CT System Opterations

Question 1

What are the 4 general steps to CT imaging?

Answer 1

data acquisition, data reconstruction, multidimensional image display, and image archival and communication

Question 2

What are the two other common names for a scout image?

Answer 2

topogram and scanogram

Question 3

What is the azimuth?

Answer 3

the relationship between the angle of the tube/detectors and patient position. AP/PA, Lateral, etc

Question 4

why do older CT gantries need to rotate in reverse after a short period of time?

Answer 4

cables used to supply electricity to the x-ray tube and detectors. As soon as the cable would reach its limit, the gantry would go in reverse to uncoil the cable.

Question 5

What is “slip-ring technology”?

Answer 5

a series of brushes in the gantry supplying electricity to the x-ray tube and detectors, and data transmission to the computer.

Question 6

T/F: Historically, axial scans did not have slip-ring technology and therefore needed to uncoil the electrical cables between scans.

Answer 6

true

Question 7

What is collimation in terms of CT acquisition?

Answer 7

slice thickness

Question 8

What is “flying focal spot technology”? What are two advantages of this?

Answer 8

During thermionic emission, the electron beam is refracted to two separate parts of the rotating anode.

1. anode’s integrity is better maintained
2. two primary beams are emitted, allowing for more data acquisition

Question 9

What is the range of mA for a CT scanner? What factors change how much to use?

Answer 9

30-800; patient size, clinical indication, and signal-to-noise ratio

Question 10

What does ATCM stand for and what does it do?

Answer 10

automatic tube current modulation; adjusts the mA during acquisition appropriate to anatomy size and indication

Question 11

What is photon fluence?

Answer 11

quantity of x-radiation; or another word for the primary beam

Question 12

What is photon flux?

Answer 12

the rate at which photon fluence passes through a unit area over time

Question 13

What is pitch?

Answer 13

the rate at which the table moves per gantry revolution

Question 14

What is effective mAs?

Answer 14

a calculated mAs value per acquired slice. table speed (pitch) is the primary controlling factor:
effective mAs = mAs / pitch

Question 15

When might be an appropriate study to use a LOWER kVp setting?

Answer 15

CTA; it increases contrast of anatomy and IV contrast

Question 16

When might be an appropriate study to use a HIGHER kVp setting?

Answer 16

when imaging dense anatomy; e.g. posterior fossa in CT Brain

Question 17

What is dual-energy CT?

Answer 17

dual energy CT uses one x-ray tube that rapidly changes its kVp setting (from high to low and back again) to get two data sets: one with high kV and one with low.

Question 18

How is dual-energy CT different from dual-source?

Answer 18

dual-source gets two data sets, however there are two x-ray tubes at 90 degrees from each other. One fires at high kV and the other at low

Question 19

What is beam-hardening? How does it happen?

Answer 19

as the primary beam travels through the patient, lower-energy photons are absorbed. The average kV of the beam rises, causing it to “harden”

Question 20

What effect does beam-hardening have on an image?

Answer 20

beam-hardening can cause artifacts

Question 21

What are examples of inherent and added filtration?

Answer 21

inherent: cooling oil, tube housing (equal 3 mm of Al equivalent)
added: thin copper filters (0.1 - 0.4 mm) and bow-tie filters

Question 22

What is a bow-tie filter?

Answer 22

a bow-tie filter is denser on the ends and thinner in the middle. This mirrors most anatomy, which tends to be cylindrical in shape

Question 23

The modern CT scanner’s generator output is what range?

Answer 23

60-100 kilowatts

Question 24

Describe MSAD.

Answer 24

multi-scan average dose is the average dose to a single section within a scan of multiple sections