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CT Scan > Computerized Tomography Process > Flashcards

Computerized Tomography Process Flashcards

1
Q

Phases of CT imaging

A
  1. Scanning the patient
  2. Data Acquisition
    i. Tube or tube and detector move
    ii. Multiple attenuation measurements are taken around the object
  3. Image reconstruction
  4. Image Display
  5. Image archival (recording)
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2
Q

stopping of x-rays with transfer of energy

A

Absorption

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3
Q

deflection of x-rays

A

Scatter

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4
Q

No. of x-ray photons falling on an object

A

Incident Intensity

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5
Q

No. of photons passing through

A

Transmitted Intensity

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6
Q

obtained by measuring and comparing the incident and transmitted intensities

A

degree of attenuation

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7
Q

cross sectional portion of the body which is scanned for the production of CT image

A

slice

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8
Q

The slice has width and therefore _____

A

volume

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9
Q

determined by the width of the x-ray beam

A

width

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10
Q

The image is represented as a _____ of numbers.

A

MATRIX

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11
Q

A two dimensional array of numbers arranged in rows and columns.

A

Matrix

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12
Q

Each individual element or number in the image matrix represents a three dimensional volume element in the object,

A

VOXEL

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13
Q

The VOXEL is represented in the image as a two-dimensional element called

A

PIXEL - (picture element

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14
Q

The numbers in the image matrix

A

CT numbers

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15
Q

Each ____ has a number which represents the x-ray attenuation in the corresponding voxel of the object

A

pixel

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16
Q

To obtain a visual image, the CT numbers are assigned

A

different shades of gray on a gray scale.

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17
Q

Basic components (Data Acquisition)

A

X-ray tube
Collimators
Detector/s

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18
Q

____ traverses the object and enters the detecto

A

Collimated x-ray beam

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19
Q

determined from the difference between incident intensity and transmitted intensity

A

attenuation

20
Q

In the basic CT system the x-ray tube and detector are translated ____ so that the beam scans the object

A

linearly

21
Q

Imaginary line between Tube & Detector

A

Ray

22
Q

Attenuation along a Ray

A

Ray Sum

23
Q

The set of ray sums in one direction

A

View

24
Q

The attenuation for each ray sum when plotted as function of its position is called

A

attenuation profile

25
Q

Attenuation of objects with different densities will change the attenuation profile

A

Object with low attenuation

Object with high attenuation

26
Q

after a view is recorded, the tube and detector rotate a small angle and the entire process is repeated until many views have been recorded for the same slice

A

translate –rotate CT

27
Q

The image is created by reflecting the attenuation profiles back in the same direction they were obtained

A

BACK PROJECTION

28
Q

The resultant image closely resembles the original object but it shows star shaped patterns around objects and streaks

A

‘Star’ and ‘streak’ artifacts

29
Q

applied to each point along the attenuation profile to eliminate these artifacts

A

filter function

30
Q

used to create sharper (higher resolution) or smoother (lower noise) images

A

Different filter functions

31
Q

process of applying the filter function to the attenuation profile

A

CONVOLUTION

32
Q

(Super imposition of the filter function and the attenuation profile)

A

CONVOLUTION

33
Q

minimizes the artifacts by changing the back projected information

A

convolution

34
Q

stored as numerical values as a function of position in the profile.
This data is used in the image reconstruction process

A

difference profile

35
Q

set of difference profiles for a complete scan

A

SCAN DATA FILE or raw data

36
Q

The actual size of a pixel is equal to the size of the area scanned

A

Field of View

37
Q

How many levels of gray can the human eye distinguish

A

20 levels of gray

38
Q

How is the low distinguishing power of the human eye solved for viewing of CT images

A

Window width and Window level

39
Q

Range of CT numbers that is displayed using the useful level of gray scale

A

Window width

40
Q

separates one CT number from another

A

Small window

41
Q

condenses more than one CT number in each of gray level

A

Large window

42
Q

Center of the range of CT numbers displayed by the window

A

Window level

43
Q

The level control moves the visible gray scale up and down the CT number scale

A

Window level

44
Q

As an honour to Hounsfield who was the pioneer of invention of CT the CT numbers are called

A

Hounsfield units

45
Q

range of Hounsfield units Is from

A

-1000 to +3000

46
Q

Standard reference points are -1000 for

A

Air

47
Q

Standard reference points are 0 for

A

Water

CT Scan (8 decks)

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