Aim: The Müller-Casty flow index (FI) is recommended for use in transcranial Doppler sonography (TCD) to measure relative changes in volume flow. We examined the ability of the FI to assess the volume flow during diameter changes of basal cerebral arteries.
Method: Nitroglycerin (NTG) was used to induce dilation of basal cerebral arteries without affecting cerebral blood flow. Transverse and sagittal sections of the middle cerebral artery (MCA) were obtained by magnetic resonance imaging (MRI) and blood flow velocities in the MCA were measured by TCD. The FI was calculated by multiplying Doppler shift frequency and signal power.
Results: NTG induced an increase of MCA-diameter in MRI. The mean FI remained approximately constant (-2.6 +/- 6%), while the mean blood flow velocity dropped significantly (-15 +/- 6%).
Conclusion: The FI can be used to estimate volume flow in basal cerebral arteries even in case of diameter change.