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PAM 2003 – Clinical Imaging 2

PAM 2003 – Clinical Imaging 2. CT – Standard Imaging Procedures. Aims & Objectives. Choice of parameters Interventional procedures Use of contrast enhancement Safe and efficient practice. Choice of Parameters. Examples of trade offs in plain film radiography

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PAM 2003 – Clinical Imaging 2

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  1. PAM 2003 – Clinical Imaging 2 CT – Standard Imaging Procedures

  2. Aims & Objectives • Choice of parameters • Interventional procedures • Use of contrast enhancement • Safe and efficient practice

  3. Choice of Parameters Examples of trade offs in plain film radiography • Use of fine / detail image receptors = ? • Use of fine focus = ?

  4. Choice of Parameters Examples of trade offs in plain film radiography • Use of fine / detail image receptors = increased radiation dose when compared with regular speed image receptors • Use of fine focus = decreased geometric unsharpness BUT increased tube loading

  5. Variable Parameters in CT • Slice thickness • kVp and mAs • Rotation time • Resolution (focal spot size) • Reconstruction & enhancement filters • Image matrix size • Pitch & effective slice thickness

  6. 1. Slice Thickness

  7. 1. Slice Thickness High resolution CT chest (1 mm slice thickness) CT chest (5 mm slice thickness)

  8. Multiplanar Reformat

  9. Streak Artefact

  10. 2. kVp and mAs • Increasing kVp = ? • Increasing mAs = ?

  11. 2. kVp and mAs • Increasing kVp = greater penetration BUT reduced radiographic contrast • Increasing mAs = reduced quantum noise BUT higher dose to the patient & higher heat loading on the tube

  12. 3. Rotation Time • Reduced rotation time = ?

  13. 3. Rotation Time • Reduced rotation time = reduced patient movement effects BUT limits the upper mAs that is achievable

  14. 4. Resolution • Increased resolution = ?

  15. 4. Resolution • Increased resolution = improved spatial resolution BUT will result in increased heat loading on the x-ray tube

  16. 5. Reconstruction & Enhancement Filters Original Image Smoothed Image

  17. 5. Reconstruction & Enhancement Filters Original Image Sharpened Image

  18. 6. Image Matrix Size 100 x 100 pixels 980 x 980 pixels

  19. 7. Pitch & Effective Slice Thickness High pitch Standard pitch Very low pitch ~ 1.5 < 1.5 <0.375

  20. Interventional Procedures • Biopsies • Drainages • Accurate positioning of interventional tools • Day case procedure

  21. Use of Contrast Enhancement Intravenous Contrast • Breaches in the blood-brain barrier • Assessment of vasculature • Assessment of blood supply to other structures Oral Contrast • Discrimination between GI tract and other structures

  22. Breaches in the Blood-Brain Barrier

  23. Assessment of the Vasculature

  24. Assessment of Blood Supply to Other Structures Benign renal cyst Malignant renal tumour

  25. Oral Contrast Agents Non contrast With oral contrast (and intravenous contrast)

  26. Safe & Efficient Practice • Radiation Safety • IRM(ER) • 10 day / 28 day rule • Contrast Agent Safety • Justification of use • Risk of anaphylaxis & other contra-indications • Safe & correct administration • Sharps safety • Infection Control • Efficiency

  27. Summary • Parameters – careful choice maximises image quality • Interventional work – great benefits for the patients but is not without associated risk • Use of contrast agents – enhances differential diagnosis • Safe & efficient practice – more than just radiation safety

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