Current understanding and future potential applications of cerebral microvascular imaging in infants

Added Value of Microvascular Imaging for the Diagnosis and Monitoring of Strokes in Newborns and Infants

BACKGROUND

Neonatal/infantile stroke is a catastrophic condition associated with significant mortality and morbidity. Magnetic resonance imaging (MRI) remains the preferred modality for detecting ischemic stroke but has procedural limitations. Microvascular imaging (MVI) ultrasound (US) allows accurate visualization of the microvasculature. We assessed the added value of MVI to improve the detection of stroke diagnosis in neonates and infants.

METHODS

We retrospectively identified patients younger than one year who underwent brain US with MVI for suspected or confirmed stroke between January 2020 and June 2023. All patients had confirmed strokes on US and/or subsequent computed tomography or MRI. A pediatric radiologist (reader 1), a neuroradiologist (reader 2), and a pediatric radiology fellow (reader 3), unaware of the results, individually evaluated the US images to detect strokes. We used the McNemar test to determine the difference in responses before and after MVI.

RESULTS

Our cohort had 11 infants, nine boys and two girls (median age 61 days [13.5 to 145.5]). The three readers performed significantly better at stroke diagnosis with MVI (29 correct of 33) compared with grayscale US alone (13 of 33) (P < 0.001). Reader 1 improved from seven of 11 correct diagnoses to 11 of 11 (P = 0.045), reader 2 improved from five of 11 to 10 of 11 (P = 0.025), and reader 3 improved from one of 11 to eight of 11 (P < 0.001).

CONCLUSIONS

Our preliminary findings suggest that MVI has potential as a complementary tool to standard brain US protocols for neonatal and infant stroke assessment.

Ultrasound Super-Resolution Imaging of Neonatal Cerebral Vascular Reorganization

During the first days of neonatal growth, the central nervous system (CNS) develops self-regulatory mechanisms to ensure constant cerebral perfusion. However, this vascular neogenesis takes place at a microscopic scale that cannot be observed with current clinical imaging techniques. Ultrasound localization microscopy (ULM) allows us to observe micro-vessels of the order of a few microns at depths of several centimeters. This can be done using conventional clinical ultrasound scanners and contrast sequences (CEUS). In this study, ULM is used to observe the human microvasculature in neonatal patients undergoing treatment for life-threatening malformations forming direct connections between the cerebral arterial and venous systems. It is observed that neuroendovascular treatment of neonatal arteriovenous malformations causes remodeling and reorganization of the cerebral vasculature by also activating corticomedullary vascular connections. ULM enables us to follow microvascular changes in human neonates with high spatio-temporal resolution. ULM may provide a novel clinical translatable tool, particularly including cerebral imaging in very young patients.

Bedside cerebral microvascular imaging of patients with disorders of consciousness: a feasibility study

Background

Efficient bedside neurofunctional monitoring is crucial for managing disorders of consciousness (DoC). Ultrafast Power Doppler Imaging (uPDI) outperforms traditional Ultrasound in bedside for assessing the microcirculatory system. However, intracranial blood flow imaging traditionally faces limitations due to the skull's impedance. This constraint is circumvented in common post-craniectomy DoC patients, who present a unique observational window for uPDI.

Methods

We conducted uPDI scans on five DoC patients of different ages and consciousness levels who had undergone decompressive craniectomy. We compared the imaging results from uPDI with traditional PDI and identified the physiological and pathological conditions with uPDI.

Results

Detailed microvascular images of both cortical and subcortical areas were obtained using uPDI through the craniectomy window. Notably, uPDI demonstrates high sensitivity and imaging depth, revealing microvessels as small as 320 μm in diameter at 4 cm depth, and detecting blood flow signals up to 6 cm beneath the scalp.

Conclusion

Through the decompressive cranial windows of DoC patients, we obtained cerebral microvascular images with significantly higher sensitivity without the need for contrast agents.

Significance

Our research provides a novel bedside cerebral microcirculation imaging method for patients with DoC, offering convenient neurofunctional assessment to improve the clinical management of DoC patients.

Exploring the feasibility and clinical impact of ultrasound microvascular flow imaging in detecting brain injury in hyperbilirubinemia neonates

Neonatal hyperbilirubinemia is a prevalent condition during the neonatal period, and in severe instances, it can result in brain damage accompanied by irreversible neurological consequences. Therefore, early detection and intervention are paramount. This research aimed to detect early-stage brain damage resulting from neonatal hyperbilirubinemia through the application of two-dimensional cranial ultrasound and microvascular blood flow (MV-Flow) imaging techniques. Clinical data, along with gray-scale and microvascular ultrasound images of the basal ganglia, were collected from 85 neonates (hyperbilirubinemia group vs. non-hyperbilirubinemia group: 51 vs. 34). The Globus Pallidus to Putamen (G/P) ratio and the vascular index (VIMV) were calculated. A comparative analysis of clinical and ultrasonographic data between the groups was conducted. The hyperbilirubinemia group had higher mean G/P ratios (1.39 ± 0.49 vs. 1.16 ± 0.12, P < 0.05) and lower VIMV, which was negatively correlated with TSB levels (coronal: r = -0.419, P < 0.05; parasagittal: r = -0.448, P < 0.05). Cranial gray-scale ultrasound demonstrates altered gray values in the basal ganglia region, and the MV-Flow technique reveals and quantifies the microvascular structure of this region. These methods may serve as potential biological markers for the early assessment of bilirubin-induced brain damage.

Microvascular imaging findings in infants with bacterial meningitis: a case series

Bacterial meningitis is a severe and life-threatening disease that rapidly progresses in neonates and infants; prompt diagnosis and appropriate treatment are lifesaving. Magnetic resonance imaging remains the primary imaging technique for diagnosing meningitis; however, due to its limited availability and cost, ultrasound is often used for initial screening. Microvascular imaging ultrasound (MVI) is an emerging technique that offers insight into the brain microvasculature beyond conventional ultrasound. Here we present three patients with confirmed bacterial meningitis and associated cerebral microvascular findings on brain MVI to instigate further validation of cerebral microvascular imaging markers of bacterial meningitis for early detection and intervention.

Cerebral Doppler imaging in neonates: A guide for clinical application and diagnosis

Cranial ultrasound reliably diagnoses many neonatal brain disorders. Adding Doppler imaging expands the spectrum by providing information on the status of the vasculature and haemodynamics that may guide further diagnostic and clinical management. Doppler imaging may identify neonates with congenital or acquired vascular abnormalities such as perinatal stroke, sinuvenous thrombosis, vein of Galen malformation, dural sinus malformation, sinus pericranii, and developmental venous anomaly. These entities may need further investigation with complementary imaging modalities such as magnetic resonance imaging and magnetic resonance angiography, or conventional angiography. This review aims to help clinicians to improve their Doppler sonography knowledge and skills in order to use this helpful tool in neonates with neurological symptoms or suspected cerebral vascular abnormalities admitted to the neonatal intensive care unit.

Neuromonitoring During ECMO Support in Children

Extracorporeal membrane oxygenation is a potentially lifesaving intervention for children with severe cardiac or respiratory failure. It is used with increasing frequency and in increasingly more complex and severe diseases. Neurological injuries are important causes of morbidity and mortality in children treated with extracorporeal membrane oxygenation and include ischemic stroke, intracranial hemorrhage, hypoxic-ischemic injury, and seizures. In this review, we discuss the epidemiology and pathophysiology of neurological injury in patients supported with extracorporeal membrane oxygenation, and we review the current state of knowledge for available modalities of monitoring neurological function in these children. These include structural imaging with computed tomography and ultrasound, cerebral blood flow monitoring with near-infrared spectroscopy and transcranial Doppler ultrasound, and physiological monitoring with electroencephalography and plasma biomarkers. We highlight areas of need and emerging advances that will improve our understanding of neurological injury related to extracorporeal membrane oxygenation and help to reduce the burden of neurological sequelae in these children.

Advanced Neuromonitoring Modalities on the Horizon: Detection and Management of Acute Brain Injury in Children

Timely detection and monitoring of acute brain injury in children is essential to mitigate causes of injury and prevent secondary insults. Increasing survival in critically ill children has emphasized the importance of neuroprotective management strategies for long-term quality of life. In emergent and critical care settings, traditional neuroimaging modalities, such as computed tomography and magnetic resonance imaging (MRI), remain frontline diagnostic techniques to detect acute brain injury. Although detection of structural and anatomical abnormalities remains crucial, advanced MRI sequences assessing functional alterations in cerebral physiology provide unique diagnostic utility. Head ultrasound has emerged as a portable neuroimaging modality for point-of-care diagnosis via assessments of anatomical and perfusion abnormalities. Application of electroencephalography and near-infrared spectroscopy provides the opportunity for real-time detection and goal-directed management of neurological abnormalities at the bedside. In this review, we describe recent technological advancements in these neurodiagnostic modalities and elaborate on their current and potential utility in the detection and management of acute brain injury.

A concise guide to transtemporal contrast-enhanced ultrasound in children

Brain contrast-enhanced ultrasound offers insights into the brain beyond the anatomic information offered by conventional grayscale ultrasound. In infants, the open fontanelles serve as acoustic windows. In children, whose fontanelles are closed, the temporal bone serves as the ideal acoustic window due to its relatively smaller thickness than the other skull bones. Diagnosis of common neurologic diseases such as stroke, hemorrhage, and hydrocephalus has been performed using the technique. Transtemporal ultrasound and contrast-enhanced ultrasound, however, are rarely used in children due to the prevalent notion that the limited acoustic penetrance degrades diagnostic quality. This review seeks to provide guidelines for the use of transtemporal brain contrast-enhanced ultrasound in children.

Evaluation of the Cerebrospinal Fluid Flow Dynamics with Microvascular Imaging Ultrasound in Infants

PURPOSE

Microvascular imaging ultrasound (MVI) can detect slow blood flow in small-caliber cerebral vessels. This technology may help assess flow in other intracranial structures, such as the ventricular system. In this study, we describe the use of MVI for characterizing intraventricular cerebrospinal fluid (CSF) flow dynamics in infants.

MATERIALS AND METHODS

We included infants with brain ultrasound that had MVI B-Flow cine clips in the sagittal plane. Two blinded reviewers examined the images, dictated a diagnostic impression, and identified the third ventricle, cerebral aqueduct, fourth ventricle, and CSF flow direction. A third reviewer evaluated the discrepancies. We evaluated the association of visualization of CSF flow as detectable with MVI, with the diagnostic impressions. We also assessed the inter-rater reliability (IRR) for detecting CSF flow.

RESULTS

We evaluated 101 infants, mean age 40 ± 53 days. Based on brain MVI B-Flow, a total of 49 patients had normal brain US scans, 40 had hydrocephalus, 26 had intraventricular hemorrhage (IVH), and 14 had hydrocephalus+IVH. Using spatially moving MVI signal in the third ventricle, cerebral aqueduct, and fourth ventricle as the criteria for CSF flow, CSF flow was identified in 10.9% (n = 11), 15.8% (n = 16), and 16.8% (n = 17) of cases, respectively. Flow direction was detected in 19.8% (n = 20) of cases; 70% (n = 14) was caudocranial, 15% (n = 3) was craniocaudal, and 15% (n = 3) bidirectional, with IRR = 0.662, p < 0.001. Visualization of CSF flow was significantly associated with the presence of IVH alone (OR 9.7 [3.3-29.0], p < 0.001) and IVH+hydrocephalus (OR 12.4 [3.5-440], p < 0.001), but not with hydrocephalus alone (p = 0.116).

CONCLUSION

This study demonstrates that MVI can detect CSF flow dynamics in infants with a history of post-hemorrhagic hydrocephalus with a high IRR.

Distribution of IntraThalamic Injury According to Nuclei and Vascular Territories in Children With Term Hypoxic-Ischemic Injury

BACKGROUND

Term hypoxic-ischemic injury (HII) on magnetic resonance imaging (MRI) is described as the basal ganglia thalamus [BGT], watershed [WS], or combined [BGT/WS] groups. We aimed to determine differences between HII groups in intrathalamic distribution.

METHODS

Delayed MRIs of children with HII and thalamic injury were reviewed. Custom tools were placed over T2-weighted and/or fluid-attenuated inversion recovery axial images to determine distribution of intrathalamic injury: (1) six subjective (whole/near-whole, central, anterior, posterior, lateral, medial); (2) four nuclear (anterior [AN], ventrolateral [VLN], medial [MN], and pulvinar [PN]); and (3) three arterial (thalamoperforating arteries [TPA], thalamogeniculate arteries [TGA], and posterior choroidal arteries [PCA]) locations. We compared the frequency of injury of the aforementioned intrathalamic locations between HII groups.

RESULTS

The 128 children (mean age at MRI 7.35 ± 3.6 years) comprised 41% (n = 53) BGT, 26% (n = 33) WS, and 33% (n = 42) BGT/WS. The VLN was the most frequent injured nuclear region (66%, n = 85), and the TGA (93%, n = 128) was the most frequent arterial region involved. VLN injury occurred more frequently in the BGT group (P < 0.001), PN in the WS group (P < 0.001), and AN (P < 0.001), MN (P < 0.001), PN (P = 0.001), and all nuclei together (P < 0.001) in the BGT/WS group. The combination of all vascular territories was significantly associated with BGT/WS (P < 0.001).

CONCLUSIONS

There are significant differences in intrathalamic nuclear and arterial injuries between the different types of HII.

Bedside Cerebral Blood Flow Quantification in Neonates

Measurement of blood flow to the brain in neonates would be a very valuable addition to the medical diagnostic armamentarium. Such conditions such as assessment of closure of a patent ductus arteriosus (PDA) would greatly benefit from such an evaluation. However, measurement of cerebral blood flow in a clinical setting has proven very difficult and, as such, is rarely employed. Present techniques are often cumbersome, difficult to perform and potentially dangerous for very low birth weight (VLBW) infants. We have been developing an ultrasound blood volume flow technique that could be routinely used to assess blood flow to the brain in neonates. By scanning through the anterior fontanelles of 10 normal, full-term newborn infants, we were able to estimate total brain blood flows that closely match those published in the literature using much more invasive and technically demanding methods. Our method is safe, easy to do, does not require contrast agents and can be performed in the baby's incubator. The method has the potential for monitoring and assessing blood flows to the brain and could be used to routinely assess cerebral blood flow in many different clinical conditions.

Utility of Cerebral Microvascular Imaging in Infants Undergoing ECMO

PURPOSE

Infants who require extracorporeal membrane oxygenation (ECMO) therapy have an increased risk of neurological complications and mortality. Microvascular imaging (MVI) is an advanced Doppler technique that allows high-resolution visualization of microvasculature in the brain. We describe the feasibility and utility of MVI for the evaluation of cerebral microvascular perfusion in patients undergoing ECMO.

METHODS

We retrospectively analyzed brain MVI scans of neonates undergoing ECMO. Two pediatric radiologists qualitatively assessed MVI scans to determine the presence or absence of tortuosity, symmetry, heterogeneity, engorgement, and hypoperfusion of the basal ganglia-thalamus (BGT) region, as well as the presence or absence of white matter vascular engorgement and increased peri-gyral flow in the cortex. We tested the association between the presence of the aforementioned brain MVI features and clinical outcomes.

RESULTS

We included 30 patients, 14 of which were male (46.7%). The time of ECMO duration was 11.8 ± 6.9 days. The most prevalent microvascular finding in BGT was lenticulostriate vessel tortuosity (26/30, 86.7%), and the most common microvascular finding in the cortex was increased peri-gyral flow (10/24, 41.7%). Cortical white matter vascular engorgement was significantly associated with the presence of any poor outcome as defined by death, seizure, and/or cerebrovascular events on magnetic resonance imaging (p = 0.03).

CONCLUSION

MVI is a feasible modality to evaluate cerebral perfusion in infants undergoing ECMO. Additionally, evidence of white matter vascular engorgement after ECMO cannulation could serve as a predictor of poor outcomes in this population.

High-resolution neurosonographic examination of the lenticulostriate vessels in neonates with hypoxic-ischemic encephalopathy

OBJECTIVE

To assess the feasibility of visualizing lenticulostriate vessels (LV) using a linear high-resolution ultrasound probe and characterize LV morphology to determine whether morphological alterations in LV are present in neonatal hypoxic-ischemic encephalopathy (HIE) as compared to the unaffected infants.

METHODS

We characterized LV by their echogenicity, width, length, tortuosity, and numbers of visualized stems/branches in neurosonographic examinations of 80 neonates. Our population included 45 unaffected (non-HIE) and 35 with clinical and/or imaging diagnosis of HIE. Of the neonates with clinical diagnosis of HIE, 16 had positive MRI findings for HIE (HIE+MRI) and 19 had negative MRI findings (HIE-MRI). Annotations were performed twice with shuffled data sets at a 1-month interval and intrarater reliability was assessed. Focused comparison was conducted between non-HIE, HIE+MRI and HIE-MRI neonates whose images were acquired with a high frequency linear transducer.

RESULTS

Studies acquired with the two most frequently utilized transducers significantly differed in number of branches (p = 0.002), vessel thickness (p = 0.007) and echogenicity (p = 0.009). Studies acquired with the two transducers also significantly differed in acquisition frequency (p < 0.001), thermal indices (p < 0.001) and use of harmonic imaging (p < 0.001). Groupwise comparison of vessels imaged with the most frequently utilized transducer found significantly fewer branches in HIE + MRI compared to HIE-MRI negative and non-HIE patients (p = 0.005).

CONCLUSION

LV can be visualized in the absence of pathology using modern high-resolution neurosonography. Visualization of LV branches varies between HIE + MRI, HIE-MRI neonates and controls.

ADVANCES IN KNOWLEDGE

High-resolution neurosonography is a feasible technique to assess LV morphology in healthy neonates and neonates with HIE.