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Flashcards in Basic CT Principles Deck (156)
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1

General radiography

Imaging modality that produces 2D images
Limitations:
-superimposition of all structures
-difficult to distinguish slight density changes of tissues
-difficult to identify precise location of abnormalities

2

Tomography

-x-ray tube and film move simultaneously and in opposite directions
-imaging modality that brings into focus only the anatomical structure lying in a plane of interest, while structures on either side of that plane are blurred
-immediate goal us to eliminate structures above and below the focused section or focal plane. This is difficult to achieve
-limitations: persistent image blurring that cannot be completely removed, degradation of image contrast because of scatter, fail to demonstrate slight differences in subject contrast (tissue), contrast cannot be adjusted after it has been recorded on film
-focal plane (aka section thickness)
▪️blur ⬆️ as distance from the focal plane ⬆️
▪️fulcrum: imaginary pivot point about which the x-ray tube and the image recpetor move
-⬆️ tomographic angle = ⬇️ section thickness

3

Focal plane

Section thickness

4

Fulcrum

-imaginary pivot point about which the x-ray tube and the image receptor move

5

Advantages of tomography vs general radiography

⬆️ radiographic contrast
⬆️ subject contrast
⬇️super imposition

6

Disadvantages of tomography vs general radiography

⬆️ patient dose

7

What is a shortcoming of radiography?

Superimposition of structures

8

What is an example of a negative contrast agent?

Air, water

9

How would a contrast agent with a high Z (atomic #) affect a radiographic image?

Increased image contrast, due to increased absorption

10

If an object is slightly less dense than water, what would be the expected HU measurement?

-10

11

The gantry houses all of the following except A) 3 phase generator B) beam collimators C) collimators D) DAS

A) 3 phase generator

12

_____ interactions produce scatter, which degrades image quality and image _____. Anytime more of these types of interactions occur image quality is _____

COMPTON interactions produce scatter, which degrades image quality and image CONTRAST. Anytime more of these types of interactions occur image quality is DECREASED

13

True or false: two essential components of a digital image processing system are the ADC and the DAC

TRUE

14

What is another name for density values?

CT numbers

15

Increasing _______ reduces patient dose, because the ____ energy photons that could be absorbed by the patient are removed from the x-ray beam

Filtration, low energy photons

16

Data acquisition in CT refers to

Getting data from the patient through a systematic motion of the x-ray tube and detectors

17

What is not a common anatomical landmark in CT?

Jugular notch

18

Give an example of a low attenuation structure

Trachea (air filled)

19

What does not produce a transverse axial sectional image?

Conventional radiography

20

An image of a hyposthenic will have _____ than an image of an asthenic patient?

Decreased radiographic density, due to exponential attenuation

21

What happens to the emission spectrum when a higher voltage waveform is utilized?

Increased amplitude; increased average energy

22

True or false: area closest to the fulcrum has less blur

TRUE
Farther away from fulcrum = more blur

23

True or false: fulcrum is dead centre on image

True

24

True or false: big angle on the tube = smaller slice

True!

25

Tomography problems

-image blurring (poor image contrast outside of focal plane)
-patient dose
-GOOD for curved structures

26

True or false: The isocenter of a gantry is not an important consideration for patient positioning

False!

27

What is a universal limitation, and what is a common concern in x-ray imaging?

Heat production; motion

28

True or false: decreasing the tomographic angle increases slice thickness

True!

29

In CT, a high kilo-voltage technique is generally used for which reason?

Decrease the dependence of attenuation coefficients on photon energy

30

When a projectile electron interacts with the nuclear field of an atom and changes directions it loses _____ energy, in the form of _____ radiation

Kinetic energy, bremsstrahlung radiation