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CT > Week 3 - Basic Instrumentation > Flashcards

Week 3 - Basic Instrumentation Flashcards

1
Q

What are the 3 major components of CT?

A

-Imaging system -scanner room
-Computer system-computer room
-Display, recording and storage system-operators room

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2
Q

T/F
There needs to be sufficient space behind the gantry for the table to continue through on a clear path

A

True

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3
Q

Mounted framework that surrounds the patient in a vertical plane

A

Gantry

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4
Q

What two components are considered the CT scanner?

A

CT gantry and CT patient table

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5
Q

What component are mounted on the rotating frame of the gantry?

A

-generator
-tube
-detectors
-collimators
-DAS

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6
Q

What is the function of the DAS - data acquisition system?

A

Converts information (electrical signal/analog information) into digital data

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7
Q

What type of generator is used in the gantry?

A

Small, solid state, high frequency

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8
Q

What is the range of hertz for the high frequency generator?

A

0.5-25 kHz

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9
Q

T/F
Because the generator is located close to the clay tube, only a short high tension cable is required to couple the xray tube and generator

A

True

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10
Q

What is the power rating of the high frequency generator?

A

30-60kW
Allows large selection of exposure techniques

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11
Q

What is the kV and mA range enabled by the power rating?

A

80-140kV

20-600mA

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12
Q

Why are higher kV setting used?

A

Higher kV reduces heat load due to lower mA used

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13
Q

T/F
The xray tubes of slip ring scanners require high instantaneous power and have larger anodes

A

True

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14
Q

What is the typical diameter of the anode?

A

5 inch diameter to support tube loading

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15
Q

What are the sizes of the focal spots used?

A

Dual - size: 0.5 and 1.0 mm
Angle: small (~12)
3600-10000 RPM

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16
Q

Why are small focal spots more effective in CT?

A

Reduce penumbra
Better spatial resolution
*heat stress can occur on small focal spots

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17
Q

T/F
Thin slices increase spatial resolution

A

True

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18
Q

What is the unit of anode heat capacity?

A

Million Heat Units (MHU)

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19
Q

What is the maximum anode heat dissipation rate unit?

A

Thousand Heat Units (KHU)

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20
Q

What must be taken into consideration when designing protocols as scan time can go above 30 seconds?

A

Million Heat Units (MHU)

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21
Q

How many filaments can be positioned in a focusing cup?

A

1 or 2

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22
Q

What parts does the anode consist of?

A

Rotor, disk, bearings

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23
Q

What are the 3 types of anode disk?

A

-all metal
-brazed graphite
-chemical Vapor deposition (CVD) graphite disk

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24
Q

Consists of base body made of titanium, zirconium, molybdenum (TMZ)
Can transfer heat from focal track very quickly

A

All metal disk
**not ideal for spiral scanners - very heavy

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25
Q

Tungsten-rhenium focal track brazed with graphite at the base
Graphite has 10x thermal capacity than that of tungsten
Tubes with spiral scan use this type

A

Brazed graphite disk

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26
Q

Tungsten-rhenium layer deposited by chemical Vapor process
Graphite based
Large, lightweight, large heat capacity, fast cooling
Also ideal for spiral scan

A

CVD graphite disk

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27
Q

What is the purpose of filtration?

A

Remove long wavelength X-rays contributing to dose and artifacts

Shapes the energy distribution across regions of the body

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28
Q

What dose a ‘hard’ beam mean?

A

Beam is more penetrating as lower energy xray photons have been removed

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29
Q

What type of filtration takes into account differential thickness?
And is useful for areas with different thicknesses, shows more uniform

A

Bowtie filter

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30
Q

T/F
A filter will be less effective if a patient is not properly isocentered

A

True
Suboptimal image will be seen, can also over radiate the patient (increased dose)

31
Q

T/F
Long wavelength X-rays are readily absorbed by the patient

A

True
They do not contribute to the image, just patient dose
Low energy, remain in patient

32
Q

When is isocentering done?

A

Before a scout is done

33
Q

What is the purpose of a bow tie filter?

A

Useful for areas with differential thickness, shows more uniform on image

34
Q

Why is filtration used?

A

It is essential that the polychromatic beam has the appearance of a monochromatic beam to satisfy the requirements of the reconstruction process

35
Q

T/F
A ‘harder’ beam can cause beam hardening artifacts

A

True

36
Q

What can beam hardening artifacts be referred to as?

A

Spectral shaping

37
Q

Desiring the beam to the anatomy of interest
Reduce scatter radiation
Decrease dose
Improve image quality
Improve contrast resolution

A

Collimation
*narrowing(decreases slice thickness)
*widening(increases slice thickness)

38
Q

T/F
Collimation is based on scout images to ensure no clipping of anatomy

A

True

39
Q

T/F
Which scout is required for a head CT? Why?

A

Lateral scout

AP not required because head is in holder

40
Q

Determines slice thickness
Determines patient dose across slice

A

Pre patient collimator

41
Q

Prevents scatter from reaching detectors

A

Post patient or predetector collimation

42
Q

T/F
Both pre and post patient collimators control slice thickness and help shape the beam

A

True

43
Q

What s the size of the aperture on most CT scanners

A

70cm

44
Q

To what degree must the gantry be able to tilt?

A

+/-30 degrees
(12-30)

Usually in 5 degree increments

45
Q

What are the laser beams used for on the gantry?

A

Positioning the patient in all 3 axes

46
Q

Measures intensity of transmitted rays from the xray source to a particular detector

A

Detector array

47
Q

What are the essential detector characteristics for CT image production

A

-efficiency
-response time
-dynamic range
-high reproducibility
-stability

48
Q

Efficiency to which the detectors can obtain photons transmitted from patient

A

Detector capture efficiency

49
Q

Number of photons absorbed by detector, which depends on
-atomic number
-physical density
-size and thickness of detector face

A

Detector Absorption efficiency

50
Q

Speed of detector detecting an xray and recovering to detect another xray
- should be very short
- defined as brief, persistent flash of scintillation (flashes of light)

A

Detector response time

51
Q

Ratio of the largest signal to be measured to the precision of the smallest signal to be discriminated
- 1M:1 in most CT scanners

A

Detector dynamic range

52
Q

Refers to the steadiness of the detector
Allows a system to be used without interruption of frequent calibration

A

Detector stability

53
Q

What is the function of a detector?

A

Capture xray photons and convert them into electrical signals (analog information)

54
Q

What are the 2 types of detectors?

A

Scintillation
Gas ionization

55
Q

T/F
Photodiodes do not exist in gas ionization detectors

A

True

56
Q

What size of detector is ideal for spatial resolution and scatter rejection?

A

Small detector

57
Q

What type of detector is used in modern CT?

A

Xenon gas detector

58
Q

T/F
The photodiode/scintillation component is eliminated in the xenon gas detector

A

True

59
Q

What type of electrical supply did early CT scanners use? What were the setbacks?

A

Recoiling system cable

-limited rotation up to 360
-limited scan/acquisition to step and shoot
-increased scanning time
(Only axial scanning, not helical)
Single slice

60
Q

What causes the gantry frame to be able to rotate continuously?

A

Slip ring technology
-electromechanical device
-circular electrical conductive rings
-brushes that transmit electrical energy across a rotating interface

61
Q

What are some advantages to slip ring technology?

A

-minimal inters can delay
-eliminates need to straighten cables
-eliminates start and stop process
-capacity for continuous acquisition protocols

62
Q

What is the table/patient couch made of?

A

Carbon fibre
-low absorption value
-excellent vibration-damping feature
-strength to support patient weight

63
Q

What is the scannable range of the patient table?

A

170-200cm
Reference point : 0
-centering
-landmark must be consistent*

64
Q

Center point of the body is in the Center of the gantry

A

Isocentering

65
Q

What is the function of the computers?

A

-image reconstruction
-image manipulation
-visualization

66
Q

Dedicated electronic circuit of high speed calculations needed in CT

A

Array processor

67
Q

Completed the computationally intensive reconstruction operations needed to provide the final image

Reduces the processing requirements of the computer

A

Graphic processing unit

68
Q

Contains algorithms for building up images from raw data

A

Reconstruction software

69
Q

Corrects data collected from detectors prior to being sent to reconstruction CPU

A

Preprocessing software

70
Q

Operate on reconstructed images to facilitate viewing

A

Image postprocessing software

71
Q

What is the typical image matrix size?

A

512x512

72
Q

To speed up transmission of information and storage requirements
Lossless: no info lost
Lossy: some info lost

A

Compression

73
Q

Controls the entire system and enables operations of various functions

A

Interested console

74
Q

T/F
Helical CT table incrementation is quantified in mm/s because the table continues to move throughout the scan

A

True

CT (6 decks)

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