Alternating Inversion Recovery Arterial Spin Research Articles

Time-Resolved Noncontrast Magnetic Resonance Perfusion Imaging of Paraspinal Muscles.

While evaluation of blood perfusion in lumbar paraspinal muscles is of interest in low back pain, it has not been performed using noncontrast magnetic resonance (MR) techniques. To introduce a novel application of a time-resolved, noncontrast MR perfusion technique for paraspinal muscles and demonstrate effect of exercise on perfusion parameters. Longitudinal. Six healthy subjects (27-48 years old, two females) and two subjects with acute low back pain (46 and 65 years old females, one with diabetes/obesity). 3-T, MR perfusion sequence. Lumbar spines of healthy subjects were imaged axially at L3 level with a tag-on and tag-off alternating inversion recovery arterial spin labeling technique that suppresses background signal and acquires signal increase ratio (SIR) from the in-flow blood at varying inversion times (TI) from 0.12seconds to 3.5 seconds. SIR vs. TI data were fit to determine the perfusion metrics of peak height (PH), time to peak (TTP), mean transit time, apparent muscle blood volume (MBV), and apparent muscle blood flow (MBF) in iliocostal, longissimus, and multifidus. Imaging was repeated immediately after healthy subjects performed a 20-minute walk, to determine the effect of exercise. Repeated measures analysis of variance. SIR vs. TI data showed well-defined leading and trailing edges, with sharply increasing SIR to TI of approximately 500 msec subsiding quickly to near zero around TI of 1500 msec. After exercise, the mean SIR at every TI increased markedly, resulting in significantly higher PH, MBV, and MBF (each P < 0.001 and F > 28.9), and a lower TTP (P < 0.05, F=4.5), regardless of the muscle. MBF increased 2- to 2.5-fold after exercise, similar to the expected increase in cardiac output, given the intensity of the exercise. Feasibility of an MR perfusion technique for muscle perfusion imaging was demonstrated, successfully detecting significantly increased perfusion after exercise. 1 TECHNICAL EFFICACY STAGE: 1.

Liver perfusion MRI in a rodent model of cirrhosis: Agreement with bulk-flow phase-contrast MRI and noninvasive evaluation of inflammation in chronic liver disease using flow-sensitive alternating inversion recovery arterial spin labelling and tissue T1.

Noninvasive measurements of liver perfusion and fibrosis in cirrhotic small animals can help develop treatments for haemodynamic complications of liver disease. Here, we measure liver perfusion in cirrhotic rodents using flow‐sensitive alternating inversion recovery arterial spin labelling (FAIR ASL), evaluating agreement with previously validated caval subtraction phase‐contrast magnetic resonance imaging (PCMRI) total liver blood flow (TLBF). Baseline differences in cirrhotic rodents and the haemodynamic effects of acute inflammation were investigated using FAIR ASL and tissue T1. Sprague–Dawley rats (nine bile duct ligated [BDL] and ten sham surgery controls) underwent baseline hepatic FAIR ASL with T1 measurement and caval subtraction PCMRI (with two‐dimensional infra‐/supra‐hepatic inferior vena caval studies), induction of inflammation with intravenous lipopolysaccharide (LPS) and repeat liver FAIR ASL with T1 measurement after ~90 minutes. The mean difference between FAIR ASL hepatic perfusion and caval subtraction PCMRI TLBF was −51 ± 30 ml/min/100 g (Bland–Altman 95% limits‐of‐agreement ±258 ml/min/100 g). The FAIR ASL coefficient of variation was smaller than for caval subtraction PCMRI (29.3% vs 50.1%; P = .03). At baseline, FAIR ASL liver perfusion was lower in BDL rats (199 ± 32 ml/min/100 g vs sham 316 ± 24 ml/min/100 g; P = .01) but liver T1 was higher (BDL 1533 ± 50 vs sham 1256 ± 18 ms; P = .0004). Post‐LPS FAIR ASL liver perfusion response differences were observed between sham/BDL rats (P = .02), approaching significance in sham (+78 ± 33 ml/min/100 g; P = .06) but not BDL rats (−49 ± 40 ml/min/100 g; P = .47). Post‐LPS differences in liver tissue T1 were nonsignificant (P = .35). FAIR ASL hepatic perfusion and caval subtraction PCMRI TLBF agreement was modest, with significant baseline FAIR ASL liver perfusion and tissue T1 differences in rodents with advanced cirrhosis compared with controls. Following inflammatory stress, differences in hepatic perfusion response were detected between cirrhotic/control animals, but liver T1 was unaffected. Findings underline the potential of FAIR ASL in the assessment of vasoactive treatments for patients with chronic liver disease and inflammation.

Hyperpolarized 13 C,15 N2 -urea T2 relaxation changes in acute kidney injury.

To investigate the correlation between renal ischemia and 13 C-urea T2 relaxation rate in an acute kidney injury (AKI) rat model. Six rats subjected to unilateral renal ischemia were investigated. Creatinine clearance, urine output, plasma creatinine as well as blood-urea nitrogen (BUN) values were acquired before and after the procedure. 1 H T2* mapping was acquired using blood oxygenation level dependent (BOLD) MRI and hyperpolarized 13 C-urea T2 mapping was acquired using a 2D golden-angle radial approach. Kidney perfusion was estimated using noncontrast flow alternating inversion recovery arterial spin labeling. All rats showed clinical signs of AKI with increased plasma creatinine and increased BUN. Whole kidney 13 C-urea T2 significantly decreased 26% (P = 0.001) 24 h after reperfusion. A significantly different (3.7 times steeper; P = 0.008) osmolality gradient was observed in the contralateral kidney (P = 0.008; R2 = 0.86) compared with the postischemic kidney (P = 0.0004, R2 =0.97). Whole kidney T2* signal (P = 0.14) and T2* gradient (P = 0.26) was similar between the two kidneys. Oxygen availability dependency on 13 C-urea T2 was investigated by means of the correlation between the BOLD and T2 signals; a statistically significant difference (P = 0.03) was found in the contralateral kidney (P = 0.0001; R2 = 0.95), but not in the postischemic kidney (P = 0.31; R2 = 0.25). We demonstrate that hyperpolarized [13 C,15 N2 ]urea T2 relaxation correlates with renal oxygen tension ( T2*) in the healthy contralateral kidney, but not in the postischemic kidney. The whole kidney T2 relaxation difference between the postischemic and contralateral kidney may originate from altered blood volume in the postischemic kidney. Magn Reson Med 80:696-702, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

MRI-based quantification of renal perfusion in mice: Improving sensitivity and stability in FAIR ASL

PurposeThe importance of the orientation of the selective inversion slice in relation to the anatomy in flow-sensitive alternating inversion recovery arterial spin labeling (FAIR ASL) kidney perfusion measurements is demonstrated by comparing the standard FAIR scheme to a scheme with an improved slice selective control experiment. MethodsA FAIR ASL method is used. The selective inversion preparation slice is set perpendicular to the measurement slice to decrease the unintended labeling of arterial spins in the control experiment. A T1*-based quantification method compensates for the effects of the imperfect inversion on the edge of the selective inversion slice. The quantified perfusion values are compared to the standard experiment with parallel orientation of imaging and selective inversion slice. ResultsPerfusion maps acquired with the perpendicular inversion slice orientation show higher sensitivity compared to the parallel orientation. The T1*-based quantification method removes artifacts arising from imperfect inversion slice profiles. The stability is improved. ConclusionAdjusting the labeling technique to the anatomy is of high importance. Improved sensitivity and reproducibility could be demonstrated. The proposed method provides a solution to the problem of FAIR ASL measurements of renal perfusion in coronal view.

Quantification of perfusion in murine myocardium: A retrospectively triggered T1 -based ASL method using model-based reconstruction.

A method for the quantification of perfusion in murine myocardium is demonstrated. The method allows for the reconstruction of perfusion maps on arbitrary time points in the heart cycle while addressing problems that arise due to the irregular heart beat of mice. A flow-sensitive alternating inversion recovery arterial spin labeling method using an untriggered FLASH-read out with random sampling is used. Look-Locker conditions are strictly maintained. No dummy pulses or mechanism to reduce deviation from Look-Locker conditions are needed. Electrocardiogram and respiratory data are recorded for retrospective gating and triggering. A model-based technique is used to reconstruct missing k-space data to cope with the undersampling inherent in retrospectively gated methods. Acquisition and reconstruction were validated numerically and in phantom measurements before in vivo experimentation. Quantitative perfusion maps were acquired within a single slice measurement time of 11 min. Perfusion values are in good accordance to literature values. Myocardial infarction could be clearly visualized and results were confirmed with histological results. The proposed method is capable of producing quantitative perfusion maps on arbitrary positions in the heart cycle within a short measurement time. The method is robust against irregular breathing patterns and heart rate changes and can be implemented on all scanners.

Multislice perfusion of the kidneys using parallel imaging: Image acquisition and analysis strategies

Flow-sensitive alternating inversion recovery arterial spin labeling with parallel imaging acquisition is used to acquire single-shot, multislice perfusion maps of the kidney. A considerable problem for arterial spin labeling methods, which are based on sequential subtraction, is the movement of the kidneys due to respiratory motion between acquisitions. The effects of breathing strategy (free, respiratory-triggered and breath hold) are studied and the use of background suppression is investigated. The application of movement correction by image registration is assessed and perfusion rates are measured. Postacquisition image realignment is shown to improve visual quality and subsequent perfusion quantification. Using such correction, data can be collected from free breathing alone, without the need for a good respiratory trace and in the shortest overall acquisition time, advantageous for patient comfort. The addition of background suppression to arterial spin labeling data is shown to reduce the perfusion signal-to-noise ratio and underestimate perfusion.

Application of variable-rate selective excitation pulses for spin labeling in perfusion MRI

Arterial spin labeling offers great potential in clinical applications for noninvasive measurement of cerebral blood flow. Arterial spin labeling tagging methods such as the flow sensitive alternating inversion recovery technique require efficient spatial inversion pulses with high inversion accuracy and sharp transition zones between inverted and noninverted magnetization, i.e., require a high performance inversion pulse. This work presents a comprehensive comparison of the advantages offered by a variable-rate selective excitation variant of the hyperbolic secant pulse against the widely used conventional hyperbolic secant pulse and the frequency offset corrected inversion pulses. Pulses were compared using simulation and experimental measurement in phantoms before being used in a flow sensitive alternating inversion recovery-arterial spin labeling perfusion measurement in normal volunteers. Both the hyperbolic secant and frequency offset corrected inversion pulses have small variations in inversion profiles that may lead to unwanted subtraction errors in arterial spin labeling at a level where the residual signal is comparable to the desired perfusion contrast. The variable-rate selective excitation pulse is shown to have improved inversion efficiency indicating its potential in perfusion MRI. The variable-rate selective excitation pulse variant also showed greatest tolerance to radiofrequency variation and off-resonance conditions, making it a robust choice for in vivo arterial spin labeling measurement.