Multi-phase CT 4.3.24

Question 1

What is a multi-phase contrast CT exam ?

Answer 1

Imaging the same region at different points in time during the same exam. Usually to observe contrast enhancement.

Individual phases may be described in relation to
* blood flow,
* organ function
* simply by time.

Protocol descriptions may relate to the number of phases in a study eg: biphasic

Multi-phasic is used in cardiac imaging but its commonly relates to the heart cycle eg: diastole, systole.

Question 2

Contrast passage recap

Answer 2

• Contrast enhancement of the organs 1st pass
- this will occur at slightly different times depending on arterial blood supply
* lesions/ abnormalities with a good arterial blood supply will enhance
~ abnormalities where arterial blood supply is compromised will not enhance as well eg: infarcts
= arterial bleeding will be best visualised at this time

Question 3

CT fluoroscopic timing / bonus tracking

Answer 3

Early contrast phases better timed dynamically as less margin for error
1 low dose slice every second
Manual trigger or region of intent (ROI ) trigger
Can also use time bonus instead

Question 4

Acute stroke protocol

Answer 4

1) pre contrast
2) CT bonus tracked carotid Angio
3) Angio +8 seconds
4) Angio + 16.5 seconds

Question 5

Contrast phase recap

Answer 5

• Pre - contrast
• pulmonary arterial phase
• arterial phase ( timed/ triggered)
• brain vascular phases
• portal venous
• delayed eg: 3 or 5 min

Question 6

How does this work with MRI?

Answer 6

• angiogram type exams use a bolus tracking technique
  
  • can also be multi- phase ( time-resolved mra)
• most tend to be fixed time post-contrast
• can also use first pass perfusion
• variety of Mr sequences

Question 7

Cardiac CT

Answer 7

Scanned over a whole heart cycle

Used to evaluate motion rather than contrast enhancement characteristics