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Ct Review Class > Ch.2 Ct Image Formation > Flashcards

Ch.2 Ct Image Formation Flashcards

1
Q

Digital images are?

P 4

A

Numerical representations of an object that can be recognized and processed by a computer

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2
Q

First step generating digital image of an object?

P 4

A

Divide the object into a grid of small regions

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3
Q

Pixel

A

Picture element that’s each small region of a grid

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4
Q

Rows and columns allows us to ?

P 4

A

Associate the location of specific structure within the object being imaged with specific pixel or group of pixels

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5
Q

Matrix

P 4

A

Grid of pixels

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6
Q

2nd step generating image

A

Sample the object in order to differentiate structures within the object and assign various shades of gray to the pixels representing the structure

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7
Q

X-ray photons that pass thru the body are measure by ______and converted into ______?

P 6

A

Detectors

Electric signals

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8
Q

Integer

P 6

A

Posit e or negative whole numbe

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9
Q

Value of integer determined by?

P 6

A

Signals strength

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10
Q

Display hardware

A

Assigns specific gray level to region of Ct image from which attenuation information was detected

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11
Q

Projection

A

View of anatomical cross section from particular vantage point

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12
Q

Ct scanning methods

P 8

A

Localizer
Conventional
Helical

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13
Q

Localizer scan

P 9

A

Obtained with stationary X-ray tube and patient table in motion

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14
Q

Why localizer scan ?

P 9

A

Aligns cross sectional slices with specific anatomical structures

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15
Q

Views used with localizer?

A

Ap
Lateral
Oblique

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16
Q

Length of anatomical coverage with localizer depends on?

P 9

A

Speed of table

Amount time X-ray is on

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17
Q

Ct localizer scan the anatomical structure appears? P 10

A

Superimposed

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18
Q

Ap localizer image used? P 10

A

Planning to specify perfectly transverse slices

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19
Q

Lateral localizer is used? P 10

A

Intend to angle gantry to specific oblique slices

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20
Q

Which ct yields the best quality image free of helical artifacts?

P12

A

Conventional ct

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21
Q

Conventional ct used today?

12

A

Neurological studies involving temporal bones

Obese patients

Cardiac calcium scoring

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22
Q

Conventional ct the tube rotates around the patient while the table?

A

Stationary

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23
Q

Raw data

P 13

A

Data measured at each projection placed in computer file

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24
Q

Single row detector

A

P 13

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25
When performing a conventional scan , raw data from ____ cross sectional slice location is collected during a single rotation of the gantry? P 13
One
26
Multi row detectors
P14
27
When performing a conventional scan of multi row detector scanner , the raw data is from ______ cross sectional slice locations collected during a single rotation of the gantry
Several
28
Raw data sample formula
Rows of detectors x # of detectors X projections required
29
Helical scan | P 16
X-rays beam spiral or corkscrew paths around patients body as the table advances through the gantry
30
Most commonly used ct today?
Helical scan
31
Several advantages of helical ct | P 16-17
``` Faster studies More coverage in breath hold No missed anatomy Less contrast agent needed Arbitrary slice positioning Ideal data for post processing ```
32
Disadvantage of helicL scan? P18
Artifacts
33
Helical path single row detector scanner in which thickness of X-ray beam _______ the thickness of the final slice
Equals
34
The helical path on multi row detector scanner in which thickness of X-ray beam is ________ over four rows of detectors
Divided
35
Interpolation
Mathematical problem in helical ct that changes helical data into raw data reconstructing it into final images
36
Most ct aytms today use reconstruction method called ? | P 21
Filter back projection
37
Two steps of filtered back projection? P 21
Applying filter to raw data and back projection
38
Back projection p21
Calculation used for reconstructing final images from raw data by adding together the attenuation information collected from all projections
39
Through back,projection _______profiles are added together p 22
Attenuation profiles
40
Convolution p 23
Reconstruction filter is Applied to raw data during image reconstruction
41
Kernel p 23
Reconstruction filter
42
Two reconstruction filters? P 23
Sharp | Smooth
43
Sharp filter p 23
Improves definition of the edges of structures but doesn't minimize grainy or speckled appearance of image
44
Smooth filter p 23
Minimizes grainy appearance of noise in image so that the contrast between tissues can be better distinguished but does not improve edge definition
45
Sharp reconstruction filter are often us for ? P 24
Musculoskeletal detail ( high contrast area)
46
Smooth reconstruction filters are often used for ? P 24
Low contrast areas such as abdomen and brain
47
If back projection was applied to raw data without convolution , what happens to tissues? P 24
Image would have blurry edges and they be more difficult to differentiate
48
Iterative reconstruction p 25
Cycle of correction calculations which maybe applied during image reconstruction to reduce image noise and which allows greatly reduced dose to be used without compromising image quality
49
Noise
Grainy appearance on image
50
Important clinical significance of iterative reconstruction ? P 26
Significant less radiation dose while maintaining optimal image quality
51
Cone beam artifact p 27
spreading of photons long patient table results in spoke or star like appearance
52
Cone beam reconstruction p 28
Reconstruction algorithm designed for multi row scanner to collect more than four slices in a single rotation
53
Back projection is used on ______row detectors and on multi row detectors that collect no more than _____slices in one rotation . Cone beam reconstruction applied to all other mdct scanners. P 28
Single | Four
54
When ct image is reconstructed it viewed on? P 29
Operators console
55
Raw data is obtained on raw data device on?
Host computer
56
Retrospective reconstruction p 29
Requires raw data, which is lost once that portion of raw data storage device is overwritten
57
On mdct scanner, a retrospective reconstruction is common,y used to modify reconstructed ? P 30
Slice thickness
58
Most Ct images are acquired in which orientation? P 31
Transverse
59
Multiplanar reconstruction p 31
Allows Reconstruction of images in planes that would be difficult or impossible to acquire
60
Multiplanar reconstruction requires ____ data ? P 31
Image data
61
Steps of multiplanar reconstruction? P 31
1. Region interest scanned to obtain transverse slices using helical imaging 2. Raw data reconstructed using filtered back projection or cone beam reconstruction and transverse imaging viewed on operators console 3. Multiplanar reconstruction initiated 4. Stacks transverse images on top each other generate volume anatomical imaging 5. Line places across stack transverse imaging indicating location of new image
62
Why curved cut line allowed on multiplanar reconstruction? P 32
Enables tracing curved structure such as vessel so that structure is displayed in cross section
63
Contiguous p 33
Slices with no gaps
64
Why must images be contiguous in multiplanar reconstruction p33
No gaps in images
65
Which type images best used for post processing techniques? P 33
Helical
66
3D shaded surface display p 34
Reconstructs images of the surfaces of the anatomical structure
67
3d SSD program process ? P 34
Stacks transverse slices to form a volume of anatomical data which must be contiguous Dependent of determining difference of tissues being scanned through a threshold
68
In 3d SSD , types of tissues are separated by ______ settings? P 34
Threshold settings
69
What is threshold value set to during 3d SSD? P 34
Equal to ct number of tissue on which we want to surface rendering
70
Volume rendering p 35
Incorporates information from entire image data set , rather from the surface into processed image enabling visualization of structures above and below the surface
71
Voxels in volume rendering p 35
Each voxel assigned opacity value as function of its density
72
Each pixel in volume rendering p 35
Represents the sum of the contributions of each voxel along a ray passed through image data set
73
Maximum intensity projection p37
Generated from transverse slices of a cta study by projecting the brightest pixels onto a plane
74
Angiography p 37
Used to evaluate the vessels and is acquired with helical scan and timed iodinated contrast
75
Most accurate mip results are obtained when ? P 38
Small volume of interest is selected
76
Volume of interest p 38
In mip, affect way vessels appear
77
Volume of interest increased? P 38
Additional anatomical structures and noise are included in the data upon which the mip algorithmn is applied - apparent vessel diameter of the mip image may decrease
78
Ct images are filmed or transferred to ____ or ____? P 40
Viewing station or pacs
79
Ct uses _____ film? P 40
Single emulsion
80
Window adjustments allow,us? P 40
High resolution detail or soft tissue contrast by varying brightness and contrast settings
81
Most ct systems today use a _______ camera ? P 40
Laser
82
Laser camera expose the image displayed on monitor directly onto _____ with a laser p 40
Film
83
Benefits of laser camera p 40
Less scattered light | Superior contrast

Ct Review Class (7 decks)

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