Medical laser applications require knowledge about the optical properties of target tissue. In this study, the optical properties of selected native and coagulated human brain structures were determined in vitro in the spectral range between 360 and 1100 nm. The tissues investigated included white brain matter, grey brain matter, cerebellum and brainstem tissues (pons, thalamus). In addition, the optical properties of two human tumours (meningioma, astrocytoma WHO grade II) were determined. Diffuse reflectance, total transmittance and collimated transmittance of the samples were measured using an integrating-sphere technique. From these experimental data, the absorption coefficients, the scattering coefficients and the anisotropy factors of the samples were determined employing an inverse Monte Carlo technique. The tissues investigated differed from each other predominantly in their scattering properties. Thermal coagulation reduced the optical penetration depth substantially. The highest penetration depths for all tissues investigated were found in the wavelength range between 1000 and 1100 nm. A comparison with data from the literature revealed the importance of the employed tissue preparation technique and the impact of the theoretical model used to extract the optical coefficients from the measured quantities.

Laser-induced thermotherapy (LITT) is a minimally invasive neurosurgical approach to the stereotactic treatment of brain tumors in poorly accessible regions. Its clinical applicability has been shown in several experimental and clinical studies under on-line monitoring by magnetic resonance imaging (MRI). This review characterizes LITT as an alternative neurosurgical approach with specific focus on the typical histological alterations and ultrastructural cellular changes following laser irradiation in the central nervous system. The spatial and temporal pattern of these changes is discussed in their relevance to the neurosurgical treatment of neoplastic lesions using LITT.

To study whether neuronal regeneration occurs after laserinduced interstitial thermotherapy (LITT) of the brain, we examined lesions and their margins in adult Lewis rats with histological and immunohistochemical methods. We used the Bodian stain and antibodies against P-amyloid precursor protein (APP), which has been associated with trophic effects in neural regeneration and against heatshock protein 72 (HSP 72) and neurofilament 68 (NF 68). The glial reaction was monitored with antibodies against glial fibrillary acidic protein (GFAP) and apolipoprotein E (Apo E). P-Amyloid precursor protein showed a distinct temporal profile in areas of lesion margins thought to be associated with neurite sprouting and regeneration. Axonal accumulation of APP started 1 h after LITT and reached a maximum after 3 days. Heat-shock protein 72 was weakly positive in isolated marginal neurons in the early postoperative period. Subsequent to GFAP expression, Apo E immunoreactivity was detected in reactive astrocytes but not in profiles thought to be axonal sprouts. The results showed that margins of LITT-induced lesions contain profiles which resemble sprouting neurites and are similar to those found after injury or ischemia but with differences in the time course of reactive proteins.