Fig. 2.

CNR (a) and SNR (b) calculated for the three 7-T TOF-MRA sequences at different spatial resolutions (black color) and for the clinical 3-T TOF-MRA images (dark gray color). Each dot represents the mean among subjects of CNR (a) or SNR (b) for a specific ROI. Data distribution is shown through box plots, where the box is determined by the 25^th and 75^th percentiles and the median and the mean are represented by the horizontal and the cross line inside the box, respectively. The whiskers represent the 5^th and 95^th percentiles. To compare results for CNR (a) or SNR (b) obtained by different acquisitions, nonparametric paired tests (Wilcoxon signed-rank test) were performed between each couple of datasets. Statistically significant differences of CNR and SNR between different acquisition schemes are reported in the graph according to the following legend: one asterisk (*) indicates p < 0.050, two asterisks (**) p < 0.010, and three asterisks (***) p < 0.001. CNR Contrast-to-noise ratio, SNR Signal-to-noise ratio, TOF-MRA Time-of-flight magnetic resonance angiography