Abstract
For standard clinical applications, ASL images are typically acquired with 4–8 mm thick slices and 3–4 mm in-plane resolution. However, in this paper we demonstrate that high-resolution continuous arterial spin labeling (CASL) perfusion images can be acquired in a clinically relevant scan time using current MRI technology. CASL was implemented with a separate neck coil for labeling the arterial blood on a 4.7T MRI using standard axial 2D GE-EPI. Typical-resolution to high-resolution (voxels of 95, 60, 45, 27, or 7 mm3) images were compared for qualitative and quantitative cerebral blood flow analysis (CBF) in nine healthy volunteers (ages: 24–32 years). The highest resolution (1.5x1.5x3 = 7 mm3) CASL implementation yielded perfusion images with improved cortex depiction and increased cortical CBF measurements (53 ± 8 ml/100g/min), consistent with reduced partial volume averaging. The 7 mm3 voxel images were acquired with 6 cm brain coverage in a clinically relevant scan of 6 minutes. Improved spatial resolution facilitates CBF measurement with reduced partial volume averaging and may be valuable for the detection of perfusion deficits in small lesions and perfusion measurement in small brain regions.
Highlights
Arterial spin labeling (ASL) measures cerebral perfusion using radiofrequency tagged blood as an endogenous contrast agent, and offers comparable perfusion deficit detection to intravenous Gd bolus tracking in acute stroke [1,2,3]
Perfusion imaging was performed on a 4.7T scanner (Varian, Walnut Creek, CA) using a butterfly neck coil for continuous arterial spin labeling with housing dimensions: length 110 mm, width 150 mm, and height 75 mm (Fig 1) (Rapid Biomedical, Rimpar, Germany)
The proportional change in signal intensity between tag and control scans (ΔSI/SIcontrol) in gray matter falls in a narrow range and is clearly greater than in white matter (~0.3% of control image intensity across image resolutions) (Table 1)
Summary
Arterial spin labeling (ASL) measures cerebral perfusion using radiofrequency tagged blood as an endogenous contrast agent, and offers comparable perfusion deficit detection to intravenous Gd bolus tracking in acute stroke [1,2,3]. While ASL protocols of this sort may be effective for large lesions, they are likely inadequate for the detection of smaller regions of perfusion deficit as may be expected in transient ischemic attack or minor stroke [5]. They are likely inadequate for the assessment of perfusion in small brain structures [6]. The need for higher spatial resolution has been recognized in two recent ASL stroke studies at 3T that used smaller voxels of 27 mm (i.e. 3 mm isotropic) and 23 mm3 [7,8]. A pseudo-continuous ASL study at 7T acquired 1.5x1.5x3
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