Evaluation of 2D Imaging Schemes for Pulsed Arterial Spin Labeling of the Human Kidney Cortex

Abstract

A number of imaging readout schemes are proposed for renal arterial spin labeling (ASL) to quantify kidney cortex perfusion, including gradient echo-based methods of balanced fast field echo (bFFE) and gradient-echo echo-planar imaging (GE-EPI), or spin echo-based schemes of spin-echo echo-planar imaging (SE-EPI) and turbo spin-echo (TSE). Here, we compare these two-dimensional (2D) imaging schemes to evaluate the optimal imaging scheme for pulsed ASL (PASL) assessment of human kidney cortex perfusion at 3 T. Ten healthy volunteers with normal renal function were scanned using each 2D multi-slice imaging scheme, in combination with a respiratory triggered flow-sensitive alternating inversion recovery (FAIR) ASL scheme on a 3 T Philips Achieva scanner. All volunteers returned for a second identical scan session within two weeks of the first scan session. Comparisons were made between the imaging schemes in terms of perfusion-weighted image (PWI) signal-to-noise ratio (SNR) and perfusion quantification, temporal SNR (tSNR), spatial coverage, and repeatability. For each imaging scheme, the renal cortex perfusion was calculated (bFFE: 276 ± 29 mL/100g/min, GE-EPI: 222 ± 18 mL/100g/min, SE-EPI: 201 ± 36 mL/100g/min, and TSE: 200 ± 20 mL/100g/min). Perfusion was found to be higher for GE-based readouts when compared with SE-based readouts, with significantly higher measured perfusion for the bFFE readout when compared with all other schemes (p < 0.05), attributed to the greater vascular signal present. Despite the PWI-SNR being significantly lower for SE-EPI when compared with all other schemes (p < 0.05), the SE-EPI readout gave the highest tSNR, and was found to be the most reproducible scheme for the assessment of kidney cortex, with a coefficient of variation (CoV) of 17.2%, whilst minimizing variability of the perfusion-weighted signal across slices for whole-kidney perfusion assessment. For the assessment of kidney cortex perfusion using 2D readout schemes, SE-EPI provides optimal tSNR, minimal variability across slices, and repeatable data acquired in a short scan time with low specific absorption rate.

Keywords: arterial spin labeling; magnetic resonance imaging (MRI); perfusion; renal ASL; renal MRI.

Figure 1

Flow-sensitive alternating inversion recovery (FAIR) scheme. Positioning of the selective and non-selective labeling slabs shown relative to the imaging volume of the kidneys and the aorta.

Figure 2

Example base magnetization (M₀) images for the balanced fast field echo (bFFE), gradient-echo echo-planar imaging (GE-EPI), spin-echo echo-planar imaging (SE-EPI), and turbo spin-echo (TSE) readout schemes.

Figure 3

Example perfusion-weighted images (PWI) for each scheme (bFFE, GE-EPI, SE-EPI, and TSE) from a single subject. The post-label delay of each slice is indicated on each image.

Figure 4

Example perfusion maps for each readout scheme (bFFE, GE-EPI, SE-EPI, and single-shot TSE) from a single subject shown for the central slice. Note the higher perfusion signal of the bFFE scheme due to contributions from the arcuate arteries of the kidney.

Figure 5

Renal cortical perfusion values measured from each readout scheme for the first visit. Values shown are the mean perfusion values with error bars showing the standard error of the mean. The bFFE readout gave significantly higher perfusion values than the other readouts (repeated measures ANOVA, p = 0.03). A significant difference was observed between SE-EPI and GE-EPI., with p-values of post-hoc paired t-tests shown.