32. CT: MULTI SLICE CT

Question 1

1. What happens when we increase the number of Detector Rows?

Answer 1

• multiple channels of data can be acquired
  simultaneously
• this is known as a Multi Detector CT
• or a Multi-Slice CT

Question 2

2. What is the advantage of a Multi-Slice CT?

Answer 2

• there is increased longitudinal coverage
• this benefits the data acquisition
• this is achieved per rotation

Question 3

3. Why are Multi-Slice CTs and their increased longitudinal coverage particularly useful for?

Answer 3

• Cardiac data acquisitions
• these deal with longer scan times
• they image non-moving organs

Question 4

4. What does the current state-of-the-art CT technology simultaneously acquire?

Answer 4

• it acquires 320 slices
• this costs about 2.5 million dollars

Question 5

5. How many rows are 320-slice scanners physically equipped with?

Answer 5

• 320 detector rows

Question 6

6. List 5 types of CT detector Systems?

Answer 6

1. 16-slice scanners
2. 32- slice scanners
3. 64- slice scanners
4. 128-slice scanners
5. 256-slice scanners

MOST CLINICS AND HOSPITALS USE:
- 128 and 256 slice scanners
- the 320 ones are too expensive

Question 7

7. How can some systems allow for twice their slice acquisition?

Answer 7

• they double sample
• they do this in a longitudinal direction

Question 8

8. What happens when we have a rapid, longitudinal alteration of the focal spot during acquisition?

Answer 8

• we will acquire two partially overlapping sets of
  projections
• they each come from slightly different positions

Question 9

9. What can be said about systems with single sampling, vs systems with double sampling?

Answer 9

UNLIKE SINGLE SAMPLING SYSTEMS:
- double sampling will result in an improved
longitudinal resolution
- it will also have a longer total scan time

Question 10

10. What does an expansion in the number of detectors result in?

Answer 10

• the individual width of each detector will decrease
• this is because the area of the ring where the detectors
  are positioned is constant

Question 11

11. How does the individual detector width change from a 4 to a 64 Slice CT detector?

Answer 11

4 SLICE DETECTOR:
- its between 1.0 - 1.25 mm

64 SLICE DETECTOR:
- it decreases to 0.4 - 0.5 mm

Question 12

12. What improves the Spatial Resolution in the Longitudinal Direction?

Answer 12

• the increase in the number of detectors
• the overlapping reconstruction of the slices

Question 13

13. What increases the coverage of the Multi-Slice CT scanner?

Answer 13

• the more active detector rows that become available

Question 14

14. What is the Dual Source CT Scanner?

Answer 14

• it is a CT scanner that is equipped with two X-Ray tubes
• we have two detectors
• these rotate at a 90° angle to each other (⟂)

Question 15

15. What is the advantage of the Dual Source CT scanner?

Answer 15

• the improvement of the Temporal Resolution

Question 16

16. Where do we apply a Dual Source CT to?

Answer 16

• we apply it to a Dual-Energy CT

Question 17

17. What happens in a Dual Source CT during the scanning of a patient?

Answer 17

• both of the tube detector systems will operate
• each detector system uses a different tube voltage (kV)
• this improves the tissue differentiation in the image

Question 18

18. Does this table of advances make sense?

Answer 18

• yes

Question 19

19. What is the image quality primarily determined by?

Answer 19

• the detector size
• the number of angular projections

Question 20

20. What is the typical resolution of Clinical CT scanners?

Answer 20

• 0.2 mm to 1 mm

Question 21

21. What is the typical slice thickness of Clinical CT scanners?

Answer 21

• 0.4 mm to 5 mm

Question 22

22. What are the 2 advantages of using a higher slice thickness?

Answer 22

• the radiation dose is reduced
• the Signal to Noise ratio is improved

Question 23

23. What is a disadvantage of using a higher slice thickness?

Answer 23

• the axial resolution worsens

Question 24

24. What does the focal spot of the X-Ray tube determine?

Answer 24

• the Image quality

Question 25

25. What does a large Focal Spot result in?

Answer 25

- a more blurred image

Question 26

26. What kind of tubes are applied in high-resolution CT scanners?

Answer 26

- special tubes with a 3µm - 5µm focal spot size