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202 MEDIMAGE > 8. Digital Image Characteristics & Image Processing > Flashcards

8. Digital Image Characteristics & Image Processing Flashcards

1
Q

what are matrices made of

A

rows and columns

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2
Q

what is the relationship between pixel size and resolution

A

inverse

greater resolution = smaller pixel size

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3
Q

each pixel has how many colours

the colour is calculated from what

A

one colour

its the average of the scale in it

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4
Q

what is the relationship between the pixel size and the blurring

A

inverse

larger pixel size = more blurring

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5
Q

what is a matrix

A

number of pixels in an image

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6
Q

what is the field of view

what is it measured in

A

measurement in mm

describes the physical size of the image

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7
Q

digital image quality is improved with a ___ matrix size that includes a ___ number of ___ pixels

A

larger matrix

greater number of smaller pixels

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8
Q

as pixels get smaller there ___ rows and columns of pixels making the image more ___

A

more rows and columns

makes image more clear

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9
Q

pixel size equation

A

pixel size = field of view/matrix size

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10
Q

is there a unit for matrix size, if so what is it

A

no unit as its the number of pixels

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11
Q

a smaller field of view with the same matrix size has what effect on the pixel size and resolution and amount of data stored

A

smaller pixels
higher spatial resolution
same amount of data to store

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12
Q

what do pixels impact

what do matrix size impact

A

pixels = spatial resolution

matrix = amount of data to store/transfer

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13
Q

what is the advantage of larger matrix size

A

clearer images

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14
Q

what are the 3 disadvantages of having a larger matrix size

A

processing time

network transmission time

digital storage space

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15
Q

what is the pixel bit depth

what is it determined by

A

number of bits determines the number of shades of gray that can be displayed

numerical value assigned to a pixel is determined by the relative attenuation of x-rays passing through the volume of tissue

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16
Q

what is a bit and what does it do

the more bits the ___ shades of greys and colors you can store

A

the 0s and 1s that stores binary info

more

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17
Q

what is contrast

A

difference in density or difference in degree of grayness between areas of the radiograph image

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18
Q

what is the resolution

A

clarity and average of the grey scale

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19
Q

what is noise

A

scatter

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20
Q

what is distortion, what are its 2 types

A

elongation and foreshortening

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21
Q

what is the pixel bit depth and contrast resolution relationship

what is the logic for it

A

greater the pixel pit depth the more precise the digitization of the analog signal and the greater number of shades of grey available for image display

increasing the number of shades of grey available to display on a digital image, improving the contrast resolution

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22
Q

what does it mean if there is more contrast resolution in terms of color and greys

A

more contrast = more colours and greys

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23
Q

the greater the number of pixels in the image matrix what happens to the pixel size

A

the smaller the pixel size

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24
Q

what is the pixel density

A

greater number of pixels per unit area

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25
Q

what is the pixel pitch

A

distance measured from the centre of a pixel to an adjacent pixel

26
Q

what is the relationship between the pixel density and pitch and spatial resolution

A

increasing density and decreasing pitch increases the resolution

27
Q

what is the spatial resolution limited to and what kind of image improves it

A

limited by size of pixel

image composed of smaller sized pixels has improved spatial resolution

28
Q

what needs to happen to the pixel density and pitch increase the spatial resolution

A

increasing pixel density and decreasing pixel pitch

29
Q

spatial frequency is defined by what

A

unit of line pairs per millimeters (lp/mm)

30
Q

small objects have ___ spatial frequency

A

higher

31
Q

increasing the number of lp/mm resolved in the imaging system results in ___ spatial resolution

A

improved

32
Q

what is the modulation transfer function

A

measure of the imaging systems ability to display the contrast of anatomic objects varying in size

33
Q

what is the range of values for the modulation transfer frequency

an imaging system that has a high MTF has what effect on the visibility

A

0-1.0

high MTF = improved anatomic detail visibility

34
Q

what is the equation for the MTF

A

MTF = (max intensity - min intensity)/(max intensity + min intensity)

35
Q

variation in the MTF comes from what

MTF of 1 is easiest to achieve when

A

Variation comes from variation in intensity exiting tissue

1 is easiest to achieve when objects have low spatial frequency

36
Q

point spread function is what

A

basic measure of resolution of an imaging system

image produced from a single point stimulus to a detector

describes the blurring properties of an imaging system

37
Q

digital image processing occurs after what and before what

A

after extraction

before display and diagnostic interpretation

38
Q

what is a histogram analysis and what 2 things is it used for

A

image processing technique

used to identify the edges of an image
used to assess raw data prior to image display

39
Q

what is histogram analysis error

A

entire imaging plate is scanned to extract the image from the photostimulable phosphor

if at least not 3 edges are not identified an histogram analysis error could occur

40
Q

histogram analysis errors are less likely to occur with DR IRs or CR IRs

why

A

DR IRs

because the image data are extracted only from the exposed detectors

41
Q

what is the exposure indicator

A

numeric value indicating the level of radiation exposure to the digital IR

42
Q

what is the deviation index

A

difference between the desired target exposure to the IR and the actual exposure to the IR

43
Q

what does >0 and <0 mean for the deviation index

A 
<0 = decreased exposure to the IR
>0 = increased exposure to the IR
44
Q

what are the 3 limitations of the deviation index

A

collimation
centering
noise

all impacts image quality

45
Q

what are look up tables and what do they do in terms of contrast and pixel distribution

A

methods for altering an original pixel values to change the display and contrast of an image

Takes low contrast images and gives more definition to lights and darks and moves the greys in between them

Changes pixel distribution from linear to non-linear

46
Q

digital IRs have ___ exposure and a ___ dynamic range

A

linear exposure

wide dynamic range

47
Q

what are the 4 categories of digital image artefacts

A

detectors

image data extraction to the ADC

during the ADC

during signal processing by the computer before display

48
Q

what are the image plate factors that can cause image artefacts

A

Stains in Imaging plate, particulates, scratches, cracks or fogging of plate

49
Q

what are the data extraction factors that can cause image artefacts

A

Artifacts occurring during data extraction on CR systems = laser optics, transport mechanisms, light guide, and laser sampling and stationary grid frequencies issues

50
Q

what is soft copy viewing

A

when an image is displayed on a workstation instead of film or other physical medium

51
Q

display monitors can be of what 2 types

A

cathode ray tubes

liquid crystal displays

52
Q

what is the LCD display monitor made of

A

LCD light passes through liquid crystal and displays image on glass base plate. Additional components include a source for the electrical signal and light

Flat faceplate and dimensions are thinner

Plasma monitors are very similar to LCD, instead of liquid crystal layer, there is a thin layer of pixel

53
Q

what is the CRT display monitor made of

A

CRT = accelerating and focusing e- strike fluorescent screen. Image scanned on screen in lines so # of lines affects image quality. Recommended that CRT monitors scan at least 525 lines per 1/30 of a second. typically has a curved faceplate, and its dimensions are thicker

54
Q

what is the relationship between the window level and the image brightness

A

direct proportional relationship

increasing window level increases the image brightness

55
Q

what is the relationship between the window width and the image brightness

A

narrow decreased window width displays higher radiograph contrast

56
Q

what does window level change

A

Window level sets midpoint of the range of brightness visible in the image. Changing it incr/decreases image brightness in the entire range.

57
Q

what does window width change

A

the contrast of the image

58
Q

what is subtraction in postprocessing

A

Remove superimposed image which allows better visualisation of anatomical region of interest

Edge enhancement improves visibility of small high contrast structures (eg can see blood vessels high contrast)

59
Q

what is blurring in postprocessing

A

blurring by digital processing fixed by digital subtraction so results in enhanced visibility of detail

60
Q

what is smoothing in postprocessing

A

suppresses image noise/quantum noise

spatial resolution is degraded

202 MEDIMAGE (18 decks)

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