1. In ASL, upstream blood protons are either unperturbed (control) or inverted (label) on alternate applications of the pulse sequence, here demonstrated by the up arrows and down arrows, respectively.
In ASL, upstream blood protons are either unperturbed (control) or inverted (label) on alternate applications of the pulse sequence, here demonstrated by the up arrows and down arrows, respectively. The signal intensity of the labeled images is approximately 1–2% lower than that of the control images due to the extraction of the negatively magnetized inverted spins into the tissue when they reach the capillary bed. Subtracting label images from control images creates a difference image proportional to CBF. Typically many such image pairs must be subtracted to achieve adequate SNR; the image of CBF in a healthy volunteer shown above was acquired in 5 minutes at 3T.
G. Zaharchuk AJNR Am J Neuroradiol 2007;28:
©2007 by American Society of Neuroradiology