Intro To CT Flashcards
What is it useful for
- diagnosis
- treatment planning
- measure progression of diseases
- emergency med; quickly assess trauma injuries
Who invented first CT scanner
Godfrey Hounsfield (1967)
How to scan a patient
- patient positioning
- patient in iso-centre
- digital radiograph obtained
- use this to plan volume of raw data acquisition
- acquire raw data (data acquisition)
What image must be taken before scan
A plan image
Uses small amount of dose
Like a ‘test’ image - if the area is desirable to scan
Sequential scanning
Table doesn’t move
scanning x-ray tube comes to a stop after each slice
Helical scanning
Table moves
bank of detectors rotating together continuously around patient during data acquisition
Advantages of sequential scanning
- less artefact
- high spatial resolution
Disadvantages of sequential scanning
- slower imaging
- compared to multi spinning CT
- limited volume scanning
What is helical/ spiral CT
- introduced late 1980s
- continuous gantry rotation and table feed
- scan data forms helical path
what is the basic 3 step process
- data acquisition
- image reconstruction
- image display and processing
what does data acquisition refer to
collection of x-ray transmission measurements (attenuation measurements)
how is data acquisition obtained in CT
by the rotation of x-ray tube and arc of detectors around patient
what do the detectors measure
amount fo x-rays that leave the patient at any point during the 360 degrees rotation
what does image reconstruction refer to
mathematical technique used to reconstruct attenuation data into axial image of required slice
- would be done on a monitor/ workstation
what is helical scanning also known as
multi-slice scanning
what is sequential scanning also known as
inter-scan delay
table is stationary during rotation
projections all in same plane
how does helical geometry achieve continuous rotation of x-ray tube and detectors
slip-ring technology
- specialised electrical connectors that allow for transmission of power and data between stationary + rotating components without need for physical cables
advantages of helical CT
- speed, fast in emergency situations
- improved image quality, data acquisition results in smoother more precise images
- 3D imaging, multi planar reconstructions
demands of helical scanning
- 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 )
what do slip ring CT scanners provide
continuous rotation of gantry by eliminating high tension cables to x-ray tube
- uninterrupted transmission of power and data
key limitations of helical scanning
- increased radiation dose
- patients unable to tolerate continuous motion, potential artefacts
- limited access to certain clinical scenarios
what happens during the pauses in sequential scanning
- needed to avoid tangling/ twisting of cables connected to x-ray tube and detectors
when would sequential scanning be used
- 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
why doesnt sequential scanning use slip ring technology
the equipment moves and stops between images allowing for cable management without need for slip rings
