Bolus + infusion models
The limitations of the transient equilibrium approach, related to non-steady-state conditions in the tissue and plasma, can be overcome by administration of the tracer as a constant infusion until the true equilibrium is achieved. To hasten the steady-state, a bolus of tracer is administered before the constant infusion.
Advantages of bolus + infusion approach:
- During true equilibrium, BP can be estimated as simple ratio
- Only one scan at certain time is required
- If no there is no reference region, DV can be estimated instead of BP as tissue-to-venous plasma ratio
- Outcome is not vulnerable to perfusion change during infusion
Disadvantages:
- Difficulties in providing constant infusion of tracer
- Optimal bolus-to-infusion ratio may vary considerably between individuals