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Optical imaging of the neonatal brain

Presented at the Neonatal Society 2006 Summer Meeting (programme).

Austin T1, Gibson AP2, Everdell NL2, Schweiger M3, Meek JH1, Arridge SR3, Wyatt JS1, Hebden JC2

1 Department of Paediatrics and Child Health, University College London, UK
2 Department of Medical Physics and Bioengineering, University College London, UK
3 Department of Computer Science, University College London, UK

Background & Aims: Optical methods provide a means of monitoring cerebral oxygenation in newborn infants at risk of brain injury. The aim of this research has been to obtain the first three dimensional tomographic images of regional cerebral blood volume (rCBV) and regional tissue oxygen saturation (rStO2) from the neonatal brain.

Methods: The optical imaging system developed at University College London is a 32-channel time-resolved device. It measures the flight times of photons transmitted between pairs of points on the surface using very short (picosecond) pulses of laser light at two wavelengths (780nm and 815nm) and 32 parallel time-resolved detectors. The optical fibre bundles are coupled onto the head using a foam-line thermoplastic helmet. A mathematical model of light transport in the brain is constructed and modelled data compared with this measured data. The model is then adjusted iteratively until acceptable correspondence is achieved and the image reconstructed.

Results: A total of 24 infants were studied. Full image data sets were acquired from 14 infants: successful static images were reconstructed in 8 of these infants and functional images in 4. Images were reconstructed using differences in data resulting from a change in optical properties. To obtain static images data was compared with a homogeneous reference phantom; dynamic images were reconstructed by comparing data before and after a physiological change, such as an evoked response. In the infants with normal cranial ultrasound scans, the static images were symmetrical with a relative decrease in rCBV and rStO2 in the central region of the brain compared to the periphery; this contrasted with the images from infants with evidence of intraventricular haemorrhage (figure 1). Functional activation following passive movement of the infants arm revealed an increase in total haemoglobin in the region of the contralateral motor cortex (figure 2).

Conclusion: Current work is being directed at improving the spatial resolution and quantitation of physiological parameters by developing more sophisticated reconstruction methods incorporating anatomical information obtained from magnetic resonance imaging scans. This research demonstrates the potential of 3D optical tomography to provide unique information on regional cerebral oxygenation in vulnerable infants.

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