Evaluation of Arterial Spin Labeling MRI—Comparison with 15O-Water PET on an Integrated PET/MR Scanner

Abstract

Cerebral blood flow (CBF) measurements are of high clinical value and can be acquired non-invasively with no radiation exposure using pseudo-continuous arterial spin labeling (ASL). The aim of this study was to evaluate accordance in resting state CBF between ASL (CBFASL) and 15O-water positron emission tomography (PET) (CBFPET) acquired simultaneously on an integrated 3T PET/MR system. The data comprised ASL and dynamic 15O-water PET data with arterial blood sampling of eighteen subjects (eight patients with focal epilepsy and ten healthy controls, age 21 to 61 years). 15O-water PET parametric CBF images were generated using a basis function implementation of the single tissue compartment model. Cortical and subcortical regions were automatically segmented using Freesurfer. Average CBFASL and CBFPET in grey matter were 60 ± 20 and 75 ± 22 mL/100 g/min respectively, with a relatively high correlation (r = 0.78, p < 0.001). Bland-Altman analysis revealed poor agreement (bias = −15 mL/100 g/min, lower and upper limits of agreements = −16 and 45 mL/100 g/min, respectively) with a negative relationship. Accounting for the negative relationship, the width of the limits of agreement could be narrowed from 61 mL/100 g/min to 35 mL/100 g/min using regression-based limits of agreements. Although a high correlation between CBFASL and CBFPET was found, the agreement in absolute CBF values was not sufficient for ASL to be used interchangeably with 15O-water PET.

Evaluation of [11C]UCB-A positron emission tomography in human brains

“…[ 15 O]water PET data were reconstructed into 22 frames (1 × 10, 8 × 5, 4 × 10, 2 × 15, 3 × 20, 2 × 30, 2 × 60 s) using an ordered subset expectation maximisation (OSEM) algorithm with 4 iterations and 28 subsets, including time-of-flight (TOF) and point spread function (PSF) recovery and 5 mm Gaussian post-filter. The reconstructed matrix size was 128 × 128 × 89 voxels with a voxel size of 2.34 × × 2.34 × 2.78 mm) [19]. [ 11 C]UCB-A PET data was reconstructed into 25 frames (6 × 10, 3 × 20, 2 × 30, 2 × 60, 2 × 150, 4 × 300, and 6 × 600 s) using TOF-OSEM with PSF and 3 mm Gaussian post-filter.…”

“…For [ 15 O]water scan data, cerebral blood flow (CBF) was determined directly from uptake rate K 1 (mL/cm 3 / min), computed via non-linear regression of the operational equation of the single tissue compartment model with a fitted delay [19]. The blood volume (V B ) was set to 5%.…”