Long-term continuous monitoring of the preterm brain with diffuse optical tomography and electroencephalography: a technical note on cap manufacturing

Abstract

Diffuse optical tomography (DOT) has recently proved useful for detecting whole-brain oxygenation changes in preterm and term newborns' brains. The data recording phase in prior explorations was limited up to a maximum of a couple of hours, a time dictated by the need to minimize skin damage caused by the protracted contact with optode holders and interference with concomitant clinical/nursing procedures. In an attempt to extend the data recording phase, we developed a new custom-made cap for multimodal DOT and electroencephalography acquisitions for the neonatal population. The cap was tested on a preterm neonate (28 weeks gestation) for a 7-day continuous monitoring period. The cap was well tolerated by the neonate, who did not suffer any evident discomfort and/or skin damage. Montage and data acquisition using our cap was operated by an attending nurse with no difficulty. DOT data quality was remarkable, with an average of 92% of reliable channels, characterized by the clear presence of the heartbeat in most of them.

Keywords: continuous monitoring; diffuse optical tomography; electroencephalography; preterm.

Figures

Fig. 1

(a) The original outer layer, with the 10−10 reference points marked on it (left) and the outer layer with all optodes’ support and electrodes’ support. (b) The inner layer created to match the dimension of the baby’s head. (c) Outer and inner layers were sewed together to create the cap (left). The holes made in the inner layer aligned with the optodes’ position and electrodes’ position of the outer layer can be clearly seen. On the right, the cap positioned on the neonate’s head, with all fibers connected to it. (d) Configuration of optodes and electrodes. The 10−5 locations, where optodes/electrodes were positioned, are displayed in red rectangles for sources, light blue ellipses for detectors, and black circles for electrodes. Green lines connecting sources and detectors show the 105 DOT channels.

Fig. 2

Pictures of the neonate’s head taken after removal of the cap toward the end of the 7-day monitoring period. Neither skin lesions nor evident pressure marks due to the cap can be observed.

Fig. 3

(a) Box-plot showing the % of reliable channels during all data segments. The median number of reliable channels across data segment was 92.38%, with only three segments of data having <78.1% of reliable channels. (b) Three representative spectrograms, showing the results of the time-frequency analysis. In the upper panel, the spectrogram depicts one segment of data (∼377  min, i.e., ∼6  h and a half) acquired during the first days, in the bottom panel on the left, the spectrogram depicts one segment of data (∼98  min) acquired halfway through the recording phase, and in the bottom panel on the right, the spectrogram depicts one segment of data (∼73  min) acquired toward the end of the 7-day period. The black ellipses highlight in each spectrogram the heartbeat component, which is consistently observable for the entire duration of the three time-series.

Fig. 4

Example of DOT intensity data of all channels at both wavelengths (210 channels) in one of the data segment. No filtering was applied to the plotted data. In the bottom panel, a particular of the above time-series is displayed. The heartbeat component is appreciable in most of the channels.

Fig. 5

Example of EEG data. The data were offline re-referenced to the average of FT9 and FT10. A notch filter (cut-off frequency=50  Hz) was applied to remove the line noise. A band-pass filter (cut-off frequency=0.5 and 60 Hz) was further applied to remove higher frequency noise and low frequency drifts.