Ch.2 Ct Image Formation Flashcards Preview

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Flashcards in Ch.2 Ct Image Formation Deck (83):
1

Digital images are?

P 4

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

2

First step generating digital image of an object?

P 4

Divide the object into a grid of small regions

3

Pixel

Picture element that's each small region of a grid

4

Rows and columns allows us to ?

P 4

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

5

Matrix

P 4

Grid of pixels

6

2nd step generating image

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

7

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

P 6

Detectors

Electric signals

8

Integer

P 6

Posit e or negative whole numbe

9

Value of integer determined by?

P 6

Signals strength

10

Display hardware

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

11

Projection

View of anatomical cross section from particular vantage point

12

Ct scanning methods
P 8

Localizer
Conventional
Helical

13

Localizer scan
P 9

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

14

Why localizer scan ?
P 9

Aligns cross sectional slices with specific anatomical structures

15

Views used with localizer?

Ap
Lateral
Oblique

16

Length of anatomical coverage with localizer depends on?
P 9

Speed of table
Amount time X-ray is on

17

Ct localizer scan the anatomical structure appears? P 10

Superimposed

18

Ap localizer image used? P 10

Planning to specify perfectly transverse slices

19

Lateral localizer is used? P 10

Intend to angle gantry to specific oblique slices

20

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

P12

Conventional ct

21

Conventional ct used today?

12

Neurological studies involving temporal bones

Obese patients

Cardiac calcium scoring

22

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

Stationary

23

Raw data
P 13

Data measured at each projection placed in computer file

24

Single row detector

P 13

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