Fig. 3. SNR measurement.

Signal intensity was measured on b0 images of water-filled bottle (A). ROI of 100 mm³ was placed in center of bottle (arrow). Noise image was obtained simultaneously with DTI and noise was measured in corresponding area of b0 images (B, arrow). Noise image was used to measure noise, as it is very difficult to measure noise directly in images when using parallel imaging. SNR was calculated using following equation: SNR = 1.253 × mean of object (ROI in b0 image) / mean of noise image (ROI in noise image). Factor of 1.253 is fixed factor expressing mean of noise image to standard deviation of object with signal at same location. DTI = diffusion tensor imaging, ROI = region-of-interest, SNR = signal-to-noise ratio