Transcranial ultrasound perfusion imaging: implementation of a low MI and a high frame rate.

PURPOSE

Conventional transcranial ultrasound perfusion imaging (UPI) depends on bolus injection and is limited to triggered imaging. To improve our set-ups, we compared two imaging modalities with two different frame rates (FR) and mechanical indices (MI), intending to approach conditions more similar to real time imaging in order to increase parameter precision.

MATERIALS AND METHODS

Fifteen healthy volunteers were investigated twice with UPI after i. v. administration of 1 ml of SonoVue(R): first, with a high MI (1.6) and a low FR (0.67 Hz)) and second, with a low MI (1.0) and a high FR (5 Hz). Apart from visual analysis, time-intensity curves were calculated from three regions of interest (ROI) and peak intensity (PI), time to PI (TP), and area-under-the-curve (AUC) were compared between the two imaging modalities.

RESULTS

Visually, only scarce contrast enhancement was observed in 10/15 probands, and penetration depth was markedly lower at the low MI/high FR setting, while the high MI/low FR setting lead to very intense enhancement in 13/15 individuals. Signal-to-noise-ratio was higher at the low MI/high FR setting. TP was not significantly different between the two set-ups (p > 0.05). PI and AUC were significantly lower at the low MI/high FR setting (p</= 0.001), and both parameters correlated well in corresponding ROIs (p < 0.05 or < 0.01 in 8/9 ROIs). Parameter images reflected the differences of these two semi-quantitative parameters.

CONCLUSION

In patients with excellent bone windows, the new set-up seems to offer highly precise kinetic analysis with an excellent signal-to-noise ratio. In the majority of patients, however, conventional transcranial UPI is limited to high MI and a resulting rather low FR to allow sufficient penetration depth and contrast enhancement.