Test-retest variability of quantitative MRI perfusion measurements with ASL underclinical conditions

Ziel/Aim:

While [O-15]H₂O PET is still considered the gold-standard for brain perfusion measurement, a native MRI sequence called arterial spin labeling (ASL) which offers a semi-quantitative alternative becomes increasingly relevant in the clinical setting and might be especially relevant for applications in combined PET/MR systems. For ASL, an accuracy and repeatability comparable to that of PET has been reported. A serious limitation of the respective studies is the fact that mainly young healthy subjects were used. Also, time and subject comfort were sacrificed to reach high repeatability. Our aim was to test the repeatability of ASL under realistic clinical conditions on elderly cancer patients.
Methodik/Methods:
Fifteen patients (age 55.5±12.8 years) with glioblastoma were scanned in two or more sessions (in total 21 sessions, 125±37 days apart). We used a pseudo-continuous ASL sequence with background suppression and 2D multi-slice
readout, labeling time/delay 1525/1650 ms, voxel size 2.75x2.75x6.6mm³, and standard CBF quantification (1). Mean CBF was assessed for regions corresponding to anterior cerebral artery (ACA), posterior CA, middle CA, and vertebral artery, respectively, on the contralateral side from the tumor. Repeatability index and mean relative CBF difference was assed for the two sessions for all regions.
Ergebnisse/Results:
The whole-brain mean CBF was 33.0±4.9 mL/min/100 g (45.5±6.1 mL/min/100 g in gray matter). The repeatability index was 30.4%, 34.3%, 29.7%, 31.5% and 36.8% in whole brain, ACA, MCA, PCA and VA regions, respectively. The mean relative difference between sessions for whole brain was 18.9% (range 0.4-63.0%, median 17.1%).
Schlussfolgerungen/Conclusions:
The repeatability index is close to the values measured by Heijtel (2) in healthy volunteers (27.6% for PET, 25.1% for ASL). A slight decrease in repeatability in elderly patients is to be expected. The mean gray matter perfusion is slightly lower than in (2) (48.5±5.6 in PET, 50.8±6.5 mL/min/100 g for ASL) which might be attributed to the known decline of CBF in elderly subjects. Our results thus show that pCASL measurements yield stable CBF values even under clinical conditions.
Literatur/References:
(1) Alsop, et al. Magnetic Resonance in Medicine. 2014.
(2) Heijtel, et al. NeuroImage, 92:182-92(2014).