Near-infrared spectroscopy versus magnetic resonance imaging to study brain perfusion in newborns with hypoxic-ischemic encephalopathy treated with hypothermia

Abstract

Background: The measurement of brain perfusion may provide valuable information for assessment and treatment of newborns with hypoxic-ischemic encephalopathy (HIE). While arterial spin labeled perfusion (ASL) magnetic resonance imaging (MRI) provides noninvasive and direct measurements of regional cerebral blood flow (CBF) values, it is logistically challenging to obtain. Near-infrared spectroscopy (NIRS) might be an alternative, as it permits noninvasive and continuous monitoring of cerebral hemodynamics and oxygenation at the bedside.

Objective: The purpose of this study is to determine the correlation between measurements of brain perfusion by NIRS and by MRI in term newborns with HIE treated with hypothermia.

Design/methods: In this prospective cohort study, ASL-MRI and NIRS performed during hypothermia were used to assess brain perfusion in these newborns. Regional cerebral blood flow (CBF) values, measured from 1-2 MRI scans for each patient, were compared to mixed venous saturation values (SctO2) recorded by NIRS just before and after each MRI. Analysis included groupings into moderate versus severe HIE based on their initial background pattern of amplitude-integrated electroencephalogram.

Results: Twelve concomitant recordings were obtained of seven neonates. Strong correlation was found between SctO2 and CBF in asphyxiated newborns with severe HIE (r=0.88; p value=0.0085). Moreover, newborns with severe HIE had lower CBF (likely lower oxygen supply) and extracted less oxygen (likely lower oxygen demand or utilization) when comparing SctO2 and CBF to those with moderate HIE.

Conclusions: NIRS is an effective bedside tool to monitor and understand brain perfusion changes in term asphyxiated newborns, which in conjunction with precise measurements of CBF obtained by MRI at particular times, may help tailor neuroprotective strategies in term newborns with HIE.

Keywords: Amplitude-Integrated Electroencephalogram; Brain; CBF; Cerebral Blood Flow; HIE; Hypoxic–Ischemic Encephalopathy; Hypoxic–ischemic encephalopathy; MRI; Magnetic Resonance Imaging; Magnetic resonance imaging; Mixed Venous Saturation; NICU; NIRS; Near-Infrared Spectroscopy; Near-infrared spectroscopy; Neonatal Intensive Care Unit; Newborn; PASL; Perfusion; Pulsed Arterial Spin Labeling; SctO(2); aEEG.

FIGURE 1. Positions of the near-infrared spectroscopy (NIRS) sensors

For the purpose of monitoring continuously mixed venous saturation (SctO2), two neonatal NIRS sensors were placed respectively on each side of the newborn’s forehead, over the area of frontal lobes.

FIGURE 2. Example of axial cerebral blood flow (CBF) (mL/100g/min) maps obtained at different brain levels with the described pulsed arterial spin labeling (PASL) MRI sequence in a normal term newborn

Perfusion was higher in the gray matter and in the basal ganglia compared to the white matter.

FIGURE 3. Comparison between cerebral blood flow (CBF) (mL/100g/min) measured by ASL-MRI and mixed venous saturation (SctO2) (%) measured by NIRS in asphyxiated newborns treated with hypothermia during the first days of life

Both SctO2 and CBF increased from day 1 to 2 in all term newborns with HIE, despite hypothermia treatment. Newborns with severe encephalopathy had lower CBF than newborns with moderate encephalopathy. A strong correlation (r = 0.88, p < 0.01) between SctO2 and CBF was found in asphyxiated newborns with initially severe encephalopathy. Newborns who developed HI brain injury had higher SctO2 than newborns who did not develop brain injury.