Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

CT > Week 2 - Attenuation > Flashcards

Week 2 - Attenuation Flashcards

1
Q

T/F
Relative transmission or attenuation measurements are sent to the computer as raw data

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

T/F
Several hundred views are needed to reconstruct the CT image

A

True

Shades of grey create the matrix and then create images

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Reduction in the intensity of the beam as it passes through matter

A

Attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

The degree to which a beam is reduced

A

Attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

The mass of a substance per unit volume

A

Density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

T/F
The number of photons that interact depends on thickness, density, atomic number of the object

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why does the number of photons that interact increase with density?

A

The more electron, neutrons, protons in each atom, the higher the likelihood of interaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The amount of xray beam that is scattered or absorbed per unit thickness of the absorber is expressed by what?

A

Linear attenuation coefficient, represented by Greek letter ‘u’

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When interacting with matter, photons are either:

A

Absorbed
Transmitted
Scattered

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does an area of low attenuation look like on an image?

A

Darker
(More photons to the detector)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Various shades of grey

A

Intermediate attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What will an area of high attenuation look like on an image?

A

White

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are factors that affect attenuation?

A

-effective atomic density (atoms/vol)
-atomic number (Z)
-density of matter
-thickness
-photon energy (125kvp, 140kvp)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

All xray photons have the same energy

A

Homogenous (monochromatic, monoenergetic)

*gamma

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What type of beam did hounsfield use in his study?

A

Monochromatic beam
(Gamma source)
Satisfied Lambert-Beer law

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is Euler’s constant?

A

2.718

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Absorber attenuates equal amounts
20% of remaining photons removed per 1cm

A

Homogenous beam
*beam energy does not change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

T/F
‘U’ is inversely proportional to photon energy

A

True
As photon energy increases, attenuation decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

T/F
‘U’ is directly proportional to atomic number and density

A

True
As density/atomic number increases, attenuation increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

The photons have different energies

A

Heterogeneous beam
(Polychromatic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

T/F
In a heterogenous beam, photons decrease but quality increases - low energy photons are removed

A

True
The beam gets “harder”

22
Q

What changed during heterogeneous attenuation?

A

Both quality and quantity

23
Q

Where does photoelectric interactions occur?

A

Absorption , inner shells

24
Q

Where does Compton interaction occur?

A

Scatter, outer shells

25
Q

T/F
PE occurs mainly in tissues with high Z (bone, positive contrast media…)
Minimal in soft tissue

A

True

26
Q

T/F
Compton effect occurs in soft tissue

A

True
Difference in tissue density produces differences in Compton interaction

27
Q

Why does a heterogenous beam not have a straightforward relationship between intensity and attenuation?

A

Because beam intensity differs

28
Q

How is the linear attenuation coefficient determined in CT?

A

Using the number of photons instead of the intensity

29
Q

Quality does not change

A

Monochromatic

30
Q

Quality and quantity change

Mean energy increases

A

Polychromatic

31
Q

Given a constant kvp, place in order of increasing ‘U’ for the following
Water, bone, air, fat, blood

A

Air
Fat
Water
Blood
Bone

32
Q

T/F
Differences in ‘U’ cause image contrast

A

True
Image is a direct reflection of ‘U’

33
Q

T/F
Density differences are needed to observe differences between structures

A

True

34
Q

What is the atomic number (Z) of barium

A

56

35
Q

What is the atomic number of iodine

A

Z=53

36
Q

Raw data (data received from detectors) undergo various pre and post processing
(Necessary for image reconstruction)

A

Data processing

37
Q

The scan data, which represent attenuation data, are converted into digital image characterized by CT numbers

A

Image reconstruction

38
Q

Conversion of the attenuation readings into CT image is accomplished by what mathematical procedure?

A

Reconstruction algorithms

39
Q

T/F
Each pixel in the reconstructed image is assigned a CT number

A

True

40
Q

What does a lower CT number represent?

A

Darker (less attenuation)

41
Q

What does a higher CT number represent?

A

White (higher attenuation)

42
Q

How are CT image attenuations quantified on any area?

A

Expressed in Hounsfield Units (H.U.)

43
Q

T/F
Hounsfield units quantify the degree that a structure attenuates an xray beam

A

True

44
Q

What HU numbers do human anatomy fall between?

A

Air (-1000) and bone (1000)

45
Q

T/F
1HU = 0.1% difference between ‘U’ of the tissue of interest compared ‘U’ of H2O

A

True

46
Q

HU inaccuracies can be due to:

A

-poor equipment calibration
-image artifacts
-volume averaging (voxel containing different material will average them)
Voxel = 3D

47
Q

Range of CT numbers

A

Window width

48
Q

Center of range of CT numbers

A

Window level

49
Q

Window width

A

Controls image contrast

50
Q

Window level

A

Controls image brightness

51
Q

What are the 3 types of windows?

A

Bone
Lung
Mediastinal

CT (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions