Clinical utility of arterial spin labeling imaging in disorders of the nervous system

Arterial Spin Labeling: Key Concepts and Progress Towards Use as a Clinical Tool

Arterial spin labeling (ASL), a non-invasive MRI technique, has emerged as a valuable tool for researchers that can measure blood flow and related parameters. This review aims to provide a qualitative overview of the technical principles and recent developments in ASL and to highlight its potential clinical applications. A growing literature demonstrates impressive ASL sensitivity to a range of neuropathologies and treatment responses. Despite its potential, challenges persist in the translation of ASL to widespread clinical use, including the lack of standardization and the limited availability of comprehensive training. As experience with ASL continues to grow, the final stage of translation will require moving beyond single site observational studies to multi-site experience and measurement of the added contribution of ASL to patient care and outcomes.

Beyond conventional imaging: Advancements in MRI for glioma malignancy prediction and molecular profiling

This review examines the advancements in magnetic resonance imaging (MRI) techniques and their pivotal role in diagnosing and managing gliomas, the most prevalent primary brain tumors. The paper underscores the importance of integrating modern MRI modalities, such as diffusion-weighted imaging and perfusion MRI, which are essential for assessing glioma malignancy and predicting tumor behavior. Special attention is given to the 2021 WHO Classification of Tumors of the Central Nervous System, emphasizing the integration of molecular diagnostics in glioma classification, significantly impacting treatment decisions. The review also explores radiogenomics, which correlates imaging features with molecular markers to tailor personalized treatment strategies. Despite technological progress, MRI protocol standardization and result interpretation challenges persist, affecting diagnostic consistency across different settings. Furthermore, the review addresses MRI's capacity to distinguish between tumor recurrence and pseudoprogression, which is vital for patient management. The necessity for greater standardization and collaborative research to harness MRI's full potential in glioma diagnosis and personalized therapy is highlighted, advocating for an enhanced understanding of glioma biology and more effective treatment approaches.

An Investigation of Cerebral Vascular Functional Properties in Middle-to-Old Age Community People With High Vascular Risk Profiles

BACKGROUND

Vascular degeneration is an important cause of brain damage in aging. Assessing the functional properties of the cerebral vascular system may aid early diagnosis and prevention.

PURPOSE

To investigate the relationships between potential vascular functional markers and vascular risks, brain parenchymal damage, and cognition.

STUDY TYPE

Retrospective.

SUBJECTS

Two hundred two general community subjects (42-80 years, males/females: 127/75).

FIELD STRENGTH/SEQUENCE

3 T, spin echo T1W/T2W/FLAIR, resting-state functional MRI with an echo-planar sequence (rsfMRI), pseudo-continuous arterial spin labeling (pCASL) with a three-dimensional gradient-spin echo sequence.

ASSESSMENT

Cerebral blood flow (CBF) in gray matter calculated using pCASL, blood transit times calculated using rsfMRI, and the SD of internal carotid arteries signal (ICAstd ) calculated using rsfMRI; visual assessment for lacunes; quantification of white matter hyperintensity volume; permutation test for quality control; collection of demographic and clinical data, Montreal Cognitive Assessment, Mini-Mental State Examination.

STATISTICAL TESTS

Kolmogorov-Smirnov test; Spearman rank correlation analysis; Multivariable linear regression analysis controlling for covariates; The level of statistical significance was set at P < 0.05.

RESULTS

Age was negatively associated with ICAstd (β = -0.180). Diabetes was associated with longer blood transit time from large arteries to capillary bed (β = 0.185, adjusted for age, sex, and intracranial volume). Larger ICAstd was associated with less presence of lacunes (odds ratio: 0.418, adjusted for age and sex). Higher gray matter CBF (β = 0.154) and larger ICAstd (β = 0.136) were associated with better MoCA scores (adjusted for age, sex, and education).

DATA CONCLUSION

Prolonged blood transit time, decreased ICAstd , and diminished CBF were associated with vascular dysfunction and cognitive impairment. They may serve as vascular functional markers in future studies.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 3.

Magnetic Resonance Imaging and Nuclear Imaging of Parkinsonian Disorders: Where do we go from here?

Parkinsonian disorders are a heterogeneous group of incurable neurodegenerative diseases that significantly reduce quality of life and constitute a substantial economic burden. Nuclear imaging (NI) and magnetic resonance imaging (MRI) have played and continue to play a key role in research aimed at understanding and monitoring these disorders. MRI is cheaper, more accessible, nonirradiating, and better at measuring biological structures and hemodynamics than NI. NI, on the other hand, can track molecular processes, which may be crucial for the development of efficient diseasemodifying therapies. Given the strengths and weaknesses of NI and MRI, how can they best be applied to Parkinsonism research going forward? This review aims to examine the effectiveness of NI and MRI in three areas of Parkinsonism research (differential diagnosis, prodromal disease identification, and disease monitoring) to highlight where they can be most impactful. Based on the available literature, MRI can assist with differential diagnosis, prodromal disease identification, and disease monitoring as well as NI. However, more work is needed, to confirm the value of MRI for monitoring prodromal disease and predicting phenoconversion. Although NI can complement or be a substitute for MRI in all the areas covered in this review, we believe that its most meaningful impact will emerge once reliable Parkinsonian proteinopathy tracers become available. Future work in tracer development and high-field imaging will continue to influence the landscape for NI and MRI.

Three-Dimensional Arterial Spin Labeling for the Evaluation of the Cerebral Hemodynamics in Ischemic and Hemorrhagic Moyamoya Disease

INTRODUCTION

Moyamoya disease (MMD) is a vascular disease with significant risk of mortality due to ischemia or hemorrhage in the brain. The goal of the study was to explore three-dimensional arterial spin labeling (3D-ASL) to improve evaluation of cerebral hemodynamics in patients with MMD.

METHODS

Our study included 54 cases of ischemic MMD and 42 cases of hemorrhagic MMD. Dynamic susceptibility contrast-enhanced perfusion-weighted imaging (DSC-PWI) and 3D-ASL were performed at 3.0 T. Based on these scans, cerebral blood flow (CBF), mean transit time (MTT), and time to peak (TTP) were calculated and compared between patients with different disease subtypes. Receiver operating characteristics analysis was used to assess the diagnostic sensitivity and specificity of different imaging procedures and parameters.

RESULTS

Our data suggested that CBF in the lesion area was more severely reduced in patients with hemorrhagic MMD than in those with ischemic MMD. The CBF parameter in 3D-ASL diagnosed hemorrhagic and ischemic MMD with a significant sensitivity and specificity of 80.59% and 57.41%, respectively, with an area under the curve (AUC) of 0.75. We also found that the relative CBF of 3D-ASL was more pronounced decreased and the relative MTT and TTP of DSC-PWI were significantly increased in patients with hemorrhagic MMD than those with ischemic MMD. Specificity and sensitivity and AUC of 3D-ASL were better than the comparison of absolute values from DSC-PWI scans.

CONCLUSION

Our study indicated that 3D-ASL is powerful in differentiating patients with cerebral ischemic or hemorrhagic MMD, providing another diagnostic tool that could potentially improve precision medicine to monitoring MMD patients.

Advanced MR Techniques for Preoperative Glioma Characterization: Part 1

Preoperative clinical magnetic resonance imaging (MRI) protocols for gliomas, brain tumors with dismal outcomes due to their infiltrative properties, still rely on conventional structural MRI, which does not deliver information on tumor genotype and is limited in the delineation of diffuse gliomas. The GliMR COST action wants to raise awareness about the state of the art of advanced MRI techniques in gliomas and their possible clinical translation or lack thereof. This review describes current methods, limits, and applications of advanced MRI for the preoperative assessment of glioma, summarizing the level of clinical validation of different techniques. In this first part, we discuss dynamic susceptibility contrast and dynamic contrast-enhanced MRI, arterial spin labeling, diffusion-weighted MRI, vessel imaging, and magnetic resonance fingerprinting. The second part of this review addresses magnetic resonance spectroscopy, chemical exchange saturation transfer, susceptibility-weighted imaging, MRI-PET, MR elastography, and MR-based radiomics applications. Evidence Level: 3 Technical Efficacy: Stage 2.

Arterial spin labeling clinical applications for brain tumors and tumor treatment complications: A comprehensive case-based review

Arterial spin labeling (ASL) is a noninvasive neuroimaging technique that allows for quantifying cerebral blood flow without intravenous contrast. Various neurovascular disorders and tumors have cerebral blood flow alterations. Identifying these perfusion changes through ASL can aid in the diagnosis, especially in entities with normal structural imaging. In addition, complications of tumor treatment and tumor progression can also be monitored using ASL. In this case-based review, we demonstrate the clinical applications of ASL in diagnosing and monitoring brain tumors and treatment complications.

Focality in Febrile Seizures: A Retrospective Assessment Using Arterial Spin Labeling MRI

PURPOSE

 Defining focality of febrile seizures (FS) in clinical practice remains controversial. We investigated focality issues in FS with a postictal arterial spin labeling (ASL) sequence.

METHODS

 We retrospectively reviewed 77 children (median: 19.0 months, range: 15.0-33.0 months) who consecutively visited our emergency room for FS and underwent brain magnetic resonance imaging (MRI), including the ASL sequence, within 24 hours of seizure onset. ASL data were visually analyzed to assess perfusion changes. Factors related to the perfusion changes were investigated.

RESULTS

 The mean time to ASL acquisition was 7.0 (interquartile range: 4.0-11.0) hours. The most common seizure classification was unknown-onset seizures (n = 37, 48%), followed by focal-onset (n = 26, 34%) and generalized-onset seizures (n = 14, 18%). Perfusion changes were observed in 43 (57%) patients: most were hypoperfusion (n = 35, 83%). The temporal regions were the most common location of perfusion changes (n = 26, 60%); the majority of these were distributed in the unilateral hemisphere. Perfusion changes were independently associated with seizure classification (focal-onset seizures, adjusted odds ratio [aOR]: 9.6, p = 0.01; unknown-onset seizures aOR: 10.4, p < 0.01), and prolonged seizures (aOR: 3.1, p = 0.04), but not with other factors (age, sex, time to MRI acquisition, previous FS, repeated FS within 24 hour, family history of FS, structural abnormality on MRI, and developmental delay). The focality scale of seizure semiology positively correlated with perfusion changes (R = 0.334, p < 0.01).

CONCLUSION

 Focality in FS may be common, and its primary origin might be the temporal regions. ASL can be useful for assessing focality in FS, particularly when seizure onset is unknown.

Detection of ictal and periictal hyperperfusion with subtraction of ictal-interictal 1.5-Tesla pulsed arterial spin labeling images co-registered to conventional magnetic resonance images (SIACOM)

Background

Our recent report showed that 1.5-T pulsed arterial spin labeling (ASL) magnetic resonance (MR) perfusion imaging (1.5-T Pulsed ASL [PASL]), which is widely available in the field of neuroemergency, is useful for detecting ictal hyperperfusion. However, the visualization of intravascular ASL signals, namely, arterial transit artifact (ATA), is more remarkable than that of 3-T pseudocontinuous ASL and is easily confused with focal hyperperfusion. To eliminate ATA and enhance the detectability of (peri) ictal hyperperfusion, we developed the subtraction of ictal-interictal 1.5-T PASL images co-registered to conventional MR images (SIACOM).

Methods

We retrospectively analyzed the SIACOM findings in four patients who underwent ASL during both (peri) ictal and interictal states and examined the detectability for (peri) ictal hyperperfusion.

Results

In all patients, the ATA of the major arteries was almost eliminated from the subtraction image of the ictal-interictal ASL. In patients 1 and 2 with focal epilepsy, SIACOM revealed a tight anatomical relationship between the epileptogenic lesion and the hyperperfusion area compared with the original ASL image. In patient 3 with situation-related seizures, SIACOM detected minute hyperperfusion at the site coinciding with the abnormal electroencephalogram area. SIACOM of patient 4 with generalized epilepsy diagnosed ATA of the right middle cerebral artery, which was initially thought to be focal hyperperfusion on the original ASL image.

Conclusion

Although it is necessary to examine several patients, SIACOM can eliminate most of the depiction of ATA and clearly demonstrate the pathophysiology of each epileptic seizure.

Cerebral blood flow alterations in migraine patients with and without aura: An arterial spin labeling study

Background

Migraine aura is a transient, fully reversible visual, sensory, or other central nervous system symptom that classically precedes migraine headache. This study aimed to investigate cerebral blood flow (CBF) alterations of migraine with aura patients (MwA) and without aura patients (MwoA) during inter-ictal periods, using arterial spin labeling (ASL).

Methods

We evaluated 88 migraine patients (32 MwA) and 44 healthy control subjects (HC) who underwent a three-dimensional pseudo-continuous ASL MRI scanning. Voxel-based comparison of normalized CBF was conducted between MwA and MwoA. The relationship between CBF variation and clinical scale assessment was further analyzed. The mean CBF values in brain regions showed significant differences were calculated and considered as imaging features. Based on these features, different machine learning–based models were established to differentiate MwA and MwoA under five-fold cross validation. The predictive ability of the optimal model was further tested in an independent sample of 30 migraine patients (10 MwA).

Results

In comparison to MwoA and HC, MwA exhibited higher CBF levels in the bilateral superior frontal gyrus, bilateral postcentral gyrus and cerebellum, and lower CBF levels in the bilateral middle frontal gyrus, thalamus and medioventral occipital cortex (all p values < 0.05). These variations were also significantly correlated with multiple clinical rating scales about headache severity, quality of life and emotion. On basis of these CBF features, the accuracies and areas under curve of the final model in the training and testing samples were 84.3% and 0.872, 83.3% and 0.860 in discriminating patients with and without aura, respectively.

Conclusion

In this study, CBF abnormalities of MwA were identified in multiple brain regions, which might help better understand migraine-stroke connection mechanisms and may guide patient-specific decision-making.

Aberrant pattern of regional cerebral blood flow in mild cognitive impairment: A meta-analysis of arterial spin labeling magnetic resonance imaging

In mild cognitive impairment (MCI), cognitive decline is associated with abnormal changes of cerebral blood flow (CBF). Arterial spin labeling magnetic resonance imaging (ASL-MRI) is an effective method for assessing regional cerebral blood flow (rCBF). However, the CBF estimated via ASL-MRI in MCI often differs between studies, and the consistency of CBF changes in MCI is unclear. In this study, 13 ASL-MRI studies with 495 MCI patients and 441 health controls were screened out from PubMed, Embase, Cochrane, Web of Science, Wanfang, and CNKI. An activation likelihood estimation (ALE) meta-analysis was performed to explore the brain regions with abnormal CBF in MCI. It showed that the decreased CBF in MCI was identified in the precuneus, inferior parietal lobule (IPL), superior occipital gyrus (SOG), middle temporal gyrus (MTG), and middle occipital gyrus (MOG), while the increased CBF in MCI was identified in the lentiform nucleus (LN) compared with healthy controls. The study characterized the abnormal pattern of regional CBF in MCI, which would promote our knowledge of MCI and might be used as a biomarker in clinic.

Arterial Spin Labeling Perfusion in Determining the IDH1 Status and Ki-67 Index in Brain Gliomas

The aim of the study was to evaluate the relationship between tumor blood flow (TBF) measured by the pseudo-continuous arterial spin labeling (PCASL) method and IDH1 mutation status of gliomas as well as Ki-67 proliferative index. Methods. The study included 116 patients with newly diagnosed gliomas of various grades. They received no chemotherapy or radiotherapy before MRI. IDH1 status assessment was performed after tumor removal in 106 cases—48 patients were diagnosed with wildtype gliomas (Grade 1−2—6 patients, Grade 3−4—42 patients) and 58 patients were diagnosed with mutant forms of gliomas (Grade 1−2—28 patients, Grade 3−4—30 patients). In 64 cases out of 116 Ki-67 index was measured. Absolute and normalized tumor blood flow values were measured on 3D PCASL maps. Results. TBF and normalized TBF (nTBF) in wildtype gliomas were significantly higher than in IDH1-mutant gliomas (p < 0.001). ASL perfusion showed high values of sensitivity and specificity in the differential diagnosis of gliomas with distinct IDH1 status (for TBF: specificity 75%, sensitivity 77.6%, AUC 0.783, cutoff 80.57 mL/100 g/min, for nTBF: specificity 77.1%, sensitivity 79.3%, AUC 0.791, cutoff 4.7). TBF and nTBF in wildtype high-grade gliomas (HGG) were significantly higher than in mutant forms (p < 0.001). ASL perfusion showed the following values of sensitivity and specificity in the diagnosis of mutant HGG and wildtype HGG (for TBF: specificity 83.3%, sensitivity 60%, AUC 0.719, cutoff 84.18 mL/100 g/min, for nTBF: specificity 88.1%, sensitivity 60%, AUC 0.729, cutoff 4.7). There was a significant positive correlation between tumor blood flow and Ki-67 (for TBF Rs = 0.63, for nTBF Rs = 0.61). Conclusion. ASL perfusion may be an informative factor in determining the IDH1 status in brain gliomas preoperative and tumor proliferative activity.

Effects of interventions on cerebral perfusion in the Alzheimer's disease spectrum: A systematic review

Cerebral perfusion dysfunctions are seen in the early stages of Alzheimer's disease (AD). We systematically reviewed the literature to investigate the effect of pharmacological and non-pharmacological interventions on cerebral hemodynamics in randomized controlled trials involving AD patients or Mild Cognitive Impairment (MCI) due to AD. Studies involving other dementia types were excluded. Data was searched in April 2021 on MEDLINE, Embase, and Web of Science. Risk of bias was assessed using Cochrane Risk of Bias Tool. A meta-synthesis was performed separating results from MCI and AD studies. 31 studies were included and involved 310 MCI and 792 CE patients. The MCI studies (n = 8) included physical, cognitive, dietary, and pharmacological interventions. The AD studies (n = 23) included pharmacological, physical interventions, and phytotherapy. Cerebral perfusion was assessed with PET, ASL, Doppler, fNIRS, DSC-MRI, Xe-CT, and SPECT. Randomization and allocation concealment methods and subject characteristics such as AD-onset, education, and ethnicity were missing in several papers. Positive effects on hemodynamics were seen in 75 % of the MCI studies, and 52 % of the AD studies. Inserting cerebral perfusion outcome measures, together with established AD biomarkers, is fundamental to target all disease mechanisms and understand the role of cerebral perfusion in AD.

Moyamoya Disease With Initial Ischemic or Hemorrhagic Attack Shows Different Brain Structural and Functional Features: A Pilot Study

Objective

Cerebral ischemia and intracranial hemorrhage are the two main phenotypes of moyamoya disease (MMD). However, the pathophysiological processes of these two MMD phenotypes are still largely unknown. Here, we aimed to use multimodal neuroimaging techniques to explore the brain structural and functional differences between the two MMD subtypes.

Methods

We included 12 patients with ischemic MMD, 10 patients with hemorrhagic MMD, and 10 healthy controls (HCs). Each patient underwent MRI scans and cognitive assessment. The cortical thickness of two MMD subtypes and HC group were compared. Arterial spin labeling (ASL) and diffusion tensor imaging (DTI) were used to inspect the cerebral blood flow (CBF) of cortical regions and the integrity of related white matter fibers, respectively. Correlation analyses were then performed among the MRI metrics and cognitive function scores.

Results

We found that only the cortical thickness in the right middle temporal gyrus (MTG) of hemorrhagic MMD was significantly greater than both ischemic MMD and HC (p < 0.05). In addition, the right MTG showed higher ASL-CBF, and its associated fiber tract (arcuate fasciculus, AF) exhibited higher fractional anisotropy (FA) values in hemorrhagic MMD. Furthermore, the cortical thickness of the right MTG was positively correlated with its ASL-CBF values (r = 0.37, p = 0.046) and the FA values of right AF (r = 0.67, p < 0.001). At last, the FA values of right AF were found to be significantly correlated with cognitive performances within patients with MMD.

Conclusions

Hemorrhagic MMD shows increased cortical thickness on the right MTG in comparison with ischemic MMD and HCs. The increased cortical thickness is associated with the higher CBF values and the increased integrity of the right AF. These findings are important to understand the clinical symptoms and pathophysiology of MMD and further applied to clinical practice.

Implications and limitations of magnetic resonance perfusion imaging with 1.5-Tesla pulsed arterial spin labeling in detecting ictal hyperperfusion during non-convulsive status epileptics

Background:

Recent our reports showed that 3-T pseudocontinuous arterial spin labeling (3-T pCASL) magnetic resonance perfusion imaging with dual post labeling delay (PLD) of 1.5 and 2.5 s clearly demonstrated the hemodynamics of ictal hyperperfusion associated with non-convulsive status epilepticus (NCSE). We aimed to examine the utility of 1.5-T pulsed arterial spin labeling (1.5-T PASL), which is more widely available for daily clinical use, for detecting ictal hyperperfusion.

Methods:

We retrospectively analyzed the findings of 1.5-T PASL with dual PLD of 1.5 s and 2.0 s in six patients and compared the findings with ictal electroencephalographic (EEG) findings.

Results:

In patients 1 and 2, we observed the repeated occurrence of ictal discharges (RID) on EEG. In patient 1, with PLDs of 1.5 s and 2.0 s, ictal ASL hyperperfusion was observed at the site that matched the RID localization. In patient 2, the RID amplitude was extremely low, with no ictal ASL hyperperfusion. In patient 3 with lateralized periodic discharges (LPD), we observed ictal ASL hyperperfusion at the site of maximal LPD amplitude, which was apparent at a PLD of 2.0 s but not 1.5 sec. Among three patients with rhythmic delta activity (RDA) of frequencies <2.5 Hz (Patients 4–6), we observed obvious and slight increases in ASL signals in patients 4 and 5 with NCSE, respectively. However, there was no apparent change in ASL signals in patient 6 with possible NCSE.

Conclusion:

The detection of ictal hyperperfusion on 1.5-T PASL might depend on the electrophysiological intensity of the epileptic ictus, which seemed to be more prominent on 1.5-T PASL than on 3-T pCASL. The 1.5-T PASL with dual PLDs showed the hemodynamics of ictal hyperperfusion in patients with RID and LPD. However, it may not be visualized in patients with extremely low amplitude RID or RDA (frequencies <2.5 Hz).

Shunt Surgery Efficacy Is Correlated With Baseline Cerebrum Perfusion in Idiopathic Normal Pressure Hydrocephalus: A 3D Pulsed Arterial-Spin Labeling Study

This study investigated the relationship between preoperative cerebral blood flow (CBF) in patients with idiopathic normal pressure hydrocephalus (INPH) and preoperative clinical symptoms and changes of clinical symptoms after shunt surgery. A total of 32 patients with diagnosed INPH and 18 age-matched healthy controls (HCs) were involved in this study. All subjects underwent magnetic resonance imaging (MRI), including 3D pulsed arterial-spin labeling (PASL) for non-invasive perfusion imaging, and clinical symptom evaluation at baseline, and all patients with INPH were reexamined with clinical tests 1 month postoperatively. Patients with INPH had significantly lower whole-brain CBF than HCs, with the most significant differences in the high convexity, temporal lobe, precuneus, and thalamus. At baseline, there was a significant correlation between the CBF in the middle frontal gyrus, calcarine, inferior and middle temporal gyrus, thalamus, and posterior cingulate gyrus and poor gait manifestation. After shunting, improvements were negatively correlated with preoperative perfusion in the inferior parietal gyrus, inferior occipital gyrus, and middle temporal gyrus. Preoperative CBF in the middle frontal gyrus was positively correlated with the severity of preoperative cognitive impairment and negatively correlated with the change of postoperative MMSE score. There was a moderate positive correlation between anterior cingulate hypoperfusion and improved postoperative urination. Our study revealed that widely distributed and intercorrelated cortical and subcortical pathways are involved in the development of INPH symptoms, and preoperative CBF may be correlative to short-term shunt outcomes.

Interplay between vascular hemodynamics and the glymphatic system in the pathogenesis of idiopathic normal pressure hydrocephalus, exploring novel neuroimaging diagnostics

As the aging population continues to grow, so will the incidence of age-related conditions, including idiopathic normal pressure hydrocephalus (iNPH). The pathogenesis of iNPH remains elusive, and this is due in part to the poor characterization of cerebral spinal fluid (CSF) dynamics within the brain. Advancements in technology and imaging techniques have enabled new breakthroughs in understanding CSF physiology, and therefore iNPH pathogenesis. This includes understanding the hemodynamic and microvascular components involved in CSF influx and flow. Namely, the glymphatic system appears to be the great mediator, facilitating perivascular CSF flow via astrocytic aquaporin channels located along the endothelium of the pial vasculature. The interplay between glymphatics and both arterial pulsatilty and venous compliance has also been recently demonstrated. It appears then that CSF flow, and therefore glymphatic function, are highly dependent on cardiocirculatory and vascular factors. Impairment in any one component, whether it be related to arterial pulsatility, microvascular changes, reduced venous drainage, or astrogliosis, contributes greatly to iNPH, although it is likely a combination thereof. The strong interplay between vascular hemodynamics and CSF flow suggests perfusion imaging and cerebral blood flow quantification may be a useful diagnostic tool in characterizing iNPH. In addition, studies detecting glymphatic flow with magnetic resonance imaging have also emerged. These imaging tools may serve to both diagnose iNPH and help delineate it from other similarly presenting disease processes. With a better understanding of the vascular and glymphatic factors related to iNPH pathogenesis, physicians are better able to select the best candidates for treatment.

Impact of the inversion time on regional brain perfusion estimation with clinical arterial spin labeling protocols

Objective

Evaluating the impact of the Inversion Time (TI) on regional perfusion estimation in a pediatric cohort using Arterial Spin Labeling (ASL).

Materials and methods

Pulsed ASL (PASL) was acquired at 3 T both at TI 1500 ms and 2020 ms from twelve MRI-negative patients (age range 9–17 years). A volume of interest (VOIs) and a voxel-wise approach were employed to evaluate subject-specific TI-dependent Cerebral Blood Flow (CBF) differences, and grey matter CBF Z-score differences. A visual evaluation was also performed.

Results

CBF was higher for TI 1500 ms in the proximal territories of the arteries (PTAs) (e.g. insular cortex and basal ganglia — P < 0.01 and P < 0.05 from the VOI analysis, respectively), and for TI 2020 ms in the distal territories of the arteries (DTAs), including the watershed areas (e.g. posterior parietal and occipital cortex — P < 0.001 and P < 0.01 from the VOI analysis, respectively). Similar differences were also evident when analyzing patient-specific CBF Z-scores and at a visual inspection.

Conclusions

TI influences ASL perfusion estimates with a region-dependent effect. The presence of intraluminal arterial signal in PTAs and the longer arterial transit time in the DTAs (including watershed areas) may account for the TI-dependent differences. Watershed areas exhibiting a lower perfusion signal at short TIs (~ 1500 ms) should not be misinterpreted as focal hypoperfused areas.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10334-021-00964-7.

Multiparametric Quantitative MRI in Neurological Diseases

Magnetic resonance imaging (MRI) is the gold standard imaging technique for diagnosis and monitoring of many neurological diseases. However, the application of conventional MRI in clinical routine is mainly limited to the visual detection of macroscopic tissue pathology since mixed tissue contrasts depending on hardware and protocol parameters hamper its application for the assessment of subtle or diffuse impairment of the structural tissue integrity. Multiparametric quantitative (q)MRI determines tissue parameters quantitatively, enabling the detection of microstructural processes related to tissue remodeling in aging and neurological diseases. In contrast to measuring tissue atrophy via structural imaging, multiparametric qMRI allows for investigating biologically distinct microstructural processes, which precede changes of the tissue volume. This facilitates a more comprehensive characterization of tissue alterations by revealing early impairment of the microstructural integrity and specific disease-related patterns. So far, qMRI techniques have been employed in a wide range of neurological diseases, including in particular conditions with inflammatory, cerebrovascular and neurodegenerative pathology. Numerous studies suggest that qMRI might add valuable information, including the detection of microstructural tissue damage in areas appearing normal on conventional MRI and unveiling the microstructural correlates of clinical manifestations. This review will give an overview of current qMRI techniques, the most relevant tissue parameters and potential applications in neurological diseases, such as early (differential) diagnosis, monitoring of disease progression, and evaluating effects of therapeutic interventions.

Vessel length on SNAP MRA and TOF MRA is a potential imaging biomarker for brain blood flow

PURPOSE

To explore feasibility of using the vessel length on time-of-flight (TOF) or simultaneous non-contrast angiography and intraplaque hemorrhage (SNAP) MRA as an imaging biomarker for brain blood flow, by using arterial spin labeling (ASL) perfusion imaging and 3D phase contrast (PC) quantitative flow imaging as references.

METHODS

In a population of thirty subjects with carotid atherosclerotic disease, the visible intracranial arteries on TOF and SNAP were semi-automatically traced and the total length of the distal segments was calculated with a dedicated software named iCafe. ASL blood flow was calculated automatically using the recommended hemodynamic model. PC blood flow was obtained by generating cross-sectional arterial images and semi-automatically drawing the lumen contours. Pearson correlation coefficients were used to assess the associations between the different whole-brain or hemispheric blood flow measurements.

RESULTS

Under the imaging protocol used in this study, TOF vessel length was larger than SNAP vessel length (P < 0.001). Both whole-brain TOF and SNAP vessel length showed a correlation with whole brain ASL and 3D PC blood flow measurements, and the correlation coefficients were higher for SNAP vessel length (TOF vs ASL: R = 0.554, P = 0.002; SNAP vs ASL: R = 0.711, P < 0.001; TOF vs 3D PC: R = 0.358, P = 0.052; SNAP vs 3D PC: R = 0.425, P = 0.019). Similar correlation results were observed for the hemispheric measurements. Hemispheric asymmetry index of SNAP vessel length also showed a significant correlation with hemispheric asymmetry index of ASL cerebral blood flow (R = 0.770, P < 0.001).

CONCLUSION

The results suggest that length of the visible intracranial arteries on TOF or SNAP MRA can serve as a potential imaging marker for brain blood flow.

Neurovascular and perfusion imaging findings in coronavirus disease 2019: Case report and literature review

Central nervous system involvement in severe acute respiratory syndrome caused by coronavirus disease 2019 (COVID-19) has increasingly been recognised in the literature, and possible mechanisms of neuroinvasion, neurotropism and neurovirulence have been described. Neurological signs have been described in 84% of COVID-19 intensive care unit patients, and haemostatic abnormalities in such patients may play an important role, with a broad spectrum of neuroimaging findings. This report describes the magnetic resonance imaging neurovascular findings in an acutely ill patient with COVID-19, including perfusion abnormalities depicted in the arterial spin labelling technique.