Assessment of cerebral perfusion in post-traumatic brain injury patients with the use of ICG-bolus tracking method.

The aim of this study was to verify the usefulness of the time-resolved optical method utilizing diffusely reflected photons and fluorescence signals combined with intravenous injection of indocyanine green (ICG) in the assessment of brain perfusion in post-traumatic brain injury patients. The distributions of times of flight (DTOFs) of diffusely reflected photons were acquired together with the distributions of times of arrival (DTAs) of fluorescence photons. The data analysis methodology was based on the observation of delays between the signals of statistical moments (number of photons, mean time of flight and variance) of DTOFs and DTAs related to the inflow of ICG to the extra- and intracerebral tissue compartments. Eleven patients with brain hematoma, 15 patients with brain edema and a group of 9 healthy subjects were included in this study. Statistically significant differences between parameters obtained in healthy subjects and patients with brain hematoma and brain edema were observed. The best optical parameter to differentiate patients and control group was variance of the DTOFs or DTAs. Results of the study suggest that time-resolved optical monitoring of inflow of the ICG seems to be a promising tool for detecting cerebral perfusion insufficiencies in critically ill patients.

An algorithm for assessment of inflow and washout of optical contrast agent to the brain by analysis of time-resolved diffuse reflectance and fluorescence signals.

In optical measurements of the brain oxygenation and perfusion the problem of contamination of the signals with the components related to the extracerebral tissues remains an obstacle limiting clinical applicability of the technique. In this paper we present an algorithm allowing for derivation of signals related to the changes in absorption in the intracerebral tissues based on analysis of time-resolved diffuse reflectance and fluorescence. The proposed method was validated in series of Monte Carlo simulations in which inflow and washout of an optical contrast agent into the two-layered human head model was considered. It was shown that the decomposed intracerebral component of the signal can be derived with uncertainty of about 5%. This result suggests that the method proposed can be applied in improved estimation of brain perfusion parameters based on the bolus-tracking technique.

UV-induced generation of rare tautomers of allopurinol and 9-methylhypoxanthine -- a matrix isolation FTIR study.

Monomers of allopurinol and 9-methylhypoxanthine were studied using the matrix isolation technique combined with Fourier transform infrared spectroscopy. The oxo tautomeric forms of both compounds were found to dominate in freshly deposited low-temperature argon matrices. For 9-methylhypoxanthine, a small amount of the hydroxy tautomer was also detected in an Ar matrix before any irradiation. Upon exposure of the matrices to the UV (lambda>230 nm or lambda>270 nm) light, a proton transfer photoreaction converting the oxo forms of both compounds into the corresponding hydroxy tautomers occurred. Generation of conjugated ketenes as minor photoproducts was also observed. For 4(3H)-pyrimidinone (a model compound for both allopurinol and 9-methylhypoxanthine), photoreversibility of the UV-induced oxo --> hydroxy transformation was experimentally proven by direct observation of the back hydroxy --> oxo photoreaction. The substrates (oxo tautomers) and products (hydroxy tautomers) of the observed phototransformations were identified by comparison of their IR spectra with the spectra theoretically predicted at the DFT(B3LYP)/6-31++G(d,p) level. The IR bands in the experimental spectra were assigned to the calculated normal modes.