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2 Opto-Electronics Review

2 2008

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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.

Detection and characterization of breast tumours by time-domain scanning optical mammography

Rinneberg H., Grosenick D., Moesta K. T., Wabnitz H., Mucke J., Wübbeler G., Macdonald R., Schlag P.

Opto-Electronics Review

2008

Vol. 16, No. 2

147-162

The paper gives a short overview of various methods of optical mammography, emphasizing scanning time-domain mammography. The results of a clinical study on time-domain optical mammography are reviewed, comprising 154 patients carrying a total of 102 carcinomas validated by histology. A visibility score attributed to each carcinoma as qualitative measure of tumour detectability indicates acceptable sensitivity but poor specificity for discrimination between malignant and benign lesions. Likewise, a multi-variate statistical analysis yields sensitivity and specificity between 80% and 85% for tumour detection and discrimination with respect to normal (healthy) breast tissue, but values less than 70% for discrimination between malignant and benign breast lesions, being too low to be of clinical relevance. For 87 of the 88 tumours detected retrospectively in both projection optical mammograms, optical properties and tissue parameters were derived based on the diffraction of photon density waves by a spherical inhomogeneity as forward model. Following injection of a bolus of indocyanine green as non-targeted absorbing contrast agent, dynamic contrast-enhanced time-domain optical mammography was carried out on a small number of patients, but no differences in wash-out kinetics of indocyanine green between tumours and healthy breast tissue were observed.