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CT > Physics And Instrumentation > Flashcards

Physics And Instrumentation Flashcards

1
Q

Measurement of the attenuation that occurs along each path through the patient from X-ray tube to detector

A

Data Acquisition

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2
Q

Angle of the tube and detectors in relationship to the patient position during scout acquisition is

A

Azimuth

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3
Q

Smaller focal spots improve the geometric efficiency of the X-ray beam, leading to a

A

Greater spatial resolution

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4
Q

Spatial resolution

A

Ability of a CT imaging system to display fine details separately (lp/cm)

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5
Q

Amount of X-ray photons passing through a specified area

A

Photon fluence

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6
Q

Rate at which the photon fluence passes through a unit area over unit time

A

Photon flux

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7
Q

Describes the calculated mAs value per acquired slice.

Main controlling factor is table speed.

A

Effective mAs

Effective mAs = mAs/
Pitch

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8
Q

Describes the spacing between two adjacent CT images.

Measured as the distance between the center of one section and the center of the next adjacent section.

A

Section interval

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9
Q

Those acquired with equal section thickness and interval

A

Contiguous images

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10
Q

Those acquired with an interval greater than the section width

A

Noncontiguous images

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11
Q

Reconstructed with a section interval that is less than the section width

A

Overlapping images

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12
Q

Describes the relationship between collimation and table movement during scanning

A

Pitch

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13
Q

Original definition of pitch may now be referred to as

A

Detector pitch

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14
Q

Original definition of pitch

SSCT

A

Pitch = table feed per rotation/

Section width

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15
Q

New adaptation of pitch in MSCT is termed beam pitch. Formula:

A

Beam pitch =
table feed per rotation/
Total collimation

Total collimation = number of sections x section width

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16
Q

The reduction of intensity of a radiation beam as it passes through a substance

A

Attenuation

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17
Q

Desired qualities of a CT detector:

A

High efficiency
Rapid signal decay
High dynamic range

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18
Q

Convert X-ray energy directly into an electrical signal

A

Gas ionization detectors

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19
Q

Convert X-ray energy first into light energy, which just then be converted into electrical signal

A

Solid-state scintillation crystal detectors

All modern MSCT systems utilize this type

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20
Q

Determines the width of the reconstructed section

A

Detector collimation

Beam collimation no longer controls section width

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21
Q

Refers to the number, length, and organization of the individual detector elements in an MSCT system

A

Detector configuration

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22
Q

3 general formats of MSCT detector configuration:

A

Uniform matrix-array: utilizes multiple detectors in the longitudinal direction, each the same length. (Same size collimation)

Adaptive-array: thinnest widths at the center, surrounded by detectors of incrementally increasing widths. (5,2.5,1,1,2.5,5)

Hybrid-array: 2 detector sizes. Narrower midline and wider outside.

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23
Q

Electronic combination of signal from adjacent detectors to form a reconstructed slice that is thicker than the individual detector width

A

Binning

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24
Q

Electronic components responsible for measuring the transmitted x-radiation absorbed by the detectors

A

DAS

Data acquisition system

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25
Q

The CPU is capable of performing multiple tasks simultaneously, a function called

A

Parallel processing

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26
Q

An additional feature of CT computers systems that further improves the speed and efficiency with which it can perform multilingual simultaneous functions

A

Pipelining

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27
Q

Primary data processing component of the CT system:

Is a separate computer with its own CPU

Responsible for receiving scan data from the host computer, performing all of the major processing of the CT image, and returning the reconstructed image to the storage memory of the host computer

A

Array processor

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28
Q

Portion of the X-ray beam transmitted through the patient and incident upon a single detector

A

Ray

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29
Q

The measurement of transmitted radiation made by an individual detector

A

Ray sun

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30
Q

Ability of an object to attenuate the X-ray beam is assigned a value termed

A

Linear attenuation coefficient

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31
Q

Primary goal of CT image reconstruction is to

A

Spatially distribute the attenuation data recorded by the detector array

32
Q

Mathematical process primarily responsible for CT image reconstruction is called

A

Back-projection

33
Q

2D grid of numbers arranged in rows and columns

A

Matrix

34
Q

Process applied to reduce image unsharpness

A

Convolution

35
Q

Current method for image reconstruction in modern MSCT

A

Filtered back projection

36
Q

Mathematical process whereby data from tube rotations just above and just below a given slice position are used for image reconstruction

A

Interpolation

37
Q

CT # (HU) of dense bone

A

+1500 to +2000

38
Q

HU of muscle

A

+50 to +65

39
Q

HU of white matter

A

+40 to +46

40
Q

HU of gray matter

A

+35 to +40

41
Q

HU of blood

A

+30 to +35

42
Q

HU of CSF

A

+15

43
Q

HU of water

A

0

44
Q

HU of fat

A

-50 to -100

45
Q

HU of lungs

A

-550 to -950

46
Q

HU of air

A

-1000

47
Q

Occurs when multiple types of tissue are represented by a single voxel.
Can be reduced by minimizing the voxel dimension

A

Partial volume averaging

48
Q

A parameter that controls the diameter of the circular data acquisition field within the CT gantry as determined by the number of activated detectors along the x-y axes

A

Scan field of view (SFOV)

Calibration field

49
Q

The diameter of the acquired attenuation data displayed across the image matrix (zoom factor or target view)

A

Display field of view (DFOV)

50
Q

Window width controls

A

Contrast

51
Q

Window level controls

A

Brightness

52
Q

Post-processing for contrast-enhanced blood vessels. Low attenuation values not displayed

A

MIP (maximum intensity projection) max pixel value

53
Q

Post-processing for biliary tree, colon, lungs, and trachea

A

Min-IP (minimum intensity projection)

54
Q

Technique that uses the concept of thresholding to limit the displayed volumetric data.
Bone threshold >300 to build skeletal model

A

Surface rendering / shaded-surface rendering (SSD)

55
Q

Adjusts the opacity of voxels included in the 3D model according to their tissue characteristics. Does not exclude voxels, but instead alters their appearance

A

Volume rendering (VR)

56
Q

Viewpoint of being within the lumen of an object

A

Perspective volume rendering (immersive rendering)

57
Q

The unwanted appearance of individual sections on a mulitplanar or 3D reformation image resulting in a loss of sharpness and detail

A

Step artifact

58
Q

Ability of a CT imaging system to display fine details separately. (lp/cm)
Ability to resolve small, closely spaced objects when they are surrounded by material that is very different in density.

A

Spatial resolution

59
Q

Larger objects of uniform density are represented by

A

Low spatial frequency signal

60
Q

Smaller dense objects and areas of sharp borders between varying densities are represented by

A

High spatial frequency signal

61
Q

A graphical representation of a CT systems response to a spatial frequency that serves as a measurement of the systems in-plane spatial resolution

A

Modulation transfer function (MTF)

62
Q

Smaller, more closely spaced detectors ________ spatial resolution

A

Improve

63
Q

Represents the amount of broadening that occurs along the z-axis during volumetric data acquisition

A

Slice sensitivity profile (SSP)

64
Q

Ability of the CT system to detect an object with a small difference in linear attenuation coefficient as compared to the surrounding tissue.
Describes the CT systems ability to differentiate between two adjacent tissues of similar attenuation values.

A

Contrast resolution (low-contrast detectability or sensitivity)

65
Q

MSCT systems are typically capable of differentiating adjacent objects with attenuation differences as small as

A

3 HU

66
Q

The stop-motion capability of a CT system.

Ability to freeze motion and provide an image free of blurring.

A

Temporal resolution

67
Q

Controlling factors of temporal resolution

A

Gantry rotation speed

Reconstruction method

68
Q

Any portion of the signal that contains no useful information.
Manifests as an overall graininess on the reconstructed image.

A

Noise

Measured as standard deviation on water phantom

69
Q

Result of an insufficient X-ray photon flux per volume

A

Quantum noise

Amount of quantum noise is inversely related to the amount of radiation exposed to each voxel

70
Q

Descriptive term used to quantify the amount of noise in a displayed CT image.
Calculated as the standard deviation in the ROI measurement of a water phantom image.

A

Signal-to-noise ratio (SNR)

71
Q

Major quality factor affecting low-contrast resolution

A

Image noise

72
Q

CT systems ability to maintain relatively consistent CT values across the entire image of an object of equal density

A

Spatial uniformity

73
Q

The relative accuracy between calculated CT numbers and their respective linear attenuation coefficients

A

Linearity

Daily calibration

74
Q

Artifact appears when the degree of beam hardening exceeds the CT systems ability to correct during the reconstruction process.
Typically manifest as areas of _______

A

Light and dark streaking bands across portions of the image

Dense bony areas of the posterior fossa of skull are especially prone.

Higher kVp may slightly reduce it (120-140)

75
Q

Occurs when a structure is only partly positioned within a voxel and the attenuation for the object is not accurately represented by a pixel value

A

Partial volume artifact

Appears as a generalized unsharpness or haziness of the borders of objects.

PF and interface between the diaphragm and abdominal contents are common locations.

Use of thin sections help eliminate this effect

76
Q

Artifact caused by the systems inability to process the high spatial frequency signal that represents the interface between two substances with widely different attenuation values

A

Edge gradient

77
Q

The unwanted appearance of individual sections on a MPR or 3D reformation image resulting in a loss of sharpness and detail

A

Step artifact

CT (4 decks)

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