Abstract
BackgroundArterial spin labeling magnetic resonance imaging (ASL-MRI) has been recognised as a valuable method for non-invasive assessment of cerebral blood flow but validation studies regarding quantification accuracy by comparison against an accepted gold standard are scarce, especially in small animals. We have conducted the present study with the aim of comparing ASL flow-sensitive alternating inversion recovery (FAIR)-derived unidirectional water uptake (K1) and 68Ga/64Cu microsphere (MS)-derived blood flow (f) in the rat brain.MethodsIn 15 animals, K1and f were determined successively in dedicated small animal positron emission tomography and MR scanners. The Renkin-Crone model modified by a scaling factor was used for the quantification of f and K1.ResultsBelow about 1 mL/min/mL, we obtain an approximately linear relationship between f and K1. At higher flow values, the limited permeability of water at the blood brain barrier becomes apparent. Within the accessed dynamic flow range (0.2 to 1.9 mL/min/mL), the data are adequately described by the Renkin-Crone model yielding a permeability surface area product of (1.53±0.46) mL/min/mL.ConclusionThe ASL-FAIR technique is suitable for absolute blood flow quantification in the rat brain when using a one-compartment model including a suitable extraction correction for data evaluation.Trial registration24-9168.21-4/2004-1 (registered in Freistadt Sachsen, Landesdirektion Dresden)
Highlights
Arterial spin labeling magnetic resonance imaging (ASL-MRI) has been recognised as a valuable method for non-invasive assessment of cerebral blood flow but validation studies regarding quantification accuracy by comparison against an accepted gold standard are scarce, especially in small animals
Similar to 15O-water positron emission tomography (PET), the method is based on the assumption of free diffusibility of water between blood and tissue
We describe the transport kinetics of the water molecules with a one-tissue compartment model, but we account for the possibility of limited firstpass extraction across the blood brain barrier (BBB) by introducing a flowdependent uptake rate K1 and a tissue clearance rate k2 which have the flow-independent ratio
Summary
Arterial spin labeling magnetic resonance imaging (ASL-MRI) has been recognised as a valuable method for non-invasive assessment of cerebral blood flow but validation studies regarding quantification accuracy by comparison against an accepted gold standard are scarce, especially in small animals. Arterial spin labeling magnetic resonance imaging (ASLMRI) has been widely recognised as a valuable method for non-invasive assessment of regional cerebral blood flow (rCBF) [1,2,3,4]. In contrast to PET, the relevant time scales for the measurement are much shorter (of the order of a few seconds) due to the rapid free decay of the longitudinal magnetisation of magnetically tagged water. A number of studies have compared ASL-MRI to other methods, notably 15O-water PET [10,11,12] and found reasonable or even good quantitative concordance between MR- and PET-derived rCBF. The principal feasibility of quantitative ASL in humans might become especially interesting in view of the recent advent of combined PET/MRI systems, offering the perspective of combined functional imaging utilising both modalities
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