Visualization of brain perfusion with harmonic gray scale and power doppler technology : an animal pilot study

It is unclear which harmonic imaging mode (power Doppler or gray-scale imaging) is superior and which measuring method is the most robust for the description of brain perfusion.

We performed an animal study on 6 beagles through the intact skull using a SONOS 5500 device and Optison injected intravenously in 3 different doses (0.15, 0.3, and 0.6 mL). Intensity versus heart-cycle plots for the brain parenchyma and the basal cerebral arteries were generated to evaluate the peak increase (PI) from baseline and the area under the curve (AUC).

With harmonic gray-scale imaging, a homogeneous increase in echo contrast of the brain parenchyma was observed. The effect was dose dependent, resulting in a significant increase in PI as well as an insignificant increase of the AUC with 0.3 mL versus 0.15 mL contrast agent (P=0.03 and P=0.65, respectively; n=5). With harmonic power Doppler, injection of the 3 different doses resulted in a nonsignificant increase in PI and AUC P=0.17, n=6 for both). After normalization of the brain signal to the peak arterial signal in individual dogs, a significant increase could be demonstrated (P=0. 03 and P=0.01, respectively; n=6). The signal pattern of harmonic power Doppler was inhomogeneous, with stronger signal increases in the anterior part of the brain.

Gray-scale imaging leads to a more homogeneous increase in echo contrast of the brain tissue and may be more suitable for displaying brain perfusion. The PI of the signal intensity seems the most robust parameter for the description of cerebral perfusion with both imaging modes under investigation.