Topic 6. CT Types

Question 1

What are the 5 types of CT

Answer 1

Sequential CT
Spiral CT
Electron beam CT
Multi-Slice CT
Dual Source CT

Question 2

Name the CT: the patient is moved forward along a longitudinal axis of the CT scanner, PAUSING AT INTERVALS to allow trans-axial images to be captured at each position along the axis.

• LONG SCAN TIME
• Rely on the physical connection of wires between the rotating elements

Answer 2

Sequencial CT

Question 3

In a Sequencial CT during the acquisition of a slice the table remains stationairy. After completion of the acquisition, the wires _____. Then the table moves to a ____ _____ to perform the next scan

Answer 3

unwind, new position

Question 4

Name the CT: This CT allows for continuous tube-detector rotation and fast acquisition of data

• Has Slip-ring technology
• continuous acquisition of data allows coverage of larger sections in the same amount of time, no splicing.

Answer 4

Spiral CT

Question 5

What is slip ring technology found in spiral CTs?

Answer 5

Transmission of energy and data via electrically conductive brushes and rotating brings, enabling spiral CT scanners to rotate continuously.

Question 6

In spiral CTs because the x-ray tube generates energy for an extended period, more ______ storage capacity is required

Answer 6

heat.

Question 7

what CT requires requires expanded storage capacity and processing capacity?

Answer 7

Spiral, because a large amount of data is produced in a very short period

Question 8

Name the CT: This CT was developed to take images of the heart, it generates/directs electrons along a STATIONARY TUNGSTEN RING. Emitted x-rays front the tungsten target ring are collimated, and after passing through
the patient, are collected by the stationary detectors on the opposite side.

• Mostly used to detect the amount of coronary calcium
• temporal resolution is 100ms

Answer 8

Electron beam CT (EBCT)

Question 9

Name the CT: An increase in the number of detector rows, multiple channels of data can be acquired simultaneously.
Has the advantage of INCREASED LONGITUDINAL COVERAGE THAT CAN BE ACHIEVED PER ROTATION/ slice.

• useful for cardiac acquisition, which deal with an inherently longer scan time compared with imaging of non-moving organs
• simultaneously acquires 300 slices
• 300 slice scanners are equipped with 320 detector rows

Answer 9

MULTI-SLICE CT

Question 10

Besides 320, CT manufactureres also offer other detector systems for multi slice with the number of

Answer 10

16, 32, 64, 128, 256

Question 11

Some Multi slice CT systems allow for twice their slice acquisition by ______ sampling in longitudinal direction

Answer 11

doubling (two cone shape x-rays)

Question 12

By rapid, longitudinal alternation of the focal sport during acquisition, 2 partially ______ sets of projections from slightly differing position are acquired

Answer 12

overlapping.

Question 13

Compared with systems with z-sampling, double z-sampling results in an IMPROVED longitudinal resolution at the penalty of

Answer 13

a longer total scan time

Question 14

increasing the number of detectors in a multi slice CT

Answer 14

decreases individual detector width

Question 15

An Increase in available detector rows=

Answer 15

increase in coverage of Multi-slice CT scanners

Question 16

Name the CT: Equipped with 2 x-ray tubes rotating at 90° angle to each other

• ADVANTAGE : IMPROVEMENT OF THE TEMPORAL RESOLUTION- - Dual-Energy CT: During scanning both tube detector systems operate using a different tube voltage (kV) → improves tissue differentiation

Answer 16

Dual source CT

Question 17

Image quality of a CT is determined by ____ size and number of _____ projections

Answer 17

detector size
angular projections

Question 18

Typical resolution of clinical CT scanners

Answer 18

0.2-1mm with a slice thickness of 0.4-5mm

Question 19

Higher slice thickness is chosen to reduce radiation dose & improve SNR at expense of axial resolution, why?

Answer 19

captures more in one go, less time spent in machine.

Question 20

what is the key determinant of the image quality

Answer 20

focal spot of x-ray tube, large focal spot blurs the image

Question 21

high resolution CT have a focal spot size of

Answer 21

3-5 micrometer

Question 22

Collimator function

Answer 22

Interaction of x-rays with tissue creates randomly scattered photons which create image noise and cloud the image

Question 23

artefacts?

Answer 23

cause any discrepancy between the CT number represented in the image and the expected CT numbers (HU units)

Question 24

list some Common artifacts

Answer 24

• Beam hardening
• Partial volume effect
• Bad detector
• Metal
• Patient motion

Question 25

Artifacts cause any discrepancy between the CT number represented in the image and the expected CT numbers (HU units)

In extreme cases, a detector element may fail giving a constant output signal. _____ _______ occurs when the x-rays pass through strongly absorbing materials. Lower-energy x-rays are absorbed and the energy peak shifts toward higher energies. Absorption values are underestimated.

Answer 25

Beam hardening

Question 26

How is beam hardening reduced?

Answer 26

by pre-hardening the beam, by placing thin
metal plate (molybdenum or tungsten) in front of the tube

Question 27

Answer 27

beam hardening

Question 28

Artifacts cause any discrepancy between the CT number represented in the image and the expected CT numbers (HU units)

What artifact occurs when A PIXEL REPRESENTS MORE THAN ONE KIND OF TISSUE. Particularly relevant when a tissue boundary lies within a CT slice.
- Blurs the intensity distinction between adjacent tissue
- Can be reduced by higher resolution or sometimes repositioning the patient

Answer 28

Partial volume effect, u can see the blur in the image

Question 29

Artifacts cause any discrepancy between the CT number represented in the image and the expected CT numbers (HU units)

Detectors must be calibrated and positioned correctly: Detectors need to be centered with respect to the source → otherwise, the image will be blurred
- Detectors need to be calibrated so that the output signal intensity is identical for all detectors with the same incident x-ray intensity.

Uncalibrated detectors create which artifact?

Answer 29

ring artifacts

Question 30

what artifact is shown here

Answer 30

ring artifact

Question 31

Metal materials can cause the streaking artifacts due to block parts of projection data
- E.g.: dental fillings, prosthetic devices, surgical clips
- Remove the metal material as possible to reduce artifact

this artifact is?

Answer 31

Metal artifact

CT image of patient w/ metal spine implants:

Question 32

This artifact occurs when patient MOVES (e.g. breathes) during the scan of one slice
- Cannot be corrected but risk of motion blur can be reduced with shorter acquisition times and with the use of the helical scanning principle
- Detailed imaging of the heart continues to pose problems

Answer 32

Patient Motion artifact

Question 33

what is this

Answer 33

the effects of reducing projections, individual cross sections visible because there are less, more projections means theirs more so their are so many they blend perfectly, you cant tell

Question 34

what is this

Answer 34

the effects of reducing rays,

Question 35

Answer 35

Question 36

Answer 36

Question 37

Answer 37

Question 38

photon starvation

Answer 38

Question 39

In 1st Gen CTs, state the number of detectors, type of beam. tube detector movement, and duration of the scan

Answer 39

Detectors: 1
Type of beam: pencil like
Tube detector movement: Translate-rotate
Duration of scan: 20-35 min

Question 40

In 2nd Gen CTs, state the number of detectors, type of beam. tube detector movement, and duration of the scan

Answer 40

Detectors: up to 30
Type of beam: fan shaped
Tube detector movement: Translate-rotate
Duration of scan: less than 90s

Question 41

In 3rd Gen CTs, state the number of detectors, type of beam. tube detector movement, and duration of the scan

Answer 41

Detectors: 288, 700+
Type of beam: fan shaped
Tube detector movement: Rotate-rotate
Duration of scan: about 5 secs

Question 42

In 4th Gen CTs, state the number of detectors, type of beam. tube detector movement, and duration of the scan

Answer 42

Detectors: more than 2000
Type of beam: fan shaped
Tube detector movement: Rotate-rotate
Duration of scan: few seconds

Question 43

Answer 43

MEMORIZE