Spin Labeling Technique Research Articles

Qualitative and Quantitative Perfusion Parameters Determined by 3D Single-Shot GRASE ASL MR Imaging

Rationale and Objectives: A particular arterial spin (ASL) labeling technique, called 3D-single-shot GRASE ASL is discussed with respect to the ability and limits of quantifying perfusion parameters. Materials and Methods: The technique enables the acquisition of perfusion weighted signal at multiple delay times (TI) in one scan. The readout part is a gradient and spin-echo combination (GRASE) that uses switched gradient rephrasing of signals to produce several times as many signals as turbo-spin-echo, which translates into faster imaging time and higher signal-to-noise ratio (SNR) per imaging time. The technique provides the possibility for model based quantification of cerebral blood flow and the determination of the bolus arrival information without use of contrast agent and thus the characterization and determina-tion of regions that are supported by collaterals. Results: Whereas for a quantification of the permeability using ASL the SNR is not high enough, at least qualitative permeability maps can be determined, if an optimal homogenous SNR was guaranteed. This was accomplished in brain regions with a high blood supply, typically given in tumors, and by using a correction for coil sensitivity at the highest possible additional scaling. Conclusion: The single-shot 3D GRASE ASL can provide information about the principal blood supply, the transit delay of the blood flow due to a stenosis or collaterals and a qualitative measure of the permeability.

高空間分解能Multiple Echo Planar Imaging Based Signal Targeting and Alternating Radiofrequencyによる頭蓋内非造影Time-resolved MR Angiography

Detailed information on anatomy and hemodynamics in cerebrovascular disorders such as AVM and Moyamoya disease is mandatory for defined diagnosis and treatment planning. Arterial spin labeling technique has come to be applied to magnetic resonance angiography (MRA) and perfusion imaging in recent years. However, those non-contrast techniques are mostly limited to single frame images. Recently we have proposed a non-contrast time-resolved MRA technique termed contrast inherent inflow enhanced multi phase angiography combining spatial resolution echo planar imaging based signal targeting and alternating radiofrequency (CINEMA-STAR). CINEMA-STAR can extract the blood flow in the major intracranial arteries at an interval of 70 ms and thus permits us to observe vascular construction in full by preparing MIP images of axial acquisitions with high spatial resolution. This preliminary study demonstrates the usefulness of the CINEMA-STAR technique in evaluating the cerebral vasculature.

Neuroimaging of Dementia Focused on Alzheimer's Disease

Remarkable progress has been recently achieved in neuroimaging of Alzheimer’s disease prominently in MRI and amyloid PET imaging. We reviewed current morphological and functional MRI and amyloid PET imaging with attention to Pittsburgh compound-B (PiB), the most extensively investigated and validated tracer. Automated voxel-based morphometry of brain MRI has been prevailed in Japan using voxel-based specific regional analysis system for Alzheimer’s disease (VSRAD) for the sensitive detection of selective atrophy in medial temporal structures. Arterial spin labeling technique for the evaluation of brain perfusion without any contrast material may replace FDG-PET or brain perfusion SPECT. PiB specifically binds to fibrillar beta-amyloid deposits in such as those found in the cerebral cortex and striatum. PiB-PET imaging is a sensitive and specific biological marker for underlying amyloid deposition that is an early event on the path to dementia. Amyloid imaging in healthy controls and mild cognitive impairment patients may offer the possibility detecting those at high risk of future AD, as so candidates for early preventive measures if and when they become available. (日本医科大学医学会雑誌 2012; 8: 280―284)

P-785 - Brain perfusion modulation by gender and serotonin transporter polymorphisms

Introduction The evidence of 5-HTTLPR effects on resting state amygdala activity is inconsistent. Investigators reported either enhanced perfusion in 5-HTTLPR short allele carriers or no genetic effect. Gender-related differences in cerebral blood flow (CBF) have been also reported. In this study we tested the hypothesis that the interaction of 5-HTTLPR gene with gender will affect the CBF in amygdala. Objectives To explore the modulation of the amygdala perfusion by gender and 5-HTTLPR polymorphisms. Methods We recruited 81 right-handed white Caucasian healthy volunteers (42 females) aged 19–55 years. Resting CBF was examined using a pseudo-continuous arterial spin labelling technique. The BOLD signal to dynamic facial expressions was acquired to determine the amygdala activation. All participants were genotyped for the 5-HTTLPR gene ( ll-ls-ss alleles and La-Lg variants). Results We found a significant main effect of gender in left (p = 0.006) and right (p s allele carriers compared with females. In the females only, the BOLD response to facial emotions significantly and negatively correlated with CBF in right amygdala. Conclusions The novelty of our results is in the demonstration of gene by gender interaction that might help to interpret some of the inconsistencies in existing literature. We suggest that CBF measure provides for an indirect estimate of susceptibility to emotional signals.

Comparison of relative cerebral blood flow maps using pseudo‐continuous arterial spin labeling and single photon emission computed tomography

Pseudo-continuous arterial spin labeling (PCASL) MRI is a relatively new arterial spin labeling technique and has the potential to extend the cerebral blood flow (CBF) measurement to all tissue types, including white matter. However, the arterial transit time (δ(a)) for white matter is not well established and a limited number of reports using multi-delay methods have yielded inconsistent findings. In this study, we used a different approach and measured white matter δ(a) (mean ± standard deviation, 1541 ± 173 ms) by determining the arrival times of exogenous contrast agent in a bolus tracking experiment. The data also confirmed δ(a) of gray matter to be 912 ± 209 ms. In the second part of this study, we used these parameters in PCASL kinetic models and compared relative CBF (rCBF, with respect to the whole brain) maps with those measured using a single photon emission computed tomography (SPECT) technique. It was found that the use of tissue-specific δ(a) in the PCASL model was helpful in improving the correspondence between the two modalities. On a regional level, the gray/white matter CBF ratios were 2.47 ± 0.39 and 2.44 ± 0.18 for PCASL and SPECT, respectively. On a single-voxel level, the variance between the modalities was still considerable, with an average rCBF difference of 0.27.

Renal Perfusion 3-T MR Imaging: A Comparative Study of Arterial Spin Labeling and Dynamic Contrast-enhanced Techniques

To investigate the feasibility of and correlation between arterial spin-labeling (ASL) and dynamic contrast material-enhanced (DCE) 3-T magnetic resonance (MR) imaging in the measurement of renal blood flow (RBF). The review board approved this study. Nineteen healthy volunteers (seven women, 12 men; age range, 25-68 years) were recruited, and each provided written informed consent. MR imaging was performed with a 3-T whole-body system. Each subject underwent back-to-back ASL and DCE MR imaging. Ten runs of ASL imaging were performed by using the pseudocontinuous tagging scheme, and each run required an 18-second breath hold. For DCE imaging, a gadopentetate dimeglumine bolus (0.0125 mmol per kilogram of body weight) was administrated intravenously in all subjects except two; in the latter subjects, a 0.025 mmol/kg gadopentetate dimeglumine bolus was administered to evaluate the T1 saturation effect. RBF was quantified with both techniques and in both the cortex and the medulla. Agreement was evaluated for RBF measurements obtained with ASL imaging and those obtained with DCE imaging by using correlation analysis. RBF was apparently overestimated with 0.025 mmol/kg gadopentetate dimeglumine, which is a concentration that is commonly adopted for 1.5-T DCE. RBF was 227 mL/100 mL/min ± 30 (standard deviation) in the cortex and 101 mL/100 mL/min ± 21 in the medulla, as measured with ASL imaging, and 272 mL/100 mL/min ± 60 in the cortex and 122 mL/100 mL/min ± 30 in the medulla, as measured with DCE imaging. In the cortex, measurements obtained with ASL and DCE imaging exhibited a linear correlation (r = 0.66; statistical power, 0.8 at the 5% significance level) and fair agreement (intraclass correlation coefficient, 0.41). ASL and DCE 3-T MR imaging are feasible in the quantification of cortical renal perfusion, yielding measurements that are correlated but not entirely comparable. Intermodality differences have yet to be solved.

Quantification of arterial cerebral blood volume using multiphase‐balanced SSFP‐based ASL

A new technique is introduced in this study for in vivo measurement of arterial cerebral blood volume by combining arterial spin labeling with a segmented multiphase balanced steady-state free precession (bSSFP) readout sequence. This technique takes advantage of the phenomenon that the longitudinal magnetization of flowing blood is not or only marginally disturbed (besides T(1) relaxation) by the bSSFP ± α pulse train. When the blood water exchanges into tissue, it becomes quickly saturated by the bSSFP pulse train due to 0 velocity and reduced T(1), T(2) relaxation times. Therefore, labeled blood water behaves like an intravascular contrast agent in multiphase bSSFP scans, and can be used to quantify arterial cerebral blood volume in a similar way as dynamic susceptibility contrast MRI. Both Bloch equation simulation and in vivo experiments were carried out to demonstrate the feasibility for quantifying cerebral blood volume in arteries, arterioles, and capillaries using two variants of the proposed method. Functional MRI of visual cortex stimulation was further performed using multiphase bSSFP-based arterial spin labeling and compared with vascular-space occupancy contrast. The proposed multiphase bSSFP-based arterial spin labeling technique may allow separation of cerebral blood volume of different vascular compartments for functional MRI studies and clinical evaluation of the cerebral vasculature.

MR perfusion imaging using the arterial spin labeling technique for breast cancer

To investigate the feasibility of perfusion imaging using an arterial spin labeling (ASL) technique for breast cancer. Thirteen female patients with primary breast cancers were included in this study. All examinations were performed on 1.5 Tesla MRI systems. Visual evaluations of the colored perfusion map and MRI perfusion values were assessed. MRI and computed tomography (CT) perfusion values were compared. Thirteen of 14 tumor lesions could be visualized on the colored perfusion map. CT perfusion examinations were performed in eight breasts, and the relationship between the blood flow values of CT perfusion and of MR perfusion showed a significant correlation. Nonenhanced MR imaging by an ASL technique is valid for depicting breast cancer, and the MR perfusion value is thought to be helpful for quantitative diagnosis of breast cancer.

Resting state functional connectivity in perfusion imaging: correlation maps with BOLD connectivity and resting state perfusion.

Functional connectivity is a property of the resting state that may provide biomarkers of brain function and individual differences. Classically, connectivity is estimated as the temporal correlation of spontaneous fluctuations of BOLD signal. We investigated differences in connectivity estimated from the BOLD and CBF signal present in volumes acquired with arterial spin labeling technique in a large sample (N = 265) of healthy individuals. Positive connectivity was observable in both BOLD and CBF signal, and was present in the CBF signal also at frequencies lower than 0.009 Hz, here investigated for the first time. Negative connectivity was more variable. The validity of positive connectivity was confirmed by the existence of correlation across individuals in its intensity estimated from the BOLD and CBF signal. In contrast, there was little or no correlation across individuals between intensity of connectivity and mean perfusion levels, suggesting that these two biomarkers correspond to distinct sources of individual differences.

Age‐related cerebral perfusion changes in the parietal and temporal lobes measured by pulsed arterial spin labeling

To investigate age-related regional perfusion changes focused on the medial temporal lobes and related parietal areas using a pulsed arterial spin labeling technique. Resting cerebral blood flow (CBF) maps were obtained from 44 healthy volunteers (18 male, 26 female; age range, 19 to 79 years) using a pulsed arterial spin labeling (PASL) MRI technique at 3 Tesla focused on the parietal and temporal lobes. Repeated measurements were performed in 20 subjects to assure the reliability and reproducibility of the applied PASL technique. Focal age-related CBF decreases were detected in the parietal cortex, cuneus and caudate, whereas increases were seen in the lateral and medial temporal lobe such as hippocampus, the calcarine gyrus and the thalamus. Moreover, repeated measurements demonstrated a high reliability and reproducibility of the applied PASL technique. Data provide evidence for regionally dissociated patterns of perfusion increases and decreases during ageing in the temporal and parietal lobes.

Reliability analysis of the resting state can sensitively and specifically identify the presence of Parkinson disease

Parkinson disease (PD) is characterized by a number of motor and behavioral abnormalities that could be considered deficits of a "no task" or "resting" state, including resting motor findings and defects in emerging from a resting state (e.g., resting tremor, elevated resting tone, abulia, akinesia, apathy). PET imaging, and recently, the MRI technique of continuous arterial spin labeling (CASL) have shown evidence of changes in metabolic patterns in individuals with PD. The purpose of this study was to learn if the presence of PD could be "predicted" based on resting fluctuations of the BOLD signal. Participants were 15 healthy controls, 14 subjects with PD, and 1 subject who presented as a control but later developed PD. The amplitude of the low frequency fluctuation (ALFF) was used as an index of brain activity level in the resting state. Participants with PD using this index showed a reliable decrease in activity in a number of regions, including the supplementary motor cortex, the mesial prefrontal cortex, the right middle frontal gyrus, and the left cerebellum (lobule VII/VIII) as well as increased activity in the right cerebellum (lobule IV/V). Using a cross validation approach we term "Reliability Mapping of Regional Differences" (RMRD) to analyze our sample, we were able to reliably distinguish participants with PD from controls with 92% sensitivity and 87% specificity. Our "pre-diagnostic" subject segregated in our analysis with the PD group. These results suggest that resting fMRI should be considered for development as a biomarker and analytical tool for evaluation of PD.

RNA dynamics: perspectives from spin labels

Dynamics are important and indispensible physical attributes that play essential roles in RNA function. RNA dynamics are complex, spanning vast timescales, and encompassing a large number of physical modes. The technique of site-directed spin labeling (SDSL), which derives information on local structural and dynamic features of a macromolecule by monitoring a chemically stable nitroxide radical using electron paramagnetic resonance spectroscopy, has been applied to monitor intrinsic dynamics at defined structural states as well as to probe conformational transition dynamics of RNAs. The current state of SDSL studies of RNA dynamics is summarized here. Further development and application of SDSL promise to open up many more opportunities for probing RNA dynamics and connecting dynamics to structure and function.

Optimal Sampling and Estimation in PASL Perfusion Imaging

Pulsed arterial spin labeling (PASL) techniques potentially allow the absolute, noninvasive quantification of brain perfusion using MRI. This can be achieved by fitting a kinetic model to the data acquired at a number of sampling times. However, the intrinsically low signal-to-noise ratio of PASL measurements usually requires substantial signal averaging, which may result in undesirably long scanning times. A judicious choice of the sampling points is, therefore, crucial in order to minimize scanning time, while optimizing estimation accuracy. On the other hand, a priori information regarding the model parameters may improve estimation performance. Here, we propose a Bayesian framework to determine an optimal sampling strategy and estimation method for the measurement of brain perfusion and arterial transit time (ATT). A Bayesian Fisher information criterion is used to determine the optimal sampling points and a MAP criterion is employed for the estimation of the model parameters, both taking into account the uncertainty in the model parameters as well as the amount of noise in the data. By Monte Carlo simulations, we show that using optimal compared to uniform sampling strategies, as well as the Bayesian estimator relative to a standard least squares approach, improves the accuracy of perfusion and ATT measurements. Moreover, we also demonstrate the applicability of the proposed approach to real data, with the advantage of reduced intersubject variability relative to conventional sampling and estimation approaches.

Non-invasive pulmonary perfusion assessment in young patients with cystic fibrosis using an arterial spin labeling MR technique at 1.5 T

To assess lung perfusion in young patients with cystic fibrosis (CF) using an arterial spin labeling (ASL) technique. Perfusion imaging was performed in 5 healthy volunteers and 33 pediatric patients (13 ± 5years) with CF using an ASL technique. Image quality was evaluated on a five-point scale (1 = excellent). Quantitative perfusion maps were calculated based on the modified Bloch equations. Perfusion differences between volunteers and CF patients and regional differences between lobes were analyzed using Student's t test. The association of perfusion values and forced expiratory volume in 1s (FEV1) was analyzed using univariate regression analysis. Mean lung perfusion was 698 ± 67ml/100g/min (range: 593-777ml/100g/min) in volunteers and 526 ± 113ml/100g/min (range: 346-724ml/100g/min) in CF patients. Median image quality was 2 in volunteers and 3 in CF patients. In CF patients, significantly lower perfusion was observed in the upper lobes compared to healthy volunteers. Mean perfusion values significantly correlated with FEV1 (r=0.84, P<0.0001). ASL perfusion imaging provides lung perfusion assessment in young CF patients. This non-invasive functional imaging technique is worth being evaluated in the clinical monitoring of CF patients.

Longitudinal diffusion tensor imaging and perfusion MRI investigation in a macaque model of neuro-AIDS: A preliminary study

The Simian immunodeficiency virus (SIV) infected macaque model exhibits neuropathological symptoms similar to those of HIV(+) patients, and is ideal for studying cognitive impairment and neuropathological sequelae of disease in repeated measurements. The aim of this study is to use Diffusion Tensor Imaging (DTI) and perfusion MRI to longitudinally access the disease development in SIV-infected monkeys under controlled conditions and to cross-validate our finding with MRI studies in HIV(+) patients. Three adult male pig-tailed macaques (Macaca nemestrina) were inoculated with the SIVsmmFGb virus. Blood was collected for enumeration of CD4+ and CD8+ T-cells. Serial time-sensitive high-resolution T(2)- weighted structural images, Cerebral Blood Flow (CBF) maps measured with the Continuous Arterial Spin Labeling (CASL) technique, and DTI images were obtained. Animals were sacrificed after 24 weeks. Cognitive behavioral tests were also carried out at each time point. Longitudinal changes in brain volume, CBF, and DTI in selected regions were analyzed statistically. In this study, CD4+ T-cell counts were found declined significantly after SIV infection in all macaques. No significant neurological behavior and brain volume changes were observed following virus inoculation. The CBF was found reduced in the caudate, inferior parietal cortex, and the prefrontal cortex. Fractional Anisotropy (FA) values in the whole brain and several Regions of Interest (ROIs) decreased significantly. These longitudinal changes in CBF and FA are correlated with CD4+ T-cell depletion and/or CD4:CD8 ratio. The MRI findings from this pilot study agree with previous results in HIV(+) patients.

MRI of blood flow of the human retina

This study reports a high-resolution MRI approach to image basal blood flow and hypercapnia-induced blood-flow changes in the unanesthetized human retina on a 3-T MRI scanner. Pseudocontinuous arterial spin labeling technique with static tissue suppression was implemented to minimize movement artifacts and improve blood-flow sensitivity. Turbo spin-echo acquisition was used to achieve high spatial resolution free of susceptibility artifacts. The size, shape, and position of a custom-made receive radiofrequency coil were optimized for sensitivity in the posterior retina. Synchronized eye blink and respiration to the end of each data readout minimized eye movement and physiological fluctuation. Robust high-contrast blood-flow MRI of the unanesthetized human retina was obtained at 500 × 800 μm(2) in-plane resolution. Blood flow in the posterior retina was 93 ± 31 mL/(100 mL min) (mean ± standard deviation, N = 5). Hypercapnic inhalation (5% CO(2)) increased blood flow by 12 ± 4% relative to air (P < 0.01, N = 5). This study demonstrates the feasibility of blood-flow MRI of the retina of unanesthetized human. Because blood flow is tightly coupled to metabolic function under normal conditions and it is often perturbed in diseases, this approach could provide unique insights into retinal physiology and serve as an objective imaging biomarker for disease staging and testing of novel therapeutic strategies. This approach could open up new avenue of retinal research.

Detection of Substrate-Dependent Conformational Changes in HP1 of the Glutamate Transporter GltPh

Glutamate acts as the primary excitatory neurotransmitter in the mammalian central nervous system. Clearance of this neurotransmitter from the synapse is accomplished by a family of glutamate transporters known as EAATs, which co-transport sodium and glutamate across the membrane. Recently, crystal structures of a related bacterial transporter, GltPh, have been solved. These structures have provided clues to the conformational changes associated with inhibitor binding as well as a large conformational change involved in switching the protein from an “outward facing” state to an “inward facing” state. However, crystallography has failed to provide data regarding the effects of sodium on the local structure of the substrate binding site. The details of how the substrate is released from the transporter are also absent. Finally, it remains undetermined which conformation(s) the protein adopts in physiological environments, and how the binding of sodium and substrate are coupled to conformational exchange. To probe these questions, we utilize the technique of site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy to explore the local structure and dynamics of residues within a helical hairpin (HP1) which has been suggested to serve as an intracellular gate. EPR spectra of labeled mutants describe a conformational change within HP1 upon addition of sodium and/or aspartate. The spectral changes are localized to the tip of the hairpin, suggesting a relatively small conformational change. In order to fully interpret these structural changes, we are currently measuring the distance between doubly-labeled residues to ascertain the global conformation (outward- vs. inward-facing) of the protein. Preliminary data suggest that in vesicles, GltPh is able to adopt a conformation which resembles the most recently solved crystal structure, which has been interpreted as an inward facing form of the transporter.

Comparing Kidney Perfusion Using Noncontrast Arterial Spin Labeling MRI and Microsphere Methods in an Interventional Swine Model

The purpose of this study was to assess the ability of a flow-sensitive alternating inversion recovery-arterial spin labeling (FAIR-ASL) technique to track renal perfusion changes during pharmacologic and physiologic alterations in renal blood flow using microspheres as a gold standard. Fluorescent microsphere and FAIR-ASL perfusion were compared in the cortex of the kidney for 11 swine across 4 interventional time points: (1) under baseline conditions, (2) during an acetylcholine and fluid bolus challenge to increase perfusion, (3) initially after switching to isoflurane anesthesia, and (4) after 2 hours of isoflurane anesthesia. In 10 of the 11 swine, a bag of ice was placed on the hilum of 1 kidney at the beginning of isoflurane administration to further reduce perfusion in 1 kidney. Both ASL and microspheres tracked the expected cortical perfusion changes (P < 0.02) across the interventions, including an increase in perfusion during the acetylcholine challenge and decrease during the administration of isoflurane. Both techniques also measured lower cortical perfusion in the iced compared with the non-iced kidneys (P ≤ 0.01). The ASL values were systematically lower compared with microsphere perfusion. Very good correlation (r = 0.81, P < 0.0001) was observed between the techniques, and the relationship appeared linear for perfusion values in the expected physiologic range (microsphere perfusion <550 mL/min/100 g) although ASL values saturated for perfusion >550 mL/min/100 g. Cortical perfusion measured with ASL correlated with microspheres and reliably detected changes in renal perfusion in response to physiologic challenge.

Conformational Distributions at the N-peptide/boxB RNA Interface Studied Using Site-Directed Spin Labeling

In bacteriophage lambda, interactions between a 22-amino acid peptide (called the N-peptide) and a stem-loop RNA element (called boxB) play a critical role in transcription anti-termination. The N-peptide/boxB complex has been extensively studied, and serves as a paradigm for understanding mechanisms of protein/RNA recognition. Particularly, ultrafast spectroscopy techniques have been applied to monitor picosecond fluorescence decay behaviors of 2-aminopurines embedded at various positions of the boxB RNA. The studies have led to a model in which the bound N-peptide exists in dynamic equilibrium between two states, with peptide C-terminal fragment either stacking on (i.e., the stacked state) or peeling away from (i.e., the unstacked state) the RNA loop. The function of the N-peptide/boxB complex seems to correlate with the fraction of the stacked state. Here, the N-peptide/boxB system is studied using the site-directed spin labeling technique, in which X-band electron paramagnetic resonance spectroscopy is applied to monitor nanosecond rotational behaviors of stable nitroxide radicals covalently attached to different positions of the N-peptide. The data reveal that in the nanosecond regime the C-terminal fragment of bound N-peptide adopts multiple discrete conformations within the complex. The characteristics of these conformations are consistent with the proposed stacked and unstacked states, and their distributions vary upon mutations within the N-peptide. These results suggest that the dynamic two-state model remains valid in the nanosecond regime, and represents a unique mode of function in the N-peptide/boxB RNA complex. It also demonstrates a connection between picosecond and nanosecond dynamics in a biological complex.

Quantification of myocardial blood flow and flow reserve in rats using arterial spin labeling MRI: comparison with a fluorescent microsphere technique

To quantify noninvasively myocardial blood flow (MBF) and MBF reserve in isoflurane-anesthetized rats using the Look-Locker flow-alternating inversion recovery gradient-echo arterial spin labeling technique (LLFAIRGE-ASL), and to compare the results with the fluorescent microsphere (FM) technique. Male Wistar rats (weight = 200-240 g, n = 21) were anesthetized with 2.0% isoflurane. Hemodynamic parameters were recorded. In seven rats, MBF was assessed on a Bruker Biospec 4.7T MR system using an ECG- and respiration-gated LLFAIRGE-ASL (pixel size = 234 × 468µm(2) , TE = 1.52ms) at rest and during adenosine infusion (140 µg/kg/min). A mixture of 200 000 FM was injected into a second group of rats at rest and during adenosine infusion (n = 7 each), under similar physiologic conditions. Hearts and skeletal muscle samples were processed for fluorescence spectroscopy. Two-tailed unpaired, paired Student's t-test and ANOVA were used to compare groups. MBF measured with LLFAIRGE-ASL was 5.2 ± 1.0 mL/g/min at rest and 13.3 ± 3.0 mL/g/min during adenosine infusion. Results obtained with fluorescent microspheres yielded 5.9 ± 2.3 mL/g/min (nonsignificant vs. LLFAIRGE-ASL, p = 0.9) at rest and 13.1 ± 2.1 mL/g/min (nonsignificant vs. LLFAIRGE-ASL, p = 0.4) during adenosine infusion. Myocardial blood flow reserve measured using LLFAIRGE-ASL and FM were not significantly different (2.5 ± 0.6 vs. 2.4 ± 0.9, respectively; p = 0.8). Hemodynamic parameters during the experiments were not different between the groups. The myocardial blood flow reserve determined under isoflurane anesthesia was 2.5 ± 0.6, which was not different from the value obtained with FM. LLFAIRGE-ASL provided MBF maps with high spatial resolution in rats under isoflurane anesthesia. LLFAIRGE-ASL is a noninvasive measure to assess myocardial blood flow reserve and provides an interesting tool for cardiovascular research.