Textbook - Chapter 1

Question 1

spatial resolution

Answer 1

ability of a system define small objects distinctly

Question 2

low-contrast solution

Answer 2

ability of a system to differentiate between objects with similar densities

Question 3

temporal resolution

Answer 3

speed that the data can be acquired

Question 4

z-axis

Answer 4

thickness of a cross-sectional slice

Question 5

pixel

Answer 5

2D picture element consisting of x and y

Question 6

x-axis

Answer 6

width

Question 7

y-axis

Answer 7

height

Question 8

voxel

Answer 8

3D volume element consisting of x, y, & z

Question 9

what’s the most common matrix size for ct?

Answer 9

512x512

Question 10

what is attenuation?

Answer 10

degree which an x-ray beam is reduced

Question 11

when photons pass through something unimpeded, what colour will it show up on the ct image?

Answer 11

black

Question 12

colour of low attenuation objects

Answer 12

black

Question 13

colour of high attenuation objects

Answer 13

white

Question 14

colour of intermediately attenuating objects

Answer 14

differing shades of grey

Question 15

number of photons that interact with an object is dependent on?

Answer 15

1. thickness
2. density
3. atomic number
   *of the object

Question 16

what is linear attenuation coefficient (µ)?

Answer 16

amount of the x-ray beam that is scattered or absorbed per unit thickness of the absorber

Question 17

____ µ = _____ photon energy

Answer 17

↓µ = ↑photon energy

Question 18

____ µ = _____ atomic number

Answer 18

↑ µ = ↑ atomic number

Question 19

____ µ = _____ density

Answer 19

↑ µ = ↑ density

Question 20

image contrast is determined by?

Answer 20

difference in linear attenuation coefficients among tissues

Question 21

soft tissues’ linear attenuation coefficient is ____ (dis/proportional) to physical density

Answer 21

proportional

Question 22

what are positive agents?

Answer 22

contrast agents that are higher in density than structures they’re introduced to

Question 23

what examples of positive agents?

Answer 23

barium sulfate and iodine

Question 24

what is an example of a negative agent?

Answer 24

water (low-density)

Question 25

what are Hounsfield units also known as?

Answer 25

CT numbers or density values

Question 26

what are HUs?

Answer 26

- indicates the degree that a structure attenuates an x-ray beam in comparison to water - average of all the attenuation measurements for the pixel

Question 27

HU of dense bone

Answer 27

+1000

Question 28

HU of air

Answer 28

-1000

Question 29

HU of distilled water

Answer 29

0

Question 30

what are the main advantages of CT over conventional radiography?

Answer 30

- can get the 3d view --> get images of cross sections - elimination of superimposed structures - differentiation between structures with similar densities - good image quality

Question 31

matrix

Answer 31

grid that is formed from the rows and columns of pixels

Question 32

what are image artifacts?

Answer 32

things that are on the image that isn't actually there

Question 33

what causes artifacts?

Answer 33

polychromatic X-rays and beam hardening

Question 34

what causes beam hardening?

Answer 34

when low energy photons are absorbed leaving high energy ones to strike the detector

Question 35

what is the anatomic position?

Answer 35

erect with arms to the side and palms facing forward

Question 36

how are x-ray photons produced?

Answer 36

when electrons strike the anode

Question 37

1 HU = ___% difference between the linear attenuation coefficient of water

Answer 37

0.1%

Question 38

what are cupping artifacts?

Answer 38

vague areas of decreased density

Question 39

Raw data

Answer 39

Data acquired by the system

Question 40

Scan data

Answer 40

Aka raw data

Question 41

Raw data have not been assigned HUs. Why?

Answer 41

Haven’t been sectioned to creat pixels

Question 42

Image reconstruction

Answer 42

Using raw data to create an image Done by processing the raw data, assigning HUs to the pixels

Question 43

Image data

Answer 43

Data included in the image through image reconstruction

Question 44

Prospective reconstruction

Answer 44

Reconstruction automatically produced during scanning

Question 45

Retrospective reconstruction

Answer 45

Using the raw data later to generate new images (even after they have undergone perspective reconstruction)

Question 46

Stop and shoot, aka?

Answer 46

Axial scanning or conventional scanning or serial scanning

Question 47

2 reasons for changing image plane from axial to coronal?

Answer 47

1. Anatomy of interest lies vertically instead of horizontally 2. Reduction of artifacts caused by surrounding structures

Question 48

mA

Answer 48

quantity of electrons

Question 49

kVp

Answer 49

voltage = intensity of x-ray beam