Houchun Harry Hu^{1}, Ruiyue Peng^{2}, Xingfeng Shao^{3}, Mark Smith^{1}, Jerome Rusin^{1}, Ramkumar Krishnamurthy^{1}, Bhavani Selvaraj^{1}, and Danny JJ Wang^{3}

Single post-labeling-delay (PLD) pCASL are commonly used to measure cerebral blood flow (CBF). A PLD of 1500-2000ms is commonly used in children and adults. Multi-delay pCASL has been developed as an alternative approach to better account for prolonged arterial transit times (ATT) and to improve the accuracy of CBF perfusion quantification. In this study, we evaluate the feasibility of multi-delay pCASL in children. We compare two algorithms (weighted-delay linear mapping vs. nonlinear iterative curve fitting) for estimating ATT and CBF. We further compare estimations of weighted-delay CBF derived from multi-delay pCASL data with those traditionally calculated from a single PLD measurement.

Typical calculation times for ATT and CBF for weighted-delay and curve fitting algorithms were 6s and 9s, respectively. Figures 1 and 2 show ATT and CBF parameter maps in several
patients. Note variability in both parameters with age, namely a trend towards shorter ATT and greater CBF with age. Figure 3
illustrates ATT and CBF maps in a patient with perfusion deficits and compares
results between weighted-delay and curve-fitting algorithms. Figure 4
summarizes linear correlation coefficients between these two
algorithms for estimated ATT and CBF values. A majority of the coefficients
are high (i.e., r>0.9), although they are noticeably lower in
neonates and young children. All were statistically significant (p<0.01). Figure 5 summarizes correlation
coefficients between a weighted-delay mean CBF using all PLD data versus individual CBFs calculated at each of the five PLDs. The weighted-delay CBF showed the highest correlations with CBF derived from single-delay
calculations for PLDs>1500ms.

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