Brainscape's Knowledge GenomeTM

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


See full index

Physics > CT > Flashcards

CT Flashcards

1
Q

Doses

A
  • CT Head - 2mSv
  • CT Chest - 7mSv
  • CT Abdo - 8mSv
  • CTPA - 10mSv
  • CT Abdo/Pelvis - 15mSv
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Partial Volume

A

Makes high contrast objects appear larger

Makes low contrast objecto appear smaller

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

Beam Hardening

A

Causes a reduction in houndsfield units towards the centre of the image

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

Anode-cathode axis

A

Parallel with centre of scanner

In Z axis

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

Fan Beam

A

Is perpendicular to the anode-cathode axis

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

What is resolution in CT?

A

Measured in line pair/cm

7lp/cm in the transaxial plane

When directly compared with radiography:

1lp/mm vs 3lp/mm for radiography

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

Is contrast resolution better in CT than plain film?

A

Yes contrast resolution better in CT

(Spatial resolution better in plain film)

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

Does a narrow window increase or decrease noise?

A

Increases noise

Smaller FOV = less signal and more noise

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

What is anode cathode axis in CT?

A

Parallel to the axis of the scanner to minimise heel effect

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

What filtration is used in CT?

A

6mm of aluminium

or

0.5mm Copper which is equilivent

In newer scanners:

  • 3mm aluminium
  • 0.1mm copper

Total filtration 6mm equivilent

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

What collimation distance is used in CT?

A

50cm usually sufficient for most patients

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

Are detectors separated in CT?

A

Yes, this is to reduce light crossover

Reduces detection efficiency however (to 80%)

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

What is cone beam effect due to?

A

Due to divergence of beam in Z axis

Usually problematic when there are more than 4 slices

Increased number of slices = worse cone beam effect

Affects outer detectors rows more

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

For same mA and kV, does slice thickness affect dose?

A

No

Dose is independent of slice thickness

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

In an obese patient, is kV or mA increased? or both?

A

Just mA is increased

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

Which part of patient receives higher dose?

A

Periphery

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

Which scanner produces more scatter? 1st or 3rd gen

A

Third generation

18
Q

Are detector crystal embedded in a matrix in CT?

A

NO

19
Q

What is pixel size formula?

A

Pixel size = FOV /matrix size

20
Q

In single slice scanners, does pitch affect noise?

A

NO

21
Q

What is CTDIw

A

CTDIw = 1/3CTDI centre + 2/3CTDI periphery

Units = mGy

22
Q

What is CTDI vol?

A

CTDIw / Pitch

Units = mGy

23
Q

What is DLP?

A

CTDIvol x Total Scan length

Units mGy/cm

24
Q

What is effective dose?

A

DLP x fiddle factor (dependent on body part)

Units are mSv

25
Q

How to calculate noise in CT?

A

1/ square root of number of photon

Inversely proportional to the square root of number of photons

26
Q

What effect will doubling of mA have on the noise?

A

Will decrease noise by a factor of:

square root of 2

Halving rotation time also decreases noise by the square root of 2

27
Q

What is filter interpolation and 2 point interpolation used in?

A

Filter interpolation = Multislice scanners

Two point interpolation = single slice scanners

28
Q

What is normal CT matrix size?

A

512 x 512

For high resolution = 1024 x 1024

Fluoro CT uses 256 x 256 for reconstruction

29
Q

How to calculate CT number?

A
30
Q

What measures can be taken to improve cupping artefact?

A

Cupping artefact is otherwise known as beam hardening

Made better by:

  • Bow tie filter
  • Algorithms
31
Q

Which has more afterglow?

Sodium iodide

vs

Bismuth germinate

A

Sodium iodidie has more afterglow

Bismuth germinante is more preferable

32
Q

Which CTDI most closely corresponds with absorbed CT dose?

A

CTDIvol

CT dose = mA/pitch

33
Q

Is effective dose measured on every CT scan?

A

No

34
Q

What is pixel size in CT?

A

0.5mm usually

35
Q

In CT does magnification increase spatial resolution?

A

Yes

36
Q

Can CT gantry tilt in the vertical axis?

A

Yes

It can tilt up to 30 degrees in the vertical axis

37
Q

What is heat capacity in CT?

A

4MJ

38
Q

What is CT fluoroscopy used for?

A

Needle guidance in IR procedures

  • 180 degree rotation
  • low dose technique
  • higher skin dose than normal CT
  • lower effective dose
39
Q

When is post patient collimation used?

A

Used in single slice scanners

Used to reduce scatter

Results in increased dose

40
Q

Do 4th gen scanners result in a higher dose?

A

Yes

The patient to detector distance is greater

They have 6x the amount of detectors than other scanners

Calibration can be adjusted through each scanning cycle

Physics (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions