Effects of atlas-based anatomy on modelled light transport in the neonatal head

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Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2023-07-07
Major/Subject
Mcode
Degree programme
Language
en
Pages
24
1-24
Series
Physics in Medicine and Biology, Volume 68, issue 13
Abstract
Objective. Diffuse optical tomography (DOT) provides a relatively convenient method for imaging haemodynamic changes related to neuronal activity on the cerebral cortex. Due to practical challenges in obtaining anatomical images of neonates, an anatomical framework is often created from an age-appropriate atlas model, which is individualized to the subject based on measurements of the head geometry. This work studies the approximation error arising from using an atlas instead of the neonate's own anatomical model. Approach. We consider numerical simulations of frequency-domain (FD) DOT using two approaches, Monte Carlo simulations and diffusion approximation via finite element method, and observe the variation in (1) the logarithm of amplitude and phase shift measurements, and (2) the corresponding inner head sensitivities (Jacobians), due to varying segmented anatomy. Varying segmentations are sampled by registering 165 atlas models from a neonatal database to the head geometry of one individual selected as the reference model. Prior to the registration, we refine the segmentation of the cerebrospinal fluid (CSF) by separating the CSF into two physiologically plausible layers. Main results. In absolute measurements, a considerable change in the grey matter or extracerebral tissue absorption coefficient was found detectable over the anatomical variation. In difference measurements, a small local 10%-increase in brain absorption was clearly detectable in the simulated measurements over the approximation error in the Jacobians, despite the wide range of brain maturation among the registered models. Significance. Individual-level atlas models could potentially be selected within several weeks in gestational age in DOT difference imaging, if an exactly age-appropriate atlas is not available. The approximation error method could potentially be implemented to improve the accuracy of atlas-based imaging. The presented CSF segmentation algorithm could be useful also in other model-based imaging modalities. The computation of FD Jacobians is now available in the widely-used Monte Carlo eXtreme software.
Description
Funding Information: We thank Dr Robert Cooper, Dr Liam Collins-Jones and their colleagues from the University College London and the Centre for the Developing Brain at King’s College London for providing us with the original neonatal head model database. PH also thanks Dr Collins-Jones for practical guidance and discussion. We acknowledge the computational resources provided by the Aalto Science-IT project. Publisher Copyright: © 2023 The Author(s). Published on behalf of Institute of Physics and Engineering in Medicine by IOP Publishing Ltd.
Keywords
approximation error, atlas models, cerebrospinal fluid, diffusion approximation, frequency-domain diffuse optical tomography, Monte Carlo methods, segmentation
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Citation
Hirvi , P , Kuutela , T , Fang , Q , Hannukainen , A , Hyvönen , N & Nissilä , I 2023 , ' Effects of atlas-based anatomy on modelled light transport in the neonatal head ' , Physics in Medicine and Biology , vol. 68 , no. 13 , 135019 , pp. 1-24 . https://doi.org/10.1088/1361-6560/acd48c