Noninvasive cerebral perfusion imaging in high-risk neonates

The perfusion index histograms predict patent ductus arteriosus requiring treatment in preterm infants

The impact of patent ductus arteriosus (PDA) on vital sign trends represented as histograms, and perfusion index in particular, is unknown. This study aimed to split continuously obtained PI and other vital signs before, during, and after medical treatment of PDA, into histogram bins, and determine the utility of PI and other vital sign histograms in the early prediction of hemodynamically significant PDA (hsPDA). In 34 infants at a mean gestational age of 26 ± 2.1 weeks, we prospectively collected vital signs for three different periods, 24 h before starting treatment of PDA, during PDA treatment, and 24 h after completion of the course of treatment, and confirmed PDA closure by echo. Histograms with three comparable periods were obtained from preterm infants who did not require treatment for PDA and analyzed for comparison. The duration of time spent in each histogram bin was determined for each time epoch. Episodes of low PI < 0.4 and high PI > 2 were significantly longer in duration in infants with PDA before treatment compared to those in infants with PDA during and after treatment. The arterial oxygen saturation (SpO₂) < 80% was also longer in duration in infants with PDA before compared to that in infants with PDA during and after treatment. Low PI < 0.4 correlated with most echocardiography indices of hsPDA.Conclusion: We conclude that a patent ductus arteriosus requiring treatment in preterm infants ≤ 29 weeks GA was associated with significant fluctuations between a low PI < 0.4 alternating with a high PI > 2, reflecting the dynamic nature of hsPDA shunt volume. PI variability may be an early marker of hsPDA. What is Known: • The perfusion index is a continuous underutilized parameter provided by pulse oximetry to assess the peripheral perfusion. • The perfusion index helps predict conditions with hemodynamic instability. What is New: • The perfusion index assessed as daily histogram trends can predict patent ductus arteriosus requiring treatment.

Near-Infrared Spectroscopy: Clinical Use in High-Risk Neonates

In this review, we describe the near-infrared spectroscopy (NIRS) technology and its clinical use in high-risk neonates in critical care settings. We searched databases (e.g., PubMed, Google Scholar, EBSCOhost) to find studies describing the use of NIRS on critically ill and high-risk neonates. Near-infrared spectroscopy provides continuous noninvasive monitoring of venous oxygen saturation. It uses technology similar to pulse oximetry to measure the oxygen saturation of hemoglobin in a tissue bed to describe the relative delivery and extraction of oxygen. Near-infrared spectroscopy can be a valuable bedside tool to provide clinicians indirect evidence of perfusion. It may prompt early interventions that promote oxygen delivery, which can improve high-risk neonatal outcomes.

Validation of diffuse correlation spectroscopy against 15O-water PET for regional cerebral blood flow measurement in neonatal piglets

Diffuse correlation spectroscopy (DCS) can non-invasively and continuously asses regional cerebral blood flow (rCBF) at the cot-side by measuring a blood flow index (BFI) in non-traditional units of cm2/s. We have validated DCS against positron emission tomography using 15O-labeled water (15O-water PET) in a piglet model allowing us to derive a conversion formula for BFI to rCBF in conventional units (ml/100g/min). Neonatal piglets were continuously monitored by the BabyLux device integrating DCS and time resolved near infrared spectroscopy (TRS) while acquiring 15O-water PET scans at baseline, after injection of acetazolamide and during induced hypoxic episodes. BFI by DCS was highly correlated with rCBF (R = 0.94, p < 0.001) by PET. A scaling factor of 0.89 (limits of agreement for individual measurement: 0.56, 1.39)×109× (ml/100g/min)/(cm2/s) was used to derive baseline rCBF from baseline BFI measurements of another group of piglets and of healthy newborn infants showing an agreement with expected values. These results pave the way towards non-invasive, cot-side absolute CBF measurements by DCS on neonates.

Neurological Monitoring and Complications of Pediatric Extracorporeal Membrane Oxygenation Support

Extracorporeal membrane oxygenation is extracorporeal life support for life-threatening cardiopulmonary failure. Since its introduction, the use of extracorporeal membrane oxygenation has expanded to patients with more complex comorbidities without change in patient mortality rates. Although many patients survive, significant neurological complications like seizures, ischemic strokes, and intracranial hemorrhage can occur during extracorporeal membrane oxygenation care. The risks of these complications often add to the complexity of decision-making surrounding extracorporeal membrane oxygenation support. In this review, we discuss the pathophysiology and incidence of neurological complications in children supported on extracorporeal membrane oxygenation, factors influencing the incidence of these complications, commonly used neurological monitoring modalities, and outcomes for this complex patient population. We discuss the current literature on the use of electroencephalography for both seizure detection and monitoring of background electroencephalographic changes, in addition to the use of less commonly used imaging modalities like transcranial Doppler. We summarize the knowledge gaps and the lack of clinical consensus guidelines for managing these potentially life-changing neurological complications. Finally, we discuss future work to further understand the pathophysiology of extracorporeal membrane oxygenation-related neurological complications.

Precise neonatal arterial ischemic stroke classification with a three-dimensional map of the arterial territories of the neonatal brain

INTRODUCTION

Data regarding neonatal arterial ischemic stroke (NAIS) topography are still sparse and inaccurate. Despite the importance of locating NAIS to predict the long-term outcome of neonates, a map of arterial territories is not yet available. Our aim was therefore to generate the first three-dimensional map of arterial territories of the neonatal brain (ATNB) and test its usefulness.

METHODS

Three-dimensional time-of-flight magnetic resonance angiography images were acquired from four neonates without NAIS. Arteries were semi-automatically segmented to build a symmetric arterial template. This allowed us to delineate the volumetric extension of each arterial territory, giving rise to the ATNB map, which is publicly available. Its applicability was tested on a sample of 34 neonates with NAIS.

RESULTS

After applying the ATNB map to the neonatal sample, the posterior trunk of the middle cerebral artery, followed by its anterior trunk, were identified as the most affected arterial territories. When comparing the results obtained employing the map with the original diagnoses made during the standard clinical evaluation of NAIS, major diagnostic errors were found in 18% of cases.

CONCLUSION

The ATNB map has been proven useful to precisely identify the arterial territories affected by an NAIS, as well as to increase the accuracy of clinical diagnoses.

Cerebral blood flow is not modulated following acute aerobic exercise in preadolescent children

Cognitive enhancements following a single bout of exercise are frequently attributed to increases in cerebral blood flow, however to date we have little understanding of the extent to which such bouts of exercise actually even influence cerebral blood flow following the cessation of exercise. To gain such insight, both regional and global changes in cerebral blood flow were assessed using 3D pseudo-continuous arterial spin-labeled magnetic resonance imaging in a sample of 41 preadolescent children. Using a within-participants randomized crossover design, cerebral blood flow as assessed prior to and following 20-min of either aerobic exercise or an active-control condition during two separate, counterbalanced sessions. The aerobic exercise condition consisted of walking/jogging on a motor driven treadmill at an intensity of approximately 70% of age-predicted maximum heart rate (HR = 136.1 ± 11.1 bpm). The active control condition consisted of walking on the treadmill at the lowest possible intensity (0.5 mph and 0% grade; HR = 92.0 ± 12.2 bpm). Findings revealed no differences in cerebral blood flow following the cessation of exercise relative to the active control condition. These findings demonstrate that cerebral blood flow may not be altered in preadolescent children following the termination of the exercise stimulus during the period when cognitive enhancements have previously been observed.

Preoperative cerebral hemodynamics from birth to surgery in neonates with critical congenital heart disease

BACKGROUND

Hypoxic-ischemic white matter brain injury commonly occurs in neonates with critical congenital heart disease. Recent work has shown that longer time to surgery is associated with increased risk for this injury. In this study we investigated changes in perinatal cerebral hemodynamics during the transition from fetal to neonatal circulation to ascertain mechanisms that might underlie this risk.

METHODS

Neonates with either transposition of the great arteries (TGA) or hypoplastic left heart syndrome (HLHS) were recruited for preoperative noninvasive optical monitoring of cerebral oxygen saturation, cerebral oxygen extraction fraction, and cerebral blood flow using diffuse optical spectroscopy and diffuse correlation spectroscopy, 2 noninvasive optical techniques. Measurements were acquired daily from day of consent until the morning of surgery. Temporal trends in these measured parameters during the preoperative period were assessed with a mixed effects model.

RESULTS

Forty-eight neonates with TGA or HLHS were studied. Cerebral oxygen saturation was significantly and negatively correlated with time, and oxygen extraction fraction was significantly and positively correlated with time. Cerebral blood flow did not significantly change with time during the preoperative period.

CONCLUSIONS

In neonates with TGA or HLHS, increasing cerebral oxygen extraction combined with an abnormal cerebral blood flow response during the time between birth and heart surgery leads to a progressive decrease in cerebral tissue oxygenation The results support and help explain the physiological basis for recent studies that show longer time to surgery increases the risk of acquiring white matter injury.

Splanchnic NIRS monitoring in neonatal care: rationale, current applications and future perspectives

Near infrared spectroscopy (NIRS) provides a non-invasive, continuous monitoring of regional tissue oxygenation. NIRS assessment of neonatal splanchnic oxygenation (SrSO₂) has gained increasing interest over the last decade, as local hypoxia and ischemia underlie the most feared gut complications in neonates. Current literature provides encouraging evidence in support of SrSO₂ reliability in detecting mesenteric hemodynamic changes related to various physiological and pathological conditions in-term and preterm infants. Even so, while splanchnic NIRS monitoring looks promising for investigating gut physiopathology in research settings, further studies are needed to evaluate its feasibility as a routine monitoring tool in neonatal care and to investigate its potential role in clinical decision making. After a brief introduction to NIRS technical principles, this review aims to provide a complete overview of current neonatal applications for splanchnic NIRS monitoring, to discuss its possible limitations and to suggest future directions for research and clinical applications.

Neuromonitoring in the neonatal ECMO patient

Utilization of extraocorporeal membrane oxygenation (ECMO) has become increasingly widespread as a bridging therapy for neonates with severe, reversible respiratory or cardiac diseases. While significant risks remain, due to advances in medical and surgical management, overall mortality has decreased. However, short and long-term neurological morbidity has remained high. Therefore, increasing attention has been focused on multimodal neuromonitoring to track and optimally, minimize or prevent intracranial injury. This review will explore the the indications, advantages, disadvantages, timing, frequency, duration, and any known correlation with neurodevelopmental outcomes of common types of neuromonitoring in the neonatal ECMO population. Investigational monitoring techniques such as NIRS will be briefly reviewed.

Near-infrared spectroscopy is a promising noninvasive technique for monitoring the effects of feeding regimens on the cerebral and splanchnic regions

AIM

The effects of different milk and, or, administration regimens on cerebro-splanchnic perfusion are still a matter of debate. We investigated the effects of the bolus administration of breast milk or formula on cerebro-splanchnic oximetry, function and perfusion, assessed by near-infrared spectroscopy (NIRS).

METHODS

This observational study of 30 infants fed with breast (n = 15) or formula (n = 15) milk, and matched for gestational age and birth weight, was carried out in the neonatal intensive care unit of the C Arrigo Children's Hospital, Alessandria, Italy, a tertiary-level referral centre, from October 2015 to December 2016. NIRS monitoring parameters, such as cerebral and splanchnic oximetry, fraction of tissue oxygen extraction and the cerebral-splanchnic ratio, were recorded before, during and after feeding.

RESULTS

Breast milk led to a significant increase in cerebro-splanchnic oximetry and tissue oxygen extraction (p < 0.001) during and after feeding, and the cerebro-splanchnic perfusion ratio was significantly higher (p < 0.001) in the breast than formula group.

CONCLUSION

Our study results suggest that breast milk was better tolerated than formula, requiring lower energy expenditure and lower cerebro-splanchnic haemodynamic redistribution. The findings could prompt investigations using NIRS as a promising noninvasive tool for cerebral and splanchnic longitudinal monitoring during neonatal feeding.

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.

Shedding light on the neonatal brain: probing cerebral hemodynamics by diffuse optical spectroscopic methods

Investigating the cerebral physiology of healthy term newborns' brains is important for better understanding perinatal brain injuries, of which the most common etiologies are hypoxia and ischemia. Hence, cerebral blood flow and cerebral oxygenation are important biomarkers of brain health. In this study, we employed a hybrid diffuse optical system consisting of diffuse correlation spectroscopy (DCS) and frequency-domain near infrared spectroscopy (FDNIRS) to measure hemoglobin concentration, oxygen saturation, and indices of cerebral blood flow and metabolism. We measured 30 term infants to assess the optical and physiological characteristics of the healthy neonatal brain in the frontal, temporal, and parietal lobes. We observed higher metabolism in the right hemisphere compared to the left and a positive correlation between gestational age and the level of cerebral hemoglobin concentration, blood volume, and oxygen saturation. Moreover, we observed higher cerebral blood flow and lower oxygen saturation in females compared to males. The delayed maturation in males and the sexual dimorphism in cerebral hemodynamics may explain why males are more vulnerable to perinatal brain injuries than females.

Shedding light on the neonatal brain: probing cerebral hemodynamics by diffuse optical spectroscopic methods

Investigating the cerebral physiology of healthy term newborns' brains is important for better understanding perinatal brain injuries, of which the most common etiologies are hypoxia and ischemia. Hence, cerebral blood flow and cerebral oxygenation are important biomarkers of brain health. In this study, we employed a hybrid diffuse optical system consisting of diffuse correlation spectroscopy (DCS) and frequency-domain near infrared spectroscopy (FDNIRS) to measure hemoglobin concentration, oxygen saturation, and indices of cerebral blood flow and metabolism. We measured 30 term infants to assess the optical and physiological characteristics of the healthy neonatal brain in the frontal, temporal, and parietal lobes. We observed higher metabolism in the right hemisphere compared to the left and a positive correlation between gestational age and the level of cerebral hemoglobin concentration, blood volume, and oxygen saturation. Moreover, we observed higher cerebral blood flow and lower oxygen saturation in females compared to males. The delayed maturation in males and the sexual dimorphism in cerebral hemodynamics may explain why males are more vulnerable to perinatal brain injuries than females.

Time-Resolved Diffuse Optical Spectroscopy and Imaging Using Solid-State Detectors: Characteristics, Present Status, and Research Challenges

Diffuse optical spectroscopy (DOS) and diffuse optical imaging (DOI) are emerging non-invasive imaging modalities that have wide spread potential applications in many fields, particularly for structural and functional imaging in medicine. In this article, we review time-resolved diffuse optical imaging (TR-DOI) systems using solid-state detectors with a special focus on Single-Photon Avalanche Diodes (SPADs) and Silicon Photomultipliers (SiPMs). These TR-DOI systems can be categorized into two types based on the operation mode of the detector (free-running or time-gated). For the TR-DOI prototypes, the physical concepts, main components, figures-of-merit of detectors, and evaluation parameters are described. The performance of TR-DOI prototypes is evaluated according to the parameters used in common protocols to test DOI systems particularly basic instrumental performance (BIP). In addition, the potential features of SPADs and SiPMs to improve TR-DOI systems and expand their applications in the foreseeable future are discussed. Lastly, research challenges and future developments for TR-DOI are discussed for each component in the prototype separately and also for the entire system.

A Comparative Study of the Effect of Nasal Intermittent Positive Pressure Ventilation and Nasal Continuous Positive Airway Pressure on the Regional Brain Tissue Oximetry in Premature Newborns Weighing <1500 g

Background:

Near-infrared spectroscopy (NIRS) provides the capability of monitoring oxygenation levels in cerebral microscopic vessels, enabling the operator to observe the spontaneous changes in the levels of hemoglobin concentration in tissue and interpret the resulting fluctuations. The current study tried to investigate whether brain's autoregulatory mechanisms in premature newborns have the potential to prevent the adverse effects caused by asynchronous changes of pressure in the rib cage. Therefore, NIRS method was applied to newborns that were alternatively shifted from nasal continuous positive airway pressure (nCPAP) to nasal intermittent positive pressure ventilation (NIPPV) and vice versa.

Methods:

This study was done as a crossover randomized clinical trial on 30 very low-weight newborns under nCPAP, who had received surfactant as a result of respiratory distress syndrome diagnosis, from April 2015 to April 2016, in Isfahan Shahid Beheshti Educational Hospital. The newborns were 72 h old, experiencing continuous distending pressure (CDP) = 4–6 cmH₂O with FiO₂ = 30%–40%. The respiratory support would alternate from nCPAP to NIPPV and vice versa (with indicators of expiratory PAP (EPAP) = CDP and inspiratory PAP = EPAP + 4 cmH₂O), and the cerebral regional oxygen saturation (CrSO₂) was monitored using NIRS.

Results:

The study results indicated that newborns significantly showed higher levels of CrSO₂₍84.93, P = 0.005) and oxygenation (94.63, P = 0.007) under nCPAP rather than NIPPV (82.43 and 93.43, respectively). The respiratory rate was also meaningfully slower when newborns were under nCPAP (P = 0.013).

Conclusions:

This study revealed that applying NIPPV may have an unfavorable effect on the premature newborn's brain tissue perfusion. However, more studies are needed to ensure solid outcomes.

The impact of integrated evaluation of hemodynamics using targeted neonatal echocardiography with indices of tissue oxygenation: a new approach

OBJECTIVE

To study the impact of integrated evaluation of hemodynamics (IEH) using targeted neonatal echocardiography, together with regional tissue oxygenation, fractional oxygen extraction using near-infrared spectroscopy on the management of infants with compromised hemodynamics.

STUDY DESIGN

Retrospective cohort comparison of two groups of infants with compromised hemodynamics. EPOCH 1: did not undergo IEH (January 2012 to March 2014); EPOCH 2: underwent IEH (April 2014 to December 2015). The primary outcome was the time to recovery.

RESULTS

In all, 340 infants were included; 158 underwent IEH with a median (IQR) of 2 (1 to 3) evaluations per infant. Reasons for assessment included PDA (60%), compromised systemic circulation (14%) and clinically suspected pulmonary hypertension (22%). The time to recovery was shorter in IEH group in patients with compromised systemic circulation median (IQR), 32 h (24 to 63) compared with none IEH group 71 h (36 to 96), pulmonary hypertension 63 h (14.2 to 102) in IEH group compared with 68 h (24 to 240) in none IEH group, there were fewer PDA-related complications in preterm infants with PDA in IEH group.

CONCLUSION

IEH was associated with shorter time to clinical recovery in infants with compromised hemodynamics.

Challenges in neurologic prognostication after neonatal brain injury

Parents often ask neonatologists and neurologists to determine neurologic prognosis in the preterm and term infant after neonatal brain injury. Prognostication in these populations remains rather full of uncertainties. Knowledge of available diagnostic tests and their limitations allows the clinician to synthesize the most likely outcomes after neurologic injury. In this review, we describe the diagnostic tools available to the clinician, active areas of research, and challenges in neurologic prognostication of the neonate.

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.

Brain Perfusion Imaging in Neonates: An Overview

The development of cognitive function in children has been related to a regional metabolic increase and an increase in regional brain perfusion. Moreover, brain perfusion plays an important role in the pathogenesis of brain damage in high-risk neonates, both preterm and full-term asphyxiated infants. In this article, we will review and discuss several existing imaging techniques for assessing neonatal brain perfusion.

Positron emission tomography/magnetic resonance hybrid scanner imaging of cerebral blood flow using (15)O-water positron emission tomography and arterial spin labeling magnetic resonance imaging in newborn piglets

Abnormality in cerebral blood flow (CBF) distribution can lead to hypoxic-ischemic cerebral damage in newborn infants. The aim of the study was to investigate minimally invasive approaches to measure CBF by comparing simultaneous (15)O-water positron emission tomography (PET) and single TI pulsed arterial spin labeling (ASL) magnetic resonance imaging (MR) on a hybrid PET/MR in seven newborn piglets. Positron emission tomography was performed with IV injections of 20 MBq and 100 MBq (15)O-water to confirm CBF reliability at low activity. Cerebral blood flow was quantified using a one-tissue-compartment-model using two input functions: an arterial input function (AIF) or an image-derived input function (IDIF). The mean global CBF (95% CI) PET-AIF, PET-IDIF, and ASL at baseline were 27 (23; 32), 34 (31; 37), and 27 (22; 32) mL/100 g per minute, respectively. At acetazolamide stimulus, PET-AIF, PET-IDIF, and ASL were 64 (55; 74), 76 (70; 83) and 79 (67; 92) mL/100 g per minute, respectively. At baseline, differences between PET-AIF, PET-IDIF, and ASL were 22% (P<0.0001) and -0.7% (P=0.9). At acetazolamide, differences between PET-AIF, PET-IDIF, and ASL were 19% (P=0.001) and 24% (P=0.0003). In conclusion, PET-IDIF overestimated CBF. Injected activity of 20 MBq (15)O-water had acceptable concordance with 100 MBq, without compromising image quality. Single TI ASL was questionable for regional CBF measurements. Global ASL CBF and PET CBF were congruent during baseline but not during hyperperfusion.

Impaired Global and Regional Cerebral Perfusion in Newborns with Complex Congenital Heart Disease

OBJECTIVE

To compare global and regional cerebral perfusion in newborns with congenital heart disease (CHD) and healthy controls using arterial spin labeling (ASL) magnetic resonance imaging (MRI) prior to open heart surgery.

STUDY DESIGN

We performed brain MRIs in 101 newborns (58 controls, 43 CHD) using 3-dimensional fast spin echo pseudo-continuous ASL. Cerebral blood flow (CBF) ASL images were linearly coregistered to T2-weighted images for anatomic delineation and selection of regions-of-interest. Anatomic regions included frontal white matter (FWM), occipital white matter (OWM), thalami, and basal ganglia (BG).

RESULTS

Newborns with single ventricle CHD demonstrated significantly lower global (P = .044) and regional BG (P = .025) CBF compared with controls. Mean regional CBF in the thalami in cyanotic newborns with CHD was lower compared with controls (P = .004). Mean regional CBF in thalami (P = .02), BG (P = .01), and OWM (P = .03) among newborns with cyanotic CHD was lower than those with acyanotic CHD. Newborns with CHD ventilated prior to MRI had increased global (P = .016) and OWM (P = .013) CBF compared with those not ventilated.

CONCLUSIONS

Newborns with uncorrected cyanotic or single ventricle CHD show disturbances in cerebral perfusion compared to healthy controls using ASL. Cardiac physiology and preoperative hemodynamic compromise play an important role in preoperative alterations in global and regional cerebral perfusion. Our data suggest that ASL may be useful for studying cerebral perfusion in newborns at high risk for cerebral ischemia, such as those with complex CHD.

A neuroradiologist's guide to arterial spin labeling MRI in clinical practice

Arterial spin labeling (ASL) is a non-invasive MRI technique to measure cerebral blood flow (CBF). This review provides a practical guide and overview of the clinical applications of ASL of the brain, as well its potential pitfalls. The technical and physiological background is also addressed. At present, main areas of interest are cerebrovascular disease, dementia and neuro-oncology. In cerebrovascular disease, ASL is of particular interest owing to its quantitative nature and its capability to determine cerebral arterial territories. In acute stroke, the source of the collateral blood supply in the penumbra may be visualised. In chronic cerebrovascular disease, the extent and severity of compromised cerebral perfusion can be visualised, which may be used to guide therapeutic or preventative intervention. ASL has potential for the detection and follow-up of arteriovenous malformations. In the workup of dementia patients, ASL is proposed as a diagnostic alternative to PET. It can easily be added to the routinely performed structural MRI examination. In patients with established Alzheimer’s disease and frontotemporal dementia, hypoperfusion patterns are seen that are similar to hypometabolism patterns seen with PET. Studies on ASL in brain tumour imaging indicate a high correlation between areas of increased CBF as measured with ASL and increased cerebral blood volume as measured with dynamic susceptibility contrast-enhanced perfusion imaging. Major advantages of ASL for brain tumour imaging are the fact that CBF measurements are not influenced by breakdown of the blood–brain barrier, as well as its quantitative nature, facilitating multicentre and longitudinal studies.

Tracer microrheology study of a hydrophobically modified comblike associative polymer

The viscoelastic properties of associative polymers are important not only for their use as rheology modifiers but also to understand their complex structure in aqueous media. In this study, the dynamics of comblike hydrophobically modified alkali swellable associative (HASE) polymers are probed using diffusing wave spectroscopy (DWS) based tracer microrheology. DWS-based tracer microrheology accurately probes the dynamics of HASE polymers, and the extracted microrheological moduli versus frequency profile obtained from this technique closely matches that obtained from rotational rheometry measurements. Quantitatively, however, the moduli extracted from DWS-based tracer microrheology measurements are slightly higher than those obtained using rotational rheometry. The creep compliance, elastic modulus, and relaxation time concentration scaling behavior exhibits a power-law dependence. The length scale associated with the elastic to glassy behavior change is obtained from the time-dependent diffusion coefficient. The Zimm-Rouse type scaling is recovered at high frequencies but shows a concentration effect switching from Zimm to more Rouse-like behavior at higher concentrations.

Bolus vs. continuous feeding: effects on splanchnic and cerebral tissue oxygenation in healthy preterm infants

BACKGROUND

Intermittent and continuous tube feeding modes are commonly used to feed preterm infants. However, there is no clear evidence regarding which method is better tolerated. We investigated the differences between bolus and continuous feeding in terms of cerebral and splanchnic oxygenation in healthy preterm infants.

METHODS

Thirty preterm infants underwent a simultaneous 6-h near-infrared-spectroscopy monitoring of cerebral and splanchnic oxygenation, during which they were fed twice through an orogastric tube: one meal was given as a 10-min bolus, and the other was given continuously over a period of 3 h. Oxygenation trends over time were evaluated and compared between bolus and continuous feeding modes.

RESULTS

Cerebral oxygenation did not change over time and did not differ between the two feeding techniques. Splanchnic oxygenation changed significantly over time and differed between the two feeding techniques, with a significant increase after bolus feeding and a remarkable reduction during continuous feeding.

CONCLUSION

Bolus and continuous feeding modes influence splanchnic oxygenation in healthy preterm infants differently. Further studies are needed to investigate possible underlying mechanisms and potential effects on feeding tolerance.

Time to surgery and preoperative cerebral hemodynamics predict postoperative white matter injury in neonates with hypoplastic left heart syndrome

OBJECTIVE

Hypoxic-ischemic white mater brain injury commonly occurs in neonates with hypoplastic left heart syndrome (HLHS). Approximately one half of HLHS survivors will exhibit neurobehavioral symptoms believed to be associated with this injury, although the exact timing of the injury is unknown.

METHODS

Neonates with HLHS were recruited for pre- and postoperative monitoring of cerebral oxygen saturation, cerebral oxygen extraction fraction, and cerebral blood flow using 2 noninvasive optical-based techniques: diffuse optical spectroscopy and diffuse correlation spectroscopy. Anatomic magnetic resonance imaging was performed before and approximately 1 week after surgery to quantify the extent and timing of the acquired white matter injury. The risk factors for developing new or worsened white matter injury were assessed using uni- and multivariate logistic regression.

RESULTS

A total of 37 neonates with HLHS were studied. On univariate analysis, neonates who developed a large volume of new, or worsened, postoperative white matter injury had a significantly longer time to surgery (P=.0003). In a multivariate model, a longer time between birth and surgery, delayed sternal closure, and greater preoperative cerebral blood flow were predictors of postoperative white matter injury. Additionally, a longer time to surgery and greater preoperative cerebral blood flow on the morning of surgery correlated with lower cerebral oxygen saturation (P=.03 and P=.05, respectively) and greater oxygen extraction fraction (P=.05 for both).

CONCLUSIONS

A longer time to surgery was associated with new postoperative white matter injury in otherwise healthy neonates with HLHS. The results suggest that earlier Norwood palliation might decrease the likelihood of acquiring postoperative white matter injury.

Cerebral oxygen metabolism in neonates with congenital heart disease quantified by MRI and optics

Neonatal congenital heart disease (CHD) is associated with altered cerebral hemodynamics and increased risk of brain injury. Two novel noninvasive techniques, magnetic resonance imaging (MRI) and diffuse optical and correlation spectroscopies (diffuse optical spectroscopy (DOS), diffuse correlation spectroscopy (DCS)), were employed to quantify cerebral blood flow (CBF) and oxygen metabolism (CMRO(2)) of 32 anesthetized CHD neonates at rest and during hypercapnia. Cerebral venous oxygen saturation (S(v)O(2)) and CBF were measured simultaneously with MRI in the superior sagittal sinus, yielding global oxygen extraction fraction (OEF) and global CMRO(2) in physiologic units. In addition, microvascular tissue oxygenation (StO(2)) and indices of microvascular CBF (BFI) and CMRO(2) (CMRO(2)(i)) in the frontal cortex were determined by DOS/DCS. Median resting-state MRI-measured OEF, CBF, and CMRO(2) were 0.38, 9.7 mL/minute per 100 g and 0.52 mL O(2)/minute per 100 g, respectively. These CBF and CMRO(2) values are lower than literature reports for healthy term neonates (which are sparse and quantified using different methods) and resemble values reported for premature infants. Comparison of MRI measurements of global S(v)O(2), CBF, and CMRO(2) with corresponding local DOS/DCS measurements demonstrated strong linear correlations (R(2)=0.69, 0.67, 0.67; P<0.001), permitting calibration of DOS/DCS indices. The results suggest that MRI and optics offer new tools to evaluate cerebral hemodynamics and metabolism in CHD neonates.

Diffuse correlation spectroscopy for non-invasive, micro-vascular cerebral blood flow measurement

Diffuse correlation spectroscopy (DCS) uses the temporal fluctuations of near-infrared (NIR) light to measure cerebral blood flow (CBF) non-invasively. Here, we provide a brief history of DCS applications in the brain with an emphasis on the underlying physical ideas, common instrumentation and validation. Then we describe recent clinical research that employs DCS-measured CBF as a biomarker of patient well-being, and as an indicator of hemodynamic and metabolic responses to functional stimuli.

The development of cardiovascular and cerebral vascular control in preterm infants

Over the past three decades there has been a steady increase in the incidence of preterm birth. The worldwide rate of preterm birth is estimated to be 9.6% of all births, a total of almost 13 million births annually. Preterm birth is associated with a range of adverse cardiovascular and central nervous system outcomes, which may be attributed to altered development of these systems following preterm birth. Preterm birth has a considerable impact on cardiovascular parameters with preterm infants displaying higher heart rates and reduced blood pressure when compared to term born infants at matched ages. Furthermore, premature infants have altered autonomic control of cardiovascular parameters which manifests as abnormalities in heart rate variability and baroreflex mediated control of heart rate and blood pressure. As a result, systemic cardiovascular parameters can be unstable following preterm birth which may place stress on the neonatal brain. The brain of a preterm infant is particularly vulnerable to these fluctuations due to immature cerebral haemodynamics. Preterm infants, particularly those who are very preterm or unwell, display fluctuating pressure-passivity between systemic blood pressure and cerebral blood flow representing a considerably increased risk of cerebral haemorrhage or hypoxia. This is further compounded by immaturity of cerebral blood flow-metabolism coupling, which means increased metabolic demand cannot adequately be met by increased cerebral blood flow. It has been suggested that adverse long-term outcomes following preterm birth may occur as a result of exposure to physiological stress either in-utero or early in infancy.

Cerebral and somatic rSO2 in sick preterm infants

Near infrared spectroscopy (NIRS) measures the regional tissue oxygen saturation (rSO2) of various organs and provides a reflection of the balance between tissue oxygen supply and demand. Oxymetry assessed via NIRS has been proposed as a 'standard of care' and today it is already widely used in the NICU. This approach allows detection of any acute change in cerebral haemodynamics and continuous monitoring of cerebral and somatic oxygenation. This work describes three clinical cases of preterm VLBW infants which showed special points of interest during both cerebral and somatic NIRS monitoring.

Doppler-assessed cerebral blood flow velocity in the neonate as estimator of global cerebral blood volume flow measured using phase-contrast magnetic resonance angiography

BACKGROUND

We hypothesized that color Doppler-measured cerebral blood flow velocity (CD-CBFV) as measured in the three feeding arteries of the brain can be used as an estimator of global cerebral blood flow.

PATIENTS AND METHODS

CD-CBFV was determined as soon as possible after determination of phase-contrast magnetic resonance angiography-measured blood volume flow (PC-MRA BVF) by adding up angle-corrected time-averaged mean flow velocities of both internal carotid arteries and basilar artery. 30 newborns (gestational age ranging from 25 to 42 weeks; actual weight ranging from 1,050 to 5,858 g; postconceptional age ranging from 225 to 369 days) were investigated.

RESULTS

Doppler-determined CBFV ranged from 37 to 131 cm/s with a median of 69 cm/s. CD-CBFV showed a positive correlation with actual weight (r = 0.56, p < 0.01) and postconceptional age (r = 0.53, p < 0.01). CD-CBFV correlated positively with PC-MRA-measured BVF (r = 0.51, p < 0.01). Gestational age at birth, mechanical ventilation or gender did not influence this relationship. The limits of agreement, however, are wide, especially at higher CD-CBFV- and PC-MRA-measured BVF.

CONCLUSION

CD-CBFV may be used as a non-invasive trend-monitoring tool to detect gross changes in global cerebral blood flow in the unstable and sick neonate.

A quantitative method for correlating observations of decreased apparent diffusion coefficient with elevated cerebral blood perfusion in newborns presenting cerebral ischemic insults

In patients presenting with cerebral ischemic injury, the outcome of injured brain tissue quantified as decreased apparent diffusion coefficient (ADC) may depend on associated alterations in cerebral blood perfusion (CBP). This study proposes a non-biased method to quantify associations between ADC and CBP in newborns with global or focal cerebral ischemia. The study population consisted of nine neonates (age: 0 to 3 days) presenting with clinical and imaging evidence of ischemia (seven with global hypoxic ischemia, and two with focal arterial ischemic stroke) with decreased ADC. Six newborns without diffusion abnormalities on magnetic resonance (MR) imaging served as a comparative cohort (age: 0 days to 4 weeks). All patients underwent MR imaging including diffusion weighted imaging (DWI) to determine ADC and axial arterial spin labeling (ASL) to determine CBP. An algorithm was developed that uses the B0 volume from the DWI raw data as a reference, co-registers the ADC and ASL-CBP data to the B0, generates mask filters, and finally performs a statistical analysis to automatically select regions of interest (ROIs) with ADC or ASL-CBP values that deviate significantly from the rest of the brain. If ROIs are identified in this analysis, the algorithm then evaluates correlation based on ROI location and volume. A significant correlation was found between decreased ADC and elevated ASL-CBP with regions of elevated ASL-CBP typically larger than the corresponding ADC abnormality. The association between decreased diffusivity and increased ASL-CBP suggests that, for this cohort, cerebral ischemia is associated with hyperperfusion.

An interdisciplinary fetal/neonatal neurology program

A fetal/neonatal neurology program should encompass interdisciplinary service, educational and research objectives, merging curricula concerning maternal, placental, fetal and neonatal contributions to brain health and disease. This approach is anchored by research in early life programming that demonstrates that prenatal and postnatal factors influence long-term neurologic health. This concept also supports the design of neuroprotective interventions during critical periods of brain development when brain circuitries more optimally adapt to maturational challenges. Preventive, rescue and repair protocols will transform pediatric medical practices, to promote improved childhood outcomes. Inclusion of life-course science and research will identify medical and socioeconomic factors that favorably or adversely affect quality of life into adulthood. Greater awareness of the convergence of developmental origins of brain health and disease and developmental aging theories will influence public health policies, to encourage financial support for programs that will improve the quality of life for the child and adult.

Evaluation of neonatal regional cerebral perfusion using power Doppler and the index fractional moving blood volume

BACKGROUND

The high cerebral morbidity of premature neonates is thought to be related to changes in tissue perfusion in vulnerable areas of the brain. Quantification of power Doppler (PD) images using the index fractional moving blood volume (FMBV) may allow measurement of regional cerebral perfusion.

OBJECTIVE

To evaluate the reproducibility of calculating FMBV using PD ultrasound images to estimate cerebral perfusion.

METHODS

Two experienced clinicians performed head ultrasounds on 24 normally-grown neonates at less than 33 weeks' gestation. Both clinicians independently acquired and stored three PD images in two different coronal planes. FMBV was calculated offline after selecting two predefined regions of interest within these planes (basal ganglia and subependymal regions). Reproducibility was evaluated by calculating the intraclass correlation coefficient (intraCC) and the interclass correlation coefficient (interCC).

RESULTS

FMBV was successfully evaluated in 24/24 neonates by both clinicians. The intraCC for repeatability for observer A was 1.00 (95% CI 1.00-1.00) for the basal ganglia and 0.99 (95% CI 0.99-1.00) for the subependymal region, and for observer B was 0.99 (95% CI 0.99-1.00) for the basal ganglia and 0.96 (95% CI 0.92-0.98) for the subependymal region. The interCC was 0.86 (95% CI 0.68-0.94) for the basal ganglia and 0.93 (95% CI 0.86-0.97) for the subependymal region.

CONCLUSION

Using standardised settings and a well-defined region of interest, the calculation of FMBV using PD images is a reproducible method of estimating neonatal regional cerebral perfusion.

Phase-contrast magnetic resonance angiography measurements of global cerebral blood flow in the neonate

Cerebral blood flow (CBF) alterations are important in pathogenesis of neonatal ischemic/hemorrhagic brain damage. In clinical practice, estimation of neonatal CBF is mostly based on Doppler-measured blood flow velocities in major intracranial arteries. Using phase-contrast magnetic resonance angiography (PC-MRA), global CBF can be estimated, but there is limited neonatal experience. The objective of this study was to gain experience with PC-MRA for the determination of global CBF in neonates. In infants eligible for MRI, PC-MRA global CBF was determined by measuring volume blood flow in both internal carotid arteries (ICAs) and basilar artery (BA). Thirty newborns (GA, 25.7-42.1 wk; weight, 1050-5858 g; postconceptional age, 225-369 d) were investigated. Total PC-MRA CBF ranged from 27 to 186 mL/min. Significant correlations between PC-MRA CBF and postconceptional age and weight were detected. When calculating PC-MRA measured CBF per kilogram body weight, brain perfusion was about stable over the range of postconceptional ages and ranged between 11 and 48 mL/min/kg (median, 25 mL/min/kg). In conclusion, neonatal PC-MRA CBF seems to be a useful technique to estimate noninvasive CBF.