Editorial for “Use of Three‐Dimensional Arterial Spin Labeling to Evaluate Renal Perfusion in Patients with Chronic Kidney Disease”

Abstract

Editorial for “Use of Three-Dimensional Arterial Spin Labeling to Evaluate Renal Perfusion in Patients with Chronic Kidney Disease” Perfusion is a physiological parameter that represents the blood flow which delivers oxygen and nutrients to tissue. In general, methods using contrast agents such as scintigraphy or dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) are preferable for perfusion imaging. However, these methods include the potential risk of nephropathy, especially for patients with renal impairments. Arterial spin labeling (ASL) does not have this issue in that it labels arterial blood using radiofrequency (RF) pulses, and uses these water signals as an endogenous tracer. However, because of the poor signal-to-noise ratio (SNR) and hardware limitations of ASL, it was hard to use in routine clinical protocols. Recent developments in pseudo-continuous ASL (pCASL) have significantly expanded the clinical usage of ASL, such as applications in stroke, neurodegenerative diseases, and epilepsy. Apart from the recent advances in ASL for use in the brain, renal ASL applications are now emerging. Specifically, pCASL is preferred over pulse-ASL (PASL) as pCASL does not involve selecting a labeling plane, while it should be carefully selected for PASL to avoid the feeding vessels. With this advantage, many studies have evaluated the clinical feasibility of pCASL in renal perfusion imaging. A study by Wu et al investigated the feasibility of using pCASL for renal blood flow (RBF) measurements and correlation with DCE-MRI. A study by Kim et al evaluated the feasibility and reproducibility of multidelay pCASL with normal subjects and compared a correlation with estimated glomerular filtration rate (eGFR). A study by Ahn et al measured renal perfusion in transplanted kidney patients in the early postoperative phase. Also, some studies discussed technical considerations for pCASL renal applications, such as strategies for breath holding, the effectiveness of background suppressions, the optimal time for labeling delay, and methods for postimage registration. However, more technical and clinical renal pCASL studies should be published to reach a clinical consensus. In this issue of JMRI, Lu et al measured RBF values in patients with chronic kidney diseases (CKDs) using pCASL. The study evaluated the clinical effectiveness of pCASL on CKD staging and compared the image quality with perfusion images acquired using PASL. pCASL with a threedimensional turbo gradient-echo spin-echo readout showed superior perfusion image quality compared to PASL and successfully distinguished the staging of CKD patient groups. One of the scientific merits that ASL has over eGFR is that ASL can show spatial distributions of renal perfusion. However, this study simply evaluated the quantitative correlation of measured mean RBF values to eGFR values. Highresolution renal perfusion imaging is needed to get more detailed spatial distributions of renal perfusion status. Furthermore, it is clear that this study provided a systemic comparison of pCASL to eGFR and PASL, and we hope this study will encourage the use of pCASL in renal perfusion studies that have been limited to PASL.