Neonatal Cranial Ultrasound: Are Current Safety Guidelines Appropriate?

Neuroinflammation in the Rat Brain After Exposure to Diagnostic Ultrasound

OBJECTIVE

To date there have been no studies exploring the potential for neuroinflammation as an intracranial bio-effect associated with diagnostic ultrasound during neonatal cranial scans in a mammalian in vivo model. The study described here was aimed at investigating the effects of B-mode and Doppler mode ultrasound on inflammation in the rat brain.

METHODS

Twelve Wistar rats (7-9 wk old) were divided into a control group and an ultrasound-exposed group (n = 6/group). A craniotomy was performed, followed by 10 min of B-mode and spectral Doppler interrogation of the middle cerebral artery. The control group was subjected to sham treatment, with the transducer held stationary over the craniotomy site, but the ultrasound machine switched off. Animals were euthanized 48 h after exposure, and the brains formalin fixed for immunohistochemical analysis using allograft inflammatory factor 1 (IBA-1) and glial fibrillary acidic protein (GFAP) as markers of microglia and astrocytes, respectively. The numbers of IBA-1- and GFAP-immunoreactive cells were manually counted and expressed as areal density (cells/mm2). Results were analyzed using Student's unpaired t-test and one-way repeated-measures analysis of variance.

RESULTS

The ultrasound-exposed brain exhibited significant increases in IBA-1 and GFAP immunoreactive cell density in all regions of B-mode and Doppler mode exposure compared with the control group (p < 0.001).

CONCLUSION

Ten minutes of B-mode and Doppler mode ultrasound may induce neuroinflammatory changes in the rat brain. This suggests that exposure of brain tissue to current diagnostic ultrasound intensities may not be completely without risk.

Brain Growth Evaluation Assessed with Transfontanellar (B-GREAT) Ultrasound. Old and New Bedside Markers to Estimate Cerebral Growth in Preterm Infants: a Pilot Study

OBJECTIVE

 We aimed to investigate the feasibility of evaluating overall preterm brain growth using a gathered set of measurements of brain structures in standard cranial ultrasound planes. We called this method of assessment Brain Growth Evaluation Assessed with Transfontanellar ultrasound (B-GREAT).

STUDY DESIGN

 In this prospective observational cohort study, cranial ultrasound was regularly performed (on day 1, 2, 3, and 7 of life, and then weekly until discharge, and at term) in preterm infants born with gestational age (GA) less than 32 weeks. We evaluated corpus callosum length, corpus callosum-fastigium length, anterior horn width, frontal white matter height, total brain surface, deep grey matter height, hemisphere height, transverse cerebellar diameter in the axial view, and transverse cerebellar diameter coronal view. Measurements obtained were used to develop growth charts for B-GREAT markers as a function of postmenstrual age. Reproducibility of B-GREAT markers was studied.

RESULTS

 A total of 528 cranial ultrasounds were performed in 80 neonates (median birth GA: 28+5 weeks and interquartile range: 27+3-30+5). The intraclass correlation coefficients for intra-observer and inter-observer analyses showed substantial agreement for all B-GREAT markers. Growth curves for B-GREAT markers were developed.

CONCLUSION

 B-GREAT is a feasible and reproducible method for bedside monitoring of the growth of the main brain structures in preterm neonates.

KEY POINTS

· Overall neonatal brain growth is not routinely monitored using ultrasound.. · Old and new markers were used to build a standardized and non-invasive tool to monitor brain growth.. · All B-GREAT measurements had a good intra-observer and inter-observer agreement..

Advanced Ultrasound Techniques for Neuroimaging in Pediatric Critical Care: A Review

Because of its portability, safety profile, and accessibility, ultrasound has been integral in pediatric neuroimaging. While conventional B-mode and Doppler ultrasound provide anatomic and limited flow information, new and developing advanced ultrasound techniques are facilitating real-time visualization of brain perfusion, microvascular flow, and changes in tissue stiffness in the brain. These techniques, which include contrast-enhanced ultrasound, microvascular imaging, and elastography, are providing new insights into and new methods of evaluating pathologies affecting children requiring critical care, including hypoxic-ischemic encephalopathy, stroke, and hydrocephalus. This review introduces advanced neurosonography techniques and their clinical applications in pediatric neurocritical care.

Lack of Progression of Intraventricular Hemorrhage in Premature Infants: Implications for Head Ultrasound Screening

Very preterm infants are at risk for germinal matrix hemorrhage- intraventricular hemorrhage (GH-IVH). Severe GH-IVH may cause death or severe neurodevelopmental disability while mild GH-IVH is considered a static, non-progressive disease. This retrospective study aimed to determine if infants with no GH-IVH or mild GH-IVH on initial screening head ultrasound (HUS) advanced to severe GH-IVH. A total of 353 eligible infants with birth gestational age ≤32 0/7 weeks who received a HUS during hospitalization were identified. Of the 343 (97%) infants who had mild GH-IVH (grade II or less) on initial screening, only 4 (1.2%) progressed to severe (grade III or IV). Each of these infants required mechanical ventilation for at least 40 days. Therefore, premature infants who have no GH-IVH or mild GH-IVH on initial routine screening HUS without other risk factors may not require follow-up HUSs. Infants with prolonged mechanical ventilation may require further screening despite reassuring initial HUS findings.

Lung Ultrasound for the Diagnosis of Neonatal Respiratory Distress Syndrome: A Meta-analysis

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Chest radiography is the primary imaging modality used for the assessment of neonatal respiratory distress syndrome (NRDS) in newborns. However, excessively exposing a growing neonate to harmful ionizing radiation may have long-term consequences. Some studies have shown that lung ultrasound (LUS) is helpful in the diagnosis of NRDS. A comprehensive search was carried out using PubMed, Embase, and the Cochrane Library to identify studies in which newborns with clinically suspected NRDS were assessed by LUS. Two investigators independently screened the literature and extracted the data. Any discrepancies were resolved via discussion with the senior author. Study quality was assessed by the Quality Assessment of Diagnostic Accuracy Studies 2 tool, and pooled sensitivity and specificity of various LUS findings for diagnosing NRDS were determined. Summary receiver operating characteristic curve was used to assess the overall performance of LUS. Ten studies with a total of 887 neonates were included in this meta-analysis. There was significant heterogeneity across the included studies. The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio for the diagnosis of NRDS using LUS were 0.92 (95% confidence interval [CI], 0.89–0.94), 0.95 (95% CI, 0.93–0.97), 20.23 (95% CI, 8.54–47.92), 0.07 (95% CI, 0.03–0.14), and 455.30 (95% CI, 153.01–1354.79), respectively. Furthermore, the summary receiver operating characteristic area under the curve was calculated to be 0.9888. The main LUS characteristics of NRDS include bilateral white lung, pleural line abnormalities, and lung consolidation. In summary, LUS is a highly valuable diagnostic technology that complements chest radiography in the diagnosis and follow-up monitoring of NRDS.

Bedside functional monitoring of the dynamic brain connectivity in human neonates

Clinicians have long been interested in functional brain monitoring, as reversible functional losses often precedes observable irreversible structural insults. By characterizing neonatal functional cerebral networks, resting-state functional connectivity is envisioned to provide early markers of cognitive impairments. Here we present a pioneering bedside deep brain resting-state functional connectivity imaging at 250-μm resolution on human neonates using functional ultrasound. Signal correlations between cerebral regions unveil interhemispheric connectivity in very preterm newborns. Furthermore, fine-grain correlations between homologous pixels are consistent with white/grey matter organization. Finally, dynamic resting-state connectivity reveals a significant occurrence decrease of thalamo-cortical networks for very preterm neonates as compared to control term newborns. The same method also shows abnormal patterns in a congenital seizure disorder case compared with the control group. These results pave the way to infants' brain continuous monitoring and may enable the identification of abnormal brain development at the bedside.

A Safety Study of the Effects of 2-Dimensional Shear Wave Elastography on Synaptic Morphologic Characteristics and Function in the Hippocampus of Neonatal Mice

OBJECTIVES

The aim of this study was to determine the effects of 2-dimensional (2D) shear wave elastography (SWE) on synaptic morphologic characteristics and function in the neonatal mouse hippocampus and whether it affects the capacity for learning and memory later in life.

METHODS

We divided neonatal mice into a control group and a 2D SWE group scanned for 10, 20, or 30 minutes. Hippocampal morphologic characteristics were assessed by hematoxylin-eosin and Nissl staining. Ultrastructures of hippocampal neurons were visualized by electron microscopy. Protein and messenger RNA expression levels of synaptophysin, N-methyl-d-aspartate receptor 1 (NMDAR1), NMDAR2A, and NMDAR2B were quantified by a western blot and polymerase chain reaction, respectively. Learning and memory of adult mice were evaluated by the Morris water maze and the novel object recognition task.

RESULTS

Compared with the control group, the hippocampal morphologic characteristics of the experimental groups did not differ under light microscopy, and the synaptic structures assessed by electron microscopy appeared normal. Western blot and polymerase chain reaction results showed that expression of synaptophysin, NMDAR1, NMDAR2A, and NMDAR2B were downregulated after exposure to 2D SWE, but there were no statistical differences between the experimental groups. This downregulation disappeared within 24 hours. The results of the Morris water maze and novel object recognition suggested that the 2D SWE scanning on neonatal mice had no effect on learning and memory in adulthood.

CONCLUSIONS

This study demonstrated that when the mice were exposed to neonatal cranial ultrasound by 2D SWE lasting for longer than 10 minutes, the expression of genes involved in synaptic function was affected, but this effect lasted no longer than 24 hours and did not affect learning and memory in adulthood.

Surveillance Practice for Sonographic Detection of Intracranial Abnormalities in Premature Neonates: A Snapshot of Current Neonatal Cranial Ultrasound Practice in Australia

There are no publications reporting on scan duration and Doppler use during neonatal cranial ultrasound scans. We investigated current practice of neonatal cranial ultrasound at four large tertiary neonatal intensive care units in Australia. Cranial scans were prospectively recorded between March 2015 and November 2016. Variables, including total number of scans, scan duration and frequency and duration of colour and spectral Doppler mode, were extracted. A total of 196 scans formed the final cohort. The median (range) number of scans for each neonate was 1 (1-12). The median (range) overall total scan duration was 309 (119-801) s. Colour mode with or without spectral Doppler mode was used in approximately half of the cohort (106/196, 54%). Our findings comport with our hypotheses. Operators performing neonatal cranial scans in Australia have low overall scan durations. Although the use of Doppler mode during neonatal cranial scans is not standard practice in all neonatal intensive care units, it is used widely irrespective of the degree of prematurity or the presence of brain pathology. Further efforts are required to incorporate recommendations on scan duration and the routine use of Doppler mode during neonatal cranial scans. This is especially imperative given that the most vulnerable neonates with the greater neural tissue sensitivity are likely to be scanned more often.

Effects of 2D-Shear Wave Elastography on Brain-Derived Neurotrophic Factor (BDNF) in the Brains of Neonatal Mice and Exploration of the Mechanism

BACKGROUND The aim of this study was to explore the effect and duration of 2-dimensional shear wave elastography (2D-SWE) irradiation on the expression of brain-derived neurotrophic factor (BDNF) in the brains of neonatal mice and to preliminarily investigate whether its mechanism is neuronal apoptosis. MATERIAL AND METHODS Neonatal mice (within 48 hours of birth) were subjected to 2D-SWE irradiation of the brain for 10 minutes (group S1), 20 minutes (group S2), and 30 minutes (group S3). The mice were sacrificed immediately after irradiation or 24 hours after irradiation. Brains were collected for real-time polymerase chain reaction (RT-PCR) and western blot experiments to determine the expression of BDNF in each group. TdT-mediated dUTP nick-end labeling (TUNEL) was performed to observe neuronal apoptosis in the brain. RESULTS The results of PCR and western blots from the brains of neonatal mice that were sacrificed immediately after irradiation show that S1, S2, and S3 were significantly different from those in the control group. The PCR and western blot results of brain tissues from neonatal mice sacrificed at 24 hours after irradiation showed that there was no significant difference between the S1, S2, S3, and control groups. The results of TUNEL experiments showed that there was no statistically significant difference in the number of apoptotic neurons between the S1, S2, S3, and control groups. CONCLUSIONS 2D-SWE irradiation of neonatal mice for more than 10 minutes downregulated the expression of BDNF. This effect disappeared within 24 hours after the irradiation, and the 2D-SWE scan seemed not to induce neuronal apoptosis.

State-of-the-art neonatal cerebral ultrasound: technique and reporting

In the past three decades, cerebral ultrasound (CUS) has become a trusted technique to study the neonatal brain. It is a relatively cheap, non-invasive, bedside neuroimaging method available in nearly every hospital. Traditionally, CUS was used to detect major abnormalities, such as intraventricular hemorrhage (IVH), periventricular hemorrhagic infarction, post-hemorrhagic ventricular dilatation, and (cystic) periventricular leukomalacia (cPVL). The use of different acoustic windows, such as the mastoid and posterior fontanel, and ongoing technological developments, allows for recognizing other lesion patterns (e.g., cerebellar hemorrhage, perforator stroke, developmental venous anomaly). The CUS technique is still being improved with the use of higher transducer frequencies (7.5-18 MHz), 3D applications, advances in vascular imaging (e.g. ultrafast plane wave imaging), and improved B-mode image processing. Nevertheless, the helpfulness of CUS still highly depends on observer skills, knowledge, and experience. In this special article, we discuss how to perform a dedicated state-of-the-art neonatal CUS, and we provide suggestions for structured reporting and quality assessment.

NeoDoppler: New ultrasound technology for continous cerebral circulation monitoring in neonates

BACKGROUND

There is a strong need for continuous cerebral circulation monitoring in neonatal care, since suboptimal cerebral blood flow may lead to brain injuries in preterm infants and other critically ill neonates. NeoDoppler is a novel ultrasound system, which can be gently fixed to the anterior fontanel and measure cerebral blood flow velocity continuously in different depths of the brain simultaneously. We aimed to study the feasibility, accuracy, and potential clinical applications of NeoDoppler in preterm infants and sick neonates.

METHOD

Twenty-five infants born at different gestational ages with a variety of diagnoses on admission were included. The probe was placed over the anterior fontanel, and blood flow velocity data were continuously recorded. To validate NeoDoppler, we compared the measurements with conventional ultrasound; agreement was assessed using Bland-Altman plots.

RESULTS

NeoDoppler can provide accurate and continuous data on cerebral blood flow velocity in several depths simultaneously. Limits of agreement between the measurements obtained with the two methods were acceptable.

CONCLUSION

By monitoring the cerebral circulation continuously, increased knowledge of cerebral hemodynamics in preterm infants and sick neonates may be acquired. Improved monitoring of these vulnerable brains during a very sensitive period of brain development may contribute toward preventing brain injuries.

Characterizing the Neonatal Brain With Ultrasound Elastography

Prematurity is associated with significant neurological injury and impaired neurodevelopment. In neonatology, ultrasonography is frequently used to assess for neurological injury. Ultrasonography allows rapid bedside imaging without radiation. Its limitations include the need for operator experience, lack of quantification, and lower prognostic power when compared with magnetic resonance imaging. Elastography is one of several technical advances used to enhance the diagnostic capability of traditional ultrasound. By detecting differences in tissue stiffness between normal and abnormal tissue, elastography has the potential to add objective and quantitative data to ultrasound imaging. Quantitative values could then be used to help detect injury, correlate outcome to predict prognosis, and guide surgical intervention. Since developmental processes such as myelination and neuropil formation may also influence brain stiffness, elastography may also serve as a unique tool to further delineate developmental differences between preterm and term infants. In this review, we provide a general overview of elastography, its application in neonatal neuroimaging, and possible future directions.

Knowledge of Safety, Training, and Practice of Neonatal Cranial Ultrasound: A Survey of Operators

OBJECTIVES

Ultrasound can lead to thermal and mechanical effects in interrogated tissues. This possibility suggests a potential risk during neonatal cranial ultrasound examinations. The aim of this study was to explore safety knowledge and training of neonatal cranial ultrasound among Australian operators who routinely perform these scans.

METHODS

An online survey was administered on biosafety and training in neonatal cranial ultrasound, targeting all relevant professionals who can perform neonatal cranial ultrasound examinations in Australia: namely, radiologists, neonatologists, sonographers, and pediatricians. The survey was conducted between November 2013 and May 2014.

RESULTS

A total of 282 responses were received. Twenty of 208 (10%) answered all ultrasound biosafety questions correctly, and 49 of 169 (29%) correctly defined the thermal index. Two-thirds (134 of 214 [63%]) of respondents failed to recognize that reducing the overall scanning time is the most effective method of reducing the total power exposure. Only 13% (31 of 237) indicated that a predetermined fixed period of training or that a specified minimum number of supervised scans was used during training. The reported number of supervised scans during training was highly variable. Almost half of the participants (82 of 181 [45%]) stated that they had received supervision for 10 to 50 scans (median, 20 scans).

CONCLUSIONS

There is a need to educate operators on biosafety issues and approaches to minimize power outputs and reduce the overall duration of cranial ultrasound scans. Development of standardized training requirements may be warranted.