Ultrasonic assessment of physiological echo-contrast agent distribution in brain parenchyma with transient response second harmonic imaging.

Abstract

The present study was designed to provide normal data of transient response second harmonic imaging (TRSHI) examinations of cerebral echo contrast enhancement using different modes of electrocardiogram (ECG) gating and echo-contrast agent doses. Fifty-five patients were examined in an axial diencephalic plane of section using the transtemporal acoustic bone window. TRSHI examinations (ECG gating: systolic, frame-rate once every 2 cardiac cycles = "basical instrument setting") could be performed in 50 individuals with adequate insonation conditions after application of 4 g of a galactose-based microbubbles suspension in a concentration of 400 mg/ml. For comparison, diastolic ECG gating (20 patients), cardiac-cycle triggering frequency of once every 2 seconds (15 patients), or an echo contrast agent dose of 2 g Levovist (15 patients) were used. Analysis of peak intensities (PIs) and areas under the curve (AUCs) was done in posterior (region of interest [ROI]a) and anterior (ROIb) parts of the thalamus, in the lentiform nucleus (ROIc), and the white matter (ROId). In 41 patients with basical instrument setting, characteristic time intensity curve (TIC) could be detected in all ROIs. In ROIa (90%) and ROIb (82%), focal contrast enhancement was most difficult to visualize, and in ROIc and ROId, characteristic TICs were observable in more than 90% of the examinations. Background subtracted PIs and AUCs were significantly higher in ROIc (mean PI: 12.2 +/- 8 acoustic units [AUs]; mean AUC: 598.8 +/- 451.1 AU x Cardiac cycles), and ROId (11.8 +/- 6.9; 559.2 +/- 404) as compared to ROIa (8.3 +/- 5.2; 368.9 +/- 242.7) and ROIb (7.1 +/- 4.7; 298.2 +/- 199.1) (P < .0001). Values for corresponding examinations with a diastolic ECG gating and a cardiac cycle triggering frequency of once every 2 seconds were not different as compared to the basical instrument setting. A 4 g Levovist dose increased the portion of typical TIC in all ROIs. PI of 4 g examinations were significantly higher in ROId and ROIb as compared to the 2 g examination. Our findings indicate that TRSHI allows noninvasive assessment of focal cerebral contrast enhancement in the majority of patients with adequate insonation conditions. This study provides data about normal quantitative and qualitative TRSHI values in patients without cerebrovascular diseases. A dose of 4 g Levovist is recommended in those individuals with inaccurate echo contrast enhancement using the 2 g dose.