Textbook 5 + 6

Question 1

high-contrast reconstruction algorithms are also known as?

Answer 1

bone or detail filters

Question 2

localizer scans

Answer 2

digital image acquisitions done by the tube being stationary and the bed is moving through the scan field

Question 3

localizer scans aka?

Answer 3

scout, surview, tomogram, scanogram, preview, and pilot

Question 4

z axis in terms of patient positioning?

Answer 4

head-foot direction

Question 5

y axis in terms of patient positioning?

Answer 5

whether the table in the gantry is too high or too low

Question 6

x axis in terms of patient positioning?

Answer 6

patient lying more to one side or not

Question 7

axial scans programmed for contiguous slices result in what?

Answer 7

when one slice abuts the next

Question 8

cine or dynamic methods

Answer 8

when scanners are programmed to repeat scans at the same slice location

Question 9

when are gapped slices used?

Answer 9

high-resolution chest studies

Question 10

overlapping slices

Answer 10

acquiring data in a noncontiguous way

Question 11

what are some disadvantages to the axial method?

Answer 11

• increased examination time
• delays in imaging can be significant
• motion artifacts
• reconstruction limitations

Question 12

misregistration

Answer 12

occurs when the patient breaths differently with each data acquisition

Question 13

when are axial scans preferred?

Answer 13

• acquisition speed isn’t a concern
• optimal resolution needed
• gapped slices needed
• interruption in exposure

Question 14

what are the key “ingredients” to a helical scan?

Answer 14

1. x-ray tube is constantly moving
2. constant x-ray output
3. uninterrupted table movement

Question 15

what are some advantages to helical scans?

Answer 15

• improved image resolution with iodinated contrast concentration
• decreased motion artifacts due to resp. and cardiac motion
• superior multiplayer or 3D reformation capabilities
• improved scanning speed

Question 16

slip rings

Answer 16

allows for the tube to move continually in the same direction
- cuts out interscan delays

Question 17

interpolation

Answer 17

statistical methods to remove slants or blur of helical images

Question 18

what are the disadvantages to interpolation?

Answer 18

more interpolation required, the decrease of image resolution and effective slice thickness

Question 19

pitch

Answer 19

distance the table travelled per 360 rotation of the x-ray tube divided by the x-ray beam collimation width

Question 20

when pitch is less than 1, what does it mean?

Answer 20

scans are overlapping because the table feed is less than the beam collimation

Question 21

in SDCT systems, the width of the collimator is what?

Answer 21

the sole determinator of slice thickness

Question 22

pitch expressed as a ratio

Answer 22

table speed:slice thickness

Question 23

↑pitch = ___ slice angle

Answer 23

as pitch increases, so does the slice angle

Question 24

↑slice angle = ____ ?

Answer 24

as slice angle increases, so does the interpolation which will decrease the image resolution

Question 25

↑pitch = ___ data acquisition for each table position

Answer 25

as pitch increases, fewer data is acquired for each table position

Question 26

overall, increasing pitch does what to acquisition time?

Answer 26

it will cover more anatomy for a given total acq. time which reduces radiation dose

Question 27

overall, decreasing pitch does what?

Answer 27

it’ll slow down the table speed which decreases the amount of anatomy covered per unit time, which increases the radiation dose