Comparison between echo contrast agent-specific imaging modes and perfusion-weighted magnetic resonance imaging for the assessment of brain perfusion.

BACKGROUND AND PURPOSE

Contrast burst imaging (CBI) and time variance imaging (TVI) are new ultrasonic imaging modes enabling the visualization of intravenously injected echo contrast agents in brain parenchyma. The aim of this study was to compare the quantitative ultrasonic data with corresponding perfusion-weighted MRI data (p-MRI) with respect to the assessment of brain perfusion.

METHODS

Twelve individuals with no vascular abnormalities were examined by CBI and TVI after an intravenous bolus injection of 4 g galactose-based microbubble suspension (Levovist) in a concentration of 400 mg/mL. Complementary, a dynamic susceptibility contrast MRI, ie, p-MRI, of each individual was obtained. In both ultrasound (US) methods and p-MRI, time-intensity curves were calculated offline, and absolute time to peak intensities (TPI), peak intensities (PI), and peak width (PW) of US investigations and TPI, relative cerebral blood flow (CBF) and relative cerebral blood volume (CBV) of p-MRI examinations were determined in the following regions of interest (ROIs): lentiform nucleus (LN), white matter (WM), posterior (PT), and anterior thalamus (AT). In addition, the M(2) segment of the middle cerebral artery (MCA) was evaluated in the US, and the precentral gyrus (PG) was examined in the p-MRI examinations. In relation to a reference parenchymal ROI (AT), relative TPIs were compared between the US and p-MRI methods and relative PI of US investigations with the ratio of CBF (rCBF) of p-MRI examinations in identical ROIs.

RESULTS

Mean TPIs varied from 18.3+/-5.0 (AT) to 20.1+/- 5.8 (WM) to 17.2+/-4.9 (MCA) seconds in CBI examinations and from 19.4+/-5.3 (AT) to 20.4+/-4.3 (WM) to 17.3+/-4.0 (MCA) seconds in TVI examinations. Mean PIs were found to vary from 581.9+/-342.4 (WM) to 1522.9+/-574.2 (LN) to 3400.9+/- 621.7 arbitrary units (MCA) in CBI mode and from 7.5+/-4.6 (WM) to 17.5+/-4.9 (LN) to 46.3+/-7.1 (MCA) arbitrary units in TVI mode. PW ranged from 7.3+/-4.5 (AT) to 9.1+/-4.0 (LN) to 24.3+/-12.8 (MCA) seconds in CBI examinations and from 7.1+/-3.9 (AT) to 8.7+/-3.5 (LN) to 26.7+/-18.2 (MCA) seconds in TVI examinations. Mean TPI was significantly shorter and mean PI and mean PW were significantly higher in the MCA compared with all other ROIs (P<0.05). Mean TPI of the p-MRI examinations ranged from 22.0+/-6.9 (LN) to 23.0+/-6.8 (WM) seconds; mean CBF ranged from 0.0093+/- 0.0041 (LN) to 0.0043+/-0.0021 (WM). There was no significant difference in rTPI in any ROI between US and p-MRI measurements (P>0.2), whereas relative PIs were significantly higher in areas with lower insonation depth such as the LN compared with rCBF.

CONCLUSIONS

In contrast to PI, TPI and rTPI in US techniques are robust parameters for the evaluation of cerebral perfusion and may help to differentiate physiological and pathological perfusion in different parenchymal regions of the brain.