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2 Opto-Electronics Review

2 2008

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Near-infrared spectroscopy extended with indocyanine green dye dilution for cerebral blood flow measurement: Median values in healthy volunteers

Mudra R., Muroi C., Niederer P., Keller E.

Opto-Electronics Review

2008

Vol. 16, No. 3

297-308

The cerebral blood flow (CBF) is an important vital parameter in neurointensive care. Currently, there is no non-invasive method for its measurement that can easily be applied at the bedside. A new tool to determine CBF is based on near-infrared spectroscopy (NIRS) applied together with indocyanine green (ICG) dye dilution. From a bilateral measurement on selected regions on the head of infrared (IR) absorption at various wavelengths during the dilution maneuver, the vascular perfusion characteristics of the two brain hemispheres can be determined in terms of mean transit time (mtt) of ICG, cerebral blood volume (CBV) and CBF. So far, on nine healthy volunteers, NIRS ICG dye dilution bihemispheric measurements were performed, which yielded to mtt given as median (range) of 9.3 s (5.1-16.3 s), CBV of 3.5 ml/100 g (1.7-4.1 ml/100 g), and CBF of 18.2 ml/(100 gxmin) [11.1-48.6 ml/(100 g×min)]. Additionally, the blood flow index (BFI) was calculated with BFI= 13.8 mg/(100 gxs) [6.6-15.2 mg/(100 gxs)]. The Spearman rank correlation coefficient between CBF and BFI was RS = 0.76. However, as the Bland & Altman plot between CBFNIRS and the CBFBFI documents, the limits of agreement are rather wide (21.9 ± 6.7). Under physiological conditions in healthy volunteers, no differences could be detected between the hemispheres.

Monte Carlo simulation of light propagation in adult brain: influence of tissue blood content and indocyanine green

Niederer P., Mudra R., Keller E.

Opto-Electronics Review

2008

Vol. 16, No. 2

124-130

Near-infrared spectroscopy (NIRS), applied to a human head, is a noninvasive method in neurointensive care to monitor cerebral hemodynamics and oxygenation. The method is particularly powerful when it is applied in combination with indocyanine green (ICG) as a tracer substance. In order to assess contributions to the measured optical density (OD) which are due to extracerebral circulation and disturb the clinically significant intracerebral signals, we simulated the light propagation in an anatomically representative model of the adult head derived from MRI measurements with the aid of Monte Carlo methods. Since the measured OD signal depends largely on the relative blood content in various transilluminated tissues, we weighted the calculated densities of the photon distribution under baseline conditions within the tissues with the changes and aberrations of the relative blood volumes which we expect to prevail under physiological conditions. Furthermore, the influence of the IGC dye as a tracer substance was assessed. We conclude that up to about different 70% of the measured OD signal may have its origin in the tissues of interest under optimal conditions, which is mainly due to the extrapolated high relative blood content of brain tissue along with the influence of ICG.