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dc.contributor.author
Kleiser, Stefan
dc.contributor.supervisor
Rudin, Markus
dc.contributor.supervisor
Wolf, Martin
dc.contributor.supervisor
Gassert, Roger
dc.date.accessioned
2017-08-09T05:37:03Z
dc.date.available
2017-08-08T15:17:36Z
dc.date.available
2017-08-09T05:37:03Z
dc.date.available
2017-06-12T19:08:32Z
dc.date.available
2017-08-09T05:17:39Z
dc.date.issued
2017
dc.identifier.uri
http://hdl.handle.net/20.500.11850/185346
dc.identifier.doi
10.3929/ethz-b-000175281
dc.description.abstract
The brain is a very vulnerable organ and damage to it is often followed by severe implications such as long-term disabilities and it may even lead to death. Cerebral oximetry by near-infrared spectroscopy (NIRS) has repeatedly been cited as promis- ing technology, potentially enabling clinicians to prevent these outcomes. Preterm neonates are likely to suffer from complications leading to brain damage and may thus benefit strongly from NIRS monitoring. Although a number of commercial NIRS oximeters are clinically approved, the method has not yet been widely established. Two of the major reasons for this are poor precision of instruments and that tissue oxygen haemoglobin saturation (StO 2 ) obtained from different oximeters and sensors are incomparable. This thesis addresses these two problems and provides solutions. OxyPrem was developed with the objective to provide an instrument with increased precision to clinicians. Two versions, OxyPrem v1.2 and v1.3, are introduced in this thesis and their performance is validated in vivo and in vitro. Both sensors are based on symmetric arrangement of light sources and detectors and employ a self-calibrating algorithm. OxyPrem v1.2 performed excellently in vivo in a precision assessment on the forearm of adults (repeatability = within-subject standard deviation (S w ) = 1.7 %). Repeata- bility in preterm neonates was S w = 3.3% which is still good, taking into account that S w in neonates is typically higher than in adults. An improved version of the instrument, OxyPrem v1.3, was assessed in vivo in neonates as well. The study demonstrated S w as good as 2.8 %. Simultaneous mea- surements with another OxyPrem v1.3 sensor and a pulse oximeter revealed unstable physiology in some neonates. In a second analysis without these confounding sub- jects, S w improved drastically to 1.9 % which is amongst the best precision values ever achieved for NIRS oximeters. To overcome the lack of comparability of different oximeters and sensors, we have performed several studies with liquid phantoms simulating optical properties of neona- tal brain tissue. We first conducted experiments with a simple, homogeneous phantom and then refined the set-up to model a more realistic two-layer geometry resembling skull and brain. Our studies showed substantially different StO 2 readings provided by different oximeters which, however, were mostly linearly related. With the improved set-up, we characterized a large number of commercially available oximeters and sen- sors and provided coefficients for their pairwise linear relation. The method showed good repeatability and helps establishing comparability. As neonates are a very heterogeneous group, we investigated the effect that a varia- tion in total haemoglobin concentration (c tHb ) has on StO 2 readings by NIRS oxime- ters. We found strong influence of c tHb on StO 2 while only OxyPrem v1.3 proved to be largely immune to this effect, which causes substantial uncertainty to readings of other instruments. As the presented phantom set-up is very versatile, we additionally investigated sev- eral other effects with slight adaptations. These showed that StO 2 readings were un- affected by a thin superficial layer, while sensitivity decreased substantially for a layer with 16 mm thickness. In another experiment, we did not observe a change in StO 2 readings for very thin clear layers such as oil on the skin of neonates, whereas thicker layers must be avoided. Partial placement of sensors on top of hair and birth marks may seriously flaw StO 2 of sensors without symmetric source-detector arrangement and self-calibrating algorithm. In summary, this thesis provides solutions to two of the problems mentioned most often in association with cerebral oxygenation monitoring by NIRS. We have intro- duced OxyPrem v1.2 and v1.3 and demonstrated superior precision of the instruments in vivo. OxyPrem v1.3 proved to be largely immune to variation in c tHb , which reduces this considerable uncertainty in StO 2 readings to a minimum. By a series of in vitro experiments with liquid phantoms we were able to establish comparability of different instruments and systematically assessed several types of influences to StO 2 readings.
en_US
dc.language.iso
en
en_US
dc.publisher
ETH Zurich
en_US
dc.subject
Tissue Oxygenation
en_US
dc.subject
Near-Infrared Spectroscopy
en_US
dc.subject
Phantom Model
en_US
dc.subject
Repeatability
en_US
dc.title
Cerebral oxygenation monitoring in neonates: improving and validating instrumentation
en_US
dc.type
Doctoral Thesis
dc.date.published
2017-08-09
ethz.size
178 p.
en_US
ethz.code.ddc
6 - Technology, medicine and applied sciences::620 - Engineering & allied operations
en_US
ethz.identifier.diss
24037
en_US
ethz.publication.place
Zurich
en_US
ethz.publication.status
published
en_US
ethz.leitzahl.certified
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02140 - Dep. Inf.technologie und Elektrotechnik / Dep. of Inform.Technol. Electrical Eng.::02631 - Institut für Biomedizinische Technik / Institute for Biomedical Engineering::03750 - Rudin, Markus (emeritus)
ethz.date.deposited
2017-06-12T19:08:55Z
ethz.source
FORM
ethz.source
ECIT
ethz.identifier.importid
imp593655299da5229754
ethz.ecitpid
pub:189822
ethz.eth
yes
en_US
ethz.availability
Embargoed
en_US
ethz.date.embargoend
2020-08-09
ethz.rosetta.installDate
2017-09-18T11:05:44Z
ethz.rosetta.lastUpdated
2019-01-02T09:30:18Z
ethz.rosetta.versionExported
true
dc.identifier.olduri
http://hdl.handle.net/20.500.11850/127026
dc.identifier.olduri
http://hdl.handle.net/20.500.11850/175281
ethz.COinS
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