title: Effect of blood in the cerebrospinal fluid on the accuracy of cerebral oxygenation measured by near infrared spectroscopy.
abstract: Near infrared spectroscopy (NIRS) is an optical technique used to examine the oxygenation state of tissues such as the brain in patients, including those with brain injury. We have examined the effect of a cerebrospinal fluid (CSF) contaminant, specifically haemoglobin, on the sensitivity of cerebral NIRS signals through computer simulation. Previous models of light transport in the head have shown that the clear CSF layer has a profound effect on the sensitivity profile of the NIRS signal due to its low absorbing, low scattering qualities. In subarachnoid haemorrhage, which may accompany brain injury, the principal near infrared chromophore, haemoglobin, is released into the CSF. Sensitivity was measured through forward modeling and the presence of haemoglobin within the CSF was modeled by increasing the absorption coefficient of the layer, with sensitivity quantified in terms of the partial pathlength of light within the brain. The model demonstrated that increases in the CSF absorption led to a marked decrease in the sensitivity to changes in the brain layer. This suggests that blood or other contaminants in the CSF may have a significant effect on the utility of NIRS for measurement of cerebral oxygenation, and merits further investigation.
authors.affiliation: Department of Medical Physics and Bioengineering, University College London, Malet Place Engineering Building, London, WC1E 6BT, UK.
authors.forename: J L
authors.initials: JL
authors.lastname: Robertson
authors.affiliation: Neurocritical Care, The National Hospital for Neurology and Neurosurgery, UCLH, London, UK.
authors.forename: A
authors.initials: A
authors.lastname: Ghosh
authors.affiliation: Department of Computer Science, University College London, London, UK.
authors.forename: T
authors.initials: T
authors.lastname: Correia
authors.affiliation: Neurocritical Care, The National Hospital for Neurology and Neurosurgery, UCLH, London, UK.
authors.forename: D
authors.initials: D
authors.lastname: Highton
authors.affiliation: Neurocritical Care, The National Hospital for Neurology and Neurosurgery, UCLH, London, UK.
authors.forename: M
authors.initials: M
authors.lastname: Smith
authors.affiliation: Department of Medical Physics and Bioengineering, University College London, Malet Place Engineering Building, London, WC1E 6BT, UK.
authors.forename: C E
authors.initials: CE
authors.lastname: Elwell
authors.affiliation: Department of Medical Physics and Bioengineering, University College London, Malet Place Engineering Building, London, WC1E 6BT, UK. t.leung@ucl.ac.uk.
authors.forename: T S
authors.initials: TS
authors.lastname: Leung
mesh_terms: D001921:Brain / Q000378:metabolism*; D002555:Cerebrospinal Fluid; D006801:Humans; D008279:Magnetic Resonance Imaging; D010100:Oxygen / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D010100:Oxygen