ABSTRACT
Cerebral blood flow is monitored in the neurointensive care unit (NICU) to avoid further brain damage caused by secondary insults following subarachnoid hemorrhage and brain trauma. Current techniques are mainly snap-shot based and focus on larger vessels. However, continuous monitoring of the smaller vessels may help detect the onset of secondary insults at an earlier stage. In this study, long-term measurements of brain microcirculation with laser Doppler flowmetry (LDF) were performed and evaluated. The aim was to identify and describe physiological signal variations and separate these from movement artifacts. Fiberoptic probes for subcortical LDF recordings of perfusion and total light intensity (TLI) were implanted in three patients with subarachnoid hemorrhage. Data were successfully collected and visualized in real-time over 4 days, resulting in 34, 12, and 8.5 h per patient. Visual observation, wavelet transforms, moving medians, and peak envelopes were used to identify and describe movement artifacts and physiological changes. Artifacts occurred in <5% of the total recording time and could be identified through signal processing. Identified physiological signal patterns included a slowly increasing perfusion trend over hours, vasomotion mainly at 2 cycles/min both in the perfusion and the TLI, and rapid, synchronized changes in the TLI and the perfusion on 38 occasions. Continuous LDF recordings indicating changes in the microvascular blood flow can increase the understanding of the microcirculation in the injured brain. In the long run, this may become a complement for the detection of secondary insults at an earlier stage than possible with today's techniques.
ABSTRACT
In brain tumor surgery it is difficult to distinguish the marginal zone with the naked eye. Fluorescence techniques can help identifying tumor tissue in the zone during resection and biopsy procedures. In this paper a novel system for combined real-time measurements of PpIX-fluorescence, microcirculation and tissue grey-whiteness is presented and experimentally evaluated. The system consists of a fluorescence hardware with a sensitive CCD spectrometer for PpIX peak detection, a laser Doppler system, optical probes, and a LabView software. System evaluation was done on static fluorescing material, human skin, and brain tumor tissue. The static material indicates reproducibility, the skin measurements exemplify simultaneous fluorescence and microcirculation measurement in real-time, and the tumor tissue showed PpIX peaks. These decreased over time, as expected, due to photo bleaching. In addition, the system was prepared for clinical use and thus laser- and electrical safety issues were considered. In summary, a system for multiparameter measurements during neurosurgery was successfully evaluated in an experimental environment. As a next step the system will be applied in clinical brain tumor biopsies and resections.