Geometric Properties Distortion
- 1. Radiographic DistortionRadiographic Distortion Principles of Radiographic Imaging
- 2. ObjectivesObjectives • Define Radiographic Distortion • Differentiate between Size and Shape Distortion • Summarize and analyze the relationship of factors that control and affect distortion. • Perform calculations to determine image magnification and percent magnification. • Explain the effects SID and OID have on image distortion • Discuss various methods of minimizing distortion • Explain elongation and foreshortening • Describe the routine relationships between central ray, anatomical part, and image receptor •
- 3. Geometric Properties Sharpness Recorded Detail Distortion Size Shape Receptor Unsharpness Geometric Unsharpness Motion Unsharpness
- 4. Assessing Radiographic DistortionAssessing Radiographic Distortion • Radiographic misrepresentation of either the size or shape of the anatomic part is called distortion • 2 Types of Distortion DISTORTION SIZE SHAPE
- 6. Size Distortion - Magnification • An increase in the object’s image size compared with its true, or actual size • There is a percentage of magnificationmagnification in every radiographic image • As the percentage of magnificationmagnification increasesincreases, the level of geometric unsharpnessunsharpness also increasesincreases
- 7. Influences of Size DistortionInfluences of Size Distortion • Size distortion is influenced by • OID and SIDOID and SID – Object-to-Image DistanceObject-to-Image Distance – Source-to-Image DistanceSource-to-Image Distance
- 8. OIDOID Shadow OID has aOID has a direct relationshipdirect relationship with size distortionwith size distortion As OID increases, size distortion/magnification increases As OID decreases, size distortion/magnification decreases
- 10. A B • SID has anSID has an inverse relationshipinverse relationship withwith size distortionsize distortion • A long SID produces less size distortion • A short SID produces more size distortion With a long SID the beam is more perpendicular creating less of a divergence SIDSID
- 12. Interactive ReviewInteractive Review • Interactive Online Reviews – Plickers – Quizstar – Qzzr • Group/Team Work
- 13. Calculating Size Distortion • Magnification Factor – indicates how much size distortion is demonstrated on a radiograph • MF = SID / SOD Source-to-Image Distance ---------------------------------------- Source-to-Object Distance • If SOD is unknown –SID - OID M SID SOD
- 15. Calculating Size Distortion •MF = I / O •If Object Size is unknown •Object Size = Image size / MF O I M
- 17. If….Then… M SID SOD O I M • If… • MF = SID / SODMF = SID / SOD • And… • MF = Image Size / Object SizMF = Image Size / Object Siz • Then… • SID / SOD = IS / OSSID / SOD = IS / OS
- 19. Assessing Radiographic DistortionAssessing Radiographic Distortion • 2 Types of Distortion DISTORTION SIZE SHAPE
- 20. Shape Distortion • True Distortion • Produces a true perversion of the structures of interest that can make the recorded image unrecognizable from the original structures of interest
- 21. Shape Distortion • Two Types: – ElongationElongation – ForeshorteningForeshortening • Due to: – AlignmentAlignment • Central rayCentral ray • Anatomical partAnatomical part • Image receptorImage receptor – AngulationAngulation • DegreeDegree • DirectionDirection
- 22. Shape Distortion • ElongationElongation refers to images of objects that appear longer than the true object • ForeshorteningForeshortening refers to images that appear shorter than the true objects
- 23. ElongationElongation Shape distortion resulting from improper alignment of the Image Receptor
- 24. ElongationElongation Shape distortion resulting from improper alignment of the x-ray tube (CR)
- 25. ForeshorteningForeshortening Shape distortion resulting from improper alignment of the part
- 26. The Affects of Distortion Take a close look at this illustration. Do you see how the bone ends at the fracture site look a little different in each radiograph? These different views result from differences in the alignment of the CR, bone, and IR.
- 27. A simple fracture may go undetected due to shape distortion
- 29. Minimizing Shape Distortion • X-ray tube alignment (CR) – Perpendicular to Part and IR – *Elongation • Image Receptor alignment – Parallel to Part – *If the IR is the piece un-aligned – (CR and part still perpendicular) – *Elongation • Part alignment – Parallel to IR – *If the Part is the piece un-aligned – (CR and IR still perpendicular) – *Foreshortening
- 30. Interactive ReviewInteractive Review • Interactive Online Reviews – Plickers – Quizstar – Qzzr • Group/Team Work
- 31. SUMMARY • Size Distortion – OID • Shortest OID – SID • Longest SID • Shape Distortion – Alignment and Angulation • Elongation – CR, IR, and Part Perpendicular • Foreshortening – Part and IR Parallel