To evaluate labeling efficiency of pseudo-continuous arterial spin labeling (PCASL) and to find the gradient parameters that increase PCASL robustness for renal perfusion measurements. Methods: Aortic blood flow was characterized in 3 groups: young healthy volunteers (YHV1), chronic kidney disease (CKD) patients (CKDP), and healthy controls (HCO). PCASL inversion efficiency was evaluated through numeric simulations considering the measured pulsatile flow velocity profiles and off-resonance effects for a wide range of gradient parameters, and the results were assessed in vivo. The most robust PCASL implementation was used to measure renal blood flow (RBF) in CKDP and HCO. Results: Aortic blood velocities reached peak values of 120 cm/s in YHV1, whereas for elderly subjects values were lower by approximately a factor of 2. Simulations and experiments showed that by reducing the gradient average (G ave) and the selective to average gradient ratio (G max /G ave), labeling efficiency was maximized and PCASL robustness to off-resonance was improved. The study in CKDP and HCO showed significant differences in RBF between groups. Conclusion: An efficient and robust PCASL scheme for renal applications requires a G max /G ave ratio of 6-7 and a G ave value that depends on the aortic blood flow velocities (0.5 mT/m being appropriate for CKDP and HCO).

Background Myocardial perfusion is evaluated in first‐pass MRI using a gadolinium‐based contrast agent, which limits its repeatability and restricts its use in patients with abnormal kidney function. Arterial spin labeling (ASL) is a promising technique for measuring myocardial perfusion without contrast injection. The ratio of stress to rest perfusion, termed myocardial perfusion reserve (MPR), is an indicator of the severity of stenosis in patients with coronary artery disease (CAD). Purpose To quantify perfusion increases with pharmacological vasodilation, explore MPR differences between segments with and without perfusion defects, and examine the correlations between quantitative ASL and semiquantitative first‐pass measurements. Study Type Prospective. Subjects Sixteen patients with suspected CAD: 10 classified as “healthy,” having normal perfusion on first‐pass and no enhancement on late gadolinium enhancement (LGE), and six as “nonhealthy,” having hypoperfused segments including ischemic and infarcted. Field Strength/Sequence Flow‐sensitive alternating inversion recovery (FAIR) rest–stress cardiac ASL with balanced steady‐state free precession (bSSFP), rest–stress first‐pass imaging using gradient‐echo and LGE using a phase‐sensitive inversion‐recovery bSSFP at 1.5T. Assessment For healthy subjects, rest–stress perfusion data were compared in global, coronary artery territory, and segment regions of interest (ROIs). A segmental MPR comparison was performed between normal segments from healthy subjects and abnormal segments from nonhealthy subjects. Correlations between ASL and first‐pass parameters were explored. Statistical Tests Wilcoxon‐signed‐rank test, nonparametric factorial analysis of variance (ANOVA), and Pearson's/Spearman's correlations. Results Perfusion increases were significant globally (P = 0.005), per coronary artery territory (P = 0.015), and per segment (P = 0.03 for all segments in ASL and first‐pass, except anteroseptal in ASL P = 0.04). MPR differences between normal and abnormal segments were significant (P = 0.0028: ASL, P = 0.033: first‐pass). ASL and first‐pass measurements were correlated (MPR: r = 0.64, P = 0.008 and perfusion: rho = 0.47, P = 0.007). Data Conclusion This study demonstrates the feasibility of ASL to detect hyperemia, the potential to differentiate segments with and without perfusion defects, and significant correlations between ASL and semiquantitative first‐pass. Level of Evidence 2 Technical Efficacy Stage 1

Renal magnetic resonance imaging (MRI) techniques are currently in vogue, as they provide in vivo information on renal volume, function, metabolism, perfusion, oxygenation, and microstructural alterations, without the need for exogenous contrast media. New imaging biomarkers can be identified using these tools, which represent a major advance in the understanding and study of the different pathologies affecting the kidney. Diabetic kidney disease (DKD) is one of the most important diseases worldwide due to its high prevalence and impact on public health. However, its multifactorial etiology poses a challenge for both basic and clinical research. Therefore, the use of novel renal MRI techniques is an attractive step forward in the comprehension of DKD, both in its pathogenesis and in its detection and surveillance in the clinical practice. This review article outlines the most promising MRI techniques in the study of DKD, with the purpose of stimulating their clinical translation as possible tools for the diagnosis, follow-up, and monitoring of the clinical impacts of new DKD treatments.

This is an open access article under the terms of the Creat ive Commo ns Attri butio n-NonCo mmerc ial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Background In patients with suspected coronary artery disease (CAD), myocardial perfusion is assessed under rest and pharmacological stress to identify ischemia. Splenic switch‐off, defined as the stress to rest splenic perfusion attenuation in response to adenosine, has been proposed as an indicator of stress adequacy. Its occurrence has been previously assessed in first‐pass perfusion images, but the use of noncontrast techniques would be highly beneficial. Purpose To explore the ability of pseudo‐continuous arterial spin labeling (PCASL) to identify splenic switch‐off in patients with suspected CAD. Study Type Prospective. Population Five healthy volunteers (age 24.8 ± 3.8 years) and 32 patients (age 66.4 ± 8.2 years) with suspected CAD. Field strength/Sequence A 1.5‐T/PCASL (spin‐echo) and first‐pass imaging (gradient‐echo). Assessment In healthy subjects, multi‐delay PCASL data (500–2000 msec) were acquired to quantify splenic blood flow (SBF) and determine the adequate postlabeling delay (PLD) for single‐delay acquisitions (PLD > arterial transit time). In patients, single‐delay PCASL (1200 msec) and first‐pass perfusion images were acquired under rest and adenosine conditions. PCASL data were used to compute SBF maps and SBF stress‐to‐rest ratios. Three observers classified patients into “switch‐off” and “failed switch‐off” groups by visually comparing rest‐stress perfusion data acquired with PCASL and first‐pass, independently. First‐pass categories were used as reference to evaluate the accuracy of quantitative classification. Statistical Tests Wilcoxon signed‐rank, Pearson correlation, kappa, percentage agreement, Generalized Linear Mixed Model, Mann–Whitney, Pearson Chi‐squared, receiver operating characteristic, area‐under‐the‐curve (AUC) and confusion matrix. Significance: P value < 0.05. Results A total of 27 patients (84.4%) experienced splenic switch‐off according to first‐pass categories. Comparison of PCASL‐derived SBF maps during stress and rest allowed assessment of splenic switch‐off, reflected in a reduction of SBF values during stress. SBF stress‐to‐rest ratios showed a 97% accuracy (sensitivity = 80%, specificity = 100%, AUC = 85.2%). Data Conclusion This study could demonstrate the feasibility of PCASL to identify splenic switch‐off during adenosine perfusion MRI, both by qualitative and quantitative assessments. Evidence Level 2 Technical Efficacy 2

A pseudocontinuous arterial spin labeling (PCASL) sequence combined with background suppression and single-shot accelerated 3D RARE stack-of-spirals was used to evaluate cerebrovascular reactivity (CVR) induced by breath-holding (BH) in ten healthy volunteers. Four different models designed using the measured change in PETCO2 induced by BH were compared, for CVR quantification. The objective of this comparison was to understand which regressor offered a better physiological model to characterize the cerebral blood flow response under BH. The BH task started with free breathing of 42 s, followed by interleaved end-expiration BHs of 21 s, for ten cycles. The total scan time was 12 min and 20 s. The accelerated readout allowed the acquisition of PCASL data with better temporal resolution than previously used, without compromising the post-labeling delay. Elevated CBF was observed in most cerebral regions under hypercapnia, which was delayed with respect to the BH challenge. Significant statistical differences in CVR were obtained between the different models in GM (p &lt; 0.0001), with ramp models yielding higher values than boxcar models and between the two tissues, GM and WM, with higher values in GM, in all the models (p &lt; 0.0001). The adjustment of the ramp amplitude during each BH cycle did not improve the results compared with a ramp model with a constant amplitude equal to the mean PETCO2 change during the experiment.

Monitoring renal allograft function after transplantation is key for the early detection of allograft impairment, which in turn can contribute to preventing the loss of the allograft. Multiparametric renal MRI (mpMRI) is a promising noninvasive technique to assess and characterize renal physiopathology; however, few studies have employed mpMRI in renal allografts with stable function (maintained function over a long time period). The purposes of the current study were to evaluate the reproducibility of mpMRI in transplant patients and to characterize normal values of the measured parameters, and to estimate the labeling efficiency of Pseudo‐Continuous Arterial Spin Labeling (PCASL) in the infrarenal aorta using numerical simulations considering experimental measurements of aortic blood flow profiles. The subjects were 20 transplant patients with stable kidney function, maintained over 1 year. The MRI protocol consisted of PCASL, intravoxel incoherent motion, and T1 inversion recovery. Phase contrast was used to measure aortic blood flow. Renal blood flow (RBF), diffusion coefficient (D), pseudo‐diffusion coefficient (D*), flowing fraction ( f), and T1 maps were calculated and mean values were measured in the cortex and medulla. The labeling efficiency of PCASL was estimated from simulation of Bloch equations. Reproducibility was assessed with the within‐subject coefficient of variation, intraclass correlation coefficient, and Bland‐Altman analysis. Correlations were evaluated using the Pearson correlation coefficient. The significance level was p less than 0.05. Cortical reproducibility was very good for T1, D, and RBF, moderate for f, and low for D*, while medullary reproducibility was good for T1 and D. Significant correlations in the cortex between RBF and f (r = 0.66), RBF and eGFR (r = 0.64), and D* and eGFR (r = −0.57) were found. Normal values of the measured parameters employing the mpMRI protocol in kidney transplant patients with stable function were characterized and the results showed good reproducibility of the techniques.

Purpose: to evaluate the prognostic potential of a multiparametric renal MRI protocol (perfusion, diffusion and T1) for the assessment of the allograft in the very early stages after transplantation. Methods: 18 transplanted patients were imaged 6 days after the transplantation with ASL, IVIM and T1 mapping sequences. 2 groups were made depending on the allograft evolution (group A: no adverse events and group B: any adverse event). Results: eGFR, album-creatinine ratio and cortical and medullary RBF were significantly higher in allografts of group A than in group B. Significant correlations between eGFR and RBF were found.