University of Twente Student Theses


Monitoring mitochondrial oxygen levels via protoporphyrin-IX triplet state lifetime technique: assessment of factors reducing measurement accuracy

Schoenmakers, M.A. (2022) Monitoring mitochondrial oxygen levels via protoporphyrin-IX triplet state lifetime technique: assessment of factors reducing measurement accuracy.

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Abstract:Rationale - With maintaining oxygen homeostasis as fundamental target in patient care, accurate monitoring at tissue level is essential. Accordingly, the protoporphyrin-IX triplet state lifetime technique (PpIX-TSLT) measures oxygen pressure levels in mitochondria (mitoPO2) via porphyrin excitation which produce 630nm delayed fluorescence (DF). This DF’s lifetime is oxygen-dependent. However, unexplained results let to hypotheses that background signal (BGS) and a self-quenching phenomenon (SQP) affect the PpIX-TSLT measurement accuracy. BGS is DF signal originating from different factors than the fluorescent porphyrins. The SQP theory proclaims that at high PpIX concentration, collision of excited porphyrins produce 670nm signal and alter the relation between DF lifetime and mitoPO2 values. We aim to identify prominent causes of BGS which disturb the measurement accuracy, and whether SQP occurs within physiological setting. Methods – The COMET (clinical application) and the laboratory laser (LL) (for cellular experiments) are assessed for BGS causes and their contribution to the DF signal (BGS-DF-ratio). The main laser is used to assess individual COMET parts’ BGS and in vivo experiments including BGS-DF-ratios over increasing 5-aminulovulinic (ALA, required for the formation of PpIX) patch application time. The occurrence of SQP is examined via in vitro experiments concerning increasing PpIX concentrations in physiological samples (i.e., mainly containing phosphate buffered saline with albumin) and evaluating - at zero oxygen level - the lifetime and the 670nm to 630nm signal intensity ratio (670nm/630nm-ratio). Additionally, this is examined in the in vivo experiment. Results – The COMET shows prominent BGS from skin measurement and its measurement fiber. The LL presents no replaceable contributor. With low porphyrin concentrations, the BGS-DF-ratio can be >50% for the COMET and LL. This decreases with increasing concentration; i.e., longer ALA application for clinical application. The COMET skin-BGS results in mitoPO2 underestimation considering normoxia and overestimation with critically low values. The SQP in vitro experiments confirm increasing PpIX concentration increases 670/630nm-ratios, which decreases the lifetimes. Longer ALA application did not increase 670/630nm-ratios, but an anticorrelation with the lifetime suggest the possibility of SQP in vivo. Conclusions and recommendations - Regarding BGS, improving mitoPO2 measurement accuracy could be achieved by boosting DF signal intensity through concentration increase – clinically, measure between 8-19hours after ALA application -; remove the measurement fiber of the COMET; and integrate a BGS correction method using average skin BGS. SQP occurrence in physiological samples disturbs the lifetime measurement, at least at zero oxygen level. The effect on (in vivo) mitoPO2 should be assessed.
Item Type:Essay (Master)
Erasmus Medical Center, Rotterdam, Netherlands
Faculty:TNW: Science and Technology
Subject:44 medicine, 50 technical science in general
Programme:Technical Medicine MSc (60033)
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