Flow Quantification with Arterial Spin Labeling: A Fantom Study

Ziele: Reliable quantification of cerebral blood flow as measured by perfusion-weighted Magnetic Resonance Imaging (MRI) is a still unsolved problem. This is particularly valid for perfusion measurements using the Arterial Spin Labeling (ASL) technique which works without application of contrast medium. In 2009 we developed a dedicated perfusion phantom. Using the known flow parameters of the phantom as a gold standard, we investigated the dependence of (1) amplitude and (2) delay of the MRI signal from the velocity of flow. Methode: The phantom mainly consists out of an MR-compatible dialysator containing a “capillary bed“ of 12800 hollow polysulfone fibers with a mean internal diameter of 200 um resulting in a total cross section of 4.02 cm2. The inflow tube into the dialysator is connected to a pump which is able to create different velocities of 1.5–7cm/s within the dialysator. MR measurements were carried out on a 3T scanner “Achieva“ (Philips) using a pulsed multi-phase ASL sequence with 16 consecutive measurements. The labeling slab was 5cm thick and either included the proximal part of the dialysator or the inflow tube only. Ergebnis: As with previous flow studies using conventional T1- and T2* susceptible MR techniques after injection of contrast medium (Maciak et al., Fortschr Röntgenstr 2010; 182: 883–890), we were able to measure highly reproducible signal intensity curves. In addition, we saw a positive relation between (1) rise time and (2) maximum of the signal and flow velocity depending on the distance between imaging and labeling slab. Schlussfolgerung: In conclusion, this phantom study demonstrates that multiphase ASL can be regarded as a semi-quantitative technique allowing at least a relative comparison of flow velocities and – in case of a constant size of the perfused capillaries – also of perfusion volumes within a given slice of measurement. In mono-phase ASL however, the time-to-arrival of the spin bolus has to be considered as an additional important factor.

Keywords: Arterial Spin Labeling, Phantom, Flow Quantification

Korrespondierender Autor: Speckter H

CEDIMAT, Radiologie und Nuklearmedizin, Plaza de la Salud, 00001 Santo Domingo

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