Brain Perfusion Measurements Using Multidelay Arterial Spin-Labeling Are Systematically Biased by the Number of Delays

A, The spatial distribution of the differences between the 7-delay sequence and the 3-delay sequence for the uncorrected and corrected flow maps. The higher estimation value for the 7-delay over the 3-delay sequences is presented in the areas corresponding to the watershed areas (yellow). The 7-delay CBF estimates were found to be half the value of the 3-delay transit time–corrected flow maps within the right insular region of the brain and frontal regions (blue). The transit time–corrected maps show a higher value for the 7-delay over the 3-delay sequence in the regions overlapping the uncorrected maps. However, the transit time–uncorrected maps show a broader signal for the difference between the 2 sequences, including more posterior regions of the brain. B, The average estimated transit-uncorrected flow and the transit-corrected flow in milliliters/minute/100 g for the 7-delay and 3-delay sequences within the voxels that displayed a significantly higher estimate for the 7-delay sequences. For these voxels, an average perfusion value of 27.62 ± 12.23 is estimated by the 7-delay versus 24.58 ± 11.70 mL/min/100 g for the 3-delay sequences in the uncorrected maps, and a perfusion value of 33.48 ± 14.92 is estimated by the 7-delay versus 30.16 ± 14.32 mL/min/100 g for the 3-delay sequences of the corrected flow maps.

A, The spatial distribution of the differences between the 7-delay sequence and the 3-delay sequence for the delay maps. The estimation of the 7-delay as inferior to the 3-delay sequence (blue) concerns peripheral areas of the brain. In contrast, within the central regions of the brain, the averaged transit-time estimates are longer for the 7-delay sequences compared with the 3-delay sequences (red). B, The average estimated transit time delay in milliseconds of the voxels that displayed a significantly higher estimate for the 7-delay and those that showed a higher estimate for the 3-delay, respectively. This figure shows the difference between the 7-delay and the 3-delay within these corresponding regions. For the regions where the 7-delay estimated a smaller arterial transit time delay than the 3-delay sequence, an average arterial transit time of 1.47755 ± 0.24242 seconds is found for the 7-delay versus 1.52408 ± 0.25236 seconds for the 3-delay. Regions with a longer arterial transit time delay for the 7-delay compared to 3-delay resulted in an average arterial transit time estimation of 1.42565 ± 0.21872 seconds by the 7-delay sequence and 1.39388 ± 0.22056 seconds by the 3-delay sequences for the transit-time delay.