Quantitative perfusion measurements using pulsed arterial spin labeling: Effects of large region‐of‐interest analysis

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Abstract
Purpose To study arterial spin labeling (ASL) MRI techniques and to investigate various problematic issues that still hinder the accurate and robust quantitative analysis of ASL data. Materials and Methods A pulsed‐ASL (PASL) sequence was implemented on a 3‐T imaging system and a protocol was developed for the measurement of perfusion based on fitting to a standard kinetic model. Both numerical simulations and multi‐inversion time MRI data were analyzed. The effect of fitting a kinetic curve to a large region of interest (ROI) with a distribution of arterial transit times was compared to a pixel‐by‐pixel (PBP) method. Results It was found that a significant underestimation of perfusion of approximately 17 ± 6% (P < 0.001) occurs in gray matter, when comparing an ROI with a PBP analysis over a group of 12 healthy subjects. Conclusion Analysis of ASL data based on a large ROI may suffer from inaccuracies arising from a distribution of transit times, implying that averaging of ASL kinetic data over such regions should therefore be avoided. When possible, a PBP fit should be performed. J. Magn. Reson. Imaging 2005;21:676–682.