Dynamic laser speckle imaging of cerebral blood flow.

Laser speckle imaging (LSI) based on the speckle contrast analysis is a simple and robust technique for imaging of heterogeneous dynamics. LSI finds frequent application for dynamical mapping of cerebral blood flow, as it features high spatial and temporal resolution. However, the quantitative interpretation of the acquired data is not straightforward for the common case of a speckle field formed by both by moving and localized scatterers such as blood cells and bone or tissue. Here we present a novel processing scheme, we call dynamic laser speckle imaging (dLSI), that can be used to correctly extract the temporal correlation parameters from the speckle contrast measured in the presence of a static or slow-evolving background. The static light contribution is derived from the measurements by cross-correlating sequential speckle images. In-vivo speckle imaging experiments performed in the rodent brain demonstrate that dLSI leads to improved results. The cerebral hemodynamic response observed through the thinned and intact skull are more pronounced in the dLSI images as compared to the standard speckle contrast analysis. The proposed method also yields benefits with respect to the quality of the speckle images by suppressing contributions of non-uniformly distributed specular reflections.

Improved in vivo two-photon imaging after blood replacement by perfluorocarbon.

Two-photon microscopy is a powerful method in biomedical research that allows functional and anatomical imaging at a subcellular resolution in vivo. The technique is seriously hampered by absorption and scattering of light by blood, which prevents imaging through large vessels. Here, we demonstrate in the rat cerebral cortex that blood replacement by perfluorocarbon emulsion, a compound also used in human critical care medicine, yields superior image quality, while preserving neuronal integrity. Shadows of large superficial vessels disappear completely and cells can be imaged underneath them. For the first time, it is possible to image complete populations of neurons and astrocytes in the upper layers of neocortex in vivo.

Measurements of hypoxia ([(18)F]-FMISO, [(18)F]-EF5) with positron emission tomography (PET) and perfusion using PET ([(15)O]-H(2)O) and power Doppler ultrasonography in feline fibrosarcomas*.

Abstract The aim of this study was to evaluate if hypoxia in feline fibrosarcomas can be detected. This was done using positron emission tomography (PET), two hypoxia tracers and polarographic pO(2) measurements. Of the seven cats included, five received [(18)F]-fluoromisonidazole and two 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide. Perfusion was evaluated with [(15)O]-H(2)O (n = 4) and with contrast-enhanced power Doppler ultrasonography (n = 5). Hypoxia was detected in three cats. Polarographic pO(2) measurements did not confirm PET results. In the ultrasonographic evaluation, low vascularity and low perfusion were seen with a peripheral vascular pattern and no perfusion in the centre of the tumour. This was in contrast to the [(15)O]-H(2)O scans, where central perfusion of the tumour was also found. In conclusion, it appears that hypoxia exists in this tumour type. The presence of tumour necrosis and heterogeneous hypoxia patterns in these tumours may explain the found discrepancies between the applied techniques.

Optical imaging of the spatiotemporal dynamics of cerebral blood flow and oxidative metabolism in the rat barrel cortex.

Oxidative metabolism and cerebral blood flow (CBF) are two of the most important measures in neuroimaging. However, results from concurrent imaging of the two with high spatial and temporal resolution have never been published. We used flavoprotein autofluorescence (AF) and laser speckle imaging (LSI) in the anaesthetized rat to map oxidative metabolism and CBF in response to single vibrissa stimulation. Autofluorescence responses reflecting oxidative metabolism demonstrated a fast increase with a delay of 0.1 s. The sign-reversed speckle contrast reflecting CBF started to rise with a delay of 0.6 s and reached its maximum 1.4 s after the stimulation offset. The fractional signal changes were 2.0% in AF and 9.7% in LSI. Pixelwise modelling revealed that CBF maps spread over an area up to 2.5-times larger than metabolic maps. The results provide evidence that the increase in cerebral oxidative metabolism in response to sensory stimulation is considerably faster and more localized than the CBF response. This suggests that future developments in functional imaging concentrating on the metabolic response promise an increased spatial resolution.

Regeneration processes in rabbit endometrium: a photodynamic therapy model.

The origin and process of regeneration in rabbit endometrium was evaluated following photodynamic epithelial destruction using topically applied aminolevulinic acid (ALA). Selective destruction of endometrial epithelium was performed using photodynamic therapy (PDT). ALA was diluted to 200 mg/ml dextran 70 shortly prior to administration. A volume of 1.2 ml was injected into the left uterus. Intrauterine illumination (wavelength 630 nm, light dose 40-80 J/cm2) was performed 3 h after drug administration. Tissue morphology was evaluated by light and scanning electron microscopy 1, 3, 7 and 28 days post-treatment (three animals at each time-point). Regeneration of the endometrium following epithelial ablation by PDT was fully activated after 24 h and was completed after 72 h. Endometrial surface generation occurred by proliferation, originating primarily in deeper regions of the glands. Findings from our morphological follow-up study support the origin of endometrial regeneration being mainly from undifferentiated stem cells and residual glandular epithelium.

Dosimetry model for photodynamic therapy with topically administered photosensitizers.

BACKGROUND AND OBJECTIVE: Photodynamic therapy (PDT) based on topical application of photosensitizers has been under development over the last years. Typical applications are treatment of basal cell carcinoma of the skin and photoablation of the endometrium. The dosimetry for topically administered photosensitizers must take a time-dependent inhomogenous drug distribution into account together with the conventional parameters such as optical scattering, absorption, and photobleaching. STUDY DESIGN/MATERIALS AND METHODS: This study presents a dosimetry model where the cytotoxic dose is calculated in a stepwise procedure. The first step calculates the time-dependent distribution of 5-aminolevulinic acid (5-ALA) from diffusion theory. In skin this distribution is dependent on drug permeability through the stratum corneum, on the diffusivity of dermis and epidermis, on the drug clearance time, and on the conversion rate from 5-ALA to protoporphyrin IX (PpIX). In the second step the distribution of PpIX is calculated from the 5-ALA distribution found in the first step taking the dynamics of the biosynthesis of 5-ALA to PpIX and the clearance time of PpIX into account. In the third step the generation of cytotoxic singlet oxygen is calculated from the optical distribution during irradiation, taking a photobleaching mechanism into account. RESULTS: The distribution of cytotoxic oxygen is predicted from the optical dose, the drug dose, and the time between the application of the drug and the irradiation. CONCLUSION: The presented dosimetry model is made as simple as possible, yet composite enough to enable all relevant parameters to be taken into account. The model that is based on a linear theory in a semi-infinite medium can, if required, be extended to take nonuniform and nonlinear phenomena into account.

Photomedicine of the endometrium: experimental concepts.

Gynaecological photomedicine offers new diagnostic and therapeutic methods based on the interaction of light with the reproductive organs. One example is photodynamic therapy (PDT) in which photosensitizers are applied systemically or topically for selective endometrial ablation. Several studies describing the potential use of PDT for this application are reviewed. Basic experimental and clinical aspects of PDT, such as photosensitizer types, application modes, irradiation parameters, optical properties of tissues and photodegradation of photosensitizers are discussed.

Photodynamic destruction of endometrial tissue with topical 5-aminolevulinic acid in rats and rabbits.

OBJECTIVE: The goal of this study was to determine the optimal parameters for photodynamic endometrial destruction with topically applied 5-aminolevulinic acid, a precursor for the endogenous synthesis of the fluorescent photosensitizer protoporphyrin IX. STUDY DESIGN: 5-Aminolevulinic acid pharmacokinetics were measured in rat and rabbit models by analyzing tissue frozen sections 3 to 12 hours after topical administration. Dose-response studies were conducted for 100 to 400 mg/ml 5-aminolevulinic acid. Photodynamic therapy was performed intraluminally, and tissue morphologic features were evaluated 3 and 7 days after treatment. RESULTS: Peak fluorescence was observed 3 hours after topical administration. Glandular fluorescence significantly exceeded stromal and myometrial in all studies, particularly for 200 mg/ml 5-aminolevulinic acid. Histologic studies revealed persistent epithelial destruction with minimal regeneration. CONCLUSION: Topical 5-aminolevulinic acid photodynamic therapy can be used for highly effective, long-lasting destruction of endometrial epithelium. However, optical dosimetry can vary, particularly in the rabbit model, and this appears to have an impact on long-term reepithelialization.

Transgenic mice expressing polyoma virus large T antigen in astrocytes develop severe dysmyelination of the central nervous system.

Transgenic mice were generated using a construct that encodes mouse polyoma virus large T antigen, one of three oncogenic products of the "early region" of the polyoma viral genome. Of 16 transgenic families developed, 1 was characterized by a neurologic disorder consisting of constant tremor and recurrent seizures. Morphologic analysis of the central nervous system (CNS) of affected transgenic mice included: classical light and electron microscopic examination; immunohistochemical assessment of the presence and localization of myelin-specific proteins, of the astrocyte marker glial fibrillary acidic protein, of the oligodendrocyte marker galactosyl cerebroside, and of large T; double immunolabeling of glial fibrillary acidic protein or galactosyl cerebroside and large T to identify the CNS cell type in which large T is expressed; and in situ hybridization to study myelin basic protein gene expression. Our results suggest that polyoma large T is expressed in astrocytes, possibly resulting in altered glial-glial interactions causing impaired oligodendroglial development and secondary dysmyelination. Transgenic oligodendrocytes exhibit features of immaturity, failing to myelinate axons properly and producing morphologic phenotypes of early stages of myelination, such as numerous mesaxonal profiles. Myelin proteins are markedly reduced in transgenic CNS, and myelin basic protein transcripts, while present, are generally decreased. We believe that expression of large T in astrocytes could influence the complex and dynamic interactions between astrocytes and oligodendrocytes, perhaps with regard to the molecular (trophic) signals in the local CNS environment, bringing about arrested oligodendroglial maturation and hypomyelination. This raises intriguing questions concerning the importance of glial-glial interactions in the CNS and the complex levels of control involved in biological expression of genetic information in glial cells.