Perfusion parameters derived from bolus-tracking perfusion imaging are immune to tracer recirculation

To investigate the impact of tracer recirculation on estimates of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT).

The theoretical model used to derive CBF, CBV, and MTT was examined. CBF and CBV estimates with and without tracer recirculation were compared in computer simulations to examine the effects of tracer recirculation.

The equations used to derive CBF, CBV, and MTT assume that the arterial input function and tissue tracer signals define the input and output signals, respectively, of a linear time-invariant system. As a result of the principle of superposition, these perfusion parameters are immune to tracer recirculation, which was confirmed by computer simulation. However, limited acquisition durations can lead to CBV and CBF errors of up to 50%.

Tracer recirculation does not impact estimation of CBF, CBV, or MTT. However, previous approaches used to remove recirculation effects may be beneficial when used to compensate for limited acquisition durations in which the passage of the bolus is not adequately captured.