X-ray attenuation measurements are widely used in medical and industrial applications. The usual results are one-to three-dimensional representations of the attenuation coefficient ͑r͒. In this paper, we present the Z projection algorithm for obtaining the density ͑r͒ and atomic number Z(r) with an energy-resolving x-ray method. As input data the algorithm uses at least two measurements 1 , 2 ,... with different spectral weightings of the source spectrum S(E) and/or detector sensitivity D(E). Analytically, is a function of 1 Ϫc 2 , cϭconst, and Z is a function of 1 / 2. The full numerical treatment yields (1 , 2) and Z(1 , 2) with S(E) and D(E) as commutative parametric functions. We tested the method with dual-energy computed tomography measurements of an organic sample and a set of chemical solutions with predefined and Z. The resulting images show and Z as complementary information: The density reflects the morphology of the objects, whereas the atomic number Zϭnumber of electrons/atom describes the material distribution. For our experimental setup we obtain an absolute precision of 0.1 for Z and 20 mg/cm 3 for. The Z projection can potentially lead to these classes of quantitative information for various scientific, industrial, and medical applications.
Spectral-domain OCT of experimental gliomas and human brain tumor specimens differentiates solid tumor, diffusely invaded brain tissue, and adjacent normal brain based on microstructure and B-scan signal characteristics. In conjunction with the rapid image acquisition rates of SD-OCT, this technology carries the potential of a novel intraoperative imaging tool for the detection of residual tumor and guidance of neurosurgical tumor resections.
Multiphoton excited fluorescence of endogenous fluorophores allows structural imaging of tumor and central nervous system histo-architecture at a subcellular level. The analysis of the decay of the fluorescent signal within specific excitation volumes by fluorescent lifetime imaging discriminates glioma cells and normal brain, and the excitation/lifetime profiles may further allow differentiation of cellular histotypes. This technology provides a noninvasive optical tissue analysis that may potentially be applied to an intraoperative analysis of resection plains in tumor surgery.
Multiphoton excitation fluorescent microscopy is a laserbased technology that allows subcellular resolution of native tissues in situ. We have recently applied this technology to the structural and photochemical imaging of cultured glioma cells and experimental gliomas ex vivo. We demonstrated that high microanatomical definition of the tumor, invasion zone, and normal adjacent brain can be obtained down to single-cell resolution in unprocessed tissue blocks. In this study, we used multiphoton excitation and four-dimensional microscopy to generate fluorescence lifetime maps of the murine brain anatomy, experimental glioma tissue, and biopsy specimens of human glial tumors. In murine brain, cellular and noncellular elements of the normal anatomy were identified. Distinct excitation profiles and lifetimes of endogenous fluorophores were identified for specific brain regions. Intracranial grafts of human glioma cell lines in mouse brain were used to study the excitation profiles and fluorescence lifetimes of tumor cells and adjacent host brain. These studies demonstrated that normal brain and tumor could be distinguished on the basis of fluorescence intensity and fluorescence lifetime profiles. Human brain specimens and brain tumor biopsies were also analyzed by multiphoton microscopy, which demonstrated distinct excitation and lifetime profiles in glioma specimens and tumor-adjacent brain. This study demonstrates that multiphoton excitation of autofluorescence can distinguish tumor tissue and normal brain based on the intensity and lifetime of fluorescence. Further technical developments in this technology may provide a means for in situ tissue analysis, which might be used to detect residual tumor at the resection edge. Neuro-Oncology 9, 103-112, 2007 (Posted to Neuro-Oncology [serial online], Doc. D06-00049, February 26, 2007 Imaging of brain and brain tumor
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