Evaluation of perinatal arterial ischemic stroke using noninvasive arterial spin labeling perfusion MRI

Multi-wavelength multi-distance diffuse correlation spectroscopy system for assessment of premature infants' cerebral hemodynamics

Infants born at an extremely low gestational age (ELGA, < 29 weeks) are at an increased risk of intraventricular hemorrhage (IVH), and there is a need for standalone, safe, easy-to-use tools for monitoring cerebral hemodynamics. We have built a multi-wavelength multi-distance diffuse correlation spectroscopy device (MW-MD-DCS), which utilizes time-multiplexed, long-coherence lasers at 785, 808, and 853 nm, to simultaneously quantify the index of cerebral blood flow (CBFi) and the hemoglobin oxygen saturation (SO2). We show characterization data on liquid phantoms and demonstrate the system performance on the forearm of healthy adults, as well as clinical data obtained on two preterm infants.

Analysis of the posterior cerebral perfusion status and clinical prognostic value in chronic unilateral middle cerebral artery occlusion using SWAN combined with 3D-ASL

To investigate the predictive value of T2 star-weighted angiography (SWAN) combined with 3-dimensional (3D) arterial spin labeling (3D-ASL) to assess cerebral perfusion status and clinical prognosis in chronic unilateral middle cerebral artery (MCA) M1 occlusion. This study included 55 patients diagnosed with chronic unilateral MCA M1 occlusion using 3D time-of-flight magnetic resonance angiography between January 2018 and July 2022. Based on the prominent vessel sign (PVS) shown in the SWAN sequence, the patients were divided into PVS-positive (n = 26) and PVS-negative (n = 29) groups. Cerebral blood flow (CBF) was selected in the affected regions of the frontal, parietal, and temporal lobes (regions of interest = 200 ± 20 mm2) using pseudo-color maps in the 3D-ASL sequence. Each patient was followed up for ischemic cerebrovascular disease within 12 months of diagnosis. The collected data were statistically analyzed to evaluate the predictive value of SWAN and 3D-ASL for the clinical prognosis of patients with chronic unilateral MCA M1 occlusion. Patients were divided into 2 groups based on the occurrence of an ischemic cerebrovascular event within 12 months (ischemic cerebrovascular event [acute ischemic stroke + transient ischemic attack] and non-ischemic cerebrovascular event groups, including 30 and 25 cases, respectively). The incidence of ischemic cerebrovascular events within 12 months was significantly higher in the PVS-positive group than in the PVS-negative group (92.31% vs 20.69%). Furthermore, the CBF values of the affected frontal, parietal, and temporal lobes were significantly lower in the ischemic cerebrovascular event group than in the non-ischemic cerebrovascular event group (P < .05). According to the receiver operating characteristic curve, the CBF values of the affected frontal, parietal, and temporal lobes in patients with chronic unilateral MCA M1 occlusion strongly correlated with ischemic cerebrovascular disease within 12 months. PVS-negative display and good collateral circulation were closely related to clinical prognosis in patients with chronic unilateral MCA M1 occlusion.

Neonatal Arterial Ischaemic Stroke: Advances in Pathologic Neural Death, Diagnosis, Treatment, and Prognosis

Neonatal arterial ischaemic stroke (NAIS) is caused by focal arterial occlusion and often leads to severe neurological sequelae. Neural deaths after NAIS mainly include necrosis, apoptosis, necroptosis, autophagy, ferroptosis, and pyroptosis. These neural deaths are mainly caused by upstream stimulations, including excitotoxicity, oxidative stress, inflammation, and death receptor pathways. The current clinical approaches to managing NAIS mainly focus on supportive treatments, including seizure control and anticoagulation. In recent years, research on the pathology, early diagnosis, and potential therapeutic targets of NAIS has progressed. In this review, we summarise the latest progress of research on the pathology, diagnosis, treatment, and prognosis of NAIS and highlight newly potential diagnostic and treatment approaches.

Expert consensus on the clinical practice of neonatal brain magnetic resonance imaging

In recent years, magnetic resonance imaging (MRI) has been widely used in evaluating neonatal brain development, diagnosing neonatal brain injury, and predicting neurodevelopmental prognosis. Based on current research evidence and clinical experience in China and overseas, the Neonatologist Society of Chinese Medical Doctor Association has developed a consensus on the indications and standardized clinical process of neonatal brain MRI. The consensus has the following main points. (1) Brain MRI should be performed for neonates suspected of hypoxic-ischemic encephalopathy, intracranial infection, stroke and unexplained convulsions; brain MRI is not considered a routine in the management of preterm infants, but it should be performed for further evaluation when cranial ultrasound finds evidence of brain injury; as for extremely preterm or extremely low birth weight infants without abnormal ultrasound findings, it is recommended that they should undergo MRI examination at term equivalent age once. (2) Neonates should undergo MRI examination in a non-sedated state if possible. (3) During MRI examination, vital signs should be closely monitored to ensure safety; the necessity of MRI examination should be strictly evaluated for critically ill neonates, and magnetic resonance compatible incubator and ventilator can be used. (4) At present, 1.5 T or 3.0 T equipment can be used for neonatal brain MRI examination, and the special coil for the neonatal head should be used to improve signal-to-noise ratio; routine neonatal brain MRI sequences should at least include axial T1 weighted image (T1WI), axial T2 weighted imaging (T2WI), diffusion-weighted imaging, and sagittal T1WI or T2WI. (5) It is recommended to use a structured and graded reporting system, and reports by at least two reviewers and multi-center collaboration are recommended to increase the reliability of the report.

Noncontrast Pediatric Brain Perfusion: Arterial Spin Labeling and Intravoxel Incoherent Motion

Noncontrast magnetic resonance imaging techniques for measuring brain perfusion include arterial spin labeling (ASL) and intravoxel incoherent motion (IVIM). These techniques provide noninvasive and repeatable assessment of cerebral blood flow or cerebral blood volume without the need for intravenous contrast. This article discusses the technical aspects of ASL and IVIM with a focus on normal physiologic variations, technical parameters, and artifacts. Multiple pediatric clinical applications are presented, including tumors, stroke, vasculopathy, vascular malformations, epilepsy, migraine, trauma, and inflammation.

Regulation of the Cerebral Circulation During Development

The cerebral microcirculation undergoes dynamic changes in parallel with the development of neurons, glia, and their energy metabolism throughout gestation and postnatally. Cerebral blood flow (CBF), oxygen consumption, and glucose consumption are as low as 20% of adult levels in humans born prematurely but eventually exceed adult levels at ages 3 to 11 years, which coincide with the period of continued brain growth, synapse formation, synapse pruning, and myelination. Neurovascular coupling to sensory activation is present but attenuated at birth. By 2 postnatal months, the increase in CBF often is disproportionately smaller than the increase in oxygen consumption, in contrast to the relative hyperemia seen in adults. Vascular smooth muscle myogenic tone increases in parallel with developmental increases in arterial pressure. CBF autoregulatory response to increased arterial pressure is intact at birth but has a more limited range with arterial hypotension. Hypoxia-induced vasodilation in preterm fetal sheep with low oxygen consumption does not sustain cerebral oxygen transport, but the response becomes better developed for sustaining oxygen transport by term. Nitric oxide tonically inhibits vasomotor tone, and glutamate receptor activation can evoke its release in lambs and piglets. In piglets, astrocyte-derived carbon monoxide plays a central role in vasodilation evoked by glutamate, ADP, and seizures, and prostanoids play a large role in endothelial-dependent and hypercapnic vasodilation. Overall, homeostatic mechanisms of CBF regulation in response to arterial pressure, neuronal activity, carbon dioxide, and oxygenation are present at birth but continue to develop postnatally as neurovascular signaling pathways are dynamically altered and integrated. © 2021 American Physiological Society. Compr Physiol 11:1-62, 2021.

Quantitative validation of MRI mapping of cerebral venous oxygenation with direct blood sampling: A graded-O2 study in piglets

PURPOSE

To validate two neonatal cerebral venous oxygenation (Y_v ) MRI techniques, T₂ relaxation under phase contrast (TRUPC) and accelerated TRUPC (aTRUPC) MRI, with oxygenation measured with direct blood sampling.

METHODS

In vivo experiments were performed on seven healthy newborn piglets. For each piglet, a catheter was placed in the superior sagittal sinus to obtain venous blood samples for blood gas oximetry measurement as a gold standard. During the MRI experiment, three to five venous oxygenation levels were achieved in each piglet by varying inhaled O₂ content and breathing rate. Under each condition, Y_v values of the superior sagittal sinus measured by TRUPC, aTRUPC, and blood gas oximetry were obtained. The Y_v quantification in TRUPC and aTRUPC used a standard bovine blood calibration model. The aTRUPC scan was repeated twice to assess its reproducibility. Agreements among TRUPC Y_v , aTRUPC Y_v , and blood gas oximetry were evaluated by intraclass correlation coefficient (ICC) and paired Student's t-test.

RESULTS

The mean hematocrit was 23.6 ± 6.5% among the piglets. Across all measurements, Y_v values were 51.9 ± 21.3%, 54.1 ± 18.8%, and 53.7 ± 19.2% for blood gas oximetry, TRUPC and aTRUPC, respectively, showing no significant difference between any two methods (P > .3). There were good correlations between TRUPC and blood gas Y_v (ICC = 0.801; P < .0001), between aTRUPC and blood gas Y_v (ICC = 0.809; P < .0001), and between aTRUPC and TRUPC Y_v (ICC = 0.887; P < .0001). The coefficient of variation of aTRUPC Y_v was 8.1 ± 9.9%.

CONCLUSION

The values of Y_v measured by TRUPC and aTRUPC were in good agreement with blood gas oximetry. These findings suggest that TRUPC and aTRUPC can provide accurate quantifications of Y_v in major cerebral veins.

Arterial spin labeling in neonatal magnetic resonance imaging - first experience and new observations

Purpose

Arterial spin labeling (ASL) is a noninvasive non-contrast technique of perfusion imaging that uses endogenous water from the blood as the perfusion tracer, with very scant data on its use in neonates. The authors present the added value of ASL in the examined babies in their own material and discuss it in the light of the existing literature.

Material and methods

During the first 10 months after the purchase of a new magnetic resonance imaging (MRI) scanner, 123 neonates were examined using it in an MR-compatible incubator, 117 of them had brain MRI, and in 104 ASL was incorporated in the routine protocol, which resulted in prolongation of the study time by approximately 4 minutes. 3D ASL sequence uses Pulsed Continuous Arterial Spin Labeling (PCASL; aka pseudo continuous) technique.

Results

The quality of the cerebral blood flow (CBF) maps was good in all cases but 2 because all the babies were sedated. Apart from the knowledge about normal perfusion patterns in the preterm and term neonatal brains, the use of ASL sequence provided important additional information in 11 cases (10.8%): increased CBF correlating with electroencephalographic seizure localization in otherwise normal MRI (n = 1), increased CBF in the cortex without clinical information about seizures and with posthaemorrhagic changes (n = 1), increased CBF in the brain stem and decreased in the upper parts of the brain (n = 2), probably reflecting the homeostatic mechanism which allows preferential perfusion of the vital structures of the brain stem, hypoperfusion (n = 1) or hypoperfusion with peripheral hyperperfusion (n = 1) in the area of stroke, hypoperfusion of the posterior areas of the brain in the presence of subarachnoid or epidural haemorrhage (n = 3), significantly increased CBF in the presumed nidus of arteriovenous malformation causing haemorrhage (n = 1), and lack of perfusion in the supratentorial compartment in a case of suspected brain death (n = 1).

Conclusions

Our short experience but relatively large volume of material encourages the use of ASL in routine neonatal MRI as a useful and non-time-consuming tool providing additional important clinical information in a significant percentage of cases.

Multi-Parametric Evaluation of Cerebral Hemodynamics in Neonatal Piglets Using Non-Contrast-Enhanced Magnetic Resonance Imaging Methods

BACKGROUND

Disruption of brain oxygen delivery and consumption after hypoxic-ischemic injury contributes to neonatal mortality and neurological impairment. Measuring cerebral hemodynamic parameters, including cerebral blood flow (CBF), oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO₂ ), is clinically important.

PURPOSE

Phase-contrast (PC), velocity-selective arterial spin labeling (VSASL), and T₂ -relaxation-under-phase-contrast (TRUPC) are magnetic resonance imaging (MRI) techniques that have shown promising results in assessing cerebral hemodynamics in humans. We aimed to test their feasibility in quantifying CBF, OEF, and CMRO₂ in piglets.

STUDY TYPE

Prospective.

ANIMAL MODEL

Ten neonatal piglets subacutely recovered from global hypoxia-ischemia (N = 2), excitotoxic brain injury (N = 6), or sham procedure (N = 2).

FIELD STRENGTH/SEQUENCE

VSASL, TRUPC, and PC MRI acquired at 3.0 T.

ASSESSMENT

Regional CBF was measured by VSASL. Global CBF was quantified by both PC and VSASL. TRUPC assessed OEF at the superior sagittal sinus (SSS) and internal cerebral veins (ICVs). CMRO₂ was calculated from global CBF and SSS-derived OEF. End-tidal carbon dioxide (EtCO₂ ) levels of the piglets were also measured. Brain damage was assessed in tissue sections postmortem by counting damaged neurons.

STATISTICAL TESTS

Spearman correlations were performed to evaluate associations among CBF (by PC or VSASL), OEF, CMRO₂ , EtCO₂ , and the pathological neuron counts. Paired t-test was used to compare OEF at SSS with OEF at ICV.

RESULTS

Global CBF was 32.1 ± 14.9 mL/100 g/minute and 30.9 ± 8.3 mL/100 g/minute for PC and VSASL, respectively, showing a significant correlation (r = 0.82, P < 0.05). OEF was 54.9 ± 8.8% at SSS and 46.1 ± 5.6% at ICV, showing a significant difference (P < 0.05). Global CMRO₂ was 79.1 ± 26.2 μmol/100 g/minute and 77.2 ± 12.2 μmol/100 g/minute using PC and VSASL-derived CBF, respectively. EtCO₂ correlated positively with PC-based CBF (r = 0.81, P < 0.05) but negatively with OEF at SSS (r = -0.84, P < 0.05). Relative CBF of subcortical brain regions and OEF at ICV did not significantly correlate, respectively, with the ratios of degenerating-to-total neurons (P = 0.30, P = 0.10).

DATA CONCLUSION

Non-contrast MRI can quantify cerebral hemodynamic parameters in normal and brain-injured neonatal piglets.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 2.

Structural and functional connectivity of motor circuits after perinatal stroke: A machine learning study

Developmental neuroplasticity allows young brains to adapt via experiences early in life and also to compensate after injury. Why certain individuals are more adaptable remains underexplored. Perinatal stroke is an ideal human model of neuroplasticity with focal lesions acquired near birth in a healthy brain. Machine learning can identify complex patterns in multi-dimensional datasets. We used machine learning to identify structural and functional connectivity biomarkers most predictive of motor function. Forty-nine children with perinatal stroke and 27 controls were studied. Functional connectivity was quantified by fluctuations in blood oxygen-level dependent (BOLD) signal between regions. White matter tractography of corticospinal tracts quantified structural connectivity. Motor function was assessed using validated bimanual and unimanual tests. RELIEFF feature selection and random forest regression models identified predictors of each motor outcome using neuroimaging and demographic features. Unilateral motor outcomes were predicted with highest accuracy (8/54 features r = 0.58, 11/54 features, r = 0.34) but bimanual function required more features (51/54 features, r = 0.38). Connectivity of both hemispheres had important roles as did cortical and subcortical regions. Lesion size, age at scan, and type of stroke were predictive but not highly ranked. Machine learning regression models may represent a powerful tool in identifying neuroimaging biomarkers associated with clinical motor function in perinatal stroke and may inform personalized targets for neuromodulation.

Arterial spin labeling perfusion in neonates

Abnormal brain perfusion is a key mechanism underlying neonatal brain injury. Understanding the mechanisms leading to brain perfusion changes in high-risk neonates and how these alterations may influence brain development is key to improve therapeutic strategies preventing brain injury and the neurodevelopmental outcome of these infants. To date, several studies demonstrated that Arterial Spin Labeling is a reliable tool to accurately and non-invasively analyze brain perfusion, facilitating the understanding of normal and pathological mechanisms underlying neonatal brain maturation and injury. This paper provides an overview of the normal pattern of brain perfusion on Arterial Spin Labeling in term and preterm neonates, and reviews perfusion abnormalities associated with common neonatal neurological disorders.

Imaging Developmental and Interventional Plasticity Following Perinatal Stroke

Perinatal stroke occurs around the time of birth and leads to lifelong neurological disabilities including hemiparetic cerebral palsy. Magnetic resonance imaging (MRI) has revolutionized our understanding of developmental neuroplasticity following early injury, quantifying volumetric, structural, functional, and metabolic compensatory changes after perinatal stroke. Such techniques can also be used to investigate how the brain responds to treatment (interventional neuroplasticity). Here, we review the current state of knowledge of how established and emerging neuroimaging modalities are informing neuroplasticity models in children with perinatal stroke. Specifically, we review structural imaging characterizing lesion characteristics and volumetrics, diffusion tensor imaging investigating white matter tracts and networks, task-based functional MRI for localizing function, resting state functional imaging for characterizing functional connectomes, and spectroscopy examining neurometabolic changes. Key challenges and exciting avenues for future investigations are also considered.

Development of a combined, sequential real-time fMRI and fNIRS neurofeedback system to enhance motor learning after stroke

BACKGROUND

After stroke, wrist extension dyscoordination precludes functional arm/hand. We developed a more spatially precise brain signal for use in brain computer interface (BCI's) for stroke survivors.

NEW METHOD

Combination BCI protocol of real-time functional magnetic resonance imaging (rt-fMRI) sequentially followed by functional near infrared spectroscopy (rt-fNIRS) neurofeedback, interleaved with motor learning sessions without neural feedback. Custom Matlab and Python code was developed to provide rt-fNIRS-based feedback to the chronic stroke survivor, system user.

RESULTS

The user achieved a maximum of 71 % brain signal accuracy during rt-fNIRS neural training; progressive focus of brain activation across rt-fMRI neural training; increasing trend of brain signal amplitude during wrist extension across rt-fNIRS training; and clinically significant recovery of arm coordination and active wrist extension.

COMPARISON WITH EXISTING METHODS

Neurorehabilitation, peripherally directed, shows limited efficacy, as do EEG-based BCIs, for motor recovery of moderate/severely impaired stroke survivors. EEG-based BCIs are based on electrophysiological signal; whereas, rt-fMRI and rt-fNIRS are based on neurovascular signal.

CONCLUSION

The system functioned well during user testing. Methods are detailed for others' use. The system user successfully engaged rt-fMRI and rt-fNIRS neurofeedback systems, modulated brain signal during rt-fMRI and rt-fNIRS training, according to volume of brain activation and intensity of signal, respectively, and clinically significantly improved limb coordination and active wrist extension. fNIRS use in this case demonstrates a feasible/practical BCI system for further study with regard to use in chronic stroke rehab, and fMRI worked in concept, but cost and some patient-use issues make it less feasible for clinical practice.

Anoxic Brain Injury Detection with the Normalized Diffusion to ASL Perfusion Ratio: Implications for Blood-Brain Barrier Injury and Permeability

BACKGROUND AND PURPOSE

Anoxic brain injury is a result of prolonged hypoxia. We sought to describe the nonquantitative arterial spin-labeling perfusion imaging patterns of anoxic brain injury, characterize the relationship of arterial spin-labeling and DWI, and evaluate the normalized diffusion-to-perfusion ratio to differentiate patients with anoxic brain injury from healthy controls.

MATERIALS AND METHODS

We identified all patients diagnosed with anoxic brain injuries from 2002 to 2019. Twelve ROIs were drawn on arterial spin-labeling with coordinate-matched ROIs identified on DWI. Linear regression analysis was performed to examine the relationship between arterial spin-labeling perfusion and diffusion signal. Normalized diffusion-to-perfusion maps were generated using a custom-built algorithm.

RESULTS

Thirty-five patients with anoxic brain injuries and 34 healthy controls were identified. Linear regression analysis demonstrated a significant positive correlation between arterial spin-labeling and DWI signal. By means of a combinatory cutoff of slope of >0 and R² of > 0.78, linear regression using arterial spin-labeling and DWI showed a sensitivity of 0.86 (95% CI, 0.71-0.94) and specificity of 0.82 (95% CI, 0.66-0.92) for anoxic brain injuries. A normalized diffusion-to-perfusion color map demonstrated heterogeneous ratios throughout the brain in healthy controls and homogeneous ratios in patients with anoxic brain injuries.

CONCLUSIONS

In anoxic brain injuries, a homogeneously positive correlation between qualitative perfusion and DWI signal was identified so that areas of increased diffusion signal showed increased ASL signal. By exploiting this relationship, the normalized diffusion-to-perfusion ratio color map may be a valuable imaging biomarker for diagnosing anoxic brain injury and potentially assessing BBB integrity.

Brain Activity and Cerebral Oxygenation After Perinatal Arterial Ischemic Stroke Are Associated With Neurodevelopment

Background and Purpose- In infants with perinatal arterial ischemic stroke (PAIS), early prognosis of neurodevelopmental outcome is important to adequately inform parents and caretakers. Early continuous neuromonitoring after PAIS may improve early prognosis. Our aim was to study early cerebral electrical activity and oxygenation measured by amplitude-integrated electroencephalography (aEEG) and near-infrared spectroscopy in term neonates with PAIS and relate these to the development of cerebral palsy and cognitive deficit. Methods- aEEG patterns and regional cerebral oxygen saturation (rScO2) levels of both hemispheres were studied for 120 hours from the first clinical symptoms of PAIS (ie, seizures) onward. Multivariable analyses were used to investigate the association between aEEG, near-infrared spectroscopy, clinical variables, and neurodevelopmental outcome. Results- In 52 patients with PAIS (gestational age, 40.4±1.4 weeks; birth weight, 3282±479 g), median time to a continuous background pattern was longer in the ipsilesional compared with the contralesional hemisphere (13.5 versus 10.0 hours; P<0.05). rScO2 decreased over time in both hemispheres but less in the ipsilesional one, resulting in a rScO2 asymmetry ratio of 4.5% (interquartile range, -4.3% to 5.9%; P<0.05) between hemispheres from day 3 after symptoms onward. Both time to normal background pattern and asymmetry in rScO2 were negatively affected by gestational age, size of the PAIS, use of antiepileptic drugs, and mechanical ventilation. After correction for size of the PAIS on magnetic resonance imaging, a slower recovery of background pattern on ipsilesional aEEG and increased rScO2 asymmetry between hemispheres was related with an increased risk for cognitive deficit (<-1 SD) at a median of 24.0 (interquartile range, 18.4-24.4) months of age. Conclusions- Recovery of background pattern on aEEG and cerebral oxygenation are both affected by PAIS and related to neurocognitive development. Both measurements may provide valuable early prognostic information. Additionally, monitoring cerebral activity and oxygenation may be useful in identifying infants eligible for early neuroprotective interventions and to detect early effects of these interventions.

Vessel-specific quantification of neonatal cerebral venous oxygenation

PURPOSE

Noninvasive measurement of cerebral venous oxygenation (Y_v ) in neonates is important in the assessment of brain oxygen extraction and consumption, and may be useful in characterizing brain development and neonatal brain diseases. This study aims to develop a rapid method for vessel-specific measurement of Y_v in neonates.

METHODS

We developed a pulse sequence, named accelerated T₂ -relaxation-under-phase-contrast (aTRUPC), which consists of velocity-encoding phase-contrast module to isolate pure blood signal, flow-insensitive T₂ -preparation to quantify blood T₂ , and turbo-field-echo (TFE) scheme for rapid image acquisition, which is critical for neonatal MRI. A series of studies were conducted. First, the pulse sequence was optimized in terms of TFE factor, velocity encoding (VENC), and slice thickness for best sensitivity. Second, to account for the influence of TFE acquisition on T₂ quantification, simulation and experiments were conducted to establish the relationship between TFE-T₂ and standard T₂ . Finally, the complete aTRUPC sequence was applied on a group of healthy neonates and normative Y_v values were determined.

RESULTS

Optimal parameters of aTRUPC in neonates were found to be a TFE factor of 15, VENC of 5 cm/s, and slice thickness of 10 mm. The TFE-T₂ was on average 3.9% lower than standard T₂ . These two measures were strongly correlated (R² = 0.86); thus their difference can be accounted for by a correction equation, T_2,standard = 1.2002 × T_2,TFE - 10.6276. Neonatal Y_v values in veins draining cortical brain and those draining central brain were 64.8 ± 2.9% and 70.2 ± 3.3%, respectively, with a significant difference (P =.02).

CONCLUSION

The aTRUPC MRI has the potential to provide vessel-specific quantification of cerebral Y_v in neonates.

Postoperative cerebral oxygenation was not associated with new brain injury in infants with congenital heart disease

OBJECTIVE

The aim of this study was to evaluate postoperative indices of cerebral oxygenation and autoregulation in infants with critical congenital heart disease in relation to new postoperative ischemic brain injury.

METHODS

This prospective, clinical cohort included 77 infants with transposition of the great arteries (N = 19), left ventricular outflow tract obstruction (N = 30), and single ventricle physiology (N = 28) undergoing surgery at 30 days or less of life. Postoperative near-infrared spectroscopy and physiologic monitoring were applied to extract mean arterial blood pressure, regional cerebral oxygen saturation, fractional tissue oxygen extraction, and regional cerebral oxygen saturation mean arterial blood pressure correlation coefficient (≥0.5 considered sign of impaired cerebral autoregulation). New postoperative ischemic injury was defined as moderate-severe white matter injury or focal infarction on magnetic resonance imaging. Low cardiac output syndrome was measured as lactate greater than 4 mmol/L with pH less than 7.30.

RESULTS

After surgery, regional cerebral oxygen saturation was decreased in all congenital heart disease groups with a notable increase in regional cerebral oxygen saturation between 6 and 12 hours after surgery, on average with a factor of 1.4 (range, 1.1-2.4). Both single ventricle physiology and postoperative low cardiac output syndrome were associated with lower regional cerebral oxygen saturation and increased time with correlation coefficient of 0.5 or greater. New postoperative ischemic injury was seen in 39 patients (53%) and equally distributed across congenital heart disease groups. Postoperative regional cerebral oxygen saturation, fractional tissue oxygen extraction, and correlation coefficient were not independently associated with new postoperative white matter injury or focal infarction (mixed-model analysis, all F > 0.12).

CONCLUSIONS

Postoperative indices of cerebral oxygenation and cerebral autoregulation are not independent predictors of new ischemic brain injury in infants with critical congenital heart disease. Further exploration of the complex interplay among low regional cerebral oxygen saturation, low cardiac output syndrome, and heart defect is required to identify potential biomarkers enabling early intervention for ischemic brain injury.

A Systemic Review of Functional Near-Infrared Spectroscopy for Stroke: Current Application and Future Directions

Background: Survivors of stroke often experience significant disability and impaired quality of life. The recovery of motor or cognitive function requires long periods. Neuroimaging could measure changes in the brain and monitor recovery process in order to offer timely treatment and assess the effects of therapy. A non-invasive neuroimaging technique near-infrared spectroscopy (NIRS) with its ambulatory, portable, low-cost nature without fixation of subjects has attracted extensive attention. Methods: We conducted a comprehensive literature review in order to review the use of NIRS in stroke or post-stroke patients in July 2018. NCBI Pubmed database, EMBASE database, Cochrane Library and ScienceDirect database were searched. Results: Overall, we reviewed 66 papers. NIRS has a wide range of application, including in monitoring upper limb, lower limb recovery, motor learning, cortical function recovery, cerebral hemodynamic changes, cerebral oxygenation, as well as in therapeutic method, clinical researches, and evaluation of the risk for stroke. Conclusions: This study provides a preliminary evidence of the application of NIRS in stroke patients as a monitoring, therapeutic, and research tool. Further studies could give more emphasize on the combination of NIRS with other techniques and its utility in the prevention of stroke.

Perinatal arterial ischemic stroke

Perinatal arterial ischemic stroke is a relatively common and serious neurologic disorder that can affect the fetus, the preterm, and the term-born infant. It carries significant long-term disabilities. Herein we describe the current understanding of its etiology, pathophysiology and classification, different presentations, and optimal early management. We discuss the role of different brain imaging modalities in defining the extent of lesions and the impact this has on the prediction of outcomes. In recent years there has been progress in treatments, making early diagnosis and the understanding of likely morbidities imperative. An overview is given of the range of possible outcomes and optimal approaches to follow-up and support for the child and their family in the light of present knowledge.

Fetal and neonatal neuroimaging

Magnetic resonance imaging (MRI) can provide detail of the soft tissues of the fetal and neonatal brain that cannot be obtained by any other imaging modality. Conventional T1 and T2 weighted sequences provide anatomic detail of the normally developing brain and can demonstrate lesions, including those associated with preterm birth, hypoxic ischemic encephalopathy, perinatal arterial stroke, infections, and congenital malformations. Specialized imaging techniques can be used to assess cerebral vasculature (magnetic resonance angiography and venography), cerebral metabolism (magnetic resonance spectroscopy), cerebral perfusion (arterial spin labeling), and function (functional MRI). A wealth of quantitative tools, most of which were originally developed for the adult brain, can be applied to study the developing brain in utero and postnatally including measures of tissue microstructure obtained from diffusion MRI, morphometric studies to measure whole brain and regional tissue volumes, and automated approaches to study cortical folding. In this chapter, we aim to describe different imaging approaches for the fetal and neonatal brain, and to discuss their use in a range of clinical applications.

Cerebral Perfusion After Repair of Congenital Diaphragmatic Hernia with Common Carotid Artery Occlusion After ECMO Therapy

AIM

To prospectively evaluate cerebral perfusion after repair of congenital diaphragmatic hernia (CDH) and right-common-carotid-artery (rCCA) occlusion after extracorporeal membrane oxygenation (ECMO) therapy.

PATIENTS AND METHODS

A total of 29 2-year-old-children with a history of CDH repair underwent cerebral magnetic resonance perfusion imaging. In 14 patients, the rCCA was occluded after ECMO therapy. Fifteen patients with CDH without ECMO served as controls. Regional cerebral-blood-flow (rCBF) was measured cortically and subcortically in both hemispheres and compared intra-individually and between both groups.

RESULTS

Patients with rCCA-occlusion showed intra-individual side differences between hemispheres, with significantly lower subcortical perfusion of the right hemisphere and reduced cortical perfusion. In one-third of patients with rCCA-occlusion, rCBF of the right-hemisphere was reduced by more than 20% when compared to the left hemisphere. Despite intra-individual side differences, mean rCBF in patients with rCCA occlusion was not reduced compared to controls.

CONCLUSION

Beside intra-individual side differences, overall right hemisphere perfusion is sufficient after rCCA-occlusion due to collateral blood supply.

Altered Cerebral Perfusion in Infants Born Preterm Compared with Infants Born Full Term

OBJECTIVES

To compare regional cerebral cortical blood flow (CBF) in infants born very preterm at term-equivalent age (TEA) and healthy newborns born full term and to examine the impact of clinical risk factors on CBF in the cohort born preterm.

STUDY DESIGN

This prospective, cross-sectional study included infants born very preterm (gestational age at birth <32 weeks; birth weight <1500 g) and healthy infants born full term. Using noninvasive 3T arterial spin labeling magnetic resonance imaging, we quantified regional CBF in the cerebral cortex: sensorimotor/auditory/visual cortex, superior medial/dorsolateral prefrontal cortex, anterior cingulate cortex (ACC)/posterior cingulate cortex, insula, and lateral posterior parietal cortex, as well as in the brainstem, and deep gray matter. Analyses were performed controlling for sex, gestational age, and age at magnetic resonance imaging.

RESULTS

We studied 202 infants: 98 born preterm and 104 born full term at TEA. Infants born preterm demonstrated greater global CBF (β = 9.03; P < .0001) and greater absolute regional CBF in all brain regions except the insula. Relative CBF in the insula, ACC and auditory cortex were decreased significantly in infants born preterm compared with their peers born at full term (P < .0001; P = .026; P = .036, respectively). In addition, the presence of parenchymal brain injury correlated with lower global and regional CBF (insula, ACC, sensorimotor, auditory, and visual cortices) whereas the need for cardiac vasopressor support correlated with lower regional CBF in the insula and visual cortex.

CONCLUSIONS

Altered regional cortical CBF in infants born very preterm at TEA may reflect early brain dysmaturation despite the absence of cerebral cortical injury. Furthermore, specific cerebral cortical areas may be vulnerable to early hemodynamic instability and parenchymal brain injury.

[Recommendations for imaging neonatal ischemic stroke]

Neuroimaging is critical for the diagnosis of neonatal arterial ischemic stroke (NAIS) and for prognosis estimation. The purpose of this work is to define guidelines of clinical neuroimaging for the diagnosis of NAIS, for the optimization of the imaging timing and for the assessment of the prognostic value of each imaging technique. A systematic search of electronic databases (Medline via Pubmed) for studies whose title and abstract were focused on NAIS has been conducted. One hundred and ten articles were selected and their results were analyzed by three Senior Practitioners of pediatric radiology using common methodology for guidelines elaboration within the group of experts gathered by Scientific Societies in the field. MRI with a diffu si on-weighted sequence (DWI) and T1, T2, and T2*-weighted sequences must be performed in the case of suspected NAIS (no sedation is required). In the first hours after the injury, an acute ischemic lesion is characterized by a hypersignal on the diffusion-weighted sequence, with a decrease of the apparent coefficient of diffusion (ADC). The best time to evaluate the extent of the ischemic lesion is between day 2 and day 4 after injury, when the ADC decrease reaches its nadir. In the acute phase, US may be useful as first imaging at the bedside to exclude other pathologies like large space-occupying hemorrhages, but its specific added value on NAIS diagnosis or prognosis assessment is very low. CT scan has no added value in NAIS, compared to MRI. Motor outcome is correlated with the extent of the lesion and with the presence of a definite injury of the corticospinal tract, which is well seen on the diffusion sequence at the acute stage. A secondary atrophy within the mesencephalon (cerebral peduncles) is tied in with a high risk of hemiplegia. Visual outcome is more often compromised in the case of lesions of the posterior cerebral artery territory.

MR imaging for accurate prediction of outcome after perinatal arterial ischemic stroke: Sooner not necessarily better

BACKGROUND

Involvement of the corticospinal tracts after perinatal arterial ischemic stroke (PAIS) is strongly correlated with adverse motor outcome.

METHODS

Two full-term infants with PAIS, with two early MRI scans available, are reported.

RESULTS

Diffusion weighted imaging (DWI)-MRI, performed within 24 h following onset of seizures and repeated 48 h later, clearly showed restricted diffusion within the middle cerebral artery territory on both MRIs, but clear patterns of signal intensity changes in the descending corticospinal tracts on the second MRI only.

CONCLUSION

Since involvement of the corticospinal tracts is essential for prediction of motor outcome, we may need to reconsider optimal timing of MR imaging for prediction of neurodevelopmental outcome after PAIS.

Brain oxygen saturation assessment in neonates using T2-prepared blood imaging of oxygen saturation and near-infrared spectroscopy

Although near-infrared spectroscopy is increasingly being used to monitor cerebral oxygenation in neonates, it has a limited penetration depth. The T₂-prepared Blood Imaging of Oxygen Saturation (T₂-BIOS) magnetic resonance sequence provides an oxygen saturation estimate on a voxel-by-voxel basis, without needing a respiratory calibration experiment. In 15 neonates, oxygen saturation measured by T₂-prepared blood imaging of oxygen saturation and near-infrared spectroscopy were compared. In addition, these measures were compared to cerebral blood flow and venous oxygen saturation in the sagittal sinus. A strong linear relation was found between the oxygen saturation measured by magnetic resonance imaging and the oxygen saturation measured by near-infrared spectroscopy ( R²= 0.64, p < 0.001). Strong linear correlations were found between near-infrared spectroscopy oxygen saturation, and magnetic resonance imaging measures of frontal cerebral blood flow, whole brain cerebral blood flow and venous oxygen saturation in the sagittal sinus ( R²= 0.71, 0.50, 0.65; p < 0.01). The oxygen saturation obtained by T₂-prepared blood imaging of oxygen saturation correlated with venous oxygen saturation in the sagittal sinus ( R²= 0.49, p = 0.023), but no significant correlations could be demonstrated with frontal and whole brain cerebral blood flow. These results suggest that measuring oxygen saturation by T₂-prepared blood imaging of oxygen saturation is feasible, even in neonates. Strong correlations between the various methods work as a cross validation for near-infrared spectroscopy and T₂-prepared blood imaging of oxygen saturation, confirming the validity of using of these techniques for determining cerebral oxygenation.

Magnetic resonance imaging based noninvasive measurements of brain hemodynamics in neonates: a review

Perinatal disturbances of brain hemodynamics can have a detrimental effect on the brain's parenchyma with consequently adverse neurodevelopmental outcome. Noninvasive, reliable tools to evaluate the neonate's brain hemodynamics are scarce. Advances in magnetic resonance imaging have provided new methods to noninvasively assess brain hemodynamics. More recently these methods have made their transition to the neonatal population. The aim of this review is twofold. Firstly, to describe these newly available noninvasive methods to investigate brain hemodynamics in neonates. Secondly, to discuss the results that were obtained with these techniques, identifying both potential clinical applications as well as gaps of knowledge.

Assessment of cerebral blood perfusion reserve with acetazolamide using 3D spiral ASL MRI: Preliminary experience in pediatric patients

PURPOSE

To demonstrate the clinical feasibility of a new non-Cartesian cylindrically-distributed spiral 3D pseudo-continuous arterial spin labeling (pCASL) magnetic resonance imaging (MRI) pulse sequence in pediatric patients in quantifying cerebral blood flow (CBF) response to an acetazolamide (ACZ) vasodilator challenge.

MATERIALS AND METHODS

MRI exams were performed on two 3 Tesla Philips Ingenia systems using 32 channel head coil arrays. After local institutional review board approval, the 3D spiral-based pCASL technique was added to a standard brain MRI exam and evaluated in 13 pediatric patients (average age: 11.7±6.4years, range: 1.4-22.2years). All patients were administered ACZ for clinically indicated reasons. Quantitative whole-brain CBF measurements were computed pre- and post-ACZ to assess cerebrovascular reserve.

RESULTS

3D spiral pCASL data were successfully reconstructed in all 13 cases. In 11 patients, CBF increased 2.8% to 93.2% after administration of ACZ. In the two remaining patients, CBF decreased by 2.4 to 6.0% after ACZ. The group average change in CBF due to ACZ was approximately 25.0% and individual changes were statistically significant (p<0.01) in all patients using a paired t-test analysis. CBF perfusion data were diagnostically useful in supporting conventional MR angiography and clinical findings.

CONCLUSION

3D cylindrically-distributed spiral pCASL MRI provides a robust approach to assess cerebral blood flow and reserve in pediatric patients.

A pilot cohort study of cerebral autoregulation and 2-year neurodevelopmental outcomes in neonates with hypoxic-ischemic encephalopathy who received therapeutic hypothermia

Background

Neurodevelopmental disabilities persist in survivors of neonatal hypoxic-ischemic encephalopathy (HIE) despite treatment with therapeutic hypothermia. Cerebrovascular autoregulation, the mechanism that maintains cerebral perfusion during changes in blood pressure, may influence outcomes. Our objective was to describe the relationship between acute autoregulatory vasoreactivity during treatment and neurodevelopmental outcomes at 2 years of age.

Methods

In a pilot study of 28 neonates with HIE, we measured cerebral autoregulatory vasoreactivity with the hemoglobin volume index (HVx) during therapeutic hypothermia, rewarming, and the first 6 h of normothermia. The HVx, which is derived from near-infrared spectroscopy, was used to identify the individual optimal mean arterial blood pressure (MAP_OPT) at which autoregulatory vasoreactivity is greatest. Cognitive and motor neurodevelopmental evaluations were completed in 19 children at 21–32 months of age. MAP_OPT, blood pressure in relation to MAP_OPT, blood pressure below gestational age + 5 (ga + 5), and regional cerebral oximetry (rSO₂) were compared to the neurodevelopmental outcomes.

Results

Nineteen children who had HIE and were treated with therapeutic hypothermia performed in the average range on cognitive and motor evaluations at 21–32 months of age, although the mean performance was lower than that of published normative samples. Children with impairments at the 2-year evaluation had higher MAP_OPT values, spent more time with blood pressure below MAP_OPT, and had greater blood pressure deviation below MAP_OPT during rewarming in the neonatal period than those without impairments. Greater blood pressure deviation above MAP_OPT during rewarming was associated with less disability and higher cognitive scores. No association was observed between rSO₂ or blood pressure below ga + 5 and neurodevelopmental outcomes.

Conclusion

In this pilot cohort, motor and cognitive impairments at 21–32 months of age were associated with greater blood pressure deviation below MAP_OPT during rewarming following therapeutic hypothermia, but not with rSO₂ or blood pressure below ga + 5. This suggests that identifying individual neonates’ MAP_OPT is superior to using hemodynamic goals based on gestational age or rSO₂ in the acute management of neonatal HIE.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-015-0464-4) contains supplementary material, which is available to authorized users.

A pilot cohort study of cerebral autoregulation and 2-year neurodevelopmental outcomes in neonates with hypoxic-ischemic encephalopathy who received therapeutic hypothermia

BACKGROUND

Neurodevelopmental disabilities persist in survivors of neonatal hypoxic-ischemic encephalopathy (HIE) despite treatment with therapeutic hypothermia. Cerebrovascular autoregulation, the mechanism that maintains cerebral perfusion during changes in blood pressure, may influence outcomes. Our objective was to describe the relationship between acute autoregulatory vasoreactivity during treatment and neurodevelopmental outcomes at 2 years of age.

METHODS

In a pilot study of 28 neonates with HIE, we measured cerebral autoregulatory vasoreactivity with the hemoglobin volume index (HVx) during therapeutic hypothermia, rewarming, and the first 6 h of normothermia. The HVx, which is derived from near-infrared spectroscopy, was used to identify the individual optimal mean arterial blood pressure (MAPOPT) at which autoregulatory vasoreactivity is greatest. Cognitive and motor neurodevelopmental evaluations were completed in 19 children at 21-32 months of age. MAPOPT, blood pressure in relation to MAPOPT, blood pressure below gestational age + 5 (ga + 5), and regional cerebral oximetry (rSO2) were compared to the neurodevelopmental outcomes.

RESULTS

Nineteen children who had HIE and were treated with therapeutic hypothermia performed in the average range on cognitive and motor evaluations at 21-32 months of age, although the mean performance was lower than that of published normative samples. Children with impairments at the 2-year evaluation had higher MAPOPT values, spent more time with blood pressure below MAPOPT, and had greater blood pressure deviation below MAPOPT during rewarming in the neonatal period than those without impairments. Greater blood pressure deviation above MAPOPT during rewarming was associated with less disability and higher cognitive scores. No association was observed between rSO2 or blood pressure below ga + 5 and neurodevelopmental outcomes.

CONCLUSION

In this pilot cohort, motor and cognitive impairments at 21-32 months of age were associated with greater blood pressure deviation below MAPOPT during rewarming following therapeutic hypothermia, but not with rSO2 or blood pressure below ga + 5. This suggests that identifying individual neonates' MAPOPT is superior to using hemodynamic goals based on gestational age or rSO2 in the acute management of neonatal HIE.

A pilot cohort study of cerebral autoregulation and 2-year neurodevelopmental outcomes in neonates with hypoxic-ischemic encephalopathy who received therapeutic hypothermia

BACKGROUND

Neurodevelopmental disabilities persist in survivors of neonatal hypoxic-ischemic encephalopathy (HIE) despite treatment with therapeutic hypothermia. Cerebrovascular autoregulation, the mechanism that maintains cerebral perfusion during changes in blood pressure, may influence outcomes. Our objective was to describe the relationship between acute autoregulatory vasoreactivity during treatment and neurodevelopmental outcomes at 2 years of age.

METHODS

In a pilot study of 28 neonates with HIE, we measured cerebral autoregulatory vasoreactivity with the hemoglobin volume index (HVx) during therapeutic hypothermia, rewarming, and the first 6 h of normothermia. The HVx, which is derived from near-infrared spectroscopy, was used to identify the individual optimal mean arterial blood pressure (MAPOPT) at which autoregulatory vasoreactivity is greatest. Cognitive and motor neurodevelopmental evaluations were completed in 19 children at 21-32 months of age. MAPOPT, blood pressure in relation to MAPOPT, blood pressure below gestational age + 5 (ga + 5), and regional cerebral oximetry (rSO2) were compared to the neurodevelopmental outcomes.

RESULTS

Nineteen children who had HIE and were treated with therapeutic hypothermia performed in the average range on cognitive and motor evaluations at 21-32 months of age, although the mean performance was lower than that of published normative samples. Children with impairments at the 2-year evaluation had higher MAPOPT values, spent more time with blood pressure below MAPOPT, and had greater blood pressure deviation below MAPOPT during rewarming in the neonatal period than those without impairments. Greater blood pressure deviation above MAPOPT during rewarming was associated with less disability and higher cognitive scores. No association was observed between rSO2 or blood pressure below ga + 5 and neurodevelopmental outcomes.

CONCLUSION

In this pilot cohort, motor and cognitive impairments at 21-32 months of age were associated with greater blood pressure deviation below MAPOPT during rewarming following therapeutic hypothermia, but not with rSO2 or blood pressure below ga + 5. This suggests that identifying individual neonates' MAPOPT is superior to using hemodynamic goals based on gestational age or rSO2 in the acute management of neonatal HIE.

Injury and repair in perinatal brain injury: Insights from non-invasive MR perfusion imaging

Injury to the developing brain remains an important complication in critically ill newborns, placing them at risk for future neurodevelopment impairments. Abnormal brain perfusion is often a key mechanism underlying neonatal brain injury. A better understanding of how alternations in brain perfusion can affect normal brain development will permit the development of therapeutic strategies that prevent and/or minimize brain injury and improve the neurodevelopmental outcome of these high-risk newborns. Recently, non-invasive MR perfusion imaging of the brain has been successfully applied to the neonatal brain, which is known to be smaller and have lower brain perfusion compared to older children and adults. This article will present an overview of the potential role of non-invasive perfusion imaging by MRI to study maturation, injury, and repair in perinatal brain injury and demonstrate why this perfusion sequence is an important addition to current neonatal imaging protocols, which already include different sequences to assess the anatomy and metabolism of the neonatal brain.

Arterial spin-labelling perfusion MRI and outcome in neonates with hypoxic-ischemic encephalopathy

PURPOSE

Hyperperfusion may be related to outcome in neonates with hypoxic-ischemic encephalopathy (HIE). The purpose of this study was to evaluate whether arterial spin labelling (ASL) perfusion is associated with outcome in neonates with HIE and to compare the predictive value of ASL MRI to known MRI predictive markers.

METHODS

Twenty-eight neonates diagnosed with HIE and assessed with MR imaging (conventional MRI, diffusion-weighted MRI, MR spectroscopy [MRS], and ASL MRI) were included. Perfusion in the basal ganglia and thalami was measured. Outcome at 9 or 18 months of age was scored as either adverse (death or cerebral palsy) or favourable.

RESULTS

The median (range) perfusion in the basal ganglia and thalami (BGT) was 63 (28-108) ml/100 g/min in the neonates with adverse outcome and 28 (12-51) ml/100 g/min in the infants with favourable outcome (p < 0.01). The area-under-the-curve was 0.92 for ASL MRI, 0.97 for MRI score, 0.96 for Lac/NAA and 0.92 for ADC in the BGT. The combination of Lac/NAA and ASL MRI results was the best predictor of outcome (r(2) = 0.86, p < 0.001).

CONCLUSION

Higher ASL perfusion values in neonates with HIE are associated with a worse neurodevelopmental outcome. A combination of the MRS and ASL MRI information is the best predictor of outcome.

KEY POINTS

• Arterial spin labelling MRI can predict outcome in neonates with hypoxic-ischemic encephalopathy • Basal ganglia and thalami perfusion is higher in neonates with adverse outcome • Arterial spin labelling complements known MRI parameters in the prediction of outcome • The combined information of ASL and MRS measurements is the best predictor of outcome.

Neonatal stroke: a review of the current evidence on epidemiology, pathogenesis, diagnostics and therapeutic options

Neonatal stroke, including perinatal arterial ischaemic stroke and cerebral sinovenous thrombosis, remains a serious problem in the neonate. This article reviews the current evidence on epidemiology, pathogenesis, diagnostics and therapeutic options.

CONCLUSION

Although our understanding of the underlying mechanisms and possible risk factors has improved, little progress has been made towards therapeutic options. Considering the high incidence of neurological sequelae, the need for therapeutic options is high and should be the focus of future research.