Arterial spin labeling in neuroimaging

k-space weighted image average (KWIA) for ASL-based dynamic MR angiography and perfusion imaging

A novel denoising algorithm termed k-space weighted image average (KWIA) was proposed to improve the signal-to-noise ratio (SNR) of dynamic MRI, such as arterial spin labeling (ASL)-based dynamic magnetic resonance angiography (dMRA) and perfusion imaging. KWIA divides the k-space of each time frame into multiple rings, the central ring of the k-space remains intact to preserve the image contrast and temporal resolution, while outer rings are progressively averaged with neighboring time frames to increase SNR. Simulations and in-vivo dMRA and multi-delay ASL studies were performed to evaluate the performance of KWIA under various MRI acquisition conditions. SNR ratios and temporal signal errors between KWIA-processed and the original data were measured. Visualization of dynamic blood flow signals as well as quantitative parametric maps were evaluated for KWIA-processed images as compared to the original images. KWIA achieved a SNR ratio of 1.73 for dMRA and 2.0 for multi-delay ASL respectively, which were in accordance with the theoretical predictions. Improved visualization of dynamic blood flow signals was demonstrated using KWIA in distal small vessels in dMRA and small brain structures in multi-delay ASL. Approximately 5% temporal errors were observed in both KWIA-processed dMRA and ASL signals. Fine anatomical features were revealed in the quantitative parametric maps of dMRA, and the residuals of model fitting were reduced for multi-delay ASL. Compared to other conventional denoising methods, KWIA is a flexible denoising algorithm that improves the SNR of ASL-based dMRA and perfusion MRI by up to 2-fold without compromising spatial and temporal resolution or quantification accuracy.

Perfusion Imaging: An Advection Diffusion Approach

Perfusion imaging is of great clinical importance and is used to assess a wide range of diseases including strokes and brain tumors. Commonly used approaches for the quantitative analysis of perfusion images are based on measuring the effect of a contrast agent moving through blood vessels and into tissue. Contrast-agent free approaches, for example, based on intravoxel incoherent motion and arterial spin labeling, also exist, but are so far not routinely used clinically. Existing contrast-agent-dependent methods typically rely on the estimation of the arterial input function (AIF) to approximately model tissue perfusion. These approaches neglect spatial dependencies. Further, as reliably estimating the AIF is non-trivial, different AIF estimates may lead to different perfusion measures. In this work we therefore propose PIANO, an approach that provides additional insights into the perfusion process. PIANO estimates the velocity and diffusion fields of an advection-diffusion model best explaining the contrast dynamics without using an AIF. PIANO accounts for spatial dependencies and neither requires estimating the AIF nor relies on a particular contrast agent bolus shape. Specifically, we propose a convenient parameterization of the estimation problem, a numerical estimation approach, and extensively evaluate PIANO. Simulation experiments show the robustness and effectiveness of PIANO, along with its ability to distinguish between advection and diffusion. We further apply PIANO on a public brain magnetic resonance (MR) perfusion dataset of acute stroke patients, and demonstrate that PIANO can successfully resolve velocity and diffusion field ambiguities and results in sensitive measures for the assessment of stroke, comparing favorably to conventional measures of perfusion.

Current approaches and advances in the imaging of stroke

A stroke occurs when the blood flow to the brain is suddenly interrupted, depriving brain cells of oxygen and glucose and leading to further cell death. Neuroimaging techniques, such as computed tomography and magnetic resonance imaging, have greatly improved our ability to visualise brain structures and are routinely used to diagnose the affected vascular region of a stroke patient's brain and to inform decisions about clinical care. Currently, these multimodal imaging techniques are the backbone of the clinical management of stroke patients and have immensely improved our ability to visualise brain structures. Here, we review recent developments in the field of neuroimaging and discuss how different imaging techniques are used in the diagnosis, prognosis and treatment of stroke.

Summary: Stroke imaging has undergone seismic shifts in the past decade. Although magnetic resonance imaging (MRI) is superior to computed tomography in providing vital information, further research on MRI is still required to bring its full potential into clinical practice.

Vascular endothelial growth factor associated dissimilar cerebrovascular phenotypes in two different mouse models of Alzheimer's Disease

Vascular perturbations and cerebral hypometabolism are emerging as important components of Alzheimer's disease (AD). While various in vivo imaging modalities have been designed to detect changes of cerebral perfusion and metabolism in AD patients and animal models, study results were often heterogenous with respect to imaging techniques and animal models. We therefore evaluated cerebral perfusion and glucose metabolism of two popular transgenic AD mouse strains, TgCRND8 and 5xFAD, at 7 and 12 months-of-age under identical conditions and analyzed possible molecular mechanisms underlying heterogeneous cerebrovascular phenotypes. Results revealed disparate findings in these two strains, displaying important aspects of AD progression. TgCRND8 mice showed significantly decreased cerebral blood flow and glucose metabolism with unchanged cerebral blood volume (CBV) at 12 months-of-age whereas 5xFAD mice showed unaltered glucose metabolism with significant increase in CBV at 12 months-of-age and a biphasic pattern of early hypoperfusion followed by a rebound to normal cerebral blood flow in late disease. Finally, immunoblotting assays suggested that VEGF dependent vascular tone change may restore normoperfusion and increase CBV in 5xFAD.

Utilizing 3D Arterial Spin Labeling to Identify Cerebrovascular Leak and Glymphatic Obstruction in Neurodegenerative Disease

New approaches are required to successfully intervene therapeutically in neurodegenerative diseases. Addressing the earliest phases of disease, blood brain barrier (BBB) leak before the accumulation of misfolded proteins has significant potential for success. To do so, however, a reliable, noninvasive and economical test is required. There are two potential methods of identifying the BBB fluid leak that results in the accumulation of normally excluded substances which alter neuropil metabolism, protein synthesis and degradation with buildup of misfolded toxic proteins. The pros and cons of dynamic contrast imaging (DCI or DCE) and 3D TGSE PASL are discussed as potential early identifying methods. The results of prior publications of the 3D ASL technique and an overview of the associated physiologic challenges are discussed. Either method may serve well as reliable physiologic markers as novel therapeutic interventions directed at the vasculopathy of early neurodegenerative disease are developed. They may serve well in addressing other neurologic diseases associated with either vascular leak and/or reduced glymphatic flow.

Correcting for Superficial Bias in 7T Gradient Echo fMRI

The arrival of submillimeter ultra high-field fMRI makes it possible to compare activation profiles across cortical layers. However, the blood oxygenation level dependent (BOLD) signal measured by gradient echo (GE) fMRI is biased toward superficial layers of the cortex, which is a serious confound for laminar analysis. Several univariate and multivariate analysis methods have been proposed to correct this bias. We compare these methods using computational simulations of 7T fMRI data from regions of interest (ROI) during a visual attention paradigm. We also tested the methods on a pilot dataset of human 7T fMRI data. The simulations show that two methods–the ratio of ROI means across conditions and a novel application of Deming regression–offer the most robust correction for superficial bias. Deming regression has the additional advantage that it does not require that the conditions differ in their mean activation over voxels within an ROI. When applied to the pilot dataset, we observed strikingly different layer profiles when different attention metrics were used, but were unable to discern any differences in laminar attention across layers when Deming regression or ROI ratio was applied. Our simulations demonstrates that accurate correction of superficial bias is crucial to avoid drawing erroneous conclusions from laminar analyses of GE fMRI data, and this is affirmed by the results from our pilot 7T fMRI data.

Measurement of retina/choroid complex perfusion with magnetic resonance imaging in eyes with acute primary angle-closure

PURPOSE

To measure retina/choroid complex perfusion with magnetic resonance imaging in eyes with acute primary angle-closure (APAC).

METHODS

Three sequences of magnetic resonance imaging, two anatomical and one perfusional using gadolinium, were acquired in patients who were diagnosed with acute primary angle-closure. Regions of interest were drawn on the perfusional sequence and overlaid to the anatomical sequence. The relative blood volume measured during the first 2 s was considered as the baseline value and the change during the subsequent 28 s was analyzed.

RESULTS

Five eyes of 5 patients with acute primary angle-closure were included (3 with unilateral and 2 with bilateral acute primary angle-closure). Three contralateral eyes and 2 eyes of 2 healthy patients, paired for age and sex, were included in the control group. Acute primary angle-closure patients included 4 (80%) women, with an average age of 65.8 ± 12.37 y, mean intraocular pressure of 56.2 ± 14.67 mmHg, mean arterial pressure of 113.4 ± 8.17 mmHg, and average ocular perfusion pressure of 57.2 ± 13.46 mmHg. In the control group, the mean intraocular pressure was 15.6 ± 2.61 mmHg (p=0.0625), the mean arterial pressure was 107.4 ± 6.57 mmHg (p=1.00), and the average ocular perfusion pressure was 91.8 ± 6.72 mmHg (p=0.0625). The relative blood volume of the retina/choroid complex was -0.127 ± 0.048 in acute primary angle-closure patients and -0.213 ± 0.116 in the controls (p=0.3125).

CONCLUSION

The magnetic resonance imaging sequence with gadolinium did not show a change in the retina/choroid complex perfusion in the eyes of patients with acute primary angle-closure.

Arterial spin labeling for head and neck lesion assessment: technical adjustments and clinical applications

PURPOSE

Despite, currently, "state-of-the-art" magnetic resonance imaging (MRI) protocols for head and neck (H&N) lesion assessment incorporate perfusion sequences, these acquisitions require the intravenous injection of exogenous gadolinium-based contrast agents (GBCAs), which may have potential risks. Alternative techniques such as arterial spin labeling (ASL) can provide quantitative microvascular information similar to conventional perfusion sequences for H&N lesions evaluation, as a potential alternative without GBCA administration.

METHODS

We review the existing literature and analyze the latest evidence regarding ASL in H&N area highlighting the technical adjustments needed for a proper ASL acquisition in this challenging region for lesion characterization, treatment monitoring, and tumor recurrence detection.

RESULTS

ASL techniques, widely used for central nervous system lesions evaluation, can be also applied to the H&N region. Technical adjustments, especially regarding post-labeling delay, are mandatory to obtain robust and reproducible results. Several studies have demonstrated the feasibility of ASL in the H&N area including the orbits, skull base, paranasal sinuses, upper airway, salivary glands, and thyroid.

CONCLUSION

ASL is a feasible technique for the assessment of H&N lesions without the need of GBCAs. This manuscript reviews ASL's physical basis, emphasizing the technical adjustments necessary for proper ASL acquisition in this unique and challenging anatomical region, and the main applications in evaluating H&N lesions.

Cerebral Blood Flow Predicts Recovery in Children with Persistent Post-Concussion Symptoms after Mild Traumatic Brain Injury

Persistent post-concussion symptoms (PPCS) following pediatric mild traumatic brain injury (mTBI) are associated with differential changes in cerebral blood flow (CBF). Given its potential as a therapeutic target, we examined CBF changes during recovery in children with PPCS. We hypothesized that CBF would decrease and that such decreases would mirror clinical recovery. In a prospective cohort study, 61 children and adolescents (mean age 14 [standard deviation = 2.6] years; 41% male) with PPCS were imaged with three-dimensional (3D) pseudo-continuous arterial spin-labelled (pCASL) magnetic resonance imaging (MRI) at 4-6 and 8-10 weeks post-injury. Exclusion criteria included any significant past medical history and/or previous concussion within the past 3 months. Twenty-three participants had clinically recovered at the time of the second scan. We found that relative and mean absolute CBF were higher in participants with poor recovery, 44.0 (95% confidence interval [CI]: 43.32, 44.67) than in those with good recovery, 42.19 (95% CI: 41.77, 42.60) mL/min/100 g gray tissue and decreased over time (β = -1.75; p < 0.001). The decrease was greater in those with good recovery (β = 2.29; p < 0.001) and predicted outcome in 77% of children with PPCS (odds ratio [OR] 0.54, 95% CI: 0.36, 0.80; p = 0.002). Future studies are warranted to validate the utility of CBF as a useful predictive biomarker of outcome in PPCS.

Improved neuropathological identification of traumatic brain injury through quantitative neuroimaging and neural network analyses: Some practical approaches for the neurorehabilitation clinician

BACKGROUND

Quantitative neuroimaging analyses have the potential to provide additional information about the neuropathology of traumatic brain injury (TBI) that more thoroughly informs the neurorehabilitation clinician.

OBJECTIVE

Quantitative neuroimaging is typically not covered in the standard radiological report, but often can be extracted via post-processing of clinical neuroimaging studies, provided that the proper volume acquisition sequences were originally obtained.

METHODS

Research and commercially available quantitative neuroimaging methods provide region of interest (ROI) quantification metrics, lesion burden volumetrics and cortical thickness measures, degree of focal encephalomalacia, white matter (WM) abnormalities and residual hemorrhagic pathology. If present, diffusion tensor imaging (DTI) provides a variety of techniques that aid in evaluating WM integrity. Using quantitatively identified structural and ROI neuropathological changes are most informative when done from a neural network approach.

RESULTS

Viewing quantitatively identifiable damage from a neural network perspective provides the neurorehabilitation clinician with an additional tool for linking brain pathology to understand symptoms, problems and deficits as well as aid neuropsychological test interpretation. All of these analyses can be displayed in graphic form, including3-D image analysis. A case study approach is used to demonstrate the utility of quantitative neuroimaging and network analyses in TBI.

CONCLUSIONS

Quantitative neuroimaging may provide additional useful information for the neurorehabilitation clinician.

APOE moderates the effect of hippocampal blood flow on memory pattern separation in clinically normal older adults

Pattern separation, the ability to differentiate new information from previously experienced similar information, is highly sensitive to hippocampal structure and function and declines with age. Functional MRI studies have demonstrated hippocampal hyperactivation in older adults compared to young, with greater task-related activation associated with worse pattern separation performance. The current study was designed to determine whether pattern separation was sensitive to differences in task-free hippocampal cerebral blood flow (CBF) in 130 functionally intact older adults. Given prior evidence that apolipoprotein E e4 (APOE e4) status moderates the relationship between CBF and episodic memory, we predicted a stronger negative relationship between hippocampal CBF and pattern separation in APOE e4 carriers. An interaction between APOE group and right hippocampal CBF was present, such that greater right hippocampal CBF was related to better lure discrimination in noncarriers, whereas the effect reversed directionality in e4 carriers. These findings suggest that neurovascular changes in the medial temporal lobe may underlie memory deficits in cognitively normal older adults who are APOE e4 carriers.

Brain perfusion magnetic resonance imaging using pseudocontinuous arterial spin labeling in 314 dogs and cats

Background

Arterial spin labeling (ASL) is a noninvasive brain perfusion magnetic resonance imaging (MRI) technique that has not been assessed in clinical veterinary medicine.

Hypothesis/Objectives

To test the feasibility of ASL using a 1.5 Tesla scanner and provide recommendations for optimal quantification of cerebral blood flow (CBF) in dogs and cats.

Animals

Three hundred fourteen prospectively selected client‐owned dogs and cats.

Methods

Each animal underwent brain MRI including morphological sequences and ≥1 ASL sequences using different sites of blood labeling and postlabeling delays (PLD). Calculated ASL success rates were compared. The CBF was quantified in animals that had morphologically normal brain MRI results and parameters of ASL optimization were investigated.

Results

Arterial spin labeling was easily implemented with an overall success rate of 95% in animals with normal brain MRI. Technical recommendations included (a) positioning of the imaging slab at the foramen magnum and (b) selected PLD of 1025 ms in cats and dogs <7 kg, 1525 ms in dogs 7 to 38 kg, and 2025 ms in dogs >38 kg. In 37 dogs, median optimal CBF in the cortex and thalamic nuclei were 114 and 95 mL/100 g/min, respectively. In 28 cats, median CBF in the cortex and thalamic nuclei were 113 and 114 mL/100 g/min, respectively.

Conclusions and Clinical Importance

Our survey of brain perfusion ASL‐MRI demonstrated the feasibility of ASL at 1.5 Tesla, suggested technical recommendations and provided CBF values that should be helpful in the characterization of various brain diseases in dogs and cats.

Contrast-Free Detection of Focused Ultrasound-Induced Blood-Brain Barrier Opening Using Diffusion Tensor Imaging

OBJECTIVE

Focused ultrasound (FUS) has emerged as a non-invasive technique to locally and reversibly disrupt the blood-brain barrier (BBB). Here, we investigate the use of diffusion tensor imaging (DTI) as a means of detecting FUS-induced BBB opening at the absence of an MRI contrast agent. A non-human primate (NHP) was repeatedly treated with FUS and preformed circulating microbubbles to transiently disrupt the BBB (n = 4). T1- and diffusion-weighted MRI scans were acquired after the ultrasound treatment, with and without gadolinium-based contrast agent, respectively. Both scans were registered with a high-resolution T1-weighted scan of the NHP to investigate signal correlations. DTI detected an increase in fractional anisotropy from 0.21 ± 0.02 to 0.38 ± 0.03 (82.6 ± 5.2% change) within the targeted area one hour after BBB opening. Enhanced DTI contrast overlapped by 77.22 ± 9.2% with hyper-intense areas of gadolinium-enhanced T1-weighted scans, indicating diffusion anisotropy enhancement only within the BBB opening volume. Diffusion was highly anisotropic and unidirectional within the treated brain region, as indicated by the direction of the principal diffusion eigenvectors. Polar and azimuthal angle ranges decreased by 35.6% and 82.4%, respectively, following BBB opening. Evaluation of the detection methodology on a second NHP (n = 1) confirmed the across-animal feasibility of the technique. In conclusion, DTI may be used as a contrast-free MR imaging modality in lieu of contrast-enhanced T1 mapping for detecting BBB opening during focused-ultrasound treatment or evaluating BBB integrity in brain-related pathologies.

Cerebral Hemodynamic Correlates of Transcutaneous Auricular Vagal Nerve Stimulation in Consciousness Restoration: An Open-Label Pilot Study

This study aimed to preliminarily illustrate the cerebral hemodynamic correlates of transcutaneous auricular vagal nerve stimulation (taVNS) in consciousness restoration. Arterial spin labeling (ASL) was adopted with functional magnetic resonance imaging (fMRI) to measure cerebral blood flow (CBF) changes before and after taVNS in 10 qualified patients with disorders of consciousness (DOC). Before taVNS, five patients responded to auditory stimuli (RtAS), and five did not respond to auditory stimuli (nRtAS). The RtAS DOC patients obtained favorable prognoses after the 4-week taVNS treatment, whereas the nRtAS ones did not. Simultaneously, taVNS increased CBF of multiple brain regions in the RtAS DOC patients, but hardly in the nRtAS ones. In conclusion, the preserved auditory function might be the prior key factor of the taVNS responders in DOC patients, and taVNS might alleviate RtAS DOC by activating the salience network, the limbic system, and the interoceptive system.

A pilot study exploring the effect of repetitive transcranial magnetic stimulation (rTMS) treatment on cerebral blood flow and its relation to clinical outcomes in severe enduring anorexia nervosa

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a novel treatment option for people with severe enduring anorexia nervosa (SE-AN), but associated neurobiological changes are poorly understood. This study investigated the effect of rTMS treatment on regional cerebral blood flow (CBF) and whether any observed changes in CBF are associated with changes in clinical outcomes in people with SE-AN.

METHODS

As part of a randomised sham-controlled feasibility trial of 20 sessions of high-frequency rTMS to the left dorsolateral prefrontal cortex, 26 of 34 trial participants completed arterial spin labelling (ASL) functional magnetic resonance imaging (fMRI) to quantify regional and global resting state CBF before (pre-randomisation baseline) and after real or sham treatment (1-month post-randomisation). A group of healthy females (n = 30) were recruited for baseline comparison. Clinical outcomes, including BMI, and depression and anxiety symptoms, were assessed at baseline, 1-, 4-, and 18-months post-randomisation.

RESULTS

No group differences in regional CBF were identified between the SE-AN and healthy comparison participants. A significant treatment-by-time interaction in a medial temporal lobe cluster with the maximal peak in the right amygdala was identified, reflecting a greater reduction in amygdala CBF following real rTMS compared to sham. Participants with the greatest rTMS-related reduction in amygdala CBF (i.e., between baseline and 1-month post-randomisation) showed the greatest sustained weight gain at 18-months post-randomisation. Higher baseline CBF in the insula predicted greater weight gain between baseline and 1-month post-randomisation and between baseline and 4-months post-randomisation.

CONCLUSIONS

This exploratory pilot study identified rTMS treatment related changes in CBF in adults with SE-AN and these were associated with changes in weight. Our preliminary findings also suggest that CBF (as measured by ASL fMRI) may be a marker of rTMS treatment response in this patient group. Future rTMS studies in AN should employ longitudinal neuroimaging to further explore the neurobiological changes related to rTMS treatment.

TRIAL REGISTRATION

ISRCTN14329415 , registered 23rd July 2015.

Semantic verbal fluency brain network: delineating a physiological basis for the functional hubs using dual-echo ASL and graph theory approach

Objective. Semantic verbal fluency (SFV) is a cognitive process that engages and modulates specific brain areas related to language comprehension and production, decision making, response inhibition, and memory retrieval. The impairment of the brain network responsible for these functions is related to various neurological conditions, and different strategies have been proposed to assess SVF-related deficits in such diseases. In the present study, the concomitant changes of brain perfusion and functional connectivity were investigated during the resting state and SVF task performance.Approach. Arterial spin labeling (ASL), a perfusion-based magnetic resonance imaging (MRI) method, was used with a pseudocontinuous labeling approach and dual-echo readout in 28 healthy right-handed Brazilian Portuguese speakers. The acquisition was performed in a resting state condition and during the performance of a SVF task.Main results. During task performance, a significant increase in cerebral blood flow (CBF) was observed in language-related regions of the frontal lobe, including Brodmann's areas 6, 9, 45, and 47, associated with semantic processing, word retrieval, and speech motor programming. Such regions, along with the posterior cingulate, showed a crucial role in the SVF functional network, assessed by seed-to-voxel and graph analysis. Our approach successfully overcame the generalization problem regarding functional MRI (fMRI) graph analysis with cognitive, task-based paradigms. Moreover, the CBF maps enabled the functional assessment of orbital frontal and temporal regions commonly affected by magnetic susceptibility artifacts in conventional T2*-weighted fMRI approaches.Significance. Our results demonstrated the capability of ASL to evaluate perfusion alterations and functional patterns simultaneously regarding the SVF network providing a quantitative physiological basis to functional hubs in this network, which may support future clinical studies.

Crossed Cerebellar Diaschisis in Alzheimer's Disease Detected by Arterial Spin-labelling Perfusion MRI

BACKGROUND

Crossed cerebellar diaschisis (CCD) is a phenomenon with depressed metabolism and hypoperfusion in the cerebellum. Using arterial spin-labelling perfusion weighted magnetic resonance imaging (ASL PWI), we investigated the frequency of CCD in patients with Alzheimer's disease (AD) and differences between patients with and without CCD.

PATIENTS AND METHODS

In patients with AD who underwent a standardized magnetic resonance imaging including ASL PWI cerebral blood flow was evaluated in the cerebellum, and brain segmentation/volumetry was performed using mdbrain (mediaire GmbH, Berlin, Germany) and FSL FIRST (Functional Magnetic Resonance Imaging of the Brain Software Library).

RESULTS

In total, 65 patients were included, and 22 (33.8%) patients were assessed as being CCD-positive. Patients with CCD had a significantly smaller whole brain volume (862.8±49.9 vs. 893.7±62.7 ml, p=0.049) as well as white matter volume (352.9±28.0 vs. 374.3±30.7, p=0.008) in comparison to patients without CCD.

CONCLUSION

It was possible to detect CCD by ASL PWI in approximately one-third of patients with AD and was associated with smaller whole brain and white matter volume.

Perfusion imaging with arterial spin labeling (ASL)-MRI predicts malignant progression in low‑grade (WHO grade II) gliomas

PURPOSE

Predicting malignant progression of grade II gliomas would allow for earlier initiation of treatment. The hypothesis for this single-centre, case-control study was that the perfusion signal on ASL-MRI predicts such malignant progression in the following 12 months.

METHODS

Consecutive patients with the following criteria were included: ≥ 18 years, grade II glioma (biopsied or resected) and an ASL-MRI 6-12 months prior to malignant progression (cases) or stable disease (controls). Malignant progression was defined either radiologically (new T1w-contrast enhancement) or histologically (neurosurgical tissue sampling). Three controls were matched with each case. Some patients served as their own control by using earlier imaging. The ASL-MRIs were reviewed by two neuroradiologists and classified as positive (hyper-intense or iso-intense compared to cortical grey matter) or negative (hypo-intense). In patients with epilepsy, a neurologist reviewed clinicoradiological data to exclude peri-ictal pseudoprogression. The statistical analysis included diagnostic test properties, a Cohen's Kappa interrater reliability coefficient and stratification for previous radiotherapy.

RESULTS

Eleven cases (median age = 48, IQR = 43-50 years) and 33 controls (43, 27-50 years) were included. Malignant progression appeared at 37 months (median, IQR = 17-44) after first surgery. Thirty ASL-MRIs were assessed as negative and 14 as positive. None of the MRIs showed signs of peri-ictal pseudoprogression. ASL significantly predicted subsequent malignant progression (sensitivity = 73%; specificity = 82%; OR = 12; 95%-CI = 2.4-59.1; p = 0.002). The interrater reliability coefficient was 0.65. In stratified analysis, ASL-MRI predicted malignant progression both in patients with previous radiotherapy and in those without (Mantel-Haenszel test, p = 0.003).

CONCLUSION

Perfusion imaging with ASL-MRI can predict malignant progression within 12 months in patients with grade II glioma.

Targeting the Cerebrovascular System: Next-Generation Biomarkers and Treatment for Mild Traumatic Brain Injury

The diagnosis, prognosis, and treatment of mild traumatic brain injuries (mTBIs), such as concussions, are significant unmet medical issues. The kinetic forces that occur in mTBI adversely affect the cerebral vasculature, making cerebrovascular injury (CVI) a pathophysiological hallmark of mTBI. Given the importance of a healthy cerebrovascular system in overall brain function, CVI is likely to contribute to neurological dysfunction after mTBI. As such, CVI and related pathomechanisms may provide objective biomarkers and therapeutic targets to improve the clinical management and outcomes of mTBI. Despite this potential, until recently, few studies have focused on the cerebral vasculature in this context. This article will begin by providing a brief overview of the cerebrovascular system followed by a review of the literature regarding how mTBI can affect the integrity and function of the cerebrovascular system, and how this may ultimately contribute to neurological dysfunction and neurodegenerative conditions. We then discuss promising avenues of research related to mTBI biomarkers and interventions that target CVI, and conclude that a clinical approach that takes CVI into account could result in substantial improvements in the care and outcomes of patients with mTBI.

Compromised resting cerebral metabolism after sport-related concussion: A calibrated MRI study

Altered resting cerebral blood flow (CBF₀) in the acute phase post-concussion may contribute to neurobehavioral deficiencies, often reported weeks after the injury. However, in addition to changes in CBF₀, little is known about other physiological mechanisms that may be disturbed within the cerebrovasculature. The aim of this study was to assess whether changes in baseline perfusion following sport-related concussion (SRC) were co-localized with changes in cerebral metabolic demand. Forty-two subjects (15 SRC patients 8.0 ± 4.6 days post-injury and 27 age-matched healthy control athletes) were studied cross-sectionally. CBF₀, cerebrovascular reactivity (CVR), resting oxygen extraction (OEF₀) and cerebral metabolic rate of oxygen consumption (CMRO_2|0) were measured using a combination of hypercapnic and hyperoxic breathing protocols, and the biophysical model developed in calibrated MRI. Blood oxygenation level dependent and perfusion data were acquired simultaneously using a dual-echo arterial spin labelling sequence. SRC patients showed significant decreases in CBF₀ spread across the grey-matter (P < 0.05, corrected), and these differences were also confounded by the effects of baseline end-tidal CO₂ (P < 0.0001). Lower perfusion was co-localized with reductions in regional CMRO_2|0 (P = 0.006) post-SRC, despite finding no group-differences in OEF₀ (P = 0.800). Higher CVR within voxels showing differences in CBF was also observed in the SRC group (P = 0.001), compared to controls. Reductions in metabolic demand despite no significant changes in OEF₀ suggests that hypoperfusion post-SRC may reflect compromised metabolic function after the injury. These results provide novel insight about the possible pathophysiological mechanisms underlying concussion that may affect the clinical recovery of athletes after sport-related head injuries.

Quantitative transport mapping (QTM) of the kidney with an approximate microvascular network

PURPOSE

Proof-of-concept study of mapping renal blood flow vector field according to the inverse solution to a mass transport model of time resolved tracer-labeled MRI data.

THEORY AND METHODS

To determine tissue perfusion according to the underlying physics of spatiotemporal tracer concentration variation, the mass transport equation is integrated over a voxel with an approximate microvascular network for fitting time-resolved tracer imaging data. The inverse solution to the voxelized transport equation provides the blood flow vector field, which is referred to as quantitative transport mapping (QTM). A numerical microvascular network modeling the kidney with computational fluid dynamics reference was used to verify the accuracy of QTM and the current Kety's method that uses a global arterial input function. Multiple post-label delay arterial spin labeling (ASL) of the kidney on seven subjects was used to assess QTM in vivo feasibility.

RESULTS

Against the ground truth in the numerical model, the error in flow estimated by QTM (18.6%) was smaller than that in Kety's method (45.7%, 2.5-fold reduction). The in vivo kidney perfusion quantification by QTM (cortex: 443 ± 58 mL/100 g/min and medulla: 190 ± 90 mL/100 g/min) was in the range of that by Kety's method (482 ± 51 mL/100 g/min in the cortex and 242 ± 73 mL/100 g/min in the medulla), and QTM provided better flow homogeneity in the cortex region.

CONCLUSIONS

QTM flow velocity mapping is feasible from multi-delay ASL MRI data based on inverting the transport equation. In a numerical simulation, QTM with deconvolution in space and time provided more accurate perfusion quantification than Kety's method with deconvolution in time only.

Three-Dimensional Pseudo-Continuous Arterial Spin Labeling Parameters Distinguish Pediatric Medulloblastoma and Pilocytic Astrocytoma

Introduction: Arterial Spin Labeling (ASL), a perfusion assessment without using gadolinium-based contrast agents, is outstandingly advantageous for pediatric patients. The differentiation of medulloblastomas from pilocytic astrocytomas in children plays a significant role in determining treatment strategies and prognosis. This study aimed to assess the use of ASL parameters during the differentiation between pediatric medulloblastoma and pilocytic astrocytoma. Methods: The institutional review board of Children's Hospital 2 approved this prospective study. The brain magnetic resonance imaging (MRI) protocol, including axial three-dimensional (3D) pseudo-continuous ASL, was evaluated in 33 patients, who were divided into a medulloblastoma group (n = 25) and a pilocytic astrocytoma group (n = 8). The quantified region of interest (ROI) values for the tumors and the tumor to parenchyma ratios were collected and compared between the two groups. Receiver operating characteristic (ROC) curve analysis and the Youden index were utilized to identify the best cut-off, sensitivity, specificity, and area under the curve (AUC) values for significant ASL parameters. Results: The cerebral blood flow (CBF) and the ratio between the CBF of the tumor relative to that of the parenchyma (rCBF) values for medulloblastomas were significantly higher than those for pilocytic astrocytomas (p < 0.05). A cut-off value of 0.51 for rCBF was able to discriminate between medulloblastoma and pilocytic astrocytoma, generating a sensitivity of 88%, a specificity of 75%, and an AUC of 83.5%. Conclusion: The rCBF measurement, obtained during MRI with 3D pseudo-continuous ASL, plays a supplemental role in the differentiation of medulloblastoma from pilocytic astrocytoma.

Determining the impact of age and sex on the psychophysical and neurophysiological response to thermal pain across the adult lifespan

AIMS

Determine sex- and age-associated psychophysical and neurophysiological differences in the processing of pain across the adult lifespan.

DESIGN

Preliminary, exploratory, cross-sectional study.

METHODS

Using psychophysics (to measure intensity and unpleasantness) and functional magnetic resonance imaging blood oxygenation level dependent methods (to measure stimulus-evoked brain activation), we will examine sex- and age-associated differences in thermal pain processing and their underlying neurophysiology in a broad range of healthy adults (ages 30-89). We will acquire resting state functional connectivity data for secondary analyses exploring whether resting state connectivity predicts psychophysical and neurophysiological responses to thermal pain. To examine the effects of altered blood flow, we will acquire resting-state arterial spin labeling magnetic resonance imaging data to quantify resting cerebral blood flow. We will interpret findings in the context of a proposed neural model of pain, ageing, and sex. Study funding was received in June of 2014. Ethical approval was obtained from the Vanderbilt University IRB prior to study initiation.

CONCLUSION

Exploring the biological reasons for age- and sex-associated differences in pain processing will increase our understanding of pain in older adults. The paucity of neurobiological evidence to support best practice pain management in older adults places these individuals at risk for poor pain management.

IMPACT

Poorly treated pain in older adults is a critical public health problem associated with a poor quality of life and increased healthcare costs. Understanding how age and sex have an impact on central processing of pain across the lifespan is a critical step toward improving personalized pain medicine.

Emerging Utility of Applied Magnetic Resonance Imaging in the Management of Traumatic Brain Injury

Traumatic brain injury (TBI) is a widespread and expensive problem globally. The standard diagnostic workup for new TBI includes obtaining a noncontrast computed tomography image of the head, which provides quick information on operative pathologies. However, given the limited sensitivity of computed tomography for identifying subtle but meaningful changes in the brain, magnetic resonance imaging (MRI) has shown better utility for ongoing management and prognostication after TBI. In recent years, advanced applications of MRI have been further studied and are being implemented as clinical tools to help guide care. These include functional MRI, diffusion tensor imaging, MR perfusion, and MR spectroscopy. In this review, we discuss the scientific basis of each of the above techniques, the literature supporting their use in TBI, and how they may be clinically implemented to improve the care of TBI patients.

A preliminary study of cerebral blood flow, aging and dementia in people with Down syndrome

BACKGROUND

People with Down syndrome (DS) develop Alzheimer's disease (AD) at an earlier age of onset than those with sporadic AD. AD neuropathology is typically present in DS by 40 years of age with an onset of dementia approximately 10 years later. This early onset is due to the overexpression of amyloid precursor protein from the third copy of chromosome 21. Cerebrovascular neuropathology is thought to contribute in 40-60% of cases sporadic AD. However, the vascular contribution to dementia in people with DS has been relatively unexplored. We hypothesised that vascular perfusion is compromised in older adults with DS relative to younger individuals and is further exacerbated in those with dementia.

METHOD

Cerebral blood flow (CBF) was measured using pulsed arterial spin labelling in 35 cognitively characterised adults with DS (26-65 years). DS participants were also compared with 15 control subjects without DS or dementia (26-65 years). Linear regression evaluated the difference in CBF across groups and diagnosis along with assessing the association between CBF and cognitive measures within the DS cohort.

RESULTS

Cerebral blood flow was significantly lower among DS participants with probable AD compared with controls (P = 0.02) and DS participants with no dementia (P = 0.01). Within the DS cohort, CBF was significantly associated with the Severe Impairment Battery (SIB) measure and the Dementia Questionnaire for People with Learning Disabilities (DLD) rating (F_3,25  = 5.13; P = 0.007). Both the SIB (β = 0.74; t = 2.71; P = 0.01) and DLD (β = -0.96; t = -3.87; P < 0.001) indicated greater impairment as global CBF decreased. Age was significantly associated with CBF among participants with DS. There was a non-linear effect of age, whereby CBF declined more rapidly after 45 years of age.

CONCLUSIONS

This preliminary study of CBF in DS indicates that cerebrovascular pathology may be a significant contributor to dementia in DS. CBF was associated with diagnosis, cognition and age. Notably, CBF decreases at a greater rate after age 45 and may represent a significant prodromal event in AD progression.

Arterial spin labeling in the grading of brain gliomas: could it help?

Background

Gliomas are characterized by high morbidity and mortality with low cure and high recurrence rates, which depends to a great degree on the angiogenesis of the tumor. Assessment of such angiogenesis by perfusion techniques is of utmost importance for the preoperative grading of gliomas. The purpose of this study was to assess the role of arterial spin labeling (ASL) perfusion as a non-contrast MRI technique in the grading of brain gliomas, in correlation with the dynamic susceptibility contrast perfusion imaging (DSC-PI). The study was carried out on 35 patients admitted to the Neurosurgery Department with MRI features of gliomas and sent for further perfusion imaging. Non-contrast ASL followed by DSC-PI was done for all cases. The final diagnosis of the cases was established by histopathology.

Results

Fourteen patients (14/35) had low-grade gliomas while twenty-one (21/35) had high-grade gliomas. In low-grade gliomas, four cases out of 14 were falsely graded as high-grade tumors showing hyperperfusion on ASL, three of which showed DSC-PI hypoperfusion. In high-grade gliomas, two cases out of 21 were interpreted as an indeterminate grade by ASL showing isoperfusion, however showed hyperperfusion on DSC-PI. ROC curve analysis showed ASL-derived rCBF > 2.08 to have 80.95% sensitivity, 85.71% specificity, and overall accuracy of 82.86% compared to 100% sensitivity, specificity, and accuracy of DSC-PI-derived rCBV and rCBF of > 1.1 and > 0.9, respectively. A significant positive correlation was noted between ASL and DSC-PI with correlation coefficient reaching r = 0.80 between ASL-rCBF and DSC-rCBF (p < 0.01) and r = 0.68 between ASL and DSC-rCBV (p < 0.01).

Conclusions

ASL is a relatively recent non-contrast perfusion technique that obtains results which are in fair agreement with the more established DSC perfusion imaging making it an alternative method for preoperative assessment of perfusion of gliomas, especially for patients with contraindications to contrast agents.

Effect of Perindopril/Indapamide on Cerebral Blood Flow in Middle-Aged, Treatment-Naïve Patients with Hypertension

INTRODUCTION

The relationship between blood pressure (BP) and cerebral blood flow (CBF) is not fully understood. This study evaluated the impact of a perindopril arginine/indapamide (Pa/I) single-pill combination (SPC) on CBF in middle-aged patients.

METHODS

A total of 22 treatment-naïve patients with essential hypertension and at least one hypertension-mediated organ damage and 41 healthy controls were enrolled. At baseline, all participants underwent brain magnetic resonance imaging (MRI); patients with hypertension underwent an additional MRI at end of follow-up. Arterial spin labeling (ASL) was used to calculate CBF in the frontal lobe cortical plate. Patients with hypertension received once-daily Pa/I 5 mg/1.25 mg SPC, which could be increased to Pa/I 10 mg/2.5 mg at 2 weeks if necessary. Patients with hypertension underwent 24-h ambulatory BP monitoring (ABPM) at baseline and end of follow-up.

RESULTS

Mean baseline BP values were 146.2/93.1 and 119.1/76.1 mmHg in the hypertension and control groups, respectively. Patients with hypertension had significantly (p < 0.001) lower CBF in the cortical plate of both left (36.2 ± 8.3 vs. 45.3 ± 3.5 ml/100 g/min) and right (37.9 ± 7.9 vs. 45.8 ± 3.2 ml/100 g/min) frontal lobes compared to normotensive controls. At the end of follow-up, there was a statistically significant (p < 0.001) increase in CBF in the cortical plate of both left (from 36.2 ± 8.3 to 47.5 ± 9.8 ml/100 g/min) and right frontal lobes (from 37.9 ± 7.9 to 47.4 ± 10.1 ml/100 g/min) compared to baseline. No significant difference was found between end of follow-up CBF levels in frontal lobes of patients with hypertension and those of healthy controls at baseline. Office BP decreased by 24.2/15.5 mmHg and 24-h ABPM from 145.5/95.3 to 120.8/79.3 mmHg.

CONCLUSION

In middle-aged, treatment-naïve patients with hypertension, Pa/I SPC was associated with increased CBF in the cortical plate of the frontal lobes, which achieved levels of normotensive controls. The increase in CBF had no clear association with observed BP changes.

REGISTRATION NUMBER

ISRCTN67799751.

Neuroinflammation and Precision Medicine in Pediatric Neurocritical Care: Multi-Modal Monitoring of Immunometabolic Dysfunction

The understanding of molecular biology in neurocritical care (NCC) is expanding rapidly and recognizing the important contribution of neuroinflammation, specifically changes in immunometabolism, towards pathological disease processes encountered across all illnesses in the NCC. Additionally, the importance of individualized inflammatory responses has been emphasized, acknowledging that not all individuals have the same mechanisms contributing towards their presentation. By understanding cellular processes that drive disease, we can make better personalized therapy decisions to improve patient outcomes. While the understanding of these cellular processes is evolving, the ability to measure such cellular responses at bedside to make acute care decisions is lacking. In this overview, we review cellular mechanisms involved in pathological neuroinflammation with a focus on immunometabolic dysfunction and review non-invasive bedside tools that have the potential to measure indirect and direct markers of shifts in cellular metabolism related to neuroinflammation. These tools include near-infrared spectroscopy, transcranial doppler, elastography, electroencephalography, magnetic resonance imaging and spectroscopy, and cytokine analysis. Additionally, we review the importance of genetic testing in providing information about unique metabolic profiles to guide individualized interpretation of bedside data. Together in tandem, these modalities have the potential to provide real time information and guide more informed treatment decisions.

PET Imaging of Tumor Perfusion: A Potential Cancer Biomarker?

Perfusion, as measured by imaging, is considered a standard of care biomarker for the evaluation of many tumors. Measurements of tumor perfusion may be used in a number of ways, including improving the visual detection of lesions, differentiating malignant from benign findings, assessing aggressiveness of tumors, identifying ischemia and by extension hypoxia within tumors, and assessing treatment response. While most clinical perfusion imaging is currently performed with CT or MR, a number of methods for PET imaging of tumor perfusion have been described. The inert PET radiotracer 15O-water PET represents the recognized gold standard for absolute quantification of tissue perfusion in both normal tissue and a variety of pathological conditions including cancer. Other cancer PET perfusion imaging strategies include the use of radiotracers with high first-pass uptake, analogous to those used in cardiac perfusion PET. This strategy produces more visually pleasing high-contrast images that provide relative rather than absolute perfusion quantification. Lastly, multiple timepoint imaging of PET tracers such as 18F-FDG, are not specifically optimized for perfusion, but have advantages related to availability, convenience, and reimbursement. Multiple obstacles have thus far blocked the routine use of PET imaging for tumor perfusion, including tracer production and distribution, image processing, patient body coverage, clinical validation, regulatory approval and reimbursement, and finally feasible clinical workflows. Fortunately, these obstacles are being overcome, especially within larger imaging centers, opening the door for PET imaging of tumor perfusion to become standard clinical practice. In the foreseeable future, it is possible that whole-body PET perfusion imaging with 15O-water will be able to be performed in a single imaging session concurrent with standard PET imaging techniques such as 18F-FDG-PET. This approach could establish an efficient clinical workflow. The resultant ability to measure absolute tumor blood flow in combination with glycolysis will provide important complementary information to inform prognosis and clinical decisions.

Structural Alterations in Deep Brain Structures in Type 1 Diabetes

Even though well known in type 2 diabetes, the existence of brain changes in type 1 diabetes (T1D) and both their neuroanatomical and clinical features are less well characterized. To fill the void in the current understanding of this disease, we sought to determine the possible neural correlate in long-duration T1D at several levels, including macrostructural, microstructural cerebral damage, and blood flow alterations. In this cross-sectional study, we compared a cohort of 61 patients with T1D with an average disease duration of 21 years with 54 well-matched control subjects without diabetes in a multimodal MRI protocol providing macrostructural metrics (cortical thickness and structural volumes), microstructural measures (T1-weighted/T2-weighted [T1w/T2w] ratio as a marker of myelin content, inflammation, and edema), and cerebral blood flow. Patients with T1D had higher T1w/T2w ratios in the right parahippocampal gyrus, the executive part of both putamina, both thalami, and the cerebellum. These alterations were reflected in lower putaminal and thalamic volume bilaterally. No cerebral blood flow differences between groups were found in any of these structures, suggesting nonvascular etiologies of these changes. Our findings implicate a marked nonvascular disruption in T1D of several essential neural nodes engaged in both cognitive and motor processing.

Multi-band MR fingerprinting (MRF) ASL imaging using artificial-neural-network trained with high-fidelity experimental data

PURPOSE

We aim to leverage the power of deep-learning with high-fidelity training data to improve the reliability and processing speed of hemodynamic mapping with MR fingerprinting (MRF) arterial spin labeling (ASL).

METHODS

A total of 15 healthy subjects were studied on a 3T MRI. Each subject underwent 10 runs of a multi-band multi-slice MRF-ASL sequence for a total scan time of approximately 40 min. MRF-ASL images were averaged across runs to yield a set of high-fidelity data. Training of a fully connected artificial neural network (ANN) was then performed using these data. The results from ANN were compared to those of dictionary matching (DM), ANN trained with single-run experimental data and with simulation data. Initial clinical performance of the technique was also demonstrated in a Moyamoya patient.

RESULTS

The use of ANN reduced the processing time of MRF-ASL data to 3.6 s, compared to DM of 3 h 12 min. Parametric values obtained with ANN and DM were strongly correlated (R² between 0.84 and 0.96). Results obtained from high-fidelity ANN were substantially more reliable compared to those from DM or single-run ANN. Voxel-wise coefficient of variation (CoV) of high-fidelity ANN, DM, and single-run ANN was 0.15 ± 0.08, 0.41 ± 0.20, 0.30 ± 0.16, respectively, for cerebral blood flow and 0.11 ± 0.06, 0.20 ± 0.19, 0.15 ± 0.10, respectively, for bolus arrival time. In vivo data trained ANN also outperformed ANN trained with simulation data. The superior performance afforded by ANN allowed more conspicuous depiction of hemodynamic abnormalities in Moyamoya patient.

CONCLUSION

Deep-learning-based parametric reconstruction improves the reliability of MRF-ASL hemodynamic maps and reduces processing time.

Immediate effects of a single session of physical exercise on cognition and cerebral blood flow: A randomized controlled study of older adults

BACKGROUND

Regular physical activity is beneficial for cognitive performance in older age. A single bout of aerobic physical exercise can transiently improve cognitive performance. Researchers have advanced improvements in cerebral circulation as a mediator of long-term effects of aerobic physical exercise on cognition, but the immediate effects of exercise on cognition and cerebral perfusion are not well characterized and the effects in older adults are largely unknown.

METHODS

Forty-nine older adults were randomized to a 30-min aerobic exercise at moderate intensity or relaxation. Groups were matched on age and cardiovascular fitness (VO2 max). Average Grey Matter Blood Flow (GMBF), measured by a pulsed arterial-spin labeling (pASL) magnetic resonance imaging (MRI) acquisition, and working memory performance, measured by figurative n-back tasks with increasing loads were assessed before and 7 min after exercising/resting.

RESULTS

Accuracy on the n-back task increased from before to after exercising/resting regardless of the type of activity. GMBF decreased after exercise, relative to the control (resting) group. In the exercise group, higher n-back performance after exercise was associated with lower GMBF in the right hippocampus, left medial frontal cortex and right orbitofrontal cortex, and higher cardiovascular fitness was associated with lower GMBF.

CONCLUSION

The decrease of GMBF reported in younger adults shortly after exercise also occurs in older adults and relates to cardiovascular fitness, potentially supporting the link between cardiovascular fitness and cerebrovascular reactivity in older age.

Recent Advances in Computed Tomography and MR Imaging

Numerous advanced MR imaging and computed tomographic techniques have been developed and implemented in clinical practice over the past several years resulting in increased diagnostic accuracy and improved patient care. In this article, the authors highlight recent and emerging imaging techniques in functional and structural MR imaging, perfusion and vascular imaging, standardization of imaging practices, and selected applications of artificial intelligence in clinical practice.

Novel use of arterial spin labelling in the imaging of peripheral vascular malformations

We present a novel use of arterial spin labelling (ASL), a MRI perfusion technique, to assess a high-flow, peripheral vascular malformation (PVM), specifically a large arteriovenous malformation in the left forearm of a 20-year-old female. While there has been experience with ASL in the assessment of intracranial vascular malformations, there has been no known use of ASL in the evaluation of PVMs. We also discuss the potential benefits and limitations of ASL in the imaging of PVMs. The promising results from this case warrant further research on ASL in the investigation of PVMs.

Regional hyperperfusion in cognitively normal APOE ε4 allele carriers in mid-life: analysis of ASL pilot data from the PREVENT-Dementia cohort

BACKGROUND

Regional cerebral hypoperfusion is characteristic of Alzheimer's disease (AD). Previous studies report conflicting findings in cognitively normal individuals at high risk of AD. Understanding early preclinical perfusion alterations may improve understanding of AD pathogenesis and lead to new biomarkers and treatment targets.

METHODS

3T arterial spin labelling MRI scans from 162 participants in the PREVENT-Dementia cohort were analysed (cognitively normal participants aged 40-59, stratified by future dementia risk). Cerebral perfusion was compared vertex-wise according to APOE ε4 status and family history (FH). Correlations between individual perfusion, age and cognitive scores (COGNITO battery) were explored.

RESULTS

Regional hyperperfusion was found in APOE ε4+group (left cingulate and lateral frontal and parietal regions p<0.01, threshold-free cluster enhancement, TFCE) and in FH +group (left temporal and parietal regions p<0.01, TFCE). Perfusion did not correlate with cognitive test scores.

CONCLUSIONS

Regional cerebral hyperperfusion in individuals at increased risk of AD in mid-life may be a very early marker of functional brain change related to AD. Increased perfusion may reflect a functional 'compensation' mechanism, offsetting the effects of early neural damage or may itself be risk factor for accelerating spread of degenerative pathology.

A voxel-based analysis of cerebral blood flow abnormalities in obsessive-compulsive disorder using pseudo-continuous arterial spin labeling MRI

Objective

To identify abnormalities of regional cerebral blood flow (rCBF) in individuals with obsessive-compulsive disorder (OCD) by conducting a voxel-based analysis of pseudo-continuous arterial spin labeling (pCASL) perfusion images.

Materials and methods

This prospective study included 23 OCD patients (nine males, 14 females; age 21–62 years; mean ± SD 37.2 ± 10.7 years) diagnosed based on DSM-IV-TR criteria and 64 healthy controls (27 males, 37 females; age 20–64 years; mean ± SD 38.3 ± 12.8 years). Subjects were recruited from October 2011 to August 2017. Imaging was performed on a 3T scanner. Quantitative rCBF maps generated from pCASL images were co-registered and resliced with the three-dimensional T1-weighted images, and then spatially normalized to a brain template and smoothed. We used statistical nonparametric mapping to assess the differences in rCBF and gray matter volume between the OCD and control groups. The significance level was set at the p-value <0.05 with family-wise error rate correction for multiple comparisons.

Results

Compared to the control group, there were significant rCBF reductions in the right putamen, right frontal operculum, left midcingulate cortex, and right temporal pole in the OCD group. There were no significant between-group differences in the gray matter volume.

Conclusion

The pCASL imaging noninvasively detected physiologically disrupted areas without structural abnormalities in OCD patients. The rCBF reductions observed in these regions in OCD patients could be associated with the pathophysiology of OCD.

The cerebral blood flow deficits in Parkinson's disease with mild cognitive impairment using arterial spin labeling MRI

Parkinson's disease (PD) with mild cognitive impairment (PD-MCI) is currently diagnosed based on an arbitrarily predefined standard deviation of neuropsychological test scores, and more objective biomarkers for PD-MCI diagnosis are needed. The purpose of this study was to define possible brain perfusion-based biomarkers of not only mild cognitive impairment, but also risky gene carriers in PD using arterial spin labeling magnetic resonance imaging (ASL-MRI). Fifteen healthy controls (HC), 26 cognitively normal PD (PD-CN), and 27 PD-MCI subjects participated in this study. ASL-MRI data were acquired by signal targeting with alternating radio-frequency labeling with Look-Locker sequence at 3 T. Single nucleotide polymorphism genotyping for rs9468 [microtubule-associated protein tau (MAPT) H1/H1 versus H1/H2 haplotype] was performed using a Stratagene Mx3005p real-time polymerase chain-reaction system (Agilent Technologies, USA). There were 15 subjects with MAPT H1/H1 and 11 subjects with MAPT H1/H2 within PD-MCI, and 33 subjects with MAPT H1/H1 and 19 subjects with MAPT H1/H2 within all PD. Voxel-wise differences of cerebral blood flow (CBF) values between HC, PD-CN and PD-MCI were assessed by one-way analysis of variance followed by pairwise post hoc comparisons. Further, the subgroup of PD patients carrying the risky MAPT H1/H1 haplotype was compared with noncarriers (MAPT H1/H2 haplotype) in terms of CBF by a two-sample t test. A pattern that could be summarized as "posterior hypoperfusion" (PH) differentiated the PD-MCI group from the HC group with an accuracy of 92.6% (sensitivity = 93%, specificity = 93%). Additionally, the PD patients with MAPT H1/H1 haplotype had decreased perfusion than the ones with H1/H2 haplotype at the posterior areas of the visual network (VN), default mode network (DMN), and dorsal attention network (DAN). The PH-type pattern in ASL-MRI could be employed as a biomarker of both current cognitive impairment and future cognitive decline in PD.

Higher cardiovascular fitness level is associated with lower cerebrovascular reactivity and perfusion in healthy older adults

Aging is accompanied by vascular and structural changes in the brain, which include decreased grey matter volume (GMV), cerebral blood flow (CBF), and cerebrovascular reactivity (CVR). Enhanced fitness in aging has been related to preservation of GMV and CBF, and in some cases CVR, although there are contradictory relationships reported between CVR and fitness. To gain a better understanding of the complex interplay between fitness and GMV, CBF and CVR, the present study assessed these factors concurrently. Data from 50 participants, aged 55 to 72, were used to derive GMV, CBF, CVR and VO2peak. Results revealed that lower CVR was associated with higher VO2peak throughout large areas of the cerebral cortex. Within these regions lower fitness was associated with higher CBF and a faster hemodynamic response to hypercapnia. Overall, our results indicate that the relationships between age, fitness, cerebral health and cerebral hemodynamics are complex, likely involving changes in chemosensitivity and autoregulation in addition to changes in arterial stiffness. Future studies should collect other physiological outcomes in parallel with quantitative imaging, such as measures of chemosensitivity and autoregulation, to further understand the intricate effects of fitness on the aging brain, and how this may bias quantitative measures of cerebral health.

A comparison of arterial spin labelling with catheter angiography in evaluating arteriovenous malformations: a systematic review

OBJECTIVES

To compare the performance of arterial spin labelling (ASL) in evaluating arteriovenous malformations (AVMs) against the current gold standard of catheter angiography.

METHODS

We systematically reviewed the published literature using EMBASE and Medline. We included studies that compared ASL to catheter angiography in the assessment of AVMs in three outcome domains: detection, angioarchitectural and haemodynamic features.

RESULTS

From 314 unique citations, 19 studies representing 289 patients with intracranial AVMs met our inclusion criteria. We did not pool data due to marked heterogeneity in study outcome measures. Seven studies showed high diagnostic performance of ASL in identifying arterial feeders, with sensitivity ranging from 84.6 to 100% and specificity ranging from 93.3 to 100%. Six studies showed strong ability in detecting arteriovenous shunting, with sensitivity ranging from 91.7 to 100% and specificity ranging from 90 to 100%. Seven studies demonstrated that ASL could identify nidal location and size as well as catheter angiography, while five studies showed relatively poorer performance in delineating venous drainage. Two studies showed 100% sensitivity of ASL in the identification of residual or obliterated AVMs following stereotactic radiosurgery.

CONCLUSIONS

Despite limitations in the current evidence base and technical challenges, this review suggests that ASL has a promising role in the work-up and post-treatment follow-up of AVMs. Larger scale prospective studies assessing the diagnostic performance of ASL are warranted.

ADVANCES IN KNOWLEDGE

ASL demonstrates overall validity in the evaluation of intracranial AVMs.

Use of Multiplied, Added, Subtracted and/or FiTted Inversion Recovery (MASTIR) pulse sequences

The group of Multiplied, Added, Subtracted and/or fiTted Inversion Recovery (MASTIR) pulse sequences in which usually two or more inversion recovery (IR) images of different types are combined is described, and uses for this type of sequence are outlined. IR sequences of different types can be multiplied, added, subtracted, and/or fitted together to produce variants of the MASTIR sequence. The sequences provide a range of options for increasing image contrast, demonstrating specific tissues and fluids of interest, and suppressing unwanted signals. A formalism using the concept of pulse sequences as tissue property filters is used to explain the signal, contrast and weighting of the pulse sequences with both univariate and multivariate filter models. Subtraction of one magnitude reconstructed IR image from another with a shorter TI can produce very high T₁ dependent positive contrast from small increases in T₁. The reverse subtracted IR sequence can provide high positive contrast enhancement with gadolinium chelates and iron deposition which decrease T₁. Additional contrast to that arising from increases in T₁ can be produced by supplementing this with contrast arising from concurrent increases in ρ_m and T₂, as well as increases or decreases in diffusion using subtraction IR with echo subtraction and/or diffusion subtraction. Phase images may show 180º differences as a result of rotating into the transverse plane both positive and negative longitudinal magnetization. Phase images with contrast arising in this way, or other ways, can be multiplied by magnitude IR images to increase the contrast of the latter. Magnetization Transfer (MT) and susceptibility can be used with IR sequences to improve contrast. Selective images of white and brown adipose tissue lipid and water components can be produced using different TIs and in and out-of-phase TEs. Selective images of ultrashort and short T₂ tissue components can be produced by nulling long T₂ tissue components with an inversion pulse and subtraction of images with longer TEs from images with ultrashort TEs. The Double Echo Sliding IR (DESIRE) sequence provides images with a wide range of TIs from which it is possible to choose values of TI to achieve particular types of tissue and/or fluid contrast (e.g., for subtraction with different TIs, as described above, and for long T₂ tissue signal nulling with UTE sequences). Unwanted tissue and fluid signals can be suppressed by addition and subtraction of phase-sensitive (ps) and magnitude reconstructed images. The sequence also offers options for synergistic use of the changes in blood and tissue ρ_m, T₁, T₂/T₂*, D* and perfusion that can be seen with fMRI of the brain. In-vivo and ex-vivo illustrative examples of normal brain, cartilage, multiple sclerosis, Alzheimer's disease, and peripheral nerve imaged with different forms of the MASTIR sequence are included.

Imaging biomarkers in neurodegeneration: current and future practices

There is an increasing role for biological markers (biomarkers) in the understanding and diagnosis of neurodegenerative disorders. The application of imaging biomarkers specifically for the in vivo investigation of neurodegenerative disorders has increased substantially over the past decades and continues to provide further benefits both to the diagnosis and understanding of these diseases. This review forms part of a series of articles which stem from the University College London/University of Gothenburg course "Biomarkers in neurodegenerative diseases". In this review, we focus on neuroimaging, specifically positron emission tomography (PET) and magnetic resonance imaging (MRI), giving an overview of the current established practices clinically and in research as well as new techniques being developed. We will also discuss the use of machine learning (ML) techniques within these fields to provide additional insights to early diagnosis and multimodal analysis.

Trapped in a Glass Bell Jar: Neural Correlates of Depersonalization and Derealization in Subjects at Clinical High-Risk of Psychosis and Depersonalization-Derealization Disorder

BACKGROUND

Depersonalization (DP) and derealization (DR) are symptoms of a disruption of perceptual integration leading to an altered quality of subjective experiences such as feelings of unreality and detachment from the self (DP) or the surroundings (DR). Both DP and DR often occur in concert with other symptoms, for example in subjects at clinical high-risk (CHR) for psychosis, but also appear isolated in the form of DP/DR disorder. Despite evidence that DP/DR causes immense distress, little is known about their neurobiological underpinnings. Therefore, we investigated the neural correlates of DP/DR using pseudo-continuous arterial spin labeling MRI.

METHODS

We evaluated the frequency of DP/DR symptoms in a clinical sample (N = 217) of help-seeking individuals from the Early Detection and Intervention Centre for Mental Crisis (CHR, n = 97; clinical controls (CC), n = 91; and first-episode psychosis (FEP), n = 29). Further, in a subsample of those CHR subjects who underwent MRI, we investigated the resting-state regional cerebral blood flow (rCBF). Here, individuals with (n = 21) and without (n = 23) DP/DR were contrasted. Finally, rCBF was measured in a small independent second sample of patients with DP/DR disorder (n = 6) and healthy controls (HC, n = 6).

RESULTS

In the complete clinical sample, significantly higher frequency of DP/DR was found in CHR compared to CC (50.5 vs. 16.5%; χ² ₍₂₎ = 24.218, p ≤ 0.001, Cramer's V = 0.359) as well as in FEP compared to CC (37.9 vs. 16.5%; χ² ₍₂₎ = 5.960, p = 0.015, Cramer's V = 0.223). In MRI, significantly lower rCBF was detected in the left orbitofrontal cortex in CHR with vs. without DP/DR (x/y/z = -16/42/-22, p < 0.05, FWE corrected). In patients with DP/DR disorder, significantly higher rCBF was detected in the left caudate nucleus (x/y/z = -18/-32/18, p < 0.05) compared to HC.

CONCLUSIONS

This study shows that DP/DR symptoms are frequently found in CHR subjects. Investigating two separate DP/DR populations with an identical neuroimaging technique, our study also indicates that there may be divergent pathophysiological mechanisms-decreased neuronal activity in the orbitofrontal cortex, but increased activity within the caudate nucleus-leading to a final common pathway with similar psychopathological symptoms. This suggests that both top-down (orbitofrontal cortex) and bottom-up (caudate nucleus) mechanisms could contribute to the emergence of DP/DR.

Brain-Blood Partition Coefficient and Cerebral Blood Flow in Canines Using Calibrated Short TR Recovery (CaSTRR) Correction Method

The brain–blood partition coefficient (BBPC) is necessary for quantifying cerebral blood flow (CBF) when using tracer based techniques like arterial spin labeling (ASL). A recent improvement to traditional MRI measurements of BBPC, called calibrated short TR recovery (CaSTRR), has demonstrated a significant reduction in acquisition time for BBPC maps in mice. In this study CaSTRR is applied to a cohort of healthy canines (n = 17, age = 5.0 – 8.0 years) using a protocol suited for application in humans at 3T. The imaging protocol included CaSTRR for BBPC maps, pseudo-continuous ASL for CBF maps, and high resolution anatomical images. The standard CaSTRR method of normalizing BBPC to gadolinium-doped deuterium oxide phantoms was also compared to normalization using hematocrit (Hct) as a proxy value for blood water content. The results show that CaSTRR is able to produce high quality BBPC maps with a 4 min acquisition time. The BBPC maps demonstrate significantly higher BBPC in gray matter (0.83 ± 0.05 mL/g) than in white matter (0.78 ± 0.04 mL/g, p = 0.006). Maps of CBF acquired with pCASL demonstrate a negative correlation between gray matter perfusion and age (p = 0.003). Voxel-wise correction for BBPC is also shown to improve contrast to noise ratio between gray and white matter in CBF maps. A novel aspect of the study was to show that that BBPC measurements can be calculated based on the known Hct of the blood sample placed in scanner. We found a strong correlation (R² = 0.81 in gray matter, R² = 0.59 in white matter) established between BBPC maps normalized to the doped phantoms and BBPC maps normalized using Hct. This obviates the need for doped water phantoms which simplifies both the acquisition protocol and the post-processing methods. Together this suggests that CaSTRR represents a feasible, rapid method to account for BBPC variability when quantifying CBF. As canines have been used widely for aging and Alzheimer’s disease studies, the CaSTRR method established in the animals may further improve CBF measurements and advance our understanding of cerebrovascular changes in aging and neurodegeneration.

Role of 3D Pseudocontinuous Arterial Spin-Labeling Perfusion in the Diagnosis and Follow-Up in Patients with Herpes Simplex Encephalitis

BACKGROUND AND PURPOSE

Early diagnosis and treatment of herpes simplex encephalitis are crucial to reduce morbidity and mortality. Our aim was to investigate the role of 3D pseudocontinuous arterial spin-labeling in herpes simplex encephalitis.

MATERIALS AND METHODS

From 2014 to 2019, seventeen consecutive patients with herpes simplex encephalitis and 15 healthy volunteers were recruited in the study. Conventional MR imaging and 3D pseudocontinuous arterial spin-labeling were performed in all subjects. According to the disease duration, the lesions were classified into 3 groups, including acute, subacute, and chronic stages, respectively. Clinical, neuroradiologic, and follow-up features were studied. The normalized lesion/normal tissue CBF values of lesions at different stages were measured and compared with those in the control group, respectively.

RESULTS

Compared with the control group, herpes simplex encephalitis demonstrated hyperperfusion in 11 acute cases and 6 subacute cases and hypoperfusion in 6 chronic cases. The mean normalized lesion/normal tissue CBF values of the lesions were 2.68 ± 0.54 in the acute stage, 2.42 ± 0.52 in the subacute stage, and 0.87 ± 0.30 in the chronic stage, respectively. The mean normalized lesion/normal tissue CBF values of acute and subacute lesions were significantly higher than those of the control group (1.33 ± 0.08; P < .001, respectively), while the mean normalized lesion/normal tissue CBF values of chronic lesions were lower than those of the control group (P < .05). Gradual perfusion reduction on serial 3D pseudocontinuous arterial spin-labeling was observed in herpes simplex encephalitis after effective therapy.

CONCLUSIONS

Conventional MR imaging remains most helpful in the diagnosis of herpes simplex encephalitis, while 3D pseudocontinuous arterial spin-labeling could be an adjunctive technique by providing dynamic CBF features at different stages in herpes simplex encephalitis.

Evaluation of Tumor Blood Flow Using Alternate Ascending/Descending Directional Navigation in Primary Brain Tumors: A Comparison Study with Dynamic Susceptibility Contrast Magnetic Resonance Imaging

Objective

Alternate ascending/descending directional navigation (ALADDIN) is a novel arterial spin labeling technique that does not require a separate spin preparation pulse. We sought to compare the normalized cerebral blood flow (nCBF) values obtained by ALADDIN and dynamic susceptibility contrast (DSC) perfusion magnetic resonance imaging (MRI) in patients with primary brain tumors.

Materials and Methods

Sixteen patients with primary brain tumors underwent MRI scans including contrast-enhanced T1-weighted imaging, DSC perfusion MRI, and ALADDIN. The nCBF values of normal gray matter (GM) and tumor areas were measured by both DSC perfusion MRI and ALADDIN, which were compared by the Wilcoxon signed rank test. Subgroup analyses according to pathology were performed with the Wilcoxon signed rank test.

Results

Higher mean nCBF values of GM regions in the bilateral frontal lobe, temporal lobe, and caudate were detected by ALADDIN than by DSC perfusion MRI (p <0.05). In terms of the mean or median nCBF values and the mean of the top 10% nCBF values from tumors, DSC perfusion MRI and ALADDIN did not statistically significantly differ either overall or in each tumor group.

Conclusion

ALADDIN tended to detect higher nCBF values in normal GM, as well as higher perfusion portions of primary brain tumors, than did DSC perfusion MRI. We believe that the high perfusion signal on ALADDIN can be beneficial in lesion detection and characterization.

Modeling Physiological Flow Variation in Fontan Models with 4d Flow Mri, Particle Image Velocimetry, and Arterial Spin Labeling

The Fontan procedure is a successful palliation for single ventricle defect. Yet, a number of complications still occur in Fontan patients due to abnormal blood flow dynamics, necessitating improved flow analysis and treatment methods. Phase-contrast magnetic resonance imaging (MRI) has emerged as a suitable method for such flow analysis. However, limitations on altering physiological blood flow conditions in the patient while in the MRI bore inhibit experimental investigation of a variety of factors that contribute to impaired cardiovascular health in these patients. Furthermore, resolution and flow regime limitations in phase contrast MRI pose a challenge for accurate and consistent flow characterization. In this study, patient-specific physical models were created based on nine Fontan geometries and MRI experiments mimicking low and high flow conditions, as well as steady and pulsatile flow, were conducted. Additionally, an optically transparent Fontan model was created for flow analyses using a particle image velocimetry (PIV) system, arterial spin labeling (ASL), and four-dimensional (4D) flow MRI. Differences, though non-statistically significant, were observed between flow conditions and between patient-specific models. Large between-model variation supported the need for further improvement for patient-specific modeling on each unique Fontan anatomical configuration. Furthermore, high resolution PIV and flow tracking ASL data provided flow information that was not obtainable with 4D flow MRI alone.

Advanced magnetic resonance imaging of cortical laminar necrosis in patients with stroke

PURPOSE

The aim of this study was to assess the novel advanced magnetic resonance imaging findings of acute stage cortical laminar necrosis developing after complicated cardiovascular or abdominal surgery.

MATERIALS AND METHODS

This institutional review board-approved study included patients with postoperative stroke due to cortical laminar necrosis imaged with magnetic resonance in the acute stage. Brain magnetic resonance imaging examinations were obtained on a 3T magnetic resonance scanner within 48 hours of the neurological symptoms, including diffusion-weighted images (b value, 1000 s/mm²) and arterial spin labelling using a pseudo-continuous arterial spin labelling method in four patients. Conventional and advanced magnetic resonance images were analysed to assess the imaging features in acute stage cortical laminar necrosis.

RESULTS

The final population consisted of 14 patients (seven men and seven women, mean age 61 years, range 32-79 years) diagnosed with stroke and acute phase cortical laminar necrosis. All the patients presented with cortical lesions showing restricted diffusion on diffusion-weighted images and hypointensity on the apparent diffusion coefficient map. Cortical hyperintensity on T2-weighted or fluid-attenuated inversion recovery images was found in three (21%) and six (43%) patients, respectively. Reduced perfusion was noted in three out of four patients imaged with arterial spin labelling, while in one case no corresponding perfusion abnormality was noted on the arterial spin labelling maps. Arterial spin labelling abnormalities were much more extensive than diffusion restriction in two patients, and they were associated with a poor outcome.

CONCLUSION

Cortical hyperintense abnormalities on diffusion-weighted imaging may be the only sign of developing cortical laminar necrosis injury. The acquisition of arterial spin labelling helps to identify perfusion alterations and the extension of the ischaemic injury.

Assessment of Glioblastoma Response in the Era of Bevacizumab: Longstanding and Emergent Challenges in the Imaging Evaluation of Pseudoresponse

Glioblastoma is the deadliest primary malignant brain neoplasm, and despite the availability of many treatment options, its prognosis remains somber. Enhancement detected by magnetic resonance imaging (MRI) was considered the best imaging marker of tumor activity in glioblastoma for decades. However, its role as a surrogate marker of tumor viability has changed with the appearance of new treatment regimens and imaging modalities. The antiangiogenic therapy created an inflection point in the imaging assessment of glioblastoma response in clinical trials and clinical practice. Although BEV led to the improvement of enhancement, it did not necessarily mean tumor response. The decrease in the enhancement intensity represents a change in the permeability properties of the blood brain barrier, and presumably, the switch of the tumor growth pattern to an infiltrative non-enhancing phenotype. New imaging techniques for the assessment of cellularity, blood flow hemodynamics, and biochemistry have emerged to overcome this hurdle; nevertheless, designing tools to assess tumor response more accurately, and in so doing, improve the assessment of response to standard of care (SOC) therapies and to novel therapies, remains challenging.