Abstract
ObjectivesWe investigated the feasibility and reproducibility of free-breathing motion-corrected multiple inversion time (multi-TI) pulsed renal arterial spin labelling (PASL), with general kinetic model parametric mapping, to simultaneously quantify renal perfusion (RBF), bolus arrival time (BAT) and tissue T1.MethodsIn a study approved by the Health Research Authority, 12 healthy volunteers (mean age, 27.6 ± 18.5 years; 5 male) gave informed consent for renal imaging at 3 T using multi-TI ASL and conventional single-TI ASL. Glyceryl trinitrate (GTN) was used as a vasodilator challenge in six subjects. Flow-sensitive alternating inversion recovery (FAIR) preparation was used with background suppression and 3D-GRASE (gradient and spin echo) read-out, and images were motion-corrected. Parametric maps of RBF, BAT and T1 were derived for both kidneys. Agreement was assessed using Pearson correlation and Bland-Altman plots.ResultsInter-study correlation of whole-kidney RBF was good for both single-TI (r2 = 0.90), and multi-TI ASL (r2 = 0.92). Single-TI ASL gave a higher estimate of whole-kidney RBF compared to multi-TI ASL (mean bias, 29.3 ml/min/100 g; p <0.001). Using multi-TI ASL, the median T1 of renal cortex was shorter than that of medulla (799.6 ms vs 807.1 ms, p = 0.01), and mean whole-kidney BAT was 269.7 ± 56.5 ms. GTN had an effect on systolic blood pressure (p < 0.05) but the change in RBF was not significant.ConclusionsFree-breathing multi-TI renal ASL is feasible and reproducible at 3 T, providing simultaneous measurement of renal perfusion, haemodynamic parameters and tissue characteristics at baseline and during pharmacological challenge.Key points• Multiple inversion time arterial spin labelling (ASL) of the kidneys is feasible and reproducible at 3 T.• This approach allows simultaneous mapping of renal perfusion, bolus arrival time and tissue T1during free breathing.• This technique enables repeated measures of renal haemodynamic characteristics during pharmacological challenge.
Highlights
The auto-regulatory feedback mechanisms that maintain renal blood flow (RBF) and glomerular filtration rate (GFR) over a wide range of haemodynamic pathophysiological conditions can be disturbed in metabolic and inflammatory disease states promoting the progression of nephropathy [1,2,3]
We investigated the feasibility and reproducibility of a free-breathing motion-corrected multi-TI pulsed renal arterial spin labelling (ASL) (PASL) sequence, with general kinetic model parametric mapping, enabling perfusion to be quantified with correction for bolus arrival time (BAT) and renal T1
Free-breathing multi-TI ASL acquired at 3 T allows simultaneous measurement of RBF, BAT and tissue T1 using a general kinetic model for parameter fitting
Summary
The auto-regulatory feedback mechanisms that maintain renal blood flow (RBF) and glomerular filtration rate (GFR) over a wide range of haemodynamic pathophysiological conditions can be disturbed in metabolic and inflammatory disease states promoting the progression of nephropathy [1,2,3]. Magnetic resonance imaging (MRI) is emerging as a noninvasive approach for assessing renal structure and function including physiological parameters such as tissue perfusion, oxygenation, and water diffusion [6]. Arterial spin labelling (ASL) is a method that uses flowing blood as an endogenous contrast agent that has been widely used in neuro-imaging applications [7], and has been shown to be feasible in healthy, transplanted and diseased kidneys [8]. ASL uses a radiofrequency (RF) pulse to magnetically label water protons in blood, so that they act as a diffusible tracer. In standard single-inversion time (TI) ASL techniques, a single inversion labelling pulse is applied, and a perfusion value is calculated using a simplified model which neglects variations in renal tissue T1 and makes assumptions concerning the bolus arrival characteristics and blood T1 [10, 11].
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