Figure 1.
Dependence of perfusion-weighted signal intensity (dM) on post-labeling delay (PLD).
Tagging duration = 1500 ms. Data is obtained from the 6th slice of a representative subject. Regions of interest are determined at a probability of 0.95 for gray matter (green lines), and both 0.95 and 0.99 for white matter (blue and red, respectively). The inset in the left panel suggests a transit delay of ~1200 ms. In both panels, background signals are zero on average with standard deviation (i.e., noise) shown in error bars. The right panel shows that labeling/control pulses cause negligible flow-irrelevant signal perturbation.
Figure 2.
Dependence of perfusion-weighted signal intensity (dM) on tagging duration (τ).
Post-labeling delay = 1800 ms. Data is obtained from the 6th slice of the subject in Figure 1. Regions of interest are determined at a probability of 0.95 for gray matter (green lines), and both 0.95 and 0.99 for white matter (blue and red, respectively). In both panels, background signals are zero on average with standard deviation (i.e., noise) shown in error bars. The right panel indicates that labeling/control pulses cause negligible flow-irrelevant signal perturbation.
Figure 3.
Percentage of voxels detectable at varying post-labeling delay PLD (left panel, tagging duration = 1500 ms) and tagging duration τ (right panel, PLD = 1800 ms).
Error bars indicate the standard deviation across 10 subjects.
Figure 4.
Maps (a) and histograms (b) of perfusion-weighted signal to noise ratio (SNRdM) obtained in three representative subjects (slice 6).
Echo-planar images at the same location are shown for anatomical reference (upper row). In (b), white bars = white matter, gray bars = gray matter. The proportion of white matter voxels with SNRdM above unity is 0.55, 0.60, and 0.58, respectively.
Figure 5.
Histogram of tissue probability.
Shown in black bars is the original histogram that only contains pixels with tissue probability above 0.95 (upper panel = white matter, lower panel = gray matter). After spatial smoothing, the probability histogram of these voxels is overlaid on the original histogram for comparison. A three-dimensional Gaussian-shaped kernel was used for smoothing (full-width-half- maximum = 3 mm as shown in gray bars and 8 mm as shown in blue bars). The insets are the blowup view of tissue probability ≥ 0.95.
Figure 6.
Maps of perfusion-weighted signal to noise ratio (SNRdM) averaged across 10 subjects.
Six slices are shown. (a) SNRdM is noticeably higher in gray matter than in white matter. To better display how SNRdM is distributed in white matter, gray matter is masked out in the lower panel and the color scale is adjusted. (b) SNRdM in white matter after spatially smoothed by a three-dimensional Gaussian-shaped kernel (full-width-half- maximum = 3 mm for the upper panel and 8 mm for the lower panel). Note that a different color scale is used to accommodate the increase of SNRdM.
Figure 7.
Simulated dependence of perfusion-weighted signal to noise ratio (SNRdM) on tagging duration and post-labeling delay in white matter.
Transit delay (δWM) is increased from 1000 ms to 3000 ms, with a step of 400 ms. The dashed lines indicate the contours where SNRdM = 1.
Figure 8.
Simulated temporal evolution of perfusion-weighted signal to noise ratio (SNRdM).
Tagging duration = 2000 ms, transit delay = 800 ms for gray matter and 1500 ms for white matter.