • Radiation beam diverges from the tube in a pyramid shape. • Photons in the center travel along a straight line – central ray • Photons along the beam’s periphery travel at an angle • When central ray in angled, image shape is distorted.

  36. Distortion of multiple objects in same image (right) due to x-ray beam not being centered over objects.

  37. Central Ray Angulation • Body parts are not always 90 degrees from one another • Central ray angulation is used to demonstrate certain details that can be hidden by superimposed body parts. • Body part rotation or obliquing the body can also help visualize superimposed anatomy.

  38. Main Factors Affecting Recorded Detail • kVp & mAs • Motion • Object Unsharpness • Focal Spot Size • SID (Source to Image Distance) • OID (Object to Image Distance) • Material Unsharpness/ Film Screen Combo

  39. Factors Affecting mAs • Patient factors: size of pt., density of tissue, pt. compliance • kVp • Distance • Grids • Film/Screen Combinations • Processing

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