Velocity offset as a function of several protocol parameters. Every data point represents an average of three samples of the same scanner-type. Standard deviation of the basic protocol was 0.4 cm/s (average for the three scanner-types). From these graphs it is clear that there are no general guidelines across different types for velocity offset optimization. Slice orientation, however, had a strong influence on the velocity offset; a transverse aortic slice gave generally the lowest offset. Results from statistical analysis of this data is shown in Table 2.