The QUASAR reproducibility study, Part II: Results from a multi-center Arterial Spin Labeling test–retest study

Abstract

Arterial Spin Labeling (ASL) is a method to measure perfusion using magnetically labeled blood water as an endogenous tracer. Being fully non-invasive, this technique is attractive for longitudinal studies of cerebral blood flow in healthy and diseased individuals, or as a surrogate marker of metabolism. So far, ASL has been restricted mostly to specialist centers due to a generally low SNR of the method and potential issues with user-dependent analysis needed to obtain quantitative measurement of cerebral blood flow (CBF).Here, we evaluated a particular implementation of ASL (called Quantitative STAR labeling of Arterial Regions or QUASAR), a method providing user independent quantification of CBF in a large test-retest study across sites from around the world, dubbed "The QUASAR reproducibility study". Altogether, 28 sites located in Asia, Europe and North America participated and a total of 284 healthy volunteers were scanned. Minimal operator dependence was assured by using an automatic planning tool and its accuracy and potential usefulness in multi-center trials was evaluated as well.Accurate repositioning between sessions was achieved with the automatic planning tool showing mean displacements of 1.87±0.95mm and rotations of 1.56±0.66°. Mean gray matter CBF was 47.4 ±7.5 [ml/100g/min] with a between subject standard variation SD b = 5.5 [ml/100g/min] and a within subject standard deviation SD w = 4.7 [ml/100g/min]. The corresponding repeatability was 13.0 [ml/ 100g/min] and was found to be within the range of previous studies.

Intra- and Multicenter Reproducibility of Pulsed, Continuous and Pseudo-Continuous Arterial Spin Labeling Methods for Measuring Cerebral Perfusion

“…This might illustrate that CASL and single TI PASL are more sensitive to site-specific differences, for example, scanner hardware instability and B0-homogeneity. Reproducibility measures of the multi TI PASL sequence were comparable with data described in the multicenter QUASAR reproducibility study performed by Petersen et al (2010), although the latter study was performed worldwide in a very large population. As the used single and multi TI PASL sequences use equal labeling modules, this implies that variations in labeling efficiency of single TI PASL probably cannot explain the observed differences in reproducibility.…”

Correlation between arterial blood volume obtained by arterial spin labelling and cerebral blood volume in intracranial tumours

“…Also, in a study comparing CBF in healthy grey matter using DSC-MRI and QUASAR the correlation between the two modalities was very good (r=0.89) [21]. In our study, ASL-CBF was 41 ml/(min 100 g), while gold standard CBF techniques typically report GM CBF values in the order of 60-80 mL/(min 100 g).…”

Pain and Plasticity: Is Chronic Pain Always Associated with Somatosensory Cortex Activity and Reorganization?

“…The pulsed ASL version, called quasar, was used for this study and the sequence and subsequent CBF quantification has been described in details previously (Petersen et al, 2006(Petersen et al, , 2010. In short, the sequence is a multislice, multiple time-points-capable sequence based on pulsed ASL and a Look-Locker readout.…”

“…CBF is subsequently estimated by model-free deconvolution, similar to what is done for gadolinium perfusion scans (Petersen et al, 2006). By adding a few dynamics at a lower flip angle, correct B1, T1, and M0 of tissue can be obtained, which are subsequently used for CBF quantification (Petersen et al, 2010). General scan parameters were as follows: TR, 4000 ms; TE, 23 ms; ⌬TI, 300 ms, TI1, 40 ms; 13 inversion times, 40 -3640 ms; matrix, 64 ϫ 64; number of slices, 7; slice thickness, 6 mm; gap, 2 mm; field of view, 240 ϫ 240; flip angle; 35/11.7°; SENSE (sensitivity encoding), 2.5; 84 averages (48 with crusher, 4 cm/s; 24 without crushers; 12 low flip angle), all implemented in a single sequence with a scan duration of 5 min 52 s.…”