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Four or More: Understanding the Basics of Multidetector-Row CT

Four or More: Understanding the Basics of Multidetector-Row CT

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Four or More: Understanding the Basics of Multidetector-Row CT

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  1. Four or More: Understanding the Basics of Multidetector-Row CT Took 28 minutes going very fast….

  2. Four or More: Understanding the Basics of Multidetector-Row CT 6th Annual International Symposium on Multidetector-Row CT San Francisco, CA June 23-26, 2004 Sandy Napel, Ph.D. Department of Radiology Stanford University School of Medicine Stanford, California USA http://www-radiology.stanford.edu/

  3. Outline • Detector and data acquisition basics • Helical mode • Pitch • Image reconstruction Goal: Provide insight into how to use MDCT

  4. Outline • Detector and data acquisition basics • Helical mode • Pitch • Image reconstruction

  5. SDCT 10 mm z Detector

  6. SDCT 10 mm z 20+ mm Detector MDCT

  7. z Detector How to slice it? Uniform or Matrix Array N elements Length = Nd d

  8. z Detector How to slice it? Uniform or Matrix Array N elements Length = Nd d Non-uniform or Adaptive Array

  9. z Detector How to slice it? Uniform or Matrix Array N elements Length = Nd d Non-uniform or Adaptive Array Hybrid Array { thinner inner elements

  10. 16 x 1.25 mm Detector 4-Slice Scanners 20 mm 5 2.5 1.5 1 1 1.5 2.5 5 32 mm 4 x 0.5 mm

  11. 4-Slice Scanners Collect 4 Simultaneous Channels of Data How do we use all 16 elements? Detector 16 elements 4 DAS channels

  12. 4 x 1.25 mm Detector Configuration X-ray Tube Focal Spot X-ray Beam Collimator Detector Switching Array

  13. 4 x 2.5 mm Detector Configuration X-ray Tube Focal Spot X-ray Beam Collimator Detector Switching Array

  14. 4 x 3.75 mm Detector Configuration X-ray Tube Focal Spot X-ray Beam Collimator Detector Switching Array

  15. 4 x 5.0 mm Detector Configuration X-ray Tube Focal Spot X-ray Beam Collimator Detector Switching Array

  16. 5 2.5 1.5 1 1 1.5 2.5 5 Detector Do I get unequally-sized slices from an MDCT scanner with a non-uniform detector array? NO!

  17. 5 2.5 1.5 1 1 1.5 2.5 5 Detector X-ray source collimation 2 x 0.5 mm slices

  18. Detector X-ray source collimation 4 x 1 mm slices 5 2.5 1.5 1 1 1.5 2.5 5

  19. Detector X-ray source collimation 4 x 2.5 mm slices 5 2.5 1.5 1 1 1.5 2.5 5

  20. Detector X-ray source collimation 4 x 5 mm slices 5 2.5 1.5 1 1 1.5 2.5 5

  21. 8-Slice Scanners Collect 8 Simultaneous Channels of Data How do we use all 16 elements? Detector 16 elements 8 DAS channels

  22. 8 x 1.25 mm Detector Configuration X-ray Tube Focal Spot X-ray Beam Collimator Detector Switching Array

  23. 8 x 2.5 mm Detector Configuration X-ray Tube Focal Spot X-ray Beam Collimator Detector Switching Array

  24. Detector 16-Slice Scanners 3 basic detector designs

  25. 16 x 0.625 mm 4 x 1.25 mm 4 x 1.25 mm 20 mm Detector 16-Slice Scanners

  26. 16 x 0.625 mm 4 x 1.25 mm 4 x 1.25 mm 20 mm 16 x 0.75 mm 4 x 1.5 mm 24 mm 4 x 1.5 mm Detector 16-Slice Scanners

  27. 16 x 0.625 mm 4 x 1.25 mm 4 x 1.25 mm 20 mm 16 x 0.75 mm 4 x 1.5 mm 24 mm 4 x 1.5 mm 16 x 0.5 mm 12 x 1 mm 12 x 1 mm 32 mm Detector 16-Slice Scanners

  28. Detector c. 2004 Multislice Scanners 4 basic detector designs

  29. 64 x 0.625 mm 40 mm Detector c. 2004 Multislice Scanners A: • 64 slice scanner: • 64 0.625 mm slices over 40 mm • Thicker slices available via software

  30. 40 mm 40 x 0.625 mm 6 x 1.25 mm 6 x 1.25 mm Detector c. 2004 Multislice Scanners B: • 40 slice scanner: • 40 0.625 mm slices over 25 mm • 32 1.25 mm slices over 40 mm • Thicker slices available via software

  31. 32 mm Detector c. 2004 Multislice Scanners C: 64 x 0.5 mm • 32 slice scanner: • 32 0.5 mm slices over 16 mm • 32 1.0 mm slices over 32 mm • Thicker slices available via software

  32. 4 x 1.2 mm 4 x 1.2 mm Detector c. 2004 Multislice Scanners D: 32 x 0.6 mm 29 mm • 64 slice scanner: • 32 0.6 mm slices over 19 mm • 24 1.2 mm slices over 29 mm • 64 0.6 mm slices over 19 mm via focal spot shift

  33. Detector c. 2004 Multislice Scanners D: .

  34. Detector c. 2004 Multislice Scanners D: .

  35. Detector c. 2004 Multislice Scanners D: ~ 0.3 mm at isocenter (~ 50% overlap) .

  36. 4 x 1.2 mm 4 x 1.2 mm Detector c. 2004 Multislice Scanners D: 32 x 0.6 mm 29 mm • 64 slice scanner: • 32 0.6 mm slices over 19 mm • 24 1.2 mm slices over 29 mm • 64 0.6 mm slices over 19 mm via focal spot shift • Thicker slices available via software

  37. Detector When M ≠ N, there may be multiple ways to make slices of a given thickness

  38. least PVA 4 x 1.2 mm 4 x 1.2 mm Detector Example: Make 3.6 mm thick slices with this detector D: 32 x 0.6 mm 29 mm • Sum 6 0.6 mm slices: • 0.6 mm slices available • Coverage/rotation = 19 mm • Sum 3 1.2 mm slices: • 0.6 mm slices NOT available • Coverage/rotation = 29 mm

  39. Outline • Detector and data acquisition basics • Helical mode • Pitch • Image reconstruction

  40. table travel per rotation (mm) table travel per rotation (mm) Pitch = Pitch = slice thickness (mm) beam width (mm) Helical Pitch • Single-Slice Helical CT: slice thickness = x-ray ( beam ) width

  41. slice thickness <=> D = detector channel width table travel per rotation (mm) Pitch = M • D (mm) where M = no. of simultaneous slices Helical Pitch • Multi-Slice Helical CT: 1.25 mm }

  42. slice thickness <=> D = detector channel width table travel per rotation (mm) Pitch = M • D (mm) where M = no. of simultaneous slices Helical Pitch • Multi-Slice Helical CT: } 2.5 mm

  43. slice thickness <=> D = detector channel width table travel per rotation (mm) Pitch = M • D (mm) where M = no. of simultaneous slices Helical Pitch • Multi-Slice Helical CT: } 3.75 mm

  44. slice thickness <=> D = detector channel width table travel per rotation (mm) Pitch = M • D (mm) where M = no. of simultaneous slices Helical Pitch • Multi-Slice Helical CT: } 5 mm

  45. table travel per rotation (mm) Pitch = M • D (mm) Helical Pitch With this definition, intuition regarding artifacts and dose as a function of pitch are independent of M.

  46. table travel per rotation (mm) Pitch = M • D (mm) Helical Pitch On a 4-slice scanner (M=4): At pitch = 0.75, table travel per rotation is: = 0.75 • 4 • D = 3 • D At pitch = 1.5, table travel per rotation is: = 1.5 • 4 • D = 6 • D

  47. table travel per rotation (mm) Pitch = M • D (mm) !! (D=.625mm 6 cm/rot) Helical Pitch On a 4-slice scanner (M=4): At pitch = 0.75, table travel per rotation is: = 0.75 • 4 • D = 3 • D On an 64-slice scanner (M=64): At pitch = 1.5, table travel per rotation is: = 1.5 • 64 • D = 96 • D

  48. Outline • Detector and data acquisition basics • Helical mode • Pitch • Image reconstruction

  49. Reconstruction Approaches • z-interpolation • Single-slice rebinning (ASSR) • Cone-beam approximations (Feldkamp)

  50. The Need for Cone Beam Reconstruction X-ray Tube Focal Spot X-ray Beam Collimator z isocenter Detector