Figure 1.
Volitional apneic paradigm and MR protocol. (a) The apnea paradigm consisted of five BH periods and 66 s of normal breathing. Blue boxes indicate 24-s instructed breath-holds. (b) Time of flight MR projection angiogram, T1-weighted MPRAGE and interleaved PC-MRI were acquired for slice prescription, brain segmentation and calibration ratio, respectively. Reconstructed radial PC-MRI to generate time-course of SSS velocity, and BOLD images for evaluation of response to volitional apnea. Two 24-s practice apneas were included in the protocol prior to 10 min of continuous scanning.