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Ct Review > Physcics > Flashcards

Physcics Flashcards

(62 cards)

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1
Q

Window width

A

•allows the adjustment of gray scale

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2
Q

Window level

A

•sets the density of the image

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3
Q

Ct numbers are usually provided in the form of

A

•hounsfield units

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4
Q

First generation Ct scanners rotated in increments of

A

•180 degrees

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5
Q

Analog to digital converter

A

•responsible for transforming analog signal from the detectors into a digital form for the computer

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6
Q

Average hounsfield unit number for bone

A

•+1000

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7
Q

Eliminates the need for cables, allows for continues gantry rotation

A

•slip rings

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8
Q

Purpose of CT focal spot size

A

•influences spatial resolution

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9
Q

Artifact unique to multislice CT (MSCT)

A

•cone beam artifact

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10
Q

A 16-slice system is capable of acquiring ______ images

A
  • 16 images

* 16 slice possesses 16 data channels and is capable of acquiring 16 images per gantry rotation.

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11
Q

Threshold setting

A

•used to include/exclude info during 3D reconstruction of a Ct scan

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12
Q

Main controlling factor of Effective mAs

A
  • pitch the table speed is the main controlling factor

* effective mAs= mAs/pitch

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13
Q

X,Y,Z

A
  • X Sagittal plane
  • Y coronal plane
  • Z axial plane
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14
Q

How Ct tube creates X-rays

A
  • tube consist of a cathode and and anode

* electrons travel from cathode and strike the anode made of tungsten

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15
Q

When the tech manipulates the mA it changes what inside the tube

A

•changes the cathode filament temperature

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16
Q

The typical kVp for Ct

A

•120 kV

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17
Q

Reducing the tube rotation does what

A

•decreases pt radiation dose

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18
Q

Equation for determining the linear dimension of each pixel

A

•DFOV display field of view / matrix

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19
Q

The window setting levels for the brain should be displayed at

A
  • +50 HU

* the brain is soft tissue so should be displayed at about +50 HU

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20
Q

Back projection method of reconstruction major disadvantage

A

•star artifact

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21
Q

Pencil thin X-ray beam is associated with

A

•first generation CT scanners

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22
Q

A modern CT scanner possess a spatial resolution of up to

A

•25 lp/mm

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23
Q

High resolution comb

A

•acts as a grid removing unwanted scatter

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24
Q

Number of pixels used to display image

A

•matrix

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25
Quality control
•corrective actions to improve performance
26
Selecting a Small filament improves
•spatial resolution
27
MSCT is capable of differentiating adjacent objects with attenuation differences as small as _______HU
•3HU
28
Possible artifact from beam hardening
•polyenergetic X-ray beam artifact varying photon energy
29
With MSCT what determines the width of the reconstructed section
•detector collimation
30
HU value for a pixel whose attenuation is less than water would be considered - positive - high contrast - negative - low contrast
•negative
31
DFOV
* display field of view * controls the amount of scanned information to be displayed on the matrix * a small DFOV will magnify the CT image on the display monitor
32
The bit depth of a digital imaging system defines the number of information bits contained with each
•pixel
33
All modern MSCT systems typically employ what type of detectors
* solid state scintillation | * accurately record X-ray energy from any angle
34
Partial volume artifact is related to
•cupping
35
3 factors that affect scatter
* field size * part thickness * kVp * directly related as factors increase scatter increases
36
Pixel
* picture element composed of x and y axis | * 2D
37
Air HU
•-1,000
38
Bone HU
•1,000
39
Blood HU
•40 HU
40
CSF HU
•15 HU
41
Fat HU
•-50 to -100 HU
42
Slice thickness and spatial resolution relation
* inversely related | * as slice thickness increases spatial resolution decreases.
43
Beam shaping filter does what
* hardens the beam | * removes low energy photons
44
Pre pt collimator
* Located just before X-ray hits the pt * controls field size on the pt * controls con beam
45
Pre-detector collimator
* located under pt after X-rays pass pt | * controls slice thickness at the detector array
46
Matrix
* made up of multiple pixels arranged in volume and rows | * as matrix number increases, image resolution increases
47
Voxel represents
* a volume of tissue | * 3D
48
Compton scatter
•removal of an outer orbit election by X-ray photon
49
Photoelectric effect
* removal of an inner orbital electron by an interacting X-ray photon * outer shell fills in void
50
Short wavelength and high frequency =
•high energy
51
Long wavelength and low frequency =
•low energy
52
Beam hardening
A streaking artifact commonly due to the beam changes in quality as it passes through different densities
53
Inherent filtration of the CT X-ray aluminum tube housing
•1.2mm
54
Dimensions of voxel
•calculated by pixel x section width
55
Pre patient collimator
* determines the range the z axis | * longitudinal collimation
56
Post pt collimator
* aka pre detector collimator * beam width * determines slice thickness
57
Detector that contains narrow elemrs flanked by wider detectors is called
•hybrid array
58
The two best factors resulting in equal lengths in all directions
* section width thinnest detector collimation to produce thin slices * using the smallest DFOV * minimizing these two factors results in equal voxel all around
59
Ring artifact typically caused by
•faulty detector
60
Spatial resolution has the ability to
•image small objects
61
The term ______ is used to describe each sample of ray sum measurement made by DAS data acquisition system
•view
62
CTDI volume
* CT dose index | * measures the radiation output from the CT scanner

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