16-64 Row Scanners: Detector Tradeoffs and Differences

1. 16-64 Row Scanners:Detector Tradeoffs and Differences June 15, 2005 San Francisco Sandy Napel, Ph.D. Professor of Radiology Stanford University School of Medicine Stanford, California USA http://www-radiology.stanford.edu/

2. Outline • From one to many • Detectors for 16 slice scanners • Detectors for 64 slice scanners • Design tradeoffs • Conclusions

3. SDCT 10 mm z Detector

4. SDCT 10 mm z 20-40 mm Detector MDCT

5. Detector 16-Slice Scanners 3 basic detector designs

6. 20-40 mm z Detector MDCT z

7. 16 x 0.625 mm 4 x 1.25 mm 4 x 1.25 mm 20 mm Detector 16-Slice Scanners A16:

8. 16 x 0.625 mm 4 x 1.25 mm 4 x 1.25 mm 20 mm M ≠ N multiple detector configurations Detector 16-Slice Scanners A16: Hold on… If this is a 16 slice scanner, why are there 24 detector elements? Let N = no. of detector elements Let M = no. of simultaneously acquired slices

9. 16 x 0.625 mm 4 x 1.25 mm 4 x 1.25 mm 20 mm Detector 16-Slice Scanners A16: 16 channels to DAS 16 0.625 mm slices over 10 mm thicker slices via software 0.625 mm retros available

10. 16 x 0.625 mm 4 x 1.25 mm 4 x 1.25 mm 20 mm Detector 16-Slice Scanners A16: 16 channels to DAS 16 1.25 mm slices over 20 mm thicker slices via software 1.25 mm are thinnest retros available

11. 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 A16: B16:

12. 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 A16: B16: C16:

13. 12 x 1 mm 12 x 1 mm 32 mm Detector 16-Slice Scanners 16 x 0.5 mm C16: 16 channels to DAS 16 0.5 mm slices over 8 mm thicker slices via software 0.5 mm retros available

14. 12 x 1 mm 12 x 1 mm 32 mm Detector 16-Slice Scanners 16 x 0.5 mm C16: 16 channels to DAS 16 1 mm slices over 16 mm thicker slices via software 1 mm are thinnest retros available

15. 12 x 1 mm 12 x 1 mm 32 mm Detector 16-Slice Scanners 16 x 0.5 mm C16: 16 channels to DAS 2 mm slices over 32 mm thicker slices via software 2 mm are thinnest retros available

16. Detector 64-Slice Scanners 3 basic detector designs

17. Detector 64-Slice Scanners A64: 64 x 0.625 mm 40 mm • 64 slice scanner: • 64 0.625 mm slices over 40 mm • Thicker slices reconstructed via software • 0.625 mm thin slice retros available

18. Detector 64-Slice Scanners B64: 64 x 0.5 mm 32 mm • 64 slice scanner: • 64 0.5 mm slices over 32 mm • Thicker slices reconstructed via software • 0.5 mm thin slice retros available

19. Detector 64-Slice Scanners C64: 32 x 0.6 mm 4 x 1.2 mm 4 x 1.2 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 (0.3 mm spacing) • Thicker slices reconstructed via software

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

21. 32 x 0.6 mm 4 x 1.2 mm 4 x 1.2 mm 29 mm Fastest Least partial volume artifact Detector Example: Make 3.6 mm thick slices with this detector C64: • Sum 6 0.6 mm slices: • Coverage/rotation = 19.2 mm • 0.6 mm slices available • Sum 3 1.2 mm slices: • Coverage/rotation = 29 mm • 0.6 mm slices NOT available

22. A16: 16@0.625mm C64: 64@0.3mm B64: 64@0.5mm A64: 64@0.625mm Detector Design Tradeoffs circular scanning: z-resolution vs. coverage What resolution and coverage does your clinical application demand? resolution vs. coverage 0 8 16 24 32 z (cm)

23. Detector Design Tradeoffs helical mode: z-resolution vs. coverage/rotation A16: 16@0.625mm C64: assume pitch=1 64@0.3mm B64: 64@0.5mm A64: 64@0.625mm 0 8 16 24 32 z (cm)

24. Detector Design Tradeoffs helical mode: z-resolution vs. coverage/rotation A16: 16@0.625mm C64: 64@0.3mm B64: 64@0.5mm A64: 64@0.625mm after 3 rotations 0 8 16 24 32 z (cm)

25. Detector Design Tradeoffs helical mode: z-resolution vs. coverage/rotation A16: 16@0.625mm C64: 64@0.3mm B64: 64@0.5mm A64: 64@0.625mm after 7 rotations 0 8 16 24 32 z (cm)

26. Detector Design Tradeoffs helical mode: z-resolution vs. coverage/rotation A16: 16@0.625mm after 31 rotations C64: 64@0.3mm after 15.8 rotations B64: 64@0.5mm after 9 rotations A64: 64@0.625mm after 7 rotations 0 8 16 24 32 z (cm)

27. Detector Design Tradeoffs helical mode: z-resolution vs. coverage/rotation What resolution and coverage does your clinical application demand? A16: 16@0.625mm after 10.3 seconds* C64: 64@0.3mm after 5.3 seconds* B64: 64@0.5mm after 3 seconds* A64: 64@0.625mm after 2.3 seconds* 0 8 16 24 32 *assuming 3 rotations/s z (cm)

28. Concluding Remarks • Discussion assumed equal gantry speeds (not true) • Subtle differences in speed and resolution

29. Concluding Remarks • Discussion assumed equal gantry speeds (not true) • Subtle differences in speed and resolution • All of these scanners are fast! • Clinical applications must drive speed/resolution tradeoff

30. What I Did Not Talk About • Noise, dose utilization • Artifacts (cone beam, scatter, helical) • 3D reconstruction quality Remember: volumetric image quality is a function of overall system design (hardware, software), and not just the detector…

31. Thank You updated slides at http://snapg4.stanford.edu/~snapel/mdct05/t1.pdf (URL printed in syllabus)