Arterial spin labeling of cerebral perfusion territories using a separate labeling coil

Abstract

Purpose: To obtain cerebral perfusion territories of the left, the right, and the posterior circulation in humans with high signal-to-noise ratio (SNR) and robust delineation.

Materials and methods: Continuous arterial spin labeling (CASL) was implemented using a dedicated radio frequency (RF) coil, positioned over the neck, to label the major cerebral feeding arteries in humans. Selective labeling was achieved by flow-driven adiabatic fast passage and by tilting the longitudinal labeling gradient about the Y-axis by theta = +/- 60 degrees .

Results: Mean cerebral blood flow (CBF) values in gray matter (GM) and white matter (WM) were 74 +/- 13 mL . 100 g(-1) . minute(-1) and 14 +/- 13 mL . 100 g(-1) . minute(-1), respectively (N = 14). There were no signal differences between left and right hemispheres when theta = 0 degrees (P > 0.19), indicating efficient labeling of both hemispheres. When theta = +60 degrees , the signal in GM on the left hemisphere, 0.07 +/- 0.06%, was 92% lower than on the right hemisphere, 0.85 +/- 0.30% (P < 1 x 10(-9)), while for theta = -60 degrees , the signal in the right hemisphere, 0.16 +/- 0.13%, was 82% lower than on the contralateral side, 0.89 +/- 0.22% (P < 1 x 10(-10)). Similar attenuations were obtained in WM.

Conclusion: Clear delineation of the left and right cerebral perfusion territories was obtained, allowing discrimination of the anterior and posterior circulation in each hemisphere.

Figure 1

a) MRA of the neck of a typical subject illustrating the labeling scheme used to selective label blood flowing just to the cerebral hemisphere of interest. The use of a tilted labeling plane makes the RF frequency offset be on resonance at the desired side, but outside the effective excitation profile of the labeling coil on the opposed side. b) Cross-sectional image of the neck showing the CCAs and VAs. The distances δ_L and δ_R are used in the planning of the selective labeling scheme according to Eqs. [1]–[3] (see text).

Figure 2

Percent signal differences (ΔS/S_c), obtained from ROIs drawn in the left and right GM and WM regions of a representative volunteer, plotted as a function of the angle in the labeling plane. Error bars represent the standard deviation of the signal inside the ROI. A sharp attenuation in perfusion on the left side is obtained for θ > 30°.

Figure 3

a) Axial echo-planar images of the brain of a typical subject. b) Corresponding whole-brain perfusion-weighted images acquired using θ=0°. c) Perfusion images of the right hemisphere, corresponding to the perfusion territory of the right CCA, acquired using θ=60° and d) of the left hemisphere, corresponding to the perfusion territory of the left CCA, acquired using θ=−60°.

Figure 4

Signal intensity averaged across all subjects obtained using θ = 0° and θ = ±60°. No difference between left and right hemispheres is observed when θ = 0°. However, a significant separation of left and right perfusion signal intensity is obtained with the use of a large tilt. (* P < 1×10⁻³, ** P < 1×10⁻⁹)

Figure 5

Color-coded perfusion territory maps showing the territories supplied by the right (red) and left (green) CCA. The posterior circulation (blue) can be obtained by post processing according to Eq. [5]. The mid brain region which contains contributions both from the right and the left circulation is showed in yellow.