What is the correct value for the brain--blood partition coefficient for water?

Retrospective correction of second-order concomitant fields in 3D axial stack-of-spirals imaging on a high-performance gradient system

PURPOSE

MRI using 3D stack-of-spirals (SoS) readout on a high-performance gradient system is subject to strong second-order, spatially varying concomitant fields, which can lead to signal dropout and blurring artifacts that become more significant at locations farther from the gradient isocenter. A method for compensating for second-order concomitant fields in 3D axial SoS image reconstruction is described.

METHODS

We retrospectively correct for second-order concomitant field-induced phase error in the 3D SoS data by slice-dependent k-space phase compensation based on the nominal spiral readout trajectories. The effectiveness of the method was demonstrated in phantom and healthy volunteer scans in which 3D pseudo-continuous arterial spin labeling imaging was performed with SoS fast spin-echo readout at 3 T.

RESULTS

Substantial reduction in blurring was observed with the proposed method. In phantom scans, blurring was reduced by about 53% at 98 mm from the gradient isocenter. In the in vivo 3D pseudo-continuous arterial spin labeling scans, differences of up to 10% were observed at 78 mm from the isocenter, especially around the white-matter and gray-matter interfaces, between the corrected and uncorrected proton density images, perfusion-weighted images, and cerebral blood flow maps.

CONCLUSIONS

The described retrospective correction method provides a means to correct erroneous phase accruals due to second-order concomitant fields in 3D axial stack-of-spirals imaging.

Optimization of Fair Arterial Spin Labeling Magnetic Resonance Imaging (ASL-MRI) for Renal Perfusion Quantification in Dogs: Pilot Study

Arterial spin labeling (ASL) MRI allows non-invasive quantification of renal blood flow (RBF) and shows great potential for renal assessment. To our knowledge, renal ASL-MRI has not previously been performed in dogs. The aim of this pilot study was to determine parameters essential for ALS-MRI-based quantification of RBF in dogs: T1, blood (longitudinal relaxation time), λ (blood tissue partition coefficient) and TI (inversion time). A Beagle was scanned at 3T with a multi-TI ASL sequence, with TIs ranging from 250 to 2500 ms, to determine the optimal TI value. The T1 of blood for dogs was determined by scanning a blood sample with a 2D IR TSE sequence. The water content of the dog's kidney was determined by analyzing kidney samples from four dogs with a moisture analyzer and was subsequently used to calculate λ. The optimal TI and the measured values for T1,blood, and λ were 2000 ms, 1463 ms and 0.91 mL/g, respectively. These optimized parameters for dogs resulted in lower RBF values than those obtained from inline generated RBF maps. In conclusion, this study determined preliminary parameters essential for ALS-MRI-based RBF quantification in dogs. Further research is needed to confirm these values, but it may help guide future research.

Enhanced parameter estimation in multiparametric arterial spin labeling using artificial neural networks

PURPOSE

Multiparametric arterial spin labeling (MP-ASL) can quantify cerebral blood flow (CBF) and arterial cerebral blood volume (CBVa). However, its accuracy is compromised owing to its intrinsically low SNR, necessitating complex and time-consuming parameter estimation. Deep neural networks (DNNs) offer a solution to these limitations. Therefore, we aimed to develop simulation-based DNNs for MP-ASL and compared the performance of a supervised DNN (DNNSup), physics-informed unsupervised DNN (DNNUns), and the conventional lookup table method (LUT) using simulation and in vivo data.

METHODS

MP-ASL was performed twice during resting state and once during the breath-holding task. First, the accuracy and noise immunity were evaluated in the first resting state. Second, CBF and CBVa values were statistically compared between the first resting state and the breath-holding task using the Wilcoxon signed-rank test and Cliff's delta. Finally, reproducibility of the two resting states was assessed.

RESULTS

Simulation and first resting-state analyses demonstrated that DNNSup had higher accuracy, noise immunity, and a six-fold faster computation time than LUT. Furthermore, all methods detected task-induced CBF and CBVa elevations, with the effect size being larger with the DNNSup (CBF, p = 0.055, Δ = 0.286; CBVa, p = 0.008, Δ = 0.964) and DNNUns (CBF, p = 0.039, Δ = 0.286; CBVa, p = 0.008, Δ = 1.000) than that with LUT (CBF, p = 0.109, Δ = 0.214; CBVa, p = 0.008, Δ = 0.929). Moreover, all the methods exhibited comparable and satisfactory reproducibility.

CONCLUSION

DNNSup outperforms DNNUns and LUT with respect to estimation performance and computation time.

Improved MRI methods to quantify retinal and choroidal blood flow applied to a model of glaucoma

Purpose

Blood flow (BF) of the retinal and choroidal vasculatures can be quantitatively imaged using MRI. This study sought to improve methods of data acquisition and analysis for MRI of layer-specific retinal and choroidal BF and then applied this approach to detect reduced ocular BF in a well-established mouse model of glaucoma from both eyes.

Methods

Quantitative BF magnetic resonance imaging (MRI) was performed on glaucomatous DBA/2J and normal C57BL/6J mice. Arterial spin labeling MRI was applied to image retinal and choroidal BF using custom-made dual eye coils that could image both eyes during the same scan. Statistics using data from a single eye or two eyes were compared. BF values were calculated using two approaches. The BF rate per quantity of tissue was calculated as commonly done, and the peak BF values of the retinal and choroidal vasculatures were taken. Additionally, the BF rate per retinal surface area was calculated using a new analysis approach to attempt to reduce partial volume and variability by integrating BF over the retinal and choroidal depths.

Results

Ocular BF of both eyes could be imaged using the dual coil setup without effecting scan time. Intraocular pressure was significantly elevated in DBA/2J mice compared to C57BL/6J mice (P<0.01). Both retinal and choroidal BF were significantly decreased in DBA/2J mice in comparison to the age-matched normal C57BL/6J mice across all measurements (P < 0.01). From simulations, the values from the integrated BF analysis method had less partial volume effect, and from in vivo scans, this analysis approach also improved power.

Conclusion

The dual eye coil setup allows bilateral eye data acquisition, increasing the amount of data acquired without increasing acquisition times in vivo. The reduced ocular BF found using the improved acquisition and analysis approaches replicated the results of previous studies on DBA/2J mice. The ocular hypertensive stress-induced BF reduction found within these mice may represent changes associated with glaucomatous progression.

Patient-specific temperature distribution prediction in laser interstitial thermal therapy: single-irradiation data-driven method

Laser interstitial thermal therapy (LITT) is popular for treating brain tumours and epilepsy. The strict control of tissue thermal damage extent is crucial for LITT. Temperature prediction is useful for predicting thermal damage extent. Accurately predictingin vivobrain tissue temperature is challenging due to the temperature dependence and the individual variations in tissue properties. Considering these factors is essential for improving the temperature prediction accuracy.Objective. To present a method for predicting patient-specific tissue temperature distribution within a target lesion area in the brain during LITT.Approach. A magnetic resonance temperature imaging (MRTI) data-driven estimation model was constructed and combined with a modified Pennes bioheat transfer equation (PBHE) to predict patient-specific temperature distribution. In the PBHE for temperature prediction, the individual specificity and temperature dependence of thermal tissue properties and blood perfusion, as well as the individual specificity of optical tissue properties were considered. Only MRTI data during one laser irradiation were required in the method. This enables the prediction of patient-specific temperature distribution and the resulting thermal damage region for subsequent ablations.Main results. Patient-specific temperature prediction was evaluated based on clinical data acquired during LITT in the brain, using intraoperative MRTI data as the reference standard. Our method significantly improved the prediction performance of temperature distribution and thermal damage region. The average root mean square error was decreased by 69.54%, the average intraclass correlation coefficient was increased by 37.5%, the average Dice similarity coefficient was increased by 43.14% for thermal damage region prediction.Significance. The proposed method can predict temperature distribution and thermal damage region at an individual patient level during LITT, providing a promising approach to assist in patient-specific treatment planning for LITT in the brain.

Loss of spontaneous vasomotion precedes impaired cerebrovascular reactivity and microbleeds in a mouse model of cerebral amyloid angiopathy

Background

Cerebral amyloid angiopathy (CAA) is a cerebral small vessel disease in which amyloid-β accumulates in vessel walls. CAA is a leading cause of symptomatic lobar intracerebral hemorrhage and an important contributor to age-related cognitive decline. Recent work has suggested that vascular dysfunction may precede symptomatic stages of CAA, and that spontaneous slow oscillations in arteriolar diameter (termed vasomotion), important for amyloid-β clearance, may be impaired in CAA.

Methods

To systematically study the progression of vascular dysfunction in CAA, we used the APP23 mouse model of amyloidosis, which is known to develop spontaneous cerebral microbleeds mimicking human CAA. Using in vivo 2-photon microscopy, we longitudinally imaged unanesthetized APP23 transgenic mice and wildtype littermates from 7 to 14 months of age, tracking amyloid-β accumulation and vasomotion in individual pial arterioles over time. MRI was used in separate groups of 12-, 18-, and 24-month-old APP23 transgenic mice and wildtype littermates to detect microbleeds and to assess cerebral blood flow and cerebrovascular reactivity with pseudo-continuous arterial spin labeling.

Results

We observed a significant decline in vasomotion with age in APP23 mice, while vasomotion remained unchanged in wildtype mice with age. This decline corresponded in timing to initial vascular amyloid-β deposition (∼8-10 months of age), although was more strongly correlated with age than with vascular amyloid-β burden in individual arterioles. Declines in vasomotion preceded the development of MRI-visible microbleeds and the loss of smooth muscle actin in arterioles, both of which were observed in APP23 mice by 18 months of age. Additionally, evoked cerebrovascular reactivity was intact in APP23 mice at 12 months of age, but significantly lower in APP23 mice by 24 months of age.

Conclusions

Our findings suggest that a decline in spontaneous vasomotion is an early, potentially pre-symptomatic, manifestation of CAA and vascular dysfunction, and a possible future treatment target.

Spatiotemporal cerebral blood flow dynamics underlies emergence of the limbic-sensorimotor-association cortical gradient in human infancy

Infant cerebral blood flow (CBF) delivers nutrients and oxygen to fulfill brain energy consumption requirements for the fastest period of postnatal brain development across lifespan. However, organizing principle of whole-brain CBF dynamics during infancy remains obscure. Leveraging a unique cohort of 100+ infants with high-resolution arterial spin labeled MRI, we found the emergence of the cortical hierarchy revealed by highest-resolution infant CBF maps available to date. Infant CBF across cortical regions increased in a biphasic pattern with initial rapid and sequentially slower rate, with break-point ages increasing along the limbic-sensorimotor-association cortical gradient. Increases in CBF in sensorimotor cortices were associated with enhanced language and motor skills, and frontoparietal association cortices for cognitive skills. The study discovered emergence of the hierarchical limbic-sensorimotor-association cortical gradient in infancy, and offers standardized reference of infant brain CBF and insight into the physiological basis of cortical specialization and real-world infant developmental functioning.

Occipital transcranial direct current stimulation in episodic migraine patients: effect on cerebral perfusion

Cerebral blood flow differs between migraine patients and healthy controls during attack and the interictal period. This study compares the brain perfusion of episodic migraine patients and healthy controls and investigates the influence of anodal transcranial direct current stimulation (tDCS) over the occipital cortex. We included healthy adult controls and episodic migraineurs. After a 28-day baseline period and the baseline visit, migraine patients received daily active or sham anodal tDCS over the occipital lobe for 28 days. All participants underwent a MRI scan at baseline; migraineurs were also scanned shortly after the stimulation period and about five months later. At baseline, brain perfusion of migraine patients and controls differed in several areas; among the stimulated areas, perfusion was increased in the cuneus of healthy controls. At the first visit, the active tDCS group had an increased blood flow in regions processing visual stimuli and a decreased perfusion in other areas. Perfusion did not differ at the second follow-up visit. The lower perfusion level in migraineurs in the cuneus indicates a lower preactivation level. Anodal tDCS over the occipital cortex increases perfusion of several areas shortly after the stimulation period, but not 5 months later. An increase in the cortical preactivation level could mediate the transient reduction of the migraine frequency.Trial registration: NCT03237754 (registered at clincicaltrials.gov; full date of first trial registration: 03/08/2017).

Role of Arterial Spin Labeling (ASL) Images in Parkinson's Disease (PD): A Systematic Review

RATIONALE AND OBJECTIVES

Parkinson's disease is a chronic progressive neurodegenerative disorder with standard structural MRIs often showing no gross abnormalities. Quantitative perfusion MRI modality Arterial Spin Labeling (ASL) is helpful in identifying PD specific perfusion patterns. Absolute Cerebral blood flow (CBF) measurement using ASL provides insights into regional perfusion abnormalities. We reviewed the role of ASL to identify specific brain regions responsible for motor, non-motor symptoms and neurovascular changes observed in PD. Challenges in assessing the blood perfusion level are discussed with future development for improving the evaluation of ASL perfusion maps.

MATERIALS AND METHODS

We included CBF quantification studies using ASL for PD diagnosis. A systematic search was performed in Pubmed, Scopus and Web of Science. The perfusion parameters CBF and arterial arrival time (AAT) measured using ASL were considered for brain region assessment. Clinical aspects of PD have been analyzed using ASL perfusion maps.

RESULTS

The systematic search identified 153 unique records. Thirty articles were selected after verification of inclusion and exclusion criteria. Voxel and region-based analyses in white and gray matter tissues have been performed to identify PD-specific perfusion patterns by reported articles. Predominant brain regions such as basal ganglia sub-regions, frontoparietal network, precuneus, occipital lobe, sensory motor area regions, visual network, which are associated with motor and non-motor symptoms in PD, were identified with CBF hypoperfusion, indicating neuronal loss and cerebrovascular dysfunction.

CONCLUSION

CBF and AAT values derived from ASL can potentially be used as biomarkers to discriminate PD from similar brain-related disorders.

Non-contrast estimate of blood-brain barrier permeability in humans using arterial spin labeling and magnetization transfer at 7 T

Blood-brain barrier (BBB) dysfunction is associated with a number of central nervous system diseases. This study demonstrates the application of a novel noninvasive technique to measure the BBB permeability in the human brain at 7 T. The technique exploits the fact that, when tissue macromolecules are saturated by off-resonance RF pulse, the intravascular and the extravascular (tissue) water experience different magnetization transfer effects. This principle was combined with arterial spin labeling to distinguish between the intravascular and the tissue water, and was used to calculate perfusion, water extraction fraction (E), and BBB permeability surface area product for water (PS). Simultaneous coregistered magnetization transfer ratio maps were also generated that can provide valuable additional information. Eighteen healthy volunteers (seven females), age = 27 ± 11 years and weight = 65 ± 9 kg, participated in the study. Average perfusion was 67 ± 5 and 29 ± 4 ml/100 g/min (p < 0.05); and E was 0.921 ± 0.025 and 0.962 ± 0.015 (p < 0.05) in the gray matter (GM) and the white matter (WM), respectively. PS was higher in the GM (171 ± 20 ml/100 g/min) compared with the WM (95 ± 18 ml/100 g/min) (p < 0.05). The parameters exhibited good reliability with test re-test experiments. The sensitivity of this technique was demonstrated by 200 mg caffeine intake, which resulted in a decrease in the resting PS by ~31%.

Multidelay pseudocontinuous arterial spin labeling to measure blood flow in the head and neck

Perfusion MRI is promising for the assessment, prediction, and monitoring of radiation toxicity in organs at risk in head and neck cancer. Arterial spin labeling (ASL) may be an attractive alternative for conventional perfusion MRI, that does not require the administration of contrast agents. However, currently, little is known about the characteristics and performance of ASL in healthy tissues in the head and neck region. Therefore, the purpose of this study was to optimize and evaluate multidelay pseudocontinuous ASL (pCASL) for the head and neck region and to explore nominal values and measurement repeatability for the blood flow (BF), and the transit time and T1 values needed for BF quantification in healthy tissues. Twenty healthy volunteers underwent a scan session consisting of four repeats of multidelay pCASL (postlabel delays: 1000, 1632, 2479 ms). Regions of interest were defined in the parotid glands, submandibular glands, tonsils, and the cerebellum (as a reference). Nominal values of BF were calculated as the average over four repeats per volunteer. The repeatability coefficient and within-subject coefficient of repeatability (wCV) of BF were calculated. The effect of T1 (map vs. cohort average) and transit time correction on BF was investigated. The mean BF (± SE) was 55.7 ± 3.1 ml/100 g/min for the parotid glands, 41.2 ± 2.8 ml/100 g/min for the submandibular glands, and 32.3 ± 2.2 ml/100 g/min for the tonsils. The best repeatability was found in the parotid glands (wCV = 13.3%-16.1%), followed by the submandibular glands and tonsils (wCV = 20.0%-24.6%). On average, the effect of T1 and transit time correction on BF was limited, although substantial bias occurred in individual acquisitions. In conclusion, we demonstrated the feasibility of BF measurements in the head and neck region using multidelay pCASL and reported on nominal BF values, BF repeatability, the effect of T1, and transit time in various tissues in the head and neck region.

Cerebral blood flow and cerebrovascular resistance across the adult lifespan: A multimodality approach

Cerebral blood flow (CBF) decreases across the adult lifespan; however, more studies are needed to understand the underlying mechanisms. This study measured CBF and cerebrovascular resistance (CVR) using a multimodality approach in 185 healthy adults (21-80 years). Color-coded duplex ultrasonography and phase-contrast MRI were used to measure CBF, CBF velocity, and vessel diameters of the internal carotid (ICA) and vertebral arteries (VA). MRI arterial spin labeling was used to measure brain perfusion. Transcranial Doppler was used to measure CBF velocity at the middle cerebral artery. Structural MRI was used to measure brain volume. CBF was presented as total blood flow (mL/min) and normalized CBF (nCBF, mL/100g/min). Mean arterial pressure was measured to calculate CVR. Age was associated with decreased CBF by ∼3.5 mL/min/year and nCBF by ∼0.19 mL/100g/min/year across the methods. CVR increased by ∼0.011 mmHg/mL/100g/min/year. Blood flow velocities in ICA and VA decreased with age ranging from 0.07-0.15 cm/s/year, while the vessel diameters remained similar among age groups. These findings suggest that age-related decreases in CBF can be attributed mainly to decreases in blood flow velocity in the large cerebral arteries and that increased CVR likely reflects the presence of cerebral vasoconstrictions in the small cerebral arterioles and/or capillaries.

Arterial spin labeling signal in the CSF: Implications for partial volume correction and blood-CSF barrier characterization

For better quantification of perfusion with arterial spin labeling (ASL), partial volume correction (PVC) is used to disentangle the signals from gray matter (GM) and white matter within any voxel. Based on physiological considerations, PVC algorithms typically assume zero signal in the cerebrospinal fluid (CSF). Recent measurements, however, have shown that CSF-ASL signal can exceed 10% of GM signal, even when using recommended ASL labeling parameters. CSF signal is expected to particularly affect PVC results in the choroid plexus. This study aims to measure the impact of CSF signal on PVC perfusion measurements, and to investigate the potential use of PVC to retrieve pure CSF-ASL signal for blood-CSF barrier characterization. In vivo imaging included six pCASL sequences with variable label duration and post-labeling delay (PLD), and an eight-echo 3D-GRASE readout. A dataset was simulated to estimate the effect of CSF-PVC with known ground-truth parameters. Differences between the results of CSF-PVC and non-CSF-PVC were estimated for regions of interest (ROIs) based on GM probability, and a separate ROI isolating the choroid plexus. In vivo, the suitability of PVC-CSF signal as an estimate of pure CSF was investigated by comparing its time course with the long-TE CSF signal. Results from both simulation and in vivo data indicated that including the CSF signal in PVC improves quantification of GM CBF by approximately 10%. In simulated data, this improvement was greater for multi-PLD (model fitting) quantification than for single PLD (~1-5% difference). In the choroid plexus, the difference between CSF-PVC and non-CSF-PVC was much larger, averaging around 30%. Long-TE (pure) CSF signal could not be estimated from PVC CSF signal as it followed a different time course, indicating the presence of residual macrovascular signal in the PVC. The inclusion of CSF adds value to PVC for more accurate measurements of GM perfusion, and especially for quantification of perfusion in the choroid plexus and study of the glymphatic system.

One-year aerobic exercise increases cerebral blood flow in cognitively normal older adults

The impact of aerobic exercise training (AET) on cerebral blood flow (CBF) regulation remains inconclusive. This study investigated the effects of one-year progressive, moderate-to-vigorous AET on CBF, central arterial stiffness, and cognitive performance in cognitively normal older adults. Seventy-three older adults were randomly assigned to AET or stretching-and-toning (SAT, active control) intervention. CBF was measured with 2D duplex ultrasonography. Central arterial stiffness, measured by carotid β-stiffness index, was assessed with the ultrasonography and applanation tonometry. Cerebrovascular resistance (CVR) was calculated as mean arterial pressure divided by CBF. A cognitive battery was administered with a focus on memory and executive function. Cardiorespiratory fitness was measured by peak oxygen consumption (V ˙ O2peak). One-year AET increased V ˙ O2peak and CBF and decreased CVR and carotid β-stiffness index. In the AET group, improved V ˙ O2peak was correlated with increased CBF (r = 0.621, p = 0.001) and decreased CVR (r = -0.412, p = 0.037) and carotid β-stiffness index (r = -0.478, p = 0.011). Further, increased Woodcock-Johnson recall score was associated with decreased CVR (r = -0.483, p = 0.012) and carotid β-stiffness index (r = -0.498, p = 0.008) in AET group (not in SAT group). In conclusion, one-year progressive, moderate-to-vigorous aerobic exercise training increased CBF and decreased carotid arterial stiffness and CVR which were associated with improved memory function in cognitively normal older adults.

Infant brain regional cerebral blood flow increases supporting emergence of the default-mode network

Human infancy is characterized by most rapid regional cerebral blood flow (rCBF) increases across lifespan and emergence of a fundamental brain system default-mode network (DMN). However, how infant rCBF changes spatiotemporally across the brain and how the rCBF increase supports emergence of functional networks such as DMN remains unknown. Here, by acquiring cutting-edge multi-modal MRI including pseudo-continuous arterial-spin-labeled perfusion MRI and resting-state functional MRI of 48 infants cross-sectionally, we elucidated unprecedented 4D spatiotemporal infant rCBF framework and region-specific physiology-function coupling across infancy. We found that faster rCBF increases in the DMN than visual and sensorimotor networks. We also found strongly coupled increases of rCBF and network strength specifically in the DMN, suggesting faster local blood flow increase to meet extraneuronal metabolic demands in the DMN maturation. These results offer insights into the physiological mechanism of brain functional network emergence and have important implications in altered network maturation in brain disorders.

Evidence of cerebral hypoperfusion consecutive to ultrasound-mediated blood-brain barrier opening in rats

PURPOSE

This work aims to explore the effect of Blood Brain Barrier (BBB) opening using ultrasound combined with microbubbles injection on cerebral blood flow in rats.

METHODS

Two groups of n = 5 rats were included in this study. The first group was used to investigate the impact of BBB opening on the Arterial Spin Labeling (ASL) signal, in particular on the arterial transit time (ATT). The second group was used to analyze the spatiotemporal evolution of the change in cerebral blood flow (CBF) over time following BBB opening and validate these results using DSC-MRI.

RESULTS

Using pCASL, a decrease in CBF of up to 29 . 6 ± 15 . 1 % $$ 29.6\pm 15.1\% $$ was observed in the target hemisphere, associated with an increase in arterial transit time. The latter was estimated to be 533 ± 121ms $$ 533\pm 12\mathrm{1ms} $$ in the BBB opening impacted regions against 409 ± 93ms $$ 409\pm 93\mathrm{ms} $$ in the contralateral hemisphere. The spatio-temporal analysis of CBF maps indicated a nonlocal hypoperfusion. DSC-MRI measurements were consistent with the obtained results.

CONCLUSION

This study provided strong evidence that BBB opening using microbubble intravenous injection induces a transient hypoperfusion. A spatiotemporal analysis of the hypoperfusion changes allows to establish some points of similarity with the cortical spreading depression phenomenon.

Twenty-four hour blood pressure variability and the prevalence and the progression of cerebral white matter hyperintensities

Blood pressure variability (BPV) is related to cerebral white matter hyperintensities (WMH), but longitudinal studies assessing WMH progression are scarce. Patients with cardiovascular disease and control participants of the Heart-Brain Connection Study underwent 24-hour ambulatory blood pressure monitoring and repeated brain MRI at baseline and after 2 years. Using linear regression, we determined whether different measures of BPV (standard deviation, coefficient of variation, average real variability (ARV), variability independent of the mean) and nocturnal dipping were associated with WMH and whether this association was mediated or moderated by baseline cerebral perfusion. Among 177 participants (mean age: 65.9 ± 8.1 years, 33.9% female), the absence of diastolic nocturnal dipping was associated with higher WMH volume at baseline (β = 0.208, 95%CI: 0.025-0.392), but not with WMH progression among 91 participants with follow-up imaging. None of the BPV measures were associated with baseline WMH. Only 24-hour diastolic ARV was significantly associated with WMH progression (β = 0.144, 95%CI: 0.030-0.258), most profound in participants with low cerebral perfusion at baseline (p-interaction = 0.042). In conclusion, absent diastolic nocturnal dipping and 24-hour diastolic ARV were associated with higher WMH volume. Whilst requiring replication, these findings suggest that blood pressure patterns and variability may be a target for prevention of small vessel disease.

Distribution ratios of ethanol and water between whole blood, plasma, serum, and erythrocytes: Recommendations for interpreting clinical laboratory results in a legal context

This article reviews the scientific literature dealing with the distribution of ethanol and water between whole blood (WB), plasma, serum, and erythrocytes (red-blood cells). Knowledge of the ethanol distribution ratio is important when analytical results derived from hospital clinical laboratories are interpreted in a forensic context, such as during the prosecution of traffic offenders. Statutory blood-alcohol concentration (BAC) limits for driving are defined as the concentration of ethanol in WB and not in plasma, serum or red-blood cells. These bio-fluids differ in their water content and thereby the concentrations of ethanol. Plasma and serum contain ~90%-92% w/w water, WB ~78%-80% w/w and erythrocytes ~64%-66% w/w. The mean plasma/WB and serum/WB distribution ratios of ethanol are therefore expected to be ~1.15:1 (91/79 = 1.15), which is in good agreement with values determined empirically. However, in individual cases, the actual distribution ratio will depend on the person's age, gender, and biochemical and hematological properties of the blood specimen, such as its hematocrit. For legal purposes, we recommend that the concentration of ethanol in plasma or serum determined at hospital laboratories is divided by a factor of 1.2, which would provide a conservative estimate of the co-existing BAC and the chance of overestimating the true value is only 1 in 2000 (0.05%).

Choroid plexus tissue perfusion and blood to CSF barrier function in rats measured with continuous arterial spin labeling

The choroid plexus (ChP) of the cerebral ventricles is a source of cerebrospinal fluid (CSF) production and also plays a key role in immune surveillance at the level of blood-to-CSF-barrier (BCSFB). In this study, we quantify ChP blood perfusion and BCSFB mediated water exchange from arterial blood into ventricular CSF using non-invasive continuous arterial spin labelling magnetic resonance imaging (CASL-MRI). Systemic administration of anti-diuretic hormone (vasopressin) was used to validate BCSFB water flow as a metric of choroidal CSF secretory function. To further investigate the coupling between ChP blood perfusion and BCSFB water flow, we characterized the effects of two anesthetic regimens known to have large-scale differential effects on cerebral blood flow. For quantification of ChP blood perfusion a multi-compartment perfusion model was employed, and we discovered that partial volume correction improved measurement accuracy. Vasopressin significantly reduced both ChP blood perfusion and BCSFB water flow. ChP blood perfusion was significantly higher with pure isoflurane anesthesia (2-2.5%) when compared to a balanced anesthesia with dexmedetomidine and low-dose isoflurane (1.0 %), and significant correlation between ChP blood perfusion and BCSFB water flow was observed, however there was no significant difference in BCSFB water flow. In summary, here we introduce a non-invasive, robust, and spatially resolved in vivo imaging platform to quantify ChP blood perfusion as well as BCSFB water flow which can be applied to study coupling of these two key parameters in future clinical translational studies.

Velocity-selective arterial spin labeling perfusion MRI: A review of the state of the art and recommendations for clinical implementation

This review article provides an overview of the current status of velocity-selective arterial spin labeling (VSASL) perfusion MRI and is part of a wider effort arising from the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group. Since publication of the 2015 consensus paper on arterial spin labeling (ASL) for cerebral perfusion imaging, important advancements have been made in the field. The ASL community has, therefore, decided to provide an extended perspective on various aspects of technical development and application. Because VSASL has the potential to become a principal ASL method because of its unique advantages over traditional approaches, an in-depth discussion was warranted. VSASL labels blood based on its velocity and creates a magnetic bolus immediately proximal to the microvasculature within the imaging volume. VSASL is, therefore, insensitive to transit delay effects, in contrast to spatially selective pulsed and (pseudo-) continuous ASL approaches. Recent technical developments have improved the robustness and the labeling efficiency of VSASL, making it a potentially more favorable ASL approach in a wide range of applications where transit delay effects are of concern. In this review article, we (1) describe the concepts and theoretical basis of VSASL; (2) describe different variants of VSASL and their implementation; (3) provide recommended parameters and practices for clinical adoption; (4) describe challenges in developing and implementing VSASL; and (5) describe its current applications. As VSASL continues to undergo rapid development, the focus of this review is to summarize the fundamental concepts of VSASL, describe existing VSASL techniques and applications, and provide recommendations to help the clinical community adopt VSASL.

Associations of Human Milk Oligosaccharides with Infant Brain Tissue Organization and Regional Blood Flow at 1 Month of Age

Animal studies have shown that human milk oligosaccharides (HMOs) are important in early brain development, yet their roles have not been assessed in humans. The purpose of this study was to determine the associations of HMOs with MRI indices of tissue microstructure and regional cerebral blood flow (rCBF) in infants. Mother–infant pairs (N = 20) were recruited at 1 month postpartum. Milk was assayed for the concentrations of the HMOs 2′-fucosyllactose (2′FL), 3-fucosyllactose (3FL), 3′-sialyllactose (3′SL), and 6′-sialyllactose (6′SL). Diffusion and arterial spin labeling measures were acquired using a 3.0-Tesla MRI scanner. Multiple linear regression was used to assess the voxel-wise associations of HMOs with fractional anisotropy (FA), mean diffusivity (MD), and rCBF values across the brain. After adjusting for pre-pregnancy BMI, sex, birthweight, and postmenstrual age at time of scan, a higher 2′FL concentration was associated with reduced FA, increased MD, and reduced rCBF in similar locations within the cortical mantle. Higher 3FL and 3′SL concentrations were associated with increased FA, reduced MD, and increased rCBF in similar regions within the developing white matter. The concentration of 6′SL was not associated with MRI indices. Our data reveal that fucosylated and sialylated HMOs differentially associate with indices of tissue microstructure and rCBF, suggesting specific roles for 2′FL, 3FL, and 3′SL in early brain maturation.

Carotid Arterial Compliance and Aerobic Exercise Training in Chronic Traumatic Brain Injury: A Pilot Study

OBJECTIVE

Decreased carotid arterial compliance (CAC) is associated with cerebral microvascular damage, cerebral blood flow (CBF) dysregulation, and increased risk for stroke and dementia, which are reported to be prevalent after traumatic brain injury (TBI). However, the effect of TBI on CAC has not been reported. The purposes of this pilot study were to (1) compare CAC between participants with chronic traumatic brain injury (cTBI) and age-matched healthy control (HC) subjects and (2) to examine whether CAC changed after 3 months of exercise training in those with cTBI.

SETTING

Community based.

PARTICIPANTS

Nineteen participants with cTBI (6-72 months postinjury) and 19 HC matched for age and sex were tested at baseline. The same cTBI cohort was enrolled in a proof-of-concept randomized controlled exercise training program to investigate the effects of 3 months of aerobic exercise training (AET) or nonaerobic stretching and toning (SAT) on cerebrovascular parameters.

DESIGN

Cross-sectional study and randomized controlled trial.

MAIN MEASURES

CAC was measured by tonometry and ultrasonography at the common carotid artery; CBF was measured by ultrasonography at the bilateral internal carotid and vertebral arteries, and pulsatile CBF was measured by transcranial Doppler ultrasonography at the middle cerebral arteries. Cerebrovascular resistance (CVR) was calculated as mean arterial pressure divided by total CBF.

RESULTS

Relative to HC, the participants with cTBI had lower CAC (0.10 ± 0.03 vs 0.12 ± 0.03 mm 2 /mm Hg, P = .046) and higher CVR (0.17 ± 0.03 vs 0.15 ± 0.03 mm Hg/mL/min, P = .028). CAC tended to increase after AET compared with SAT ( P = .080). Increases in CAC were associated with decreased pulsatile CBF ( r = -0.689, P = .003).

CONCLUSION

These findings suggest that the individuals with cTBI have decreased CAC, which may potentially be improved by AET.

Early alterations in brain glucose metabolism and vascular function in a transgenic rat model of Alzheimer's disease

Alteration in brain metabolism predates clinical onset of Alzheimer's Disease (AD). Realizing its potential as an early diagnostic marker, however, requires understanding how early AD metabolic dysregulation manifests on non-invasive brain imaging. We presently utilized magnetic resonance imaging and spectroscopy to map glucose and ketone metabolic profiles and image cerebrovascular function in a rat model of early stage AD - 9-month-old TgF344-AD (TgAD) rats - and their age-matched non-transgenic (nTg) littermates. Compared to the nTg rats, TgAD rats displayed attenuation in global cerebral and hippocampal vasoreactivity to hypercapnia, by 49±17% and 58±19%, respectively, while their functional hyperemia to somatosensory stimulation diminished by 69±5%. To assess brain glucose uptake, rats were fasted overnight and then challenged with an intravenous infusion of 2-deoxy-D-glucose (2DG). Compared to their non-transgenic littermates, TgAD rats exhibited 99±10% and 52±5% smaller glucose uptake in the entorhinal cortex and the hippocampus, respectively. Moreover, hippocampal glucose uptake reduction in male TgAD rats compared to the nTg was 54±36% greater than the reduction seen in female TgAD rats. TgAD rats also showed a 59±42% increase in total choline level in the hippocampus, suggesting increased membrane turnover. In combination with our earlier findings of impaired electrophysiological metrics at this early stage of AD pathology progression, our findings suggest that subtle neuronal function alterations that would be difficult to assess in a clinical population may be accompanied by MRI-detectable changes in brain glucose metabolism and cerebrovascular function.

MRI evaluation of cerebral metabolic rate of oxygen (CMRO2) in obstructive sleep apnea

Patients with obstructive sleep apnea (OSA) are at elevated risk of developing systemic vascular disease and cognitive dysfunction. Here, cerebral oxygen metabolism was assessed in patients with OSA by means of a magnetic resonance-based method involving simultaneous measurements of cerebral blood flow rate and venous oxygen saturation in the superior sagittal sinus for a period of 10 minutes at an effective temporal resolution of 1.3 seconds before, during, and after repeated 24-second breath-holds mimicking spontaneous apneas, yielding, along with pulse oximetry-derived arterial saturation, whole-brain CMRO2 via Fick's Principle. Enrolled subjects were classified based on their apnea-hypopnea indices into OSA (N = 31) and non-sleep apnea reference subjects (NSA = 21), and further compared with young healthy subjects (YH, N = 10). OSA and NSA subjects were matched for age and body mass index. CMRO2 was lower in OSA than in the YH group during normal breathing (105.6 ± 14.1 versus 123.7 ± 22.8 μmol O2/min/100g, P = 0.01). Further, the fractional change in CMRO2 in response to a breath-hold challenge was larger in OSA than in the YH group (15.2 ± 9.2 versus 8.5 ± 3.4%, P = 0.04). However, there was no significant difference in CMRO2 between OSA and NSA subjects. The data suggest altered brain oxygen metabolism in OSA and possibly in NSA as well.

Reliability and Sensitivity to Longitudinal CBF Changes in Steno-Occlusive Diseases: ASL Versus 123 I-IMP-SPECT

BACKGROUND

Noninvasive cerebral blood flow (CBF) monitoring using arterial spin labeling (ASL) magnetic resonance imaging is useful for managing large cerebral artery steno-occlusive diseases. However, knowledge about its measurement characteristics in comparison with reference standard perfusion imaging is limited.

PURPOSE

To evaluate perfusion in a longitudinal manner in patients with steno-occlusive disease using ASL and compare with single-photon emission computed tomography (SPECT).

STUDY TYPE

Prospective.

POPULATION

Moyamoya (n = 10, eight females) and atherosclerotic diseases (n = 2, two males).

FIELD STRENGTH/SEQUENCE

3.0 T; gradient-echo three-dimensional T₁ -weighted and spin-echo ASL.

ASSESSMENT

Multi-delay ASL and [¹²³ I]-iodoamphetamine SPECT CBF measurements were performed both before and within 9 days of anterior-circulation revascularization. Reliability and sensitivity to whole-brain voxel-wise CBF changes (ΔCBF) and their postlabeling delay (PLD) dependency with varied PLDs (in milliseconds) of 1000, 2333, and 3666 were examined.

STATISTICAL TESTS

Reliability and sensitivity to ΔCBF were examined using within-subject standard deviation (Sw) and intraclass correlation coefficients (ICCs). For statistical comparisons, standard deviation of longitudinal ΔCBF within the hemisphere contralateral to surgery, and the ratio between it and average ΔCBF within the ipsilateral regions of interest were subjected to paired t tests, respectively. P < 0.05 was considered statistically significant.

RESULTS

ASL test-retest time interval was 31 ± 18 days. Test-retest reliability was significantly lower for SPECT (0.16 ± 0.02) than ASL (0.13 ± 0.04). Sensitivity to postoperative changes was significantly higher for ASL (2.71 ± 2.79) than SPECT (0.27 ± 0.62). Test-retest reliability was significantly higher for a PLD of 2333 (0.13 ± 0.04) than 3666 (0.19 ± 0.05), and sensitivity to ΔCBF was significantly higher for PLDs of 1000 (2.53 ± 2.50) and 2333 than 3666 (0.79 ± 1.88). ICC maps also showed higher reliability for ASL than SPECT.

DATA CONCLUSION

Higher test-retest reliability led to better ASL sensitivity than SPECT for postoperative ΔCBF. ASL test-retest reliability and sensitivity to ΔCBF were higher with a PLD of 2333.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 2.

Perilesional Perfusion in Chronic Stroke-Induced Aphasia and Its Response to Behavioral Treatment Interventions

Stroke-induced alterations in cerebral blood flow (perfusion) may contribute to functional language impairments in chronic aphasia, particularly in perilesional tissue. Abnormal perfusion in this region may also serve as a biomarker for predicting functional improvements with behavioral treatment interventions. Using pseudo-continuous arterial spin labeling in magnetic resonance imaging (MRI), we examined perfusion in chronic aphasia, in perilesional rings in the left hemisphere and their right hemisphere homologues. In the left hemisphere we found a gradient pattern of decreasing perfusion closer to the lesion. The opposite pattern was found in the right hemisphere, with significantly increased perfusion close to the lesion homologue. Perfusion was also increased in the right hemisphere lesion homologue region relative to the surrounding tissue. We next examined changes in perfusion in two groups: one group who underwent MRI scanning before and after three months of a behavioral treatment intervention that led to significant language gains, and a second group who was scanned twice at a three-month interval without a treatment intervention. For both groups, there was no difference in perfusion over time in either the left or the right hemisphere. Moreover, within the treatment group pre-treatment perfusion scores did not predict treatment response; neither did pre-treatment perfusion predict post-treatment language performance. These results indicate that perfusion is chronically abnormal in both hemispheres, but chronically abnormal perfusion did not change in response to our behavioral treatment interventions, and did not predict responsiveness to language treatment.

Noninvasive Quantification of Cerebral Blood Flow Using Hybrid PET/MR Imaging to Extract the [15 O]H2 O Image-Derived Input Function Free of Partial Volume Errors

BACKGROUND

Quantification of cerebral blood flow (CBF) with [¹⁵ O]H₂ O-positron emission tomography (PET) requires arterial sampling to measure the input function. This invasive procedure can be avoided by extracting an image-derived input function (IDIF); however, IDIFs are sensitive to partial volume errors due to the limited spatial resolution of PET.

PURPOSE

To present an alternative hybrid PET/MR imaging of CBF (PMRFlow_IDIF ) that uses phase-contrast (PC) MRI measurements of whole-brain (WB) CBF to calibrate an IDIF extracted from a WB [¹⁵ O]H₂ O time-activity curve.

STUDY TYPE

Technical development and validation.

ANIMAL MODEL

Twelve juvenile Duroc pigs (83% female).

POPULATION

Thirteen healthy individuals (38% female).

FIELD STRENGTH/SEQUENCES

3 T; gradient-echo PC-MRI.

ASSESSMENT

PMRFlow_IDIF was validated against PET-only in a porcine model that included arterial sampling. CBF maps were generated by applying PMRFlow_IDIF and two previous PMRFlow methods (PC-PET and double integration method [DIM]) to [¹⁵ O]H₂ O-PET data acquired from healthy individuals.

STATISTICAL TESTS

PMRFlow and PET CBF measurements were compared with regression and correlation analyses. Paired t-tests were performed to evaluate differences. Potential biases were assessed using one-sample t-tests. Reliability was assessed by intraclass correlation coefficients. Statistical significance: α  = 0.05.

RESULTS

In the animal study, strong agreement was observed between PMRFlow_IDIF (average voxel-wise CBF, 58.0 ± 16.9 mL/100 g/min) and PET (63.0 ± 18.9 mL/100 g/min). In the human study, PMRFlow_DIM (y = 1.11x - 5.16, R²  = 0.99 ± 0.01) and PMRFlow_PC-PET (y = 0.87x + 3.82, R²  = 0.97 ± 0.02) performed similarly to PMRFlow_IDIF, and CBF was within the expected range (eg, 49.7 ± 7.2 mL/100 g/min for gray matter).

DATA CONCLUSION

Accuracy of PMRFlow_IDIF was confirmed in the animal study with the primary source of error attributed to differences in WB CBF measured by PC MRI and PET. In the human study, differences in CBF from PMRFlow_IDIF , PMRFlow_DIM , and PMRFlow_PC-PET were due to the latter two not accounting for blood-borne activity.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 1.

Whole-brain 3D mapping of oxygen metabolism using constrained quantitative BOLD

Quantitative BOLD (qBOLD) MRI permits noninvasive evaluation of hemodynamic and metabolic states of the brain by quantifying parametric maps of deoxygenated blood volume (DBV) and hemoglobin oxygen saturation level of venous blood (Y_v), and along with a measurement of cerebral blood flow (CBF), the cerebral metabolic rate of oxygen (CMRO₂). The method, thus should have potential to provide important information on many neurological disorders as well as normal cerebral physiology. One major challenge in qBOLD is to separate de-oxyhemoglobin’s contribution to R₂′ from other sources modulating the voxel signal, for instance, R₂, R₂′ from non-heme iron (R′_2,nh), and macroscopic magnetic field variations. Further, even with successful separation of the several confounders, it is still challenging to extract DBV and Y_v from the heme-originated R₂′ because of limited sensitivity of the qBOLD model. These issues, which have not been fully addressed in currently practiced qBOLD methods, have so far precluded 3D whole-brain implementation of qBOLD. Thus, the purpose of this work was to develop a new 3D MRI oximetry technique that enables robust qBOLD parameter mapping across the entire brain. To achieve this goal, we employed a rapid, R₂′-sensitive, steady-state 3D pulse sequence (termed ‘AUSFIDE’) for data acquisition, and implemented a prior-constrained qBOLD processing pipeline that exploits a plurality of preliminary parameters obtained via AUSFIDE, along with additionally measured cerebral venous blood volume. Numerical simulations and in vivo studies at 3 T were performed to evaluate the performance of the proposed, constrained qBOLD mapping in comparison to the parent qBOLD method. Measured parameters (Y_v, DBV, R′_2,nh, nonblood magnetic susceptibility) in ten healthy subjects demonstrate the expected contrast across brain territories, while yielding group-averages of 64.0 ± 2.3 % and 62.2 ± 3.1 % for Y_v and 2.8 ± 0.5 % and 1.8 ± 0.4 % for DBV in cortical gray and white matter, respectively. Given the Y_v measurements, additionally quantified CBF in seven of the ten study subjects enabled whole-brain 3D CMRO₂ mapping, yielding group averages of 134.2 ± 21.1 and 79.4 ± 12.6 µmol/100 g/min for cortical gray and white matter, in good agreement with literature values. The results suggest feasibility of the proposed method as a practical and reliable means for measuring neurometabolic parameters over an extended brain coverage.

Abnormal Oxidative Metabolism in the Cuprizone Mouse Model of Demyelination: an in vivo NIRS-MRI Study

Disruptions in oxidative metabolism may occur in multiple sclerosis and other demyelinating neurological diseases. The impact of demyelination on metabolic rate is also not understood. It is possible that mitochondrial damage may be associated with many such neurological disorders. To study oxidative metabolism with one model of demyelination, we implemented a novel multimodal imaging technique combining Near-Infrared Spectroscopy (NIRS) and MRI to cuprizone mouse model. The cuprizone model is used to study demyelination and may be associated with inhibition of mitochondrial function. Cuprizone mice showed reduced oxygen extraction fraction (-39.1%, p≤0.001), increased tissue oxygenation (6.4%, p≤0.001), and reduced cerebral metabolic rate of oxygen in cortical gray matter (-62.1%, p≤0.001). These changes resolved after the cessation of cuprizone exposure and partial remyelination. A decrease in hemoglobin concentration (-34.4%, p≤0.001), but no change in cerebral blood flow were also observed during demyelination. The oxidized state of the mitochondrial enzyme, Cytochrome C Oxidase (CCO) increased (46.3%, p≤0.001) while the reduced state decreased (-34.4%, p≤0.05) significantly in cuprizone mice. The total amount of CCO did not change significantly during cuprizone exposure. Total CCO did decline after recovery both in control (-23.1%, p≤0.01) and cuprizone (-28.8%, p≤0.001) groups which may relate to age. A reduction in the magnetization transfer ratio, indicating demyelination, was found in the cuprizone group in the cerebral cortex (-3.2%, p≤0.01) and corpus callosum (-5.5%, p≤0.001). In summary, we were able to detect evidence of altered CCO metabolism during cuprizone exposure, consistent with a mitochondrial defect. We observed increased oxygenation and reduced metabolic rate associated with reduced myelination in the gray and white matter. The novel multimodal imaging technique applied here shows promise for noninvasively assessing parameters associated with oxidative metabolism in both mouse models of neurological disease and for translation to study oxidative metabolism in the human brain.

Measuring Arterial Pulsatility With Dynamic Inflow Magnitude Contrast

The pulsatility of blood flow through cerebral arteries is clinically important, as it is intrinsically associated with cerebrovascular health. In this study we outline a new MRI approach to measuring the real-time pulsatile flow in cerebral arteries, which is based on the inflow phenomenon associated with fast gradient-recalled-echo acquisitions. Unlike traditional phase-contrast techniques, this new method, which we dub dynamic inflow magnitude contrast (DIMAC), does not require velocity-encoding gradients as sensitivity to flow velocity is derived purely from the inflow effect. We achieved this using a highly accelerated single slice EPI acquisition with a very short TR (15 ms) and a 90° flip angle, thus maximizing inflow contrast. We simulate the spoiled GRE signal in the presence of large arteries and perform a sensitivity analysis. The sensitivity analysis demonstrates that in the regime of high inflow contrast, DIMAC shows much greater sensitivity to flow velocity over blood volume changes. We support this theoretical prediction with in-vivo data collected in two separate experiments designed to demonstrate the utility of the DIMAC signal contrast. We perform a hypercapnia challenge experiment in order to experimentally modulate arterial tone within subjects, and thus modulate the arterial pulsatile flow waveform. We also perform a thigh-cuff release challenge, designed to induce a transient drop in blood pressure, and demonstrate that the continuous DIMAC signal captures the complex transient change in the pulsatile and non-pulsatile components of flow. In summary, this study proposes a new role for a well-established source of MR image contrast and demonstrates its potential for measuring both steady-state and dynamic changes in arterial tone.

Pattern of Altered Magnetization Transfer Rate in Alzheimer's Disease

BACKGROUND

Biomarkers for Alzheimer's disease (AD) are crucial for early diagnosis and treatment monitoring once disease modifying therapies become available.

OBJECTIVE

This study aims to quantify the forward magnetization transfer rate (kfor) map from brain tissue water to macromolecular protons and use it to identify the brain regions with abnormal kfor in AD and AD progression.

METHODS

From the Cardiovascular Health Study (CHS) cognition study, magnetization transfer imaging (MTI) was acquired at baseline from 63 participants, including 20 normal controls (NC), 18 with mild cognitive impairment (MCI), and 25 AD subjects. Of those, 53 participants completed a follow-up MRI scan and were divided into four groups: 15 stable NC, 12 NC-to-MCI, 12 stable MCI, and 14 MCI/AD-to-AD subjects. kfor maps were compared across NC, MCI, and AD groups at baseline for the cross-sectional study and across four longitudinal groups for the longitudinal study.

RESULTS

We found a lower kfor in the frontal gray matter (GM), parietal GM, frontal corona radiata (CR) white matter (WM) tracts, frontal and parietal superior longitudinal fasciculus (SLF) WM tracts in AD relative to both NC and MCI. Further, we observed progressive decreases of kfor in the frontal GM, parietal GM, frontal and parietal CR WM tracts, and parietal SLF WM tracts in stable MCI. In the parietal GM, parietal CR WM tracts, and parietal SLF WM tracts, we found trend differences between MCI/AD-to-AD and stable NC.

CONCLUSION

Forward magnetization transfer rate is a promising biomarker for AD diagnosis and progression.

Ultra-long-TE arterial spin labeling reveals rapid and brain-wide blood-to-CSF water transport in humans

The study of brain clearance mechanisms is an active area of research. While we know that the cerebrospinal fluid (CSF) plays a central role in one of the main existing clearance pathways, the exact processes for the secretion of CSF and the removal of waste products from tissue are under debate. CSF is thought to be created by the exchange of water and ions from the blood, which is believed to mainly occur in the choroid plexus. This exchange has not been thoroughly studied in vivo.

We propose a modified arterial spin labeling (ASL) MRI sequence and image analysis to track blood water as it is transported to the CSF, and to characterize its exchange from blood to CSF. We acquired six pseudo-continuous ASL sequences with varying labeling duration (LD) and post-labeling delay (PLD) and a segmented 3D-GRASE readout with a long echo train (8 echo times (TE)) which allowed separation of the very long-T₂ CSF signal. ASL signal was observed at long TEs (793 ms and higher), indicating presence of labeled water transported from blood to CSF. This signal appeared both in the CSF proximal to the choroid plexus and in the subarachnoid space surrounding the cortex. ASL signal was separated into its blood, gray matter and CSF components by fitting a triexponential function with T₂s taken from literature. A two-compartment dynamic model was introduced to describe the exchange of water through time and TE. From this, a water exchange time from the blood to the CSF (T_bl->CSF) was mapped, with an order of magnitude of approximately 60 s.

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.

Separating spin compartments in arterial spin labeling using delays alternating with nutation for tailored excitation (DANTE) pulse: A validation study using T2 -relaxometry and application to arterial cerebral blood volume imaging

PURPOSE

To clarify the type of spin compartment in arterial spin labeling (ASL) that is eliminated by delays alternating with nutation for tailored excitation (DANTE) pulse using T₂ -relaxometry, and to demonstrate the feasibility of arterial cerebral blood volume (CBV_a ) imaging using DANTE-ASL in combination with a simplified two-compartment model.

METHOD

The DANTE and T₂ -preparation modules were combined into a single ASL sequence. T₂ values under the application of DANTE were determined to evaluate changes in T₂ , along with the post-labeling delay (PLD) and the relationship between transit time without DANTE (TT_noVS ) and T₂ . The reference tissue T₂ (T_{2_ref} ) was also obtained. Subsequently, the DANTE module was embedded into the Hadamard-encoded ASL. Cerebral blood flow (CBF) and CBV_a were computed using two Hadamard-encoding datasets (with and without DANTE) in a rest and breath-holding (BH) task.

RESULTS

While T₂ without DANTE (T_{2_noVS} ) decreased as the PLD increased, T₂ with DANTE (T_{2_DANTE} ) was equivalent to T_{2_ref} and did not change with the PLD. Although there was a significant positive correlation between TT_noVS and T_{2_noVS} with short PLD, T_{2_DANTE} was not correlated with TT_noVS nor PLD. Baseline CBV_a values obtained at rest were 0.64 ± 0.12, 0.64 ± 0.11, and 0.58 ± 0.15 mL/100 g for anterior, middle, and posterior cerebral arteries, respectively. Significant CBF and CBV_a elevations were observed in the BH task.

CONCLUSION

Microvascular compartment signals were eliminated from the total ASL signals by DANTE. CBV_a can be measured using Hadamard-encoded DANTE-ASL in combination with a simplified two-compartment model.

Sensitivity of arterial Spin labeling for characterization of longitudinal perfusion changes in Frontotemporal dementia and related disorders

•

This study demonstrates the value of ASL for longitudinal monitoring of perfusion in FTD patients.

•

Good agreement was found in repeat measures of CBF in patients and controls.

•

Transit times were not a significant source of error for the selected post labeling delay (2 s).

Background

Advances in the understanding of the pathophysiology of frontotemporal dementia (FTD) and related disorders, along with the development of novel candidate disease modifying treatments, have stimulated the need for tools to assess the efficacy of new therapies. While perfusion imaging by arterial spin labeling (ASL) is an attractive approach for longitudinal imaging biomarkers of neurodegeneration, sources of variability between sessions including arterial transit times (ATT) and fluctuations in resting perfusion can reduce its sensitivity. Establishing the magnitude of perfusion changes that can be reliably detected is necessary to delineate longitudinal perfusion changes related to disease processes from the effects of these sources of error.

Purpose

To assess the feasibility of ASL for longitudinal monitoring of patients with FTD by quantifying between-session variability of perfusion on a voxel-by-voxel basis.

Methods and materials

ASL data were collected in 13 healthy controls and 8 patients with FTD or progressive supra-nuclear palsy. Variability in cerebral blood flow (CBF) by single delay pseudo-continuous ASL (SD-pCASL) acquired one month apart were quantified by the coefficient of variation (CV) and intraclass correlation coefficient (ICC). Additionally, CBF by SD-pCASL and ATT by low-resolution multiple inversion time ASL (LowRes-pCASL) were compared to Hadamard encoded sequences which are able to simultaneously measure CBF and ATT with improved time-efficiency.

Results

Agreement of grey-matter perfusion between sessions was found for both patients and controls (CV = 10.8% and 8.3% respectively) with good reliability for both groups (ICC > 0.6). Intensity normalization to remove day-to-day fluctuations in resting perfusion reduced the CV by 28%. Less than 5% of voxels had ATTs above the chosen post labelling delay (2 s), indicating that the ATT was not a significant source of error. Hadamard-encoded perfusion imaging yielded systematically higher CBF compared to SD-pCASL, but produced similar transit-time measurements. Power analysis revealed that SD-pCASL has the sensitivity to detect longitudinal changes as low as 10% with as few as 10 patient participants.

Conclusion

With the appropriate labeling parameters, SD-pCASL is a promising approach for assessing longitudinal changes in CBF associated with FTD.

Effect of hematocrit on cerebral blood flow measured by pseudo-continuous arterial spin labeling MRI: A comparative study with 15O-water positron emission tomography

INTRODUCTION

In cerebral blood flow (CBF) quantification with pseudo-continuous arterial spin labeling (pCASL) MRI, arterial blood T1 (T1a) is usually fixed to a typical value (e.g., 1650 ms). However, individual T1a depends strongly on hematocrit (Hct) level. To investigate the utility of Hct-based T1a as an alternative to the fixed T1a method, we performed a comparative study with ¹⁵O-water positron emission tomography (PET).

METHODS

For patients with unilateral occlusion or stenosis of major arteries, hemispheric CBF on the healthy side was measured using pCASL and ¹⁵O-water PET. The pCASL CBFs were calculated with both (a) fixed T1a (1650 ms) and (b) individual T1a estimated from blood-sampled Hct (Hct-based T1a). Correlation coefficients of Hct-CBF were calculated and compared between pCASL and PET.

RESULTS

In pCASL, CBF with fixed T1a showed a strong negative correlation with Hct (r = -0.568), which was reduced with individual Hct-based T1a (r = -0.341 to -0.190), consistent with the Hct-CBF relation measured with PET (r = -0.349).

DISCUSSION AND CONCLUSION

We demonstrated that Hct-based T1a resulted in smaller inter-individual variations in pCASL CBF and an inverse Hct-CBF relationship more similar to that of PET. Care must be taken in the interpretation of pCASL CBF imaging in relation to Hct level even in subjects without anemia. Further comparative studies are needed to investigate whether advanced techniques improve pCASL CBF quantification at the individual level.

One-Year Aerobic Exercise Reduced Carotid Arterial Stiffness and Increased Cerebral Blood Flow in Amnestic Mild Cognitive Impairment

BACKGROUND

Central arterial stiffness and brain hypoperfusion are emerging risk factors of Alzheimer's disease (AD). Aerobic exercise training (AET) may improve central arterial stiffness and brain perfusion.

OBJECTIVE

To investigate the effects of AET on central arterial stiffness and cerebral blood flow (CBF) in patients with amnestic mild cognitive impairment (MCI), a prodromal stage of AD.

METHODS

This is a proof-of-concept, randomized controlled trial that assigned 70 amnestic MCI patients into a 12-month program of moderate-to-vigorous AET or stretching-and-toning (SAT) intervention. Carotid β-stiffness index and CBF were measured by color-coded duplex ultrasonography and applanation tonometry. Total CBF was measured as the sum of CBF from both the internal carotid and vertebral arteries, and divided by total brain tissue mass assessed with MRI to obtain normalized CBF (nCBF). Episodic memory and executive function were assessed using standard neuropsychological tests (CVLT-II and D-KEFS). Changes in cardiorespiratory fitness were measured by peak oxygen uptake (VO2peak).

RESULTS

Total 48 patients (29 in SAT and 19 in AET) were completed one-year training. AET improved VO2peak, decreased carotid β-stiffness index and CBF pulsatility, and increased nCBF. Changes in VO2peak were associated positively with changes in nCBF (r = 0.388, p = 0.034) and negatively with carotid β-stiffness index (r = -0.418, p = 0.007) and CBF pulsatility (r = -0.400, p = 0.014). Decreases in carotid β-stiffness were associated with increases in cerebral perfusion (r = -0.494, p = 0.003). AET effects on cognitive performance were minimal compared with SAT.

CONCLUSION

AET reduced central arterial stiffness and increased CBF which may precede its effects on neurocognitive function in patients with MCI.

Optimized cervical spinal cord perfusion MRI after traumatic injury in the rat

Despite the potential to guide clinical management of spinal cord injury and disease, noninvasive methods of monitoring perfusion status of the spinal cord clinically remain an unmet need. In this study, we optimized pseudo-continuous arterial spin labeling (pCASL) for the rodent cervical spinal cord and demonstrate its utility in identifying perfusion deficits in an acute contusion injury model. High-resolution perfusion sagittal images with reduced imaging artifacts were obtained with optimized background suppression and imaging readout. Following moderate contusion injury, perfusion was clearly and reliably decreased at the site of injury. Implementation of time-encoded pCASL confirmed injury site perfusion deficits with blood flow measurements corrected for variability in arterial transit times. The noninvasive protocol of pCASL in the spinal cord can be utilized in future applications to examine perfusion changes after therapeutic interventions in the rat and translation to patients may offer critical implications for patient management.

Arterial Transit Time-Based Multidelay Combination Strategy Improves Arterial Spin Labeling Cerebral Blood Flow Measurement Accuracy in Severe Steno-Occlusive Diseases

BACKGROUND

Although perfusion imaging plays a key role in the management of steno-occlusive diseases, the clinical usefulness of arterial spin labeling (ASL) is limited by technical issues.

PURPOSE

To examine the effect of arterial transit time (ATT) prolongation on cerebral blood flow (CBF) measurement accuracy and identify the best CBF measurement protocol for steno-occlusive diseases.

STUDY TYPE

Prospective.

POPULATION

Moyamoya (n = 10) and atherosclerotic diseases (n = 8).

FIELD STRENGTH/SEQUENCE

A 3.0T/3DT₁ -weighted and ASL.

ASSESSMENT

Hadamard-encoded multidelay ASL scans with/without vessel suppression (VS) and single-delay ASL scans with long-label duration (LD) and long postlabeling delay (PLD), referred to as long-label long-delay (LLLD), were acquired. CBF measurement accuracy and its ATT dependency, measured as the correlation between the relative CBF measurement difference (ASL-single-photon emission computed tomography [SPECT]) and ATT, were compared among 1) Combo (incorporating multidelay and LLLD data based on ATT), 2) standard (LD/PLD = 1333/2333 msec), and 3) LLLD (LD/PLD = 4000/4000 msec) protocols, using whole-brain voxel-wise correlation with reference standard SPECT CBF. The effect of VS on CBF measurement accuracy was also assessed.

STATISTICAL TESTS

Pearson's correlation coefficient, repeated-measures analysis of variance, t-test. P< 0.05 was considered significant.

RESULTS

Pearson's correlation coefficients between ASL and SPECT CBF measurements were as follows: Combo = 0.55 ± 0.09; standard = 0.52 ± 0.12; LLLD = 0.41 ± 0.10. CBF measurement was least accurate in LLLD and most accurate in Combo. VS significantly improved overall CBF measurement accuracy in the standard protocol and in moyamoya patients for the Combo. ATT dependency analysis revealed that, compared with Combo, the standard and LLLD protocols showed significantly lower and negative and significantly higher and positive correlations, respectively (standard = -0.12 ± 0.04, Combo = -0.04 ± 0.03, LLLD = 0.17 ± 0.03).

DATA CONCLUSION

By using ATT-corrected CBF derived from LD/PLD = 1333/2333 msec as a base and by compensating underestimation in delayed regions using multidelay scans, the ATT-based Combo strategy improves CBF measurement accuracy compared with single-delay protocols in severe steno-occlusive diseases.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 2.

Time-encoded golden angle radial arterial spin labeling: Simultaneous acquisition of angiography and perfusion data

The objective of the current study was to combine a time-encoded pseudocontinuous arterial spin labeling (te-pCASL) scheme with a golden angle radial readout for simultaneous acquisition of angiography and perfusion images from one single dataset, both in a highly flexible single-slice approach as well as within a multislice setting. A te-pCASL preparation and the golden angle radial readout were both used as a temporal resolution tool to retrospectively choose the temporal window for the reconstruction of both angiography and perfusion images from a single-slice dataset. The temporal window could be chosen retrospectively and adjusted to the hemodynamics of the volunteer on the scanner for the single-slice dataset. Angiographic images were reconstructed at a minimum temporal resolution of 69 ms. For the perfusion phase, only the densely sampled center of k-space was included in the reconstruction. For a multislice acquisition, the golden angle radial readout allowed reconstruction of images with different spatial resolutions to provide angiographic and perfusion information over 10 slices. The te-pCASL preparation was used as the only source for dynamic information. The multislice acquisition shows the ability of the golden angle radial readout to display the inflow of the labeled blood into the arteries as well as the perfusion in the tissue with full brain coverage. By combining a te-pCASL preparation with a golden angle radial readout, single-slice high temporal resolution angiography and good quality perfusion images were reconstructed in a flexible manner from a single dataset. Optimizing the golden angle radial readout for reconstructions at multiple spatial resolutions allows for multislice acquisition.

Preliminary Report: Localized Cerebral Blood Flow Mediates the Relationship between Progesterone and Perceived Stress Symptoms among Female Collegiate Club Athletes after Mild Traumatic Brain Injury

Female athletes are under-studied in the field of concussion research, despite evidence of higher injury prevalence and longer recovery time. Hormonal fluctuations caused by the natural menstrual cycle (MC) or hormonal contraceptive (HC) use impact both post-injury symptoms and neuroimaging findings, but the relationships among hormone, symptoms, and brain-based measures have not been jointly considered in concussion studies. In this preliminary study, we compared cerebral blood flow (CBF) measured with arterial spin labeling between concussed female club athletes 3-10 days after mild traumatic brain injury (mTBI) and demographic, HC/MC matched controls (CON). We tested whether CBF statistically mediates the relationship between progesterone serum levels and post-injury symptoms, which may support a hypothesis for progesterone's role in neuroprotection. We found a significant three-way relationship among progesterone, CBF, and perceived stress score (PSS) in the left middle temporal gyrus for the mTBI group. Higher progesterone was associated with lower (more normative) PSS, as well as higher (more normative) CBF. CBF mediates 100% of the relationship between progesterone and PSS (Sobel p value = 0.017). These findings support a hypothesis for progesterone having a neuroprotective role after concussion and highlight the importance of controlling for the effects of sex hormones in future concussion studies.

Quantification of Regional Cerebral Blood Flow Using Diffusion Imaging With Phase Contrast

BACKGROUND

The perfusion-related diffusion coefficient obtained from triexponential diffusion analysis is closely correlated with regional cerebral blood flow (rCBF), as assessed by arterial spin labeling (ASL) methods. However, this provides only a semiquantitative measure of rCBF, thereby making absolute rCBF quantification challenging.

PURPOSE

To obtain rCBF in a noninvasive manner using a novel diffusion imaging method with phase contrast (DPC), in which the total CBF from phase-contrast (PC) MRI was utilized to convert perfusion-related diffusion coefficients to rCBF values.

STUDY TYPE

Prospective.

SUBJECTS

Eleven healthy volunteers (nine men and two women; mean age, 23.9 years) participated in this study.

FIELD STRENGTH/SEQUENCE

A 3.0 T, single-shot diffusion echo-planar imaging with multiple b-values (0-3000 s/mm² ), PC-MRI, pulsed continuous ASL, and 3D T₁ -weighted fast field echo.

ASSESSMENT

rCBF and its correlations in the gray matter (GM) and white matter (WM) were compared between DPC and ASL methods. rCBF in the GM and WM and the GM/WM ratio were compared with the literature values obtained using [¹⁵ O]-water positron emission tomography (¹⁵ O-H₂ O PET).

STATISTICAL TESTS

Spearman's correlation coefficient and Wilcoxon signed-rank test were used. Significance was set at P < 0.05.

RESULTS

A significant positive correlation between DPC and ASL in terms of rCBF was observed in GM (R = 0.9), whereas the correlation between the two methods was poor in WM (R = 0.09). The rCBF in GM and WM and the GM/WM ratio obtained using DPC were consistent with the literature values assessed using ¹⁵ O-H₂ O PET. The rCBF value obtained using DPC was significantly higher in the GM and WM than that using ASL.

DATA CONCLUSION

DPC enabled noninvasive quantification of rCBF.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.

Three-dimensional whole-brain mapping of cerebral blood volume and venous cerebral blood volume using Fourier transform-based velocity-selective pulse trains

PURPOSE

To develop 3D MRI methods for cerebral blood volume (CBV) and venous cerebral blood volume (vCBV) estimation with whole-brain coverage using Fourier transform-based velocity-selective (FT-VS) pulse trains.

METHODS

For CBV measurement, FT-VS saturation pulse trains were used to suppress static tissue, whereas CSF contamination was corrected voxel-by-voxel using a multi-readout acquisition and a fast CSF T₂ scan. The vCBV mapping was achieved by inserting an arterial-nulling module that included a FT-VS inversion pulse train. Using these methods, CBV and vCBV maps were obtained on 6 healthy volunteers at 3 T.

RESULTS

The mean CBV and vCBV values in gray matter and white matter in different areas of the brain showed high correlation (r = 0.95 and P < .0001). The averaged CBV and vCBV values of the whole brain were 5.4 ± 0.6 mL/100 g and 2.5 ± 0.3 mL/100 g in gray matter, and 2.6 ± 0.5 mL/100 g and 1.5 ± 0.2 mL/100 g in white matter, respectively, comparable to the literature.

CONCLUSION

The feasibility of FT-VS-based CBV and vCBV estimation was demonstrated for 3D acquisition with large spatial coverage.

Comparative Assessment of the Proteolytic Stability and Impact of Poly-Arginine Peptides R18 and R18D on Infarct Growth and Penumbral Tissue Preservation Following Middle Cerebral Artery Occlusion in the Sprague Dawley Rat

Poly-arginine peptides R18 and R18D have previously been demonstrated to be neuroprotective in ischaemic stroke models. Here we examined the proteolytic stability and efficacy of R18 and R18D in reducing infarct core growth and preserving the ischaemic penumbra following middle cerebral artery occlusion (MCAO) in the Sprague Dawley rat. R18 (300 or 1000 nmol/kg), R18D (300 nmol/kg) or saline were administered intravenously 10 min after MCAO induced using a filament. Serial perfusion and diffusion-weighted MRI imaging was performed to measure changes in the infarct core and penumbra from time points between 45- and 225-min post-occlusion. Repeated measures analyses of infarct growth and penumbral tissue size were evaluated using generalised linear mixed models (GLMMs). R18D (300 nmol/kg) was most effective in slowing infarct core growth (46.8 mm3 reduction; p < 0.001) and preserving penumbral tissue (21.6% increase; p < 0.001), followed by R18 at the 300 nmol/kg dose (core: 29.5 mm3 reduction; p < 0.001, penumbra: 12.5% increase; p < 0.001). R18 at the 1000 nmol/kg dose had a significant impact in slowing core growth (19.5 mm3 reduction; p = 0.026), but only a modest impact on penumbral preservation (6.9% increase; p = 0.062). The in vitro anti-excitotoxic neuroprotective efficacy of R18D was also demonstrated to be unaffected when preincubated for 1-3 h or overnight, in a cell lysate prepared from dying neurons or with the proteolytic enzyme, plasmin, whereas the neuroprotective efficacy of R18 was significantly reduced after a 2-h incubation. These findings highlight the capacity of poly-arginine peptides to reduce infarct growth and preserve the ischaemic penumbra, and confirm the superior efficacy and proteolytic stability of R18D, which indicates that this peptide is likely to retain its neuroprotective properties when co-administered with alteplase during thrombolysis for acute ischaemic stroke.

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.

Non-linear fitting with joint spatial regularization in arterial spin labeling

Multi-Delay single-shot arterial spin labeling (ASL) imaging provides accurate cerebral blood flow (CBF) and, in addition, arterial transit time (ATT) maps but the inherent low SNR can be challenging. Especially standard fitting using non-linear least squares often fails in regions with poor SNR, resulting in noisy estimates of the quantitative maps. State-of-the-art fitting techniques improve the SNR by incorporating prior knowledge in the estimation process which typically leads to spatial blurring. To this end, we propose a new estimation method with a joint spatial total generalized variation regularization on CBF and ATT. This joint regularization approach utilizes shared spatial features across maps to enhance sharpness and simultaneously improves noise suppression in the final estimates. The proposed method is evaluated at three levels, first on synthetic phantom data including pathologies, followed by in vivo acquisitions of healthy volunteers, and finally on patient data following an ischemic stroke. The quantitative estimates are compared to two reference methods, non-linear least squares fitting and a state-of-the-art ASL quantification algorithm based on Bayesian inference. The proposed joint regularization approach outperforms the reference implementations, substantially increasing the SNR in CBF and ATT while maintaining sharpness and quantitative accuracy in the estimates.

Brain Perfusion Bridges Virtual-Reality Spatial Behavior to TPH2 Genotype for Head Acceleration Events

Neuroimaging demonstrates that athletes of collision sports can suffer significant changes to their brain in the absence of concussion, attributable to head acceleration event (HAE) exposure. In a sample of 24 male Division I collegiate football players, we examine the relationships between tryptophan hydroxylase 2 (TPH2), a gene involved in neurovascular function, regional cerebral blood flow (rCBF) measured by arterial spin labeling, and virtual reality (VR) motor performance, both pre-season and across a single football season. For the pre-season, TPH2 T-carriers showed lower rCBF in two left hemisphere foci (fusiform gyrus/thalamus/hippocampus and cerebellum) in association with higher (better performance) VR Reaction Time, a dynamic measure of sensory-motor reactivity and efficiency of visual-spatial processing. For TPH2 CC homozygotes, higher pre-season rCBF in these foci was associated with better performance on VR Reaction Time. A similar relationship was observed across the season, where TPH2 T-carriers showed improved VR Reaction Time associated with decreases in rCBF in the right hippocampus/amygdala, left middle temporal lobe, and left insula/putamen/pallidum. In contrast, TPH2 CC homozygotes showed improved VR Reaction Time associated with increases in rCBF in the same three clusters. These findings show that TPH2 T-carriers have an abnormal relationship between rCBF and the efficiency of visual-spatial processing that is exacerbated after a season of high-impact sports in the absence of diagnosable concussion. Such gene-environment interactions associated with behavioral changes after exposure to repetitive HAEs have been unrecognized with current clinical analytical tools and warrant further investigation. Our results demonstrate the importance of considering neurovascular factors along with traumatic axonal injury to study long-term effects of repetitive HAEs.

Intravenous Infusion of Mesenchymal Stem Cells Enhances Therapeutic Efficacy of Reperfusion Therapy in Cerebral Ischemia

OBJECTIVE

Reperfusion therapy is a standard therapeutic strategy for acute stroke. Non-favorable outcomes are thought to partially result from impaired microcirculatory flow in ischemic tissue. Intravenous infusion of mesenchymal stem cells (MSCs) reduces stroke volume and improves behavioral function in stroke. One suggested therapeutic mechanism is the restoration of the microvasculature. The goal of this study was to determine whether infused MSCs enhance the therapeutic efficacy of reperfusion therapy following stroke in rats.

METHODS

First, to establish a transient middle cerebral artery occlusion (MCAO) model displaying approximately identical neurologic function and lesion volume as seen in permanent MCAO (pMCAO) at day 7 after stroke induction, we transiently occluded the MCA for 90, 110, and 120 minutes. We found that the 110-minute occlusion met these criteria and was used as the transient MCAO (tMCAO) model. Next, 4 MCAO groups were used to compare the therapeutic efficacy of infused MSCs: (1) pMCAO+vehicle, (2) tMCAO+vehicle, (3) pMCAO+MSC, and (4) tMCAO+MSC. Our ischemic model was a unique ischemic model system in which both pMCAO and tMCAO provided similar outcomes during the study period in the groups without MSC infusion groups. Behavioral performance, ischemic volume, and regional cerebral blood flow (rCBF) using arterial spin labeling-magnetic resonance imaging and histologic evaluation of microvasculature was performed.

RESULTS

The behavioral function, rCBF, and restoration of microvasculature were greater in group 4 than in group 3. Thus, infused MSCs facilitated the therapeutic efficacy of MCA reperfusion in this rat model system.

CONCLUSIONS

Intravenous infusion of MSCs may enhance therapeutic efficacy of reperfusion therapy.

Cerebral blood flow and cerebrovascular reactivity are preserved in a mouse model of cerebral microvascular amyloidosis

Impaired cerebrovascular function is an early biomarker for cerebral amyloid angiopathy (CAA), a neurovascular disease characterized by amyloid-β accumulation in the cerebral vasculature, leading to stroke and dementia. The transgenic Swedish Dutch Iowa (Tg-SwDI) mouse model develops cerebral microvascular amyloid-β deposits, but whether this leads to similar functional impairments is incompletely understood. We assessed cerebrovascular function longitudinally in Tg-SwDI mice with arterial spin labeling (ASL)-magnetic resonance imaging (MRI) and laser Doppler flowmetry (LDF) over the course of amyloid-β deposition. Unexpectedly, Tg-SwDI mice showed similar baseline perfusion and cerebrovascular reactivity estimates as age-matched wild-type control mice, irrespective of modality (ASL or LDF) or anesthesia (isoflurane or urethane and α-chloralose). Hemodynamic changes were, however, observed as an effect of age and anesthesia. Our findings contradict earlier results obtained in the same model and question to what extent microvascular amyloidosis as seen in Tg-SwDI mice is representative of cerebrovascular dysfunction observed in CAA patients.

Sex-related differences in arterial spin-labelled perfusion of metabolically active brain structures in neonatal hypoxic-ischaemic encephalopathy

AIM

To investigate the sex-related differences in arterial spin-labelled (ASL) perfusion of metabolically active brain structures in neonatal hypoxic-ischaemic encephalopathy (HIE).

MATERIALS AND METHODS

Seventy-three term neonates were identified for a retrospective case-control study following an institutional review board (IRB) approved protocol. The cerebral pulsed arterial spin labelling values were compared by permutation test to identify metabolically active brain structures with significant perfusion changes between 10 male controls and eight female controls, and between 31 HIE males and 24 HIE females.

RESULTS

In the perfusion comparison between HIE male and female neonates, significantly lower perfusion was found in the thalamus in males (p=0.02). The other brain clusters, including basal ganglia, hippocampus cluster, cingulate gyrus cluster, brainstem cluster, sensorimotor cortex cluster, and cerebellum and peduncle cluster, demonstrated no significant differences between HIE males and females. In the perfusion comparison between male and female controls, there were no significant perfusion changes in those brain clusters.

CONCLUSION

Brain perfusion in neonatal HIE differs between males and females in the thalamus, a metabolically active region within neonates, with males demonstrating lower perfusion. This difference in perfusion may reflect sex-related disparities in response to and recovery from hypoxic-ischaemic events.