Diagnostic and Prognostic Potential of Multiparametric Renal MRI in Kidney Transplant Patients.

BACKGROUND: Multiparametric MRI provides assessment of functional and structural parameters in kidney allografts. It offers a non-invasive alternative to the current reference standard of kidney biopsy. PURPOSE: To evaluate the diagnostic and prognostic utility of MRI parameters in the assessment of allograft function in the first 3-months post-transplantation. STUDY TYPE: Prospective. SUBJECTS: 32 transplant recipients (54 ± 17 years, 20 females), divided into two groups according to estimated glomerular filtration rate (eGFR) at 3-months post-transplantation: inferior graft function (IGF; eGFR<45 mL/min/1.73 m2 , n = 10) and superior graft function (SGF; eGFR ≥ 45 mL/min/1.73 m2 , n = 22). Further categorization was based on the need for hemodialysis (C1) and decrease in s-creatinine (C2) at 1-week post-transplantation: delayed-graft-function (DGF: n = 4 C1, n = 10 C2) and early graft-function (EGF: n = 28 C1, n = 22 C2). FIELD STRENGTH/SEQUENCE: 3-T, pseudo-continuous arterial spin labeling, T1-mapping, and diffusion-weighted imaging. ASSESSMENT: Multiparametric MRI was evaluated at 1-week in all patients and 3-months after transplantation in 28 patients. Renal blood flow (RBF), diffusion coefficients (ADC, ΔADC, D, ∆ $$ \Delta $$ D, D*, flowing fraction f), T1 and ∆ $$ \Delta $$ T1 were calculated in cortex and medulla. The diagnostic and prognostic value of these parameters, obtained at 3-months and 1-week post-transplantation, respectively, was evaluated in the cortex to discriminate between DGF and EGF, and between SGF and IGF. STATISTICAL TESTS: Logistic regression, receiver-operating-characteristics, area-under-the-curve (AUC), confidence intervals (CIs), analysis-of-variance, t-test, Wilcoxon-Mann-Whitney test, Fisher's exact test, Pearson's correlation. P-value<0.05 was considered significant. RESULTS: DGF patients exhibited significantly lower cortical RBF and f and higher D*. The diagnostic value of MRI for detecting DGF was excellent (AUC = 100%). Significant differences between patients with IGF and SGF were found in RBF, ∆T1 , and ∆D. Multiparametric MRI showed higher diagnostic (AUC = 95.32%; CI: 88%-100%) and prognostic (AUC = 97.47%, CI: 92%-100%) values for detecting IGF than eGFR (AUC = 89.50%, CI: 79%-100%). DATA CONCLUSION: Multiparametric MRI may show high diagnostic and prognostic value in transplanted patients, yielding better results compared to eGFR measurements. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 1.

Clinical utility of intraoperative arterial spin labeling for resection control in brain tumor surgery at 3 T.

Resection control in brain tumor surgery can be achieved in real time with intraoperative MRI (iMRI). Arterial spin labeling (ASL), a technique that measures cerebral blood flow (CBF) non-invasively without the use of intravenous contrast agents, can be performed intraoperatively, providing morpho-physiological information. This study aimed to evaluate the feasibility, image quality and potential to depict residual tumor of a pseudo-continuous ASL (PCASL) sequence at 3 T. Seventeen patients with brain tumors, primary (16) or metastatic (1), undergoing resection surgery with iMRI monitoring, were prospectively recruited (nine men, age 56 ± 16.6 years). A PCASL sequence with long labeling duration (3000 ms) and postlabeling delay (2000 ms) was added to the conventional protocol, which consisted of pre- and postcontrast 3D T1 -weighted (T1w) images, optional 3D-FLAIR, and diffusion. Three observers independently assessed the image quality (four-point scale) of PCASL-derived CBF maps. In those with diagnostic quality (Scores 2-4) they evaluated the presence of residual tumor using the conventional sequences first, and the CBF maps afterwards (three-point scale). Inter-observer agreement for image quality and the presence of residual tumor was assessed using Fleiss kappa statistics. The intraoperative CBF ratio of the surgical margins (i.e., perilesional CBF values normalized to contralateral gray matter CBF) was compared with preoperative CBF ratio within the tumor (Wilcoxon's test). Diagnostic ASL image quality was observed in 94.1% of patients (interobserver Fleiss κ = 0.76). PCASL showed additional foci suggestive of high-grade residual component in three patients, and a hyperperfused area extending outside the enhancing component in one patient. Interobserver agreement was almost perfect in the evaluation of residual tumor with the conventional sequences (Fleiss κ = 0.92) and substantial for PCASL (Fleiss κ = 0.80). No significant differences were found between pre and intraoperative CBF ratios (p = 0.578) in patients with residual tumor (n = 7). iMRI-PCASL perfusion is feasible at 3 T and is useful for the intraoperative assessment of residual tumor, providing in some cases additional information to the conventional sequences.

Assessment of Splenic Switch-Off With Arterial Spin Labeling in Adenosine Perfusion Cardiac MRI.

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.

Optimal repetition time for free breathing myocardial arterial spin labeling.

The aim of this study was to improve the scan efficiency of ASL in the myocardium. Free breathing FAIR-ASL scans with different TRs were compared, while keeping the acquisition time constant. Scans were named by the trigger pulse that started each acquisition: every two (TP1), four (TP2) and six (TP3) cardiac cycles. TP2 offered the best alternative with a coefficient of variation of 17.15% intrasession and 36.85% intersession. Mean MBF increased by 0.22 ± 0.41 ml/g/min with mild stress.

Arterial spin labeling (ASL) offers a noninvasive and repeatable measurement of tissue blood flow, but its application in the human heart is still challenging. The aim of this study was to improve the scan efficiency of flow-sensitive alternating inversion recovery (FAIR) ASL using a single inversion time. First, by evaluating a free breathing acquisition without navigators. Second, by shortening TR to acquire more ASL pairs. A FAIR ASL with balanced steady state free precession (bSSFP) readout was implemented at 3 T and tested in 14 healthy volunteers. Three cardiac-triggered ASL scans with different TRs were compared while maintaining a constant acquisition time. These scans were named by the trigger pulse (TP) that started each acquisition: every two (TP1), four (TP2) and six (TP3) cardiac cycles. Two studies were performed on different days to assess the reproducibility of TP2 and TP3 scans. Perfusion response during passive leg raising was also evaluated. Student t-test and nonparametric equivalent were computed for perfusion differences. Bland-Altman and coefficient of variation (CV) were calculated for the reproducibility assessment. Mean myocardial blood flow (MBF) values measured at rest were: 1.47 ± 0.91 ml/g/min (TP1), 1.95 ± 0.93 ml/g/min (TP2) and 1.94 ± 1.41 ml/g/min (TP3). Intrasession CV was 17.15% (TP2) and 24.17% (TP3) and intersession CV was 36.86% (TP2) and 18.38% (TP3). Mean MBF was found to increase with passive stress by 0.22 ± 0.41 ml/g/min for TP2 (P = 0.037). Mean MBF values were consistent with the literature, although in the high end of the normal range. The lower MBF values measured in TP1 scans are attributable to saturation of blood outside the slice because of shorter TR. Free breathing FAIR cardiac ASL without navigators is feasible. A TR of approximately four seconds (TP2) offers the best alternative with similar mean ASL and tSNR than longer TR acquisitions.