The Role of Arterial Spin Labeling Functional MRI in Assessing Perfusion Impairment of Renal Allografts: A Systematic Review

Abstract

Arterial spin labeling (ASL) is a functional magnetic resonance imaging (fMRI) technique that uses water in arterial blood as a tracer to map an area of interest where the intravascular and extravascular compartments exchange. Our review article focuses primarily on the role of ASL fMRI in assessing perfusion impairment in renal allografts in order to take appropriate steps to eliminate the cause of perfusion impairment at an early stage, thereby extending graft life. The study also highlights various other fMRI techniques that are used to analyze other parameters that affect kidney transplants both acutely and chronically. We gathered our data in accordance with the 2020 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and our search strategy included exclusion/inclusion criteria. Several databases were used in the search strategy, including PubMed, Cochrane, and Science Direct, and the Medical Subject Headings (MeSH) strategy was specifically used for PubMed, and two people scrutinized those papers to conclude that a total of 10 research papers are included in our study. This review article includes papers involving 20 to 98 subjects who had renal allografts within the previous six months and had renal cortical perfusion values measured by ASL fMRI ranging from 35 to 304 ml/100 g/min. Furthermore, when compared to healthy kidney transplant patients, renal ASL perfusion values were significantly lower in subjects with the functional imbalance of kidney transplants. It had a positive correlation with the estimated glomerular filtration rate (eGFR). To summarize, ASL fMRI is critical in detecting renal allograft perfusion impairment.

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“…Based on this knowledge, a pilot study lead by Brown et al paired MRE technology to arterial spin labeling (ASL), a noninvasive fMRI technique through which RBF can be reliably quantified and which promises early-stage detection of CKD [ 32 – 34 ]. In ASL, water in arterial blood is used as an endogenous tracer to map of regional perfusion [ 35 , 36 ]. Two image types are captured: a contrast-free control image and a labeled image in which an electromagnetic pulse magnetizes arterial blood [ 36 ].…”

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“…Blood supply to the kidneys comes from a single system, is distributed between segments, and has no collateral circulation, providing a theoretical basis for the application of ASL [32]. ASL allows for the noninvasive measurement of the local blood perfusion of the kidney, and its repeatability and reliability have been recognized by most scholars [16,[33][34][35][36]. At present, ASL has been preliminarily applied in the diagnosis of acute and chronic kidney injury [16], obstructive hydronephrosis [33], kidney tumor [34], kidney allograft [35], and RAS [36].…”

“…ASL allows for the noninvasive measurement of the local blood perfusion of the kidney, and its repeatability and reliability have been recognized by most scholars [16,[33][34][35][36]. At present, ASL has been preliminarily applied in the diagnosis of acute and chronic kidney injury [16], obstructive hydronephrosis [33], kidney tumor [34], kidney allograft [35], and RAS [36]. Some researchers have found that the RBF values of the renal cortex and medulla in patients with acute kidney injury were markedly lower than those in the control group [37].…”

Editorial for “Significance of Arterial Spin Labeling for Reducing Biopsies in Patients With Kidney Allograft Dysfunction”

“…3 A recent meta-analysis reviews the role of ASL in assessing perfusion impairment in renal allografts, indicating that compared with healthy kidney transplant patients, renal ASL perfusion values were significantly lower in subjects with the functional imbalance of kidney transplants, with a positive correlation in the estimated glomerular filtration rate. 4 In this issue, the authors assess the significance of ASL in 46 patients, in order to discriminate those with posttransplant allograft dysfunction who need biopsy from those who do not. 5 Cortical ASL in the group who needed biopsy was significantly lower than in the other group.…”

“…Several ASL imaging techniques have been shown to get a reliable measurement of the renal perfusion for both healthy volunteers and those patients with one or more of the following pathologies: renal diseases, arterial stenosis, renal neoplasms, and allografts 3 . A recent meta‐analysis reviews the role of ASL in assessing perfusion impairment in renal allografts, indicating that compared with healthy kidney transplant patients, renal ASL perfusion values were significantly lower in subjects with the functional imbalance of kidney transplants, with a positive correlation in the estimated glomerular filtration rate 4 …”