Arterial spin labelling MRI to measure renal perfusion: a systematic review and statement paper

Abstract

Renal perfusion provides the driving pressure for glomerular filtration and delivers the oxygen and nutrients to fuel solute reabsorption. Renal ischaemia is a major mechanism in acute kidney injury and may promote the progression of chronic kidney disease. Thus, quantifying renal tissue perfusion is critically important for both clinicians and physiologists. Current reference techniques for assessing renal tissue perfusion have significant limitations. Arterial spin labelling (ASL) is a magnetic resonance imaging (MRI) technique that uses magnetic labelling of water in arterial blood as an endogenous tracer to generate maps of absolute regional perfusion without requiring exogenous contrast. The technique holds enormous potential for clinical use but remains restricted to research settings. This statement paper from the PARENCHIMA network briefly outlines the ASL technique and reviews renal perfusion data in 53 studies published in English through January 2018. Renal perfusion by ASL has been validated against reference methods and has good reproducibility. Renal perfusion by ASL reduces with age and excretory function. Technical advancements mean that a renal ASL study can acquire a whole kidney perfusion measurement in less than 5–10 min. The short acquisition time permits combination with other MRI techniques that might inform drug mechanisms and renal physiology. The flexibility of renal ASL has yielded several variants of the technique, but there are limited data comparing these approaches. We make recommendations for acquiring and reporting renal ASL data and outline the knowledge gaps that future research should address.

Magnetic resonance elastography‐derived stiffness of the kidneys and its correlation with water perfusion

“…Other noninvasive imaging techniques such as arterial spin labeling (ASL) and dynamic contrast‐enhancement are being used to asses perfusion in the kidneys . However, they have limitations.…”

In vivo demonstration of microscopic anisotropy in the human kidney using multidimensional diffusion MRI

“…In addition to STE, double‐diffusion encoding methods, which encode diffusion along 2 directions before readout, provide planar b ‐tensors that also allow quantification of µFA . Contrast‐agent free quantitative biomarkers are actively being sought‐after in the field of renal MRI . In diffusion tensor imaging (DTI), FA has been widely used in the kidneys as a non‐invasive probe of tubular integrity and the geometric arrangement of microscopic structure.…”

Dissolved hyperpolarized xenon‐129 MRI in human kidneys

“…A more comparable uptake between the kidneys was measured with the more homogeneous volumetric coil, which reflects the small variations in perfusion expected in healthy volunteers. In the ASL literature, these variations between left and right kidney have been reported to be at maximum 7% . Here, other factors such as the position of the kidneys within the imaging plane could also contribute to the observed inhomogeneities.…”

“…This is normally alleviated by averaging multiple images that require adequate motion correction and registration of the input images to account for breathing motion and pulsation. Additionally, apart from the sequence and imaging parameters, there are a multitude of parameters that need to be accurately adjusted, such as position and characteristics of the labeling plane (delay, duration, B 1 , and thickness), T 1 of blood, and background suppression, to name the most relevant …”