31. CT: TYPES OF BEAMS Flashcards
1
Q
- How can we increase the Spatial Resolution?
A
- we can use multiple detectors
2
Q
- What kind of beam is shown in this image?
A
- a Fan Beam
- it is positioned in order to obtain slices
THIS KIND OF CT IS VERY USEFUL:
- when we have to obtain images of the whole body
3
Q
- What kind of beam does this image show?
A
- the Cone Beam
- the beam is in the shape of a Cone
THIS KIND OF CT IS VERY USEFUL:
- in dentistry
- it is used for localised abnormalities
4
Q
- What kind of beam does this image represent?
A
- Multiple Pencil Beams
5
Q
- What did the stop-and-shoot principle result in?
A
- all the CT scanners sequentially acquired axial slices
6
Q
- What happens during Sequential scanning?
A
- the slice is acquired
- the table remains stationary through this process
- it does this until the Gantry completes a full rotation
7
Q
- What happens after the slice has been acquired in Sequential Scanning?
A
- the table moves to a new position inside the Gantry
- the next scan is then performed
NB:
- this is known as the Stop and Shoot Principle
8
Q
- What is the disadvantage of the Sequential Scanning Method?
A
- it takes a relatively long time
9
Q
- What is the Gantry in a CT scan?
A
- this is the scanning unit of the CT
- it rotates
- it looks like a big circle
10
Q
- What does the Gantry contain?
A
- the X-ray tube
- shielding elements
- photon detectors
11
Q
- What do Spiral CT scanners allow for?
A
- they allow for continuous Tube-Detector rotations
- the data is acquired faster
IT INVOLVES:
- taking a series of cross sectional images
- these correspond to one continuous spiral
12
Q
- What technology gave way to Spiral CT scanners?
A
- Slip Ring Technology
13
Q
- What can be said about the table in Spiral CT Scanner situations?
A
- the table is not stationary
- it is moved inside the Gantry
- the Gantry then obtains images for different areas of
the patient
14
Q
- What do Sequential CT Scanners rely on?
A
- they rely on a physical connection
- this is in the form of cables
- these are found between the rotating elements
15
Q
- What are the rotating elements of the Sequential CT scanner?
A
- the X-Ray tube
- the detectors
- the stationary base
16
Q
- What happens after each part of data is acquired in a Sequential CT scan?
A
- the wires unwind
17
Q
- What do Spiral CTs transmit?
A
- they transmit energy and data
- they do this using electrically conductive brushes
- the rotating rings also help the transmission
18
Q
- What can be said about the rotation of the Spiral CT scanners?
A
- they rotate continuously
- the table will also move at a constant speed through
the gantry
19
Q
- Does this diagram make sense?
A
- yes
20
Q
- What kind of CT is a multi-splice spiral CT?
A
- it is a Mechanical CT
21
Q
- What happens in a Mechanical CT?
A
- the X-Ray tube and the detector array will physically
rotate around the table
22
Q
- What creates the forces in a Mechanical CT?
A
- the rotation
23
Q
- What are the forces in the Mechanical CT responsible for?
A
- they restrict the rotation speed
- they restrict the temporal resolution
24
Q
- Why was the Electron Beam CT developed?
A
- to image the heart
25
Q
- What does the Electron Beam CT do instead of physically rotating the Tube-Detector unit?
A
- the Electron Beam (EBCT) generates and directs
electrons - it does this along a stationary Tungsten target ring
- this then emits X-Rays
- there is no Gantry
- there is no X-Ray tube or detector
26
Q
- What happens to the X-Rays after they are emitted from the Tungsten ring?
A
- they are collimated
- this means that they are made to be accurately parallel
- they then pass through the patient
27
Q
- What happens to the X-Rays after they pass through the patient?
A
- they are collected by the Stationary Detectors
- these are found on the opposite side
28
Q
- In the absence of rotating parts, what is the Temporal Resolution of the Electron Beam CT?
A
- 100 ms
29
Q
- What do we use the Electron Beam CT for?
A
- non-invasive coronary angiography
IT IS MOST OFTEN USED FOR:
- the qualification of Coronary Calcium
