Intro To CT

Question 1

What is it useful for

Answer 1

• diagnosis
• treatment planning
• measure progression of diseases
• emergency med; quickly assess trauma injuries

Question 2

Who invented first CT scanner

Answer 2

Godfrey Hounsfield (1967)

Question 3

How to scan a patient

Answer 3

• patient positioning
• patient in iso-centre
• digital radiograph obtained
• use this to plan volume of raw data acquisition
• acquire raw data (data acquisition)

Question 4

What image must be taken before scan

Answer 4

A plan image
Uses small amount of dose
Like a ‘test’ image - if the area is desirable to scan

Question 5

Sequential scanning

Answer 5

Table doesn’t move
scanning x-ray tube comes to a stop after each slice

Question 6

Helical scanning

Answer 6

Table moves
bank of detectors rotating together continuously around patient during data acquisition

Question 7

Advantages of sequential scanning

Answer 7

• less artefact
• high spatial resolution

Question 8

Disadvantages of sequential scanning

Answer 8

• slower imaging
• compared to multi spinning CT
• limited volume scanning

Question 9

What is helical/ spiral CT

Answer 9

• introduced late 1980s
• continuous gantry rotation and table feed
• scan data forms helical path

Question 10

what is the basic 3 step process

Answer 10

• data acquisition
• image reconstruction
• image display and processing

Question 11

what does data acquisition refer to

Answer 11

collection of x-ray transmission measurements (attenuation measurements)

Question 12

how is data acquisition obtained in CT

Answer 12

by the rotation of x-ray tube and arc of detectors around patient

Question 13

what do the detectors measure

Answer 13

amount fo x-rays that leave the patient at any point during the 360 degrees rotation

Question 14

what does image reconstruction refer to

Answer 14

mathematical technique used to reconstruct attenuation data into axial image of required slice
- would be done on a monitor/ workstation

Question 15

what is helical scanning also known as

Answer 15

multi-slice scanning

Question 16

what is sequential scanning also known as

Answer 16

inter-scan delay
table is stationary during rotation
projections all in same plane

Question 17

how does helical geometry achieve continuous rotation of x-ray tube and detectors

Answer 17

slip-ring technology
- specialised electrical connectors that allow for transmission of power and data between stationary + rotating components without need for physical cables

Question 18

advantages of helical CT

Answer 18

• speed, fast in emergency situations
• improved image quality, data acquisition results in smoother more precise images
• 3D imaging, multi planar reconstructions

Question 19

demands of helical scanning

Answer 19

• continuous table movement
• x-ray tube has high heat storage and cooling capacity
• continuously rotating x-ray tube and detectors based on slip-ring technology
• increase in data processing + storage (more images )

Question 20

what do slip ring CT scanners provide

Answer 20

continuous rotation of gantry by eliminating high tension cables to x-ray tube
- uninterrupted transmission of power and data

Question 21

key limitations of helical scanning

Answer 21

• increased radiation dose
• patients unable to tolerate continuous motion, potential artefacts
• limited access to certain clinical scenarios

Question 22

what happens during the pauses in sequential scanning

Answer 22

• needed to avoid tangling/ twisting of cables connected to x-ray tube and detectors

Question 23

when would sequential scanning be used

Answer 23

• relevant in situations where precise positioning + lower radiation dose are priorities
• eg joint studies = sequential scanning allowing for precise alignment of anatomy and reduces unnecessary to other areas

Question 24

why doesnt sequential scanning use slip ring technology

Answer 24

the equipment moves and stops between images allowing for cable management without need for slip rings