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

Ultrasound Diagnosis and Near-Infrared Spectroscopy in the Study of Encephalopathy in Neonates Born under Asphyxia: Narrative Review

Brain injury resulting from adverse events during pregnancy and delivery is the leading cause of neonatal morbidity and disability. Surviving neonates often suffer long-term motor, sensory, and cognitive impairments. Birth asphyxia is among the most common causes of neonatal encephalopathy. The integration of ultrasound, including Doppler ultrasound, and near-infrared spectroscopy (NIRS) offers a promising approach to understanding the pathology and diagnosis of encephalopathy in this special patient population. Ultrasound diagnosis can be very helpful for the assessment of structural abnormalities associated with neonatal encephalopathy such as alterations in brain structures (intraventricular hemorrhage, infarcts, hydrocephalus, white matter injury) and evaluation of morphologic changes. Doppler sonography is the most valuable method as it provides information about blood flow patterns and outcome prediction. NIRS provides valuable insight into the functional aspects of brain activity by measuring tissue oxygenation and blood flow. The combination of ultrasonography and NIRS may produce complementary information on structural and functional aspects of the brain. This review summarizes the current state of research, discusses advantages and limitations, and explores future directions to improve applicability and efficacy.

Evaluation of neonatal cerebral perfusion using three-dimensional power Doppler ultrasound volumes

AIM

Despite improvement in preterm survival, neurological morbidity remains high. 3D fractional moving blood volume (3D-FMBV) quantifies neonatal cerebral perfusion by calculating a standardised measure of the amount of moving blood in a region of interest and correlates with tissue perfusion in animal studies. However, its feasibility and reproducibility are yet to be assessed in newborn infants.

METHODS

Fractional moving blood volume analysis was performed on three-dimensional power Doppler ultrasound (PD-US) volumes from a cohort of preterm infants recruited in 2015 from the Royal Hospital for Women Neonatal Intensive Care Unit. The volumes were acquired by two sonographers and analysed by two different observers. The 3D-FMBV algorithm was applied to calculate an estimate for perfusion. Reproducibility and agreement were assessed using intra-class correlation coefficients (ICC) and Bland-Altman plots.

RESULTS

All 3D PD-US volumes were analysed successfully. Intra-observer reliability was excellent with an ICC of 0.907 (95% CI 0.751-0.968) and 0.906 (95% CI 0.741-0.967) for two independent observers respectively. The inter-observer reliability of the entire technique was good with an ICC of 0.752 (CI: 0.404-0.909).

CONCLUSION

We have successfully shown the feasibility and reliability of applying the 3D-FMBV technique to the neonatal brain in a healthy preterm population.

The Influence of Hyperoxygenation on Fetal Brain Vascularity Measured Using 3D Power Doppler Ultrasound and the Index "Fractional Moving Blood Volume"

INTRODUCTION

Maternal hyperoxygenation effects on fetal cerebral hemodynamics are largely unknown. This study aimed to determine efficacy and reliability of a validated power Doppler ultrasound (US) index, fractional moving blood volume (FMBV), at measuring fetal cerebral vasculature changes during maternal hyperoxia.

METHODS

The fetal cerebral effects of 10 min of hyperoxygenation at 2 flow rates (52%/60% FiO2) were evaluated in women in their third trimester of pregnancy. 2D-US and 3D-US in a transverse plane were performed before, during, and following maternal hyperoxygenation with FMBV estimation performed offline.

RESULTS

Forty-five cases provided data for analysis. Mean intraobserver ICCs were 0.89 (3D-FMBV) and 0.84 (2D-FMBV). A significant difference in vascularity before and during and before and after 60% hyperoxia was observed (p < 0.05), whereas no significant differences were found at 52% hyperoxia (p > 0.05). Significant differences in vascularity were found between 2D-FMBV and 3D-FMBV (p < 0.01).

CONCLUSION

Measurement of fetal cerebral vascularity by 3D-FMBV and 2D-FMBV was highly reproducible. The differing cerebral vascular changes seen with 60% but not 52% FiO2 suggest a possible "threshold effect" that may have influenced prior studies. Further studies are needed to assess cerebral effects of maternal hyperoxygenation on compromised fetuses.

Brain perfusion imaging in neonates

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MRI is the modality of choice to image and quantify cerebral perfusion.

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Imaging of neonatal brain perfusion is possible using MRI and ultrasound.

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Novel ultrafast ultrasound imaging allows for excellent spatiotemporal resolution.

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Understanding cerebral hemodynamic changes of neonatal adaptation is key.

Abnormal variations of the neonatal brain perfusion can result in long-term neurodevelopmental consequences and cerebral perfusion imaging can play an important role in diagnostic and therapeutic decision-making. To identify at-risk situations, perfusion imaging of the neonatal brain must accurately evaluate both regional and global perfusion. To date, neonatal cerebral perfusion assessment remains challenging. The available modalities such as magnetic resonance imaging (MRI), ultrasound imaging, computed tomography (CT), near-infrared spectroscopy or nuclear imaging have multiple compromises and limitations. Several promising methods are being developed to achieve better diagnostic accuracy and higher robustness, in particular using advanced MRI and ultrasound techniques.

The objective of this state-of-the-art review is to analyze the methodology and challenges of neonatal brain perfusion imaging, to describe the currently available modalities, and to outline future perspectives.

Dual-Imaging Modality Approach to Evaluate Cerebral Hemodynamics in Growth-Restricted Fetuses: Oxygenation and Perfusion

OBJECTIVE

To evaluate a dual-imaging modality approach to obtain a combined estimation of venous blood oxygenation (SνO2) using susceptibility-weighted magnetic resonance imaging (SWI-MRI), and blood perfusion using power Dopp-ler ultrasound (PDU) and fractional moving blood volume (FMBV) in the brain of normal growth and growth-restricted fetuses.

METHODS

Normal growth (n = 33) and growth-restricted fetuses (n = 10) from singleton pregnancies between 20 and 40 weeks of gestation were evaluated. MRI was performed and SνO2 was calculated using SWI-MRI data obtained in the straight section of the superior sagittal sinus. Blood perfusion was estimated using PDU and FMBV from the frontal lobe in a mid-sagittal plane of the fetal brain. The association between fetal brain SνO2 and FMBV, and the distribution of SνO2 and FMBV values across gestation were calculated for both groups.

RESULTS

In growth-restricted fetuses, the brain SνO2 values were similar, and the FMBV values were higher across gestation as compared to normal growth fetuses. There was a significantly positive association between SνO2 and FMBV values (slope = 0.38 ± 0.12; r = 0.7; p = 0.02) in growth-restricted fetuses. In normal growth fetuses, SνO2 showed a mild decreasing trend (slope = -0.7 ± 0.4; p = 0.1), whereas FMBV showed a mild increasing trend (slope = 0.2 ± 0.2; p = 0.2) with advancing gestation, and a mild but significant negative association (slope = -0.78 ± 0.3; r = -0.4; p = 0.04) between these two estimates.

CONCLUSION

Combined MRI (SWI) and ultrasound (FMBV) techniques showed a significant association between cerebral blood oxygenation and blood perfusion in normal growth and growth-restricted fetuses. This dual-imaging approach could contribute to the early detection of fetal "brain sparing" and brain oxygen saturation changes in high-risk pregnancies.

Basal ganglia perfusion in the preterm infant during transition

BACKGROUND

The preterm brain is susceptible to changes in blood flow. Using power Doppler images, digital imaging techniques have been developed to measure the total amount of blood flow in a defined area, giving the index: fractional moving blood volume (FMBV). The aim of this study was to investigate temporal changes in basal ganglia perfusion during the transitional period after birth.

METHODS

Twenty-four preterm infants were examined with serial cranial ultrasounds at four time points during the first 48 h of life. FMBV was calculated using power Doppler images at each time point.

RESULTS

All infants had analyzable data and FMBV was successfully calculated at all time points. Twenty-three of the 24 infants had an increasing trend in FMBV over time. The median FMBV increased from 17% at 6 h to 25% at 48 h. One-way repeated measures ANOVA showed a significant increase in values at P < 0.001 at each of the four time points.

CONCLUSION

We have demonstrated changes in basal ganglia blood flow as the cerebral circulation adapts to extrauterine life. With further investigation, this technique may be useful in the assessment of preterm circulatory adaptation, either alone or in conjunction with other modes of evaluating cerebral blood flow.

Spatiotemporal Image Correlation and Volumetric Impedance Indices in the Neonatal Brain: Proof of Concept and Preliminary Reproducibility

OBJECTIVES

Changes in tissue perfusion can be critically important in the vulnerable neonate, but they are very difficult to assess at the bedside. Spatiotemporal image correlation (STIC) sonography is an exciting concept that allows assessment of blood flow by rearranging and merging multiple 2-dimensional color images to create serial 3-dimensional images showing regional blood flow throughout the cardiac cycle. Variations in tissue blood flow may reflect tissue impedance and perfusion. The aim of this study was to demonstrate that it is possible to use STIC images to evaluate tissue impedance in the neonatal brain.

METHODS

Spatiotemporal image correlation data sets were acquired by cranial sonography in 19 neonates. Offline data analysis was performed by using virtual organ computer-aided analysis. With the use of STIC images from different phases of the cardiac cycle, impedance indices were calculated, based on maximum (systolic), minimum (diastolic), and mean virtual organ computer-aided analysis values, in the same way that resistive indices are calculated in 2-dimensional sonography.

RESULTS

Volumetric indices for tissue impedance were obtained for all neonates. Intraclass correlation coefficients (95% confidence intervals) for volumetric impedance indices were as follows: systolic/diastolic ratio, 0.793 (0.615-0.906); pulsatility index, 0.790 (0.609-0.905); and resistive index, 0.783 (0.598-0.901). Interclass correlation coefficients for image processing and analysis were as follows: systolic/diastolic ratio, 0.868 (0.692-0.947); pulsatility index, 0.904 (0.772-0.962); and resistive index, 0.914 (0.794-0.966).

CONCLUSIONS

This study shows that STIC data sets can be used to calculate volumetric impedance indices in the neonatal brain. Preliminary assessment shows that this technique appears reliable and allows evaluation of regional tissue impedance in the neonate.

Reference Ranges for Neonatal Basal Ganglia Perfusion as Measured by Fractional Moving Blood Volume

BACKGROUND

Regional changes in cerebral blood flow and perfusion are implicated in the pathogenesis of adverse neurological events that lead to death and severe disability in the newborn infant. The basal ganglia, in particular, are extremely sensitive to acute hypoxia in the perinatal period, but normal perfusion to this area is unknown.

OBJECTIVES

To establish a reference range for regional basal ganglia perfusion using fractional moving blood volume (FMBV) as an index.

METHODS

Head ultrasounds were performed on neonates from 25 to 41 weeks' gestation. Power Doppler images were obtained from a pre-specified coronal plane. FMBV was calculated offline after selecting the basal ganglia as a region of interest. The average of five calculations was considered to be representative of the regional perfusion for each neonate. The data were analysed, and a neonatal reference range was defined.

RESULTS

124 neonates were included in the study, and all had analysable data. The mean FMBV was 28.8% (±9.6) with a reference range defined as 10-48%. The mean FMBV for neonates <32 weeks', 32-35 weeks' and >35 weeks' gestation were 29.4% (±7.8), 29.2% (±11.0) and 27.4% (±9.7), respectively. Analysis of variance showed no significant difference between neonates based on gestation.

CONCLUSIONS

We have successfully used the index FMBV to define a reference range for perfusion in the basal ganglia. These data can be used as a reference for subsequent studies that evaluate basal ganglia perfusion in pathological conditions.