Scan Parameters

Question 1

Axial CT

Answer 1

Step-n-Shoot; table moves in between each slice acq

Question 2

Helical CT (definition)

Answer 2

X-ray tube spirals around Pt as table moves

Question 3

Volume CT scans:
Volume CT requires (2)

Answer 3

Entire area of interest scanned in a single rotation
Very large detector arrays/advanced scanners

Question 4

Axial CT advantage

Answer 4

Increased spatial resolution

Question 5

Axial CT Disadvantages (4)

Answer 5

Increased scan time
Increased patient dose
Undesirable for IV contrast (acq too slow)
Table induces Pt motion

Question 6

Helical CT Advantages (4)

Answer 6

Decreased scan time
Decreases Pt dose
Preferred for IV contrast (shorter scan time)
More post-processing options

Question 7

Helical CT Disadvantage

Answer 7

Decreased spatial resolution d/t image interpolation

Question 8

Acquisition Thickness (definition)

Answer 8

Width of each detector row used during scan

Question 9

Reconstruction Thickness–definition

Answer 9

amount of anatomical data averaged into each image

Question 10

Slice Thickness:
Thin offers…
Thick offers…

Answer 10

Thin: higher spatial resolution in z-axis
Thick: Lower image noise

Question 11

RE: Acquisition Slice Thickness
High Resolution scans use:
High-speed scans use:

Answer 11

High-Res: use thinner detector rows
High-Speed: combine rows

Question 12

Slice Interval rule of thumb

Answer 12

Should match Reconstruction thickness (to avoid overlap or gaps b/w slices)

Question 13

DFOV

Answer 13

Display Field-of-View
Area selected for processing: usually smaller than total area scanned

Question 14

Contrast Admin: purpose

Answer 14

Enhance tissue discrimination
Differentiate b/w normal tissues
Differentiate b/w normal tissues and abnormalities

Question 15

Differential Attenuation

Answer 15

Variation of radiation beam based on tissue density/atomic constituents/etc.
(Basis of CT imaging)

Question 16

CT contrast Admin: Routes

Answer 16

IV
Oral
Rectal
Intra-articular (joint)
Intra-Thecal (ITh)

Question 17

Phases of IV Contrast Enhancement: Non-Contrast (2 examples)

Answer 17

Brain hemorrhage
Renal Calculi

Question 18

Phases of IV Contrast Enhancement: Arterial–definition

Answer 18

Peak enhancement of aa. as contrast enters organ

Question 19

Phases of IV Contrast Enhancement: Venous–definition

Answer 19

Peak enhancement of vv. as contrast leaves organ (2nd phase)

Question 20

Phases of IV Contrast Enhancement: Portal Venous occurs during:
(At around: _______)

Answer 20

Peak enhancement of portal venous syst (~60sec post admin)

Question 21

Phases of IV Contrast Enhancement: Delayed (2)

Answer 21

“Equilibrium Phase”
…after all contrast has washed out of most organs

Question 22

Enhancement of liver mass during arterial phase

Answer 22

Indication of Primary Liver Cancer (HCC)

Question 23

3 Factors affecting IV Contrast Volume

Answer 23

Protocol Selection
Speed of CT imaging syst
Size of patient

Question 24

Routine Venous Phase Imaging Dose: average sized adults

Answer 24

100 mL

Question 25

Routine Venous Phase Imaging Dose: Smaller Adults/Children

Answer 25

1 mL/lb

Question 26

Contrast Admin: Routine Arterial/Angiographic Studies: 4-8 slice v 16+ slice

Answer 26

Longer Scans/Slower Systems (4-8) require more contrast to maintain optimal arterial enhancement: 120-150 mL
Shorter Scans/Faster Systems (16+) require less contrast: 75-100 mL

Question 27

Arterial Phase/Angiographic CT Injection Rate

Answer 27

4-6 mL/sec needed for dense bolus

Question 28

Venous Phase CT Injection Rate

Answer 28

3mL/sec (dependent upon IV patency)

Question 29

Pressure Injector Heating Sleeve warms contrast to _______ _______in order to _______ _______ and risk of_______

Answer 29

Warms contrast to 35 deg C to reduce viscosity/risk of extravasation

Question 30

Pressure Injector: Motor that drives plungers forward to maintain prescribed injection rate

Answer 30

High Pressure Mechanism/Drive Motor

Question 31

Pressure Injector: Control Panel

Answer 31

Used to set parameters: PSI, Volume, Rate

Question 32

Saline Trailer trails contrast bolus in order to _______ _______ _______ in chest and reduce _______ _______ _______ needed for scan

Answer 32

enhance image quality
total contrast volume

Question 33

Scan Delay Time (“Prep Time”)

Answer 33

amount of time b/w initiation of contrast injection & the scan

Question 34

Scan Delay/Prep Time: Chest delay is_______ for _______ ________.

Answer 34

30 sec for venous phase

Question 35

Scan Delay/Prep Time: Abdomen

Answer 35

60 sec for venous phase imaging

Question 36

Bolus Tracking (3)

Answer 36

Most common/accurate method for timing angiography scans
Use of ROI to measure enhancement of selected vessel as contrast enters syst: Ensures scan initiated at exact moment of peak contrast enhancement

Question 37

Timing Bolus

Answer 37

Small bolus injected and monitored at console. Once bolus is done, ROI used to identify time of highest contrast enhancement: that time then used as “scan delay time”

Question 38

Most common/accurate method for timing angiography scans

Answer 38

Bolus Tracking

Question 39

Portal Venous Phase

Answer 39

Third Phase
Blood/contrast is leaving intestines and being directed up into liver

Question 40

Increased WL yields _______ brightness

Answer 40

darker/decreased

Question 41

Decreased WW yields _______ contrast

Answer 41

Increased