Arterial Spin Labeling Perfusion Magnetic Resonance Imaging Research Articles

“Brain on Fire”: Hyperperfusion as a Hallmark of Hyperammonemic Encephalopathy

AbstractWe describe a very rare case of acute fulminant hepatic failure as a complication of acute viral hepatitis caused by hepatitis A virus, complicated by hyperammonemic encephalopathy. The brain magnetic resonance imaging (MRI) findings were suggestive of cytotoxic edema involving bilateral cerebral hemispheres. The novel findings of hyperperfusion on arterial spin labeling perfusion MRI and hyperemic hypoxia on susceptibility weighted imaging are discussed. The patient had a rapid progression of cerebral edema and succumbed to the illness despite supportive care. Characteristic neuroimaging findings may help in the diagnosis of acute hyperammonemic encephalopathy of brain MRI, which may be useful in leading to appropriate clinical workup and diagnosis of the underlying cause of hyperammonemia. In our case, hyperammonemic encephalopathy was precipitated by fulminant hepatic failure caused by hepatitis A virus, which is a rare occurrence.

MRI-based parameter inference for cerebral perfusion modelling in health and ischaemic stroke

Cerebral perfusion modelling is a promising tool to predict the impact of acute ischaemic stroke treatments on the spatial distribution of cerebral blood flow (CBF) in the human brain. To estimate treatment efficacy based on CBF, perfusion simulations need to become suitable for group-level investigations and thus account for physiological variability between individuals. However, computational perfusion modelling to date has been restricted to a few patient-specific cases. This study set out to establish automated parameter inference for perfusion modelling based on neuroimaging data and thus enable CBF simulations of groups. Magnetic resonance imaging (MRI) data from 75 healthy senior adults were utilised. Brain geometries were computed from healthy reference subjects’ T1-weighted MRI. Haemodynamic model parameters were determined from spatial CBF maps measured by arterial spin labelling (ASL) perfusion MRI. Thereafter, perfusion simulations were conducted in 75 healthy cases followed by 150 acute ischaemic stroke cases representing an occlusion and CBF cessation in the left and right middle cerebral arteries. The anatomical fitness of the brain geometries was evaluated by comparing the simulated grey (GM) and white matter (WM) volumes to measurements in healthy reference subjects. Strong positive correlations were found in both tissue types (GM: Pearson’s r 0.74, P<0.001; WM: Pearson’s r 0.84, P<0.001). Haemodynamic parameter tuning was verified by comparing the total volumetric blood flow rate to the brain in healthy reference subjects and simulations (Pearson’s r 0.89, P<0.001). In acute ischaemic stroke cases, the simulated infarct volume using a perfusion-based estimate was 197±25 ml. Computational predictions were in agreement with anatomical and haemodynamic values from the literature concerning T1-weighted, T2-weighted, and phase-contrast MRI measurements in healthy scenarios and acute ischaemic stroke cases. The acute stroke simulations did not capture small infarcts (left tail of the distribution), which could be explained by neglected compensatory mechanisms, e.g. collaterals. The proposed parameter inference method provides a foundation for group-level CBF simulations and for in silico clinical stroke trials which could assist in medical device and drug development.

Diagnostic Value of Dynamic Contrast-Enhanced (DCE), Dynamic Susceptibility Contrast (DSC) and Arterial Spin Labeling (ASL) Perfusion MRI for Differentiation of High-Grade and Low-Grade Gliomas

Objective: To evaluate dynamic contrast-enhanced (DCE), dynamic susceptibility contrast (DSC), and arterial spin labeling (ASL)-derived perfusion magnetic resonance imaging (MRI) parameters as a non-invasive technique for differentiating between high-grade gliomas (HGGs) and low-grade gliomas (LGGs), and to determine the diagnostic value of each parameter. Materials and Methods: Twenty-four patients with histopathologically confirmed HGGs or LGGs underwent DCE-, DSC-, and ASL-magnetic resonance perfusion (MRP). Retrospective qualitative and quantitative assessment of MRP-derived parameters, including DCE-Ktrans, DCE-Ve, DCE-Vp, DSC-rCBV, DSC-rCBF, and ASL-rCBF were performed, and the diagnostic value of each parameter was determined using ROC analysis. Results: Of the 24 patients enrolled in the present study, which included 10 LGGs and 14 HGGs, DCE-derived Vp showed the best diagnostic performance for differentiating between HGGs and LGGs (AUC 0.833, cutoff &gt;0.0002 mL/100 g, p=0.018, 100% sensitivity, 28.6% specificity), followed by DCE-derived Ktrans (AUC 0.75, cutoff &gt;0.024 min⁻¹, p=0.011, 58.3% sensitivity, 100% specificity) and DSC-derived normalized rCBV (AUC 0.75, p=0.021, cutoff &gt;1.15, 100% sensitivity, 37.5% specificity). The ASL-derived normalized rCBF showed no statistically significant difference between HGGs and LGGs (AUC 0.457, p=0.757). Conclusion: DCE-derived Vp, DCE-derived Ktrans, and DSC-derived rCBV are helpful perfusion MRI parameters for differentiating HGGs and LGGs, with DCE-derived Vp showing the best diagnostic performance in the present study. Keywords: DCE; DSL; ASL; Perfusion MR; Glioma

MRI assessment of cerebral perfusion in clinical trials.

Neurodegenerative mechanisms affect the brain through a variety of processes that are reflected as changes in brain structure and physiology. Although some biomarkers for these changes are well established, others are at different stages of development for use in clinical trials. One of the most challenging biomarkers to harmonize for clinical trials is cerebral blood flow (CBF). There are several magnetic resonance imaging (MRI) methods for quantifying CBF without the use of contrast agents, in particular arterial spin labeling (ASL) perfusion MRI, which has been increasingly applied in clinical trials. In this review, we present ASL MRI techniques, including strategies for implementation across multiple imaging centers, levels of confidence in assessing disease progression and treatment effects, and details of image analysis.

Apathy in depression: An arterial spin labeling perfusion MRI study

IntroductionApathy, as defined as a deficit in goal-directed behaviors, is a critical clinical dimension in depression associated with chronic impairment. Little is known about its cerebral perfusion specificities in depression. To explore neurovascular mechanisms underpinning apathy in depression by pseudo-continuous arterial spin labeling (pCASL) magnetic resonance imaging (MRI). MethodsPerfusion imaging analysis was performed on 90 depressed patients included in a prospective study between November 2014 and February 2017. Imaging data included anatomical 3D T1-weighted and perfusion pCASL sequences. A multiple regression analysis relating the quantified cerebral blood flow (CBF) in different regions of interest defined from the FreeSurfer atlas, to the Apathy Evaluation Scale (AES) total score was conducted. ResultsAfter confound adjustment (demographics, disease and clinical characteristics) and correction for multiple comparisons, we observed a strong negative relationship between the CBF in the left anterior cingulate cortex (ACC) and the AES score (standardized beta = −0.74, corrected p value = 0.0008). ConclusionOur results emphasized the left ACC as a key region involved in apathy severity in a population of depressed participants. Perfusion correlates of apathy in depression evidenced in this study may contribute to characterize different phenotypes of depression.

Advanced neuroimaging techniques for evaluating pediatric epilepsy.

Accurate localization of the seizure onset zone is important for better seizure outcomes and preventing deficits following epilepsy surgery. Recent advances in neuroimaging techniques have increased our understanding of the underlying etiology and improved our ability to noninvasively identify the seizure onset zone. Using epilepsy-specific magnetic resonance imaging (MRI) protocols, structural MRI allows better detection of the seizure onset zone, particularly when it is interpreted by experienced neuroradiologists. Ultra-high-field imaging and postprocessing analysis with automated machine learning algorithms can detect subtle structural abnormalities in MRI-negative patients. Tractography derived from diffusion tensor imaging can delineate white matter connections associated with epilepsy or eloquent function, thus, preventing deficits after epilepsy surgery. Arterial spin-labeling perfusion MRI, simultaneous electroencephalography (EEG)-functional MRI (fMRI), and magnetoencephalography (MEG) are noinvasive imaging modalities that can be used to localize the epileptogenic foci and assist in planning epilepsy surgery with positron emission tomography, ictal single-photon emission computed tomography, and intracranial EEG monitoring. MEG and fMRI can localize and lateralize the area of the cortex that is essential for language, motor, and memory function and identify its relationship with planned surgical resection sites to reduce the risk of neurological impairments. These advanced structural and functional imaging modalities can be combined with postprocessing methods to better understand the epileptic network and obtain valuable clinical information for predicting long-term outcomes in pediatric epilepsy.

Cerebrovascular Reactivity Measured with ASL Perfusion MRI, Ivy Sign, and Regional Tissue Vascularization in Moyamoya

Arterial spin labeling (ASL) perfusion magnetic resonance imaging (MRI) may be used to determine brain regions at risk for ischemia in patients with moyamoya vasculopathy and to identify patients who may benefit from surgical revascularization. We aimed to investigate whether 1) the severity of moyamoya is related to the presence of leptomeningeal collaterals and cerebrovascular reactivity (CVR), 2) the presence of collaterals and ivy sign reflects disturbed CVR, and 3) arterial transit artefacts (ATAs) and ivy sign reflect the presence of collaterals. We determined severity of moyamoya on digital subtraction angiography (DSA) according to the modified Suzuki classification in 20 brain regions and scored regional tissue revascularization using a 4-point scale. Regional CVR and ATAs were assessed on ASL perfusion MRI, ivy sign on fluid attenuation inversion recovery MRI. In 11 patients (median age 36 years; 91% female), we studied 203 regions. ATAs were associated with the presence of collaterals on DSA (P < 0.01). Of all regions with clearly visible collateral vessels on DSA, however, only 24% had ATAs. Ivy sign was not related to the presence or absence of collaterals nor to CVR. In 10% of regions with good vascularization on DSA, CVR was poor or showed steal. ATAs were associated with the presence of collaterals on DSA. Although DSA vascularization scores correlated with CVR, 10% of regions with good vascularization on DSA had absent CVR or steal on ASL-MRI. DSA and ivy sign did not provide adequate information on the hemodynamic status of brain tissue in patients with moyamoya vasculopathy.

Cortical Perfusion and Tubular Function as Evaluated by Magnetic Resonance Imaging Correlates with Annual Loss in Renal Function in Moderate Chronic Kidney Disease

Background: Chronic hypoxia is a well-recognized factor in the pathogenesis of chronic kidney disease (CKD). Loss of microcirculation is thought to lead to enhanced renal hypoxia, which in turn results in the development of fibrosis, a hallmark of progressive CKD. To evaluate the role of functional magnetic resonance imaging (MRI), we performed perfusion, oxygenation, and diffusion MRI measurements in individuals with diabetes and stage 3 CKD. Methods: Fifty-four subjects (41 individuals with diabetes and stage 3 CKD and 13 healthy controls) participated in this study. Data with blood oxygenation level dependent (BOLD), arterial spin labeling perfusion and diffusion MRI were acquired using a 3T scanner. Results: Renal cortical perfusion was reduced in CKD compared to the controls (109.54 ± 25.38 vs. 203.17 ± 27.47 mL/min/100 g; p < 0.001). Cortical apparent diffusion coefficient showed no significant reduction in CKD compared to controls (1,596.10 ± 196.64 vs. 1,668.72 ± 77.29 × 10^–6 mm²/s; p = 0.45) but was significantly associated with perfusion. Cortical R2* values were modestly increased in CKD (20.76 ± 4.08 vs. 18.74 ± 2.37 s^–1; p = 0.12). Within the CKD group, R2*_Medulla and R2*_Kidney were moderately and negatively associated with estimated glomerular filtration rate. There was a significant association between cortical perfusion and medullary response to furosemide with annual loss of renal function, used as an estimate of CKD progression. Conclusions: Subjects with a moderate degree of CKD had significantly lower renal perfusion. Diffusion and BOLD MRI showed more modest differences between the groups. Individuals with progressive CKD had lower perfusion and response to furosemide.

Utility of arterial spin labelling MRI for discriminating atypical high-grade glioma from primary central nervous system lymphoma

To evaluate the ability of arterial spin labelling (ASL) magnetic resonance imaging (MRI) in differentiating primary central nervous system lymphoma (PCNSL) from atypical high-grade glioma (HGG), as well as exploring the underlying pathological mechanisms. Twenty-three patients with PCNSL and 17 patients with atypical HGG who underwent ASL-MRI were identified retrospectively. Absolute cerebral blood flow (aCBF) and normalised cerebral blood flow (nCBF) values were obtained, and were compared between PCNSL and atypical HGG using the Mann-Whitney U-test. The performance in discriminating between PCNSL and atypical HGG was evaluated using receiver-operating characteristics analysis and area-under-the-curve (AUC) values for aCBF and nCBF. The correlation between microvessel density (MVD) and aCBF was determined by Spearman's correlation analysis. Atypical HGG demonstrated significantly higher aCBF, nCBF, and MVD values than PCNSL (p<0.05). The diagnostic accuracy of discriminating PCNSL from atypical HGG showed AUC=0.877 (95% confidence interval [CI] 0.735-0.959) for aCBF, and AUC=0.836 (95% confidence interval [CI] 0.685-0.934) for nCBF. There was a moderate positive correlation between aCBF values of region of interest (ROI >30 mm2) in the enhanced area and MVD values (rho=0.579, p=0.0001), and a strong positive correlation between aCBF values MVD based on "point-to-point biopsy" (rho=0.83, p=0.0029). Interobserver agreements for aCBF and nCBF were excellent (ICC >0.75). ASL perfusion MRI is a useful imaging technique for the discrimination between atypical HGG and PCNSL, which may be determined by the difference of MVD between them.

Common and dissociable regional cerebral blood flow differences associate with dimensions of psychopathology across categorical diagnoses.

The high comorbidity among neuropsychiatric disorders suggests a possible common neurobiological phenotype. Resting-state regional cerebral blood flow (CBF) can be measured noninvasively with MRI and abnormalities in regional CBF are present in many neuropsychiatric disorders. Regional CBF may also provide a useful biological marker across different types of psychopathology. To investigate CBF changes common across psychiatric disorders, we capitalized upon a sample of 1,042 youths (ages 11 to 23 years) who completed cross-sectional imaging as part of the Philadelphia Neurodevelopmental Cohort. CBF during a resting state was quantified on a voxelwise basis using arterial spin labeled perfusion MRI at 3T. A dimensional measure of psychopathology was constructed using a bifactor model of item-level data from a psychiatric screening interview, which delineated four factors (fear, anxious-misery, psychosis, and behavioral symptoms) plus a general factor: overall psychopathology. Overall psychopathology was associated with elevated perfusion in several regions including the right dorsal anterior cingulate cortex (ACC) and left rostral ACC. Furthermore, several clusters were associated with specific dimensions of psychopathology. Psychosis symptoms were related to reduced perfusion in the left frontal operculum and insula, whereas fear symptoms were associated with less perfusion in the right occipital/fusiform gyrus and left subgenual ACC. Follow-up functional connectivity analyses using resting-state fMRI collected in the same participants revealed that overall psychopathology was associated with decreased connectivity between the dorsal ACC and bilateral caudate. Together, the results of this study demonstrate common and dissociable CBF abnormalities across neuropsychiatric disorders in youth.

The role of high-field magnetic resonance imaging in parkinsonian disorders: Pushing the boundaries forward.

Historically, magnetic resonance imaging (MRI) has contributed little to the study of Parkinson's disease (PD), but modern MRI approaches have unveiled several complementary markers that are useful for research and clinical applications. Iron- and neuromelanin-sensitive MRI detect qualitative changes in the substantia nigra. Quantitative MRI markers can be derived from diffusion weighted and iron-sensitive imaging or volumetry. Functional brain alterations at rest or during task performance have been captured with functional and arterial spin labeling perfusion MRI. These markers are useful for the diagnosis of PD and atypical parkinsonism, to track disease progression from the premotor stages of these diseases and to better understand the neurobiological basis of clinical deficits. A current research goal using MRI is to generate time-dependent models of the evolution of PD biomarkers that can help understand neurodegeneration and provide reliable markers for therapeutic trials. This article reviews recent advances in MRI biomarker research at high-field (3T) and ultra high field-imaging (7T) in PD and atypical parkinsonism. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Differentiation of Glioblastoma from Brain Metastasis: Qualitative and Quantitative Analysis Using Arterial Spin Labeling MR Imaging.

PurposeTo evaluate the diagnostic performance of cerebral blood flow (CBF) by using arterial spin labeling (ASL) perfusion magnetic resonance (MR) imaging to differentiate glioblastoma (GBM) from brain metastasis.Materials and MethodsThe institutional review board of our hospital approved this retrospective study. The study population consisted of 128 consecutive patients who underwent surgical resection and were diagnosed as either GBM (n = 89) or brain metastasis (n = 39). All participants underwent preoperative MR imaging including ASL. For qualitative analysis, the tumors were visually graded into five categories based on ASL-CBF maps by two blinded reviewers. For quantitative analysis, the reviewers drew regions of interest (ROIs) on ASL-CBF maps upon the most hyperperfused portion within the tumor and upon peritumoral T2 hyperintensity area. Signal intensities of intratumoral and peritumoral ROIs for each subject were normalized by dividing the values by those of contralateral normal gray matter (nCBFintratumoral and nCBFperitumoral, respectively). Visual grading scales and quantitative parameters between GBM and brain metastasis were compared. In addition, the area under the receiver-operating characteristic curve was used to evaluate the diagnostic performance of ASL-driven CBF to differentiate GBM from brain metastasis.ResultsFor qualitative analysis, GBM group showed significantly higher grade compared to metastasis group (p = 0.001). For quantitative analysis, both nCBFintratumoral and nCBFperitumoral in GBM were significantly higher than those in metastasis (both p < 0.001). The areas under the curve were 0.677, 0.714, and 0.835 for visual grading, nCBFintratumoral, and nCBFperitumoral, respectively (all p < 0.001).ConclusionASL perfusion MR imaging can aid in the differentiation of GBM from brain metastasis.

Patterns of postictal cerebral perfusion in idiopathic generalized epilepsy: a multi-delay multi-parametric arterial spin labelling perfusion MRI study

The cerebral haemodynamic status of idiopathic generalized epilepsy (IGE) is a very complicated process. Little attention has been paid to cerebral blood flow (CBF) alterations in IGE detected by arterial spin labelling (ASL) perfusion magnetic resonance imaging (MRI). However, the selection of an optimal delay time is difficult for single-delay ASL. Multi-delay multi-parametric ASL perfusion MRI overcomes the limitations of single-delay ASL. We applied multi-delay multi-parametric ASL perfusion MRI to investigate the patterns of postictal cerebral perfusion in IGE patients with absence seizures. A total of 21 IGE patients with absence seizures and 24 healthy control subjects were enrolled. IGE patients exhibited prolonged arterial transit time (ATT) in the left superior temporal gyrus. The mean CBF of IGE patients was significantly increased in the left middle temporal gyrus, left parahippocampal gyrus and left fusiform gyrus. Prolonged ATT in the left superior temporal gyrus was negatively correlated with the age at onset in IGE patients. This study demonstrated that cortical dysfunction in the temporal lobe and fusiform gyrus may be related to epileptic activity in IGE patients with absence seizures. This information can play an important role in elucidating the pathophysiological mechanism of IGE from a cerebral haemodynamic perspective.

Capability of arterial spin labeling MR imaging in localizing seizure focus in clinical seizure activity

PurposeThe purpose of this study was to evaluate cerebral blood flow using arterial spin labeling (ASL) perfusion magnetic resonance (MR) imaging in patients with clinical seizure activity and determine its diagnostic performance in identifying seizure focus. Materials and methodsInstitutional Review Board of our hospital approved this retrospective study. Informed consent was waived. Clinical seizure focus was determined by a neurologist based on seizure semiology, electroencephalography, and conventional imaging modalities. The diagnostic performance of ASL perfusion MR imaging to identifying seizure focus compared to clinical seizure focus was analyzed. ResultsClinical seizure focus was localized in 95% (42/44) of patients. The sensitivity and specificity of ASL perfusion MR imaging for identifying seizure focus were 74% (95% CI: 58%, 86%) (clinical seizure focus was localizable in 31 of 42 patients, including complete concordance in 10 patients and partial concordance in 21 patients) and 0% (95% CI: 0%, 84%) (for the two patients whose clinical seizure foci were not localizable, they were identified by ASL perfusion MR imaging), respectively. Thus, the overall accuracy of ASL perfusion MR imaging for localizing seizure focus was 70% (33/44). For 4 patients who had abnormal perfusion on ASL, their seizure foci based on ASL perfusion MR imaging were discordant with clinical seizure foci. ConclusionASL perfusion MR imaging can provide information about perfusion status and important diagnostic clue in localizing seizure focus in patients with clinical seizure activity. It has the potential as a non-invasive complementary diagnostic tool for patients with clinical seizure activity.

Differentiation between recurrent gliomas and radiation necrosis using arterial spin labeling perfusion imaging.

Arterial spin labeling (ASL) magnetic resonance (MR) perfusion imaging has been proposed as an effective method to measure brain tumor perfusion. The aim of the present study was to evaluate the utility of this technique in the differentiation of recurrent gliomas from radiation necrosis. Twenty-one patients with surgically treated primary gliomas, including 16 cases of recurrent glioma and 5 of radiation necrosis were examined using 3.0T MR imaging (MRI). ASL and dynamic susceptibility contrast-weighted (DSC) perfusion MRI scans were performed. Maps of normalized cerebral blood flow (CBF) in ASL imaging and cerebral blood volume (CBV) in DSC imaging were computed and analyzed in the regions of interest. In cases of glioma recurrence, the normalized ASL-CBF ratio (4.45±2.72) was higher than that in cases of radiation injury (1.22±0.61) (P<0.01). The normalized DSC-relative CBV ratio was also significantly higher in glioma recurrence (3.38±2.08) than it was in radiation injury (1.09±0.55) (P<0.05). A close linear correlation was found between the ASL and DSC MRI techniques (linear regression coefficient, R=0.85; P=0.005) in the differentiation of recurrent glioma from radiation injury. The results indicate that ASL perfusion is an accurate method of distinguishing between glioma recurrence and radiation necrosis.

ASSESSMENT OF CEREBRAL PERFUSION IN PATIENTS WITH HEMODYNAMIC ISCHEMIC STROKE UNDERGOING RECONSTRUCTIVE BRACHIOCEPHALIC ARTERY INTERVENTIONS

The paper deals with the assessment of cerebral perfusion in patients in the acute period of acute cerebrovascular accident before and after revascularization surgery. It gives a clinical example of using contrast-free perfusion magnetic resonance imaging (MRI) in a patient with hemodynamic ischemic stroke. The use of this technique made it possible to determine indications for early carotid endarterectomy for the contralateral internal carotid artery and to evaluate positive postoperative changes in cerebral perfusion and the patient’s neurological status. The authors analyzed the current literature on this problem with a particular emphasis on the possibilities of using dynamic susceptibility contrast-enhanced and arterial spin-labeling contrast-free perfusion MRI in this category of patients. Carotid endarterectomy in the acute period of acute cerebrovascular accident can improve cerebral hemodynamics and the patient’s neurological status and prevent recurrent cerebral circulatory disorders. Indications for this surgery should be determined by taking into consideration the results of perfusion MRI techniques (single-photon computed tomography contrastenhanced and contrast-free perfusion MRI).

Volumetric Arterial Spin-labeled Perfusion Imaging of the Kidneys with a Three-dimensional Fast Spin Echo Acquisition

Renal perfusion measurements using noninvasive arterial spin-labeled (ASL) magnetic resonance imaging techniques are gaining interest. Currently, focus has been on perfusion in the context of renal transplant. Our objectives were to explore the use of ASL in patients with renal cancer, and to evaluate three-dimensional (3D) fast spin echo (FSE) acquisition, a robust volumetric imaging method for abdominal applications. We evaluate 3D ASL perfusion magnetic resonance imaging in the kidneys compared to two-dimensional (2D) ASL in patients and healthy subjects. Isotropic resolution (2.6 × 2.6 × 2.8 mm(3)) 3D ASL using segmented FSE was compared to 2D single-shot FSE. ASL used pseudo-continuous labeling, suppression of background signal, and synchronized breathing. Quantitative perfusion values and signal-to-noise ratio (SNR) were compared between 3D and 2D ASL in four healthy volunteers and semiquantitative assessments were made by four radiologists in four patients with known renal masses (primary renal cell carcinoma). Renal cortex perfusion in healthy subjects was 284 ± 21 mL/100 g/min, with test-retest repeatability of 8.8%. No significant differences were found between the quantitative perfusion value and SNR in volunteers between 3D ASL and 2D ASL, or in 3D ASL with synchronized or free breathing. In patients, semiquantitative assessment by radiologists showed no significant difference in image quality between 2D ASL and 3D ASL. In one case, 2D ASL missed a high perfusion focus in a mass that was seen by 3D ASL. 3D ASL renal perfusion imaging provides isotropic-resolution images, with comparable quantitative perfusion values and image SNR in similar imaging time to single-slice 2D ASL.

Postischemic hyperperfusion on arterial spin labeled perfusion MRI is linked to hemorrhagic transformation in stroke.

The purpose of this study was to investigate the relationship between hyperperfusion and hemorrhagic transformation (HT) in acute ischemic stroke (AIS). Pseudo-continuous arterial spin labeling (ASL) with background suppressed 3D GRASE was performed during routine clinical magnetic resonance imaging (MRI) on AIS patients at various time points. Arterial spin labeling cerebral blood flow (CBF) maps were visually inspected for the presence of hyperperfusion. Hemorrhagic transformation was followed during hospitalization and was graded on gradient recalled echo (GRE) scans into hemorrhagic infarction (HI) and parenchymal hematoma (PH). A total of 361 ASL scans were collected from 221 consecutive patients with middle cerebral artery stroke from May 2010 to September 2013. Hyperperfusion was more frequently detected posttreatment (odds ratio (OR) = 4.8, 95% confidence interval (CI) 2.5 to 8.9, P < 0.001) and with high National Institutes of Health Stroke Scale (NIHSS) scores at admission (P<0.001). There was a significant association between having hyperperfusion at any time point and HT (OR = 3.5, 95% CI 2.0 to 6.3, P < 0.001). There was a positive relationship between the grade of HT and time-hyperperfusion with the Spearman's rank correlation of 0.44 (P = 0.003). Arterial spin labeling hyperperfusion may provide an imaging marker of HT, which may guide the management of AIS patients post tissue-type plasminogen activator (tPA) and/or endovascular treatments. Late hyperperfusion should be given more attention to prevent high-grade HT.

Intra-Arterial Signal on Arterial Spin Labeling Perfusion MRI to Identify the Presence of Acute Middle Cerebral Artery Occlusion

Background: The susceptibility vessel sign on gradient echo-type-T2*-weighted imaging is a well-known marker of arterial occlusion. Stagnant flow in front of the middle cerebral artery (MCA) occlusion sites may contribute to the intra-arterial, high-intensity signal on arterial spin labeling magnetic resonance imaging (MRI), making it another potential marker of MCA occlusion. We compared the intra-arterial, high-intensity signal and susceptibility vessel sign in patients with symptomatic MCA occlusion and patients without major vessel occlusion. Methods: We identified transient ischemic attack or ischemic stroke patients with (1) 3-T MRI performed within 24 h after clinical onset including arterial spin labeling, T2*-weighted imaging, and magnetic resonance angiography (MRA) and (2) either having MCA occlusion (n = 34 patients) or without major vessel occlusion (n = 24 patients). The intra-arterial, high-intensity signal was defined as an enlarged circular or linear bright hyperintensity within the artery. The susceptibility vessel sign was defined as an enlarged spot of hypointensity within the MCA, in which the diameter of the hypointense signal within the vessel exceeded the contralateral vessel diameter. The presence or absence of the intra-arterial, high-intensity signal and susceptibility vessel sign were assessed, along with their inter-rater agreement and consistency with the presence of MCA occlusion on MRA. Results: The intra-arterial, high-intensity signal was detectable in 30 patients (52%), and susceptibility vessel sign was observed in 17 patients (29%). The sensitivity of the intra-arterial high-intensity signal was significantly higher than that of the susceptibility vessel sign (88% vs. 50%; p < 0.05). The accuracy of the intra-arterial high-intensity signal was also higher than that of the susceptibility vessel sign (93% vs. 71%; p < 0.05). The intra-arterial high-intensity signal was situated in the proximal regions of the susceptibility vessel sign on T2*WI within the MCA. Neither the intra-arterial high-intensity signal nor the susceptibility vessel sign was observed in patients without major vessel occlusion. Inter-rater agreement was good for intra-arterial high-intensity signal detection (κ = 0.73) and moderate for susceptibility vessel sign detection (κ = 0.47). The presence or absence of the intra-arterial high-intensity signal was highly consistent with that of MCA occlusion on MRA (κ = 0.74). Conclusions: The intra-arterial high-intensity signal on arterial spin labeling appears to be useful to identify the presence of acute MCA occlusion and may be associated with stagnant flow in front of occlusion sites. The intra-arterial high-intensity signal may also be used to identify the occlusion site.

Arterial Spin Labeling Perfusion MRI in Children and Young Adults with Previous Ischemic Stroke and Unilateral Intracranial Arteriopathy

Background: Little is known about cerebral blood flow (CBF) in young patients with ischemic stroke caused by an intracranial arteriopathy. Arterial spin labeling (ASL) perfusion is a noninvasive technique for measuring CBF. We aimed to investigate whether, in young patients with unilateral intracranial arteriopathy and previous ischemic stroke, CBF is compromised in noninfarcted brain areas of the symptomatic hemisphere and whether this is related to the severity of the arteriopathy. Methods: Patients aged 5-50 years, with previous middle cerebral artery (MCA) territory infarction and a unilateral intracranial arteriopathy, underwent magnetic resonance imaging (MRI), MR angiography and pseudocontinuous ASL perfusion MRI. We assessed the severity of stenosis of arteries that fed the symptomatic MCA territory, quantified CBF in the noninfarcted cortex of both MCA territories and generated CBF maps for visual CBF interpretation. Results: A total of 17 patients were included (median age 29 years, range 5-49, 29% male). We found a similar median quantified CBF in the symptomatic and asymptomatic MCA territories (86 ml·100 g^-1·min^-1). CBF maps showed hypoperfusion in the symptomatic MCA territory in 59% of patients compared to 18% based on quantified CBF. Patients with a severe arteriopathy more often showed hypoperfusion on CBF maps than patients with a mild arteriopathy. In 53% of patients, small foci of increased signal intensity were visible on CBF maps around an area of hypoperfusion, indicating vascular artifacts. In these patients, we found large intraindividual variation in the quantified CBF in the symptomatic hemisphere. In 47% of patients, the visual interpretation of perfusion did not correspond with the quantified CBF. Conclusions: This study shows that more than half of young patients with previous ischemic stroke in the MCA territory and a unilateral intracranial arteriopathy have hypoperfusion in the noninfarcted cortex of the symptomatic hemisphere when CBF is visually assessed using a CBF map, in particular in patients with a severe arteriopathy. In the same patients, quantification of CBF shows hypoperfusion in the symptomatic hemisphere in only 18%. This discrepancy is caused by labeled blood within the arteries that has not yet reached the tissue at the time of imaging. Visual assessment can show hypoperfusion, while the quantified CBF in a similar region appears higher when the intravascular labeled blood is included in the region of interest. Further research should focus on elucidating whether cerebral perfusion deficits in young stroke patients with intracranial arteriopathy might help to identify patients who are at risk of poor outcome or stroke recurrence.