Week 3 Lecture 1

Question 1

scanning

Answer 1

defined by the beam geometry used
- size, shape, motion of the beam, path

Question 2

what are the 2 methods of CT data acquisition?

Answer 2

1. axial
2. helical

Question 3

when are scouts acquired?

Answer 3

PRIOR to both axial or helical scans

Question 4

AP (in terms of scouts)

Answer 4

tube above patient

Question 5

Lateral (in terms of scouts)

Answer 5

tube is beside patient

Question 6

what part of the equipment is stationary?

Answer 6

the tube is
the table will be moving the patient into the gantry

Question 7

scouts can be used to set what?

Answer 7

• DFOV
• Image center
• gantry tilt (tube angle)

Question 8

in ap scouts, where should your image center be to indicate that you are isocentered?

Answer 8

image center over the spine

Question 9

what can result due to miscentering?

Answer 9

• not scanning all required anatomy
• out-of-field artifacts
• higher patient doses

Question 10

if the indicated patient position is wrong, what can happen?

Answer 10

misdiagnosis

Question 11

during image display, what can scouts do for us?

Answer 11

it can be used to reference the location of a cross-sectional slice
- can show us the selected SFOV, DFOV and location of that slice

Question 12

what are the steps to axial acquisition?

Answer 12

1. 360 degree tube rotation around patient
2. tube stops + table moves in

Question 13

movement of the table correlates to?

Answer 13

slice thickness

Question 14

what are the advantages to axial acquisition?

Answer 14

+ image quality
+ acquisition variability

Question 15

contiguous

Answer 15

slices are side-by-side

Question 16

gapped

Answer 16

slices are spaced apart

Question 17

overlapped

Answer 17

slices double expose parts of anatomy

Question 18

helical acquisition aka?

Answer 18

spiral beam geometry

Question 19

what 3 things are required of the helical acquisition method?

Answer 19

1. slip rings to allow the tube to rotate continuously
2. constant x-ray output
3. continuous table movement

Question 20

in terms of irradiation, what is the difference between axial and helical?

Answer 20

axial = irradiates slice-by-slice
helical = irradiating a volume of tissue

Question 21

what are the advantages to helical scanning?

Answer 21

+ *reduces chance of misregistration
+ more data manipulation capabilities
+ decreased scan times
+ less chance for motion artifacts from specific types of patients
+reduces amount of contrast used in enhanced studies

Question 22

what are the disadvantages to helical scanning?

Answer 22

low image quality because the full 360 degrees’s data is not obtained

Question 23

extrapolation/interpolation

Answer 23

• removes the “slant” from an image slice
• creates motion-free images

Question 24

what type of data is only accessible on the CONSOLE COMPUTERS hard disks?

Answer 24

raw data

Question 25

hard disks are (short/long)-term storage

Answer 25

hard disks = short-term storage

Question 26

what type of data is needed for retrospective reconstructions?

Answer 26

raw data

Question 27

image data requires (lots/less) storage space and is stored in (short/long)-term storage.

Answer 27

image data = less storage + long-term

Question 28

where is image data stored?

Answer 28

PACS or workstation monitors

Question 29

what are the data manipulation capabilities like for image data?

Answer 29

limited

Question 30

the limit to data manipulation capabilities for image data, what does that do to retrospective reconstructions?

Answer 30

disables retrospective reconstructions so adjustment to DFOV AFTER a scan acq. isn’t able to be done

Question 31

matrix size is typically compared between scanners, as the matrix size of a CT system can’t be adjusted

Question 32

↑ matrix size = (↑/↓) pixel size = (↑/↓) spatial resolution

Answer 32

↑ matrix size = ↓ pixel size = ↑ spatial resolution

Question 33

↓ matrix size = (↑/↓) pixel size = (↑/↓) spatial resolution

Answer 33

↓ matrix size = ↑ pixel size = ↓ spatial resolution

Question 34

height of pixel = ___ axis and describes?

Answer 34

height of pixel = y axis and describes the tissue’s thickness

Question 35

width of pixel = ____ axis

Answer 35

width of pixel = x axis

Question 36

pixels bit depth affects what?

Answer 36

contrast resolution

Question 37

voxel

Answer 37

represents a volume of tissue – slice thickness

Question 38

z axis

Answer 38

thickness of the slice

Question 39

localizer scans are also used to set the extent of anatomic coverage. t/f

how?

Answer 39

true

by selecting the location of the first and last cross-sectional slices

Question 40

localizers are used for positioning. t/f

Answer 40

false
it should never be used for positioning as it gives patient a dose

Question 41

how much can a patient’s dose be increased if you don’t isocenter them?

Answer 41

by 140%

Question 42

anisotropic

Answer 42

more rectangular in shape