The optical properties of the media (i

The optical properties of the media (i.e., sand a) were predetermined by using fitting of the time- and spatially resolved photon profiles as explained in ref.23and were assumed to be equal for both the excitation and emission photons. The calculated weight function was corrected for the finite (1 mm) virtual detector size arising from segmenting of the CCD image and the result was further convolved with the temporal impulseresponse function of our imaging system, so that the appropriate forward model for a given time gate could be calculated. animals in vivo. Keywords:malignancy, optical, diffuse, molecular, imaging Pioneering developments in the engineering of fluorescent proteins, probes, and the chemistry of nanomaterials and fluorochromes have enabled in vivo imaging of cells and their constituents in unperturbed environments in recent years (1,2). Fluorescent proteins have become essential reporter molecules of gene expression and regulation, protein function, and cell motility in living organisms (35). Similarly, extrinsically administered fluorescent probes have demonstrated high sensitivity in targeting specific cells [for example, malignancy cells (5)] or identifying proteins and molecular pathways of development, function, and disease in vivo. Further enhanced by sensing of spectrally separated fluorescent molecules, fluorescence microscopy currently offers unequalled insights in the study of cellular and protein interactions. In principle, fluorescence technology could be similarly used to 42-(2-Tetrazolyl)rapamycin study normal and diseased tissues at the whole-organ and live-animal 42-(2-Tetrazolyl)rapamycin level. However, there remain significant difficulties in imaging beyond a few hundred micrometers in depth because of the high degree of light scatter in tissues, which arises from photon interactions with cellular membranes and organelles. Currently, fluorescence macroscopic imaging is largely performed by illuminating tissue at the fluorochrome’s excitation wavelength and detecting the emission from within the animal’s body by using appropriate spectral filters. Photographic and planar-fluorescence-imaging implementations of this approach offer only 2-dimensional views and largely qualitative data, because they do not consider the nonlinear relation of photon strength to lesion depth and tissue optical properties. In response, tomographic methods have been developed to overcome the limitations of these methods (68). Optical tomography utilizes multiprojection measurements and physical models of photon propagation to quantitatively retrieve fluorochrome biodistribution in tissues. However, the physical limits of imaging overall performance of current tomographic implementations ultimately depend around the tissue optical propertiesprimarily scatteringwhich prospects to a highly ill-posed (i.e., inaccurate) inverse problem that reduces the spatial resolution and yields images that are highly dependent on the particulars of the reconstruction algorithm used. To develop a next-generation optical tomographic method that can selectively reduce the effects of tissue scattering to improve imaging accuracy, we developed a system to use early arriving photons, that is, photons emitted from an ultrafast laser source (i.e., pulse width <1 ps) that propagate through tissue and are the first to arrive at a time-gated detector a distance away from the source (916). The scattering of these early photons is usually strongly biased in the forward direction and correspondingly they experience a lower quantity of total scattering events. As a result, they preferentially propagate along significantly less diffusive paths connecting the source and the detector versus ungated photons and can therefore be used to significantly improve imaging resolution. Early photons have been used previously in planar transillumination studies of breast tissue samples (9,10). The use of early photons in combination with theoretical models of early-photon propagation have also been considered in the past and yielded systems with the ability to localize relatively simple objects such as 1 or 2 2 absorbing or fluorescent spheres embedded in a homogenous scattering fluid (13,14) or, as in our previous work, complex shaped absorbing optical phantoms (15,16). These methods, however, were by no means extended to in vivo imaging and consequently they have not been shown to be biologically Rabbit polyclonal to DCP2 useful. Here, we use early-photon technology for performing high-fidelity fluorescence tomography in living tissues. The imaging approach differed from previous work in that it used (i) high-spatial sampling of photon fields and projections over 360 view angles, comparable in implementation to X-ray CT, but using near-infrared photons; (ii) a dual-wavelength data-normalization plan that proved necessary for imaging in tissue-related optical heterogeneity; and (iii) a corresponding theoretical model that allowed accurate 42-(2-Tetrazolyl)rapamycin modeling of light propagation in tissue at early occasions. It was further found that despite the significant photon rejection associated with the utilization of early photons, this implementation can run at signal-to-noise ratio (SNR) statistics virtually identical to methods using all available photons (e.g., versus continuous-wave techniques) but at a significantly higher imaging fidelity. Applied in vivo to imaging.