We propose a “gradient filter” reconstruction scheme for solving the dynamic pharmacokinetic problem using fluorescence-photoacoustic tomography in a shape based framework. The proposed method is validated using cancer mimicking phantoms.
We present a time-domain, model-based scheme for X-ray induced acoustic tomography (XACT). In comparison to the commonly used analytic schemes, the model-based reconstructions exhibit less limited-view and noisy artifacts and enable incorporating detector sizes and sound speed variations. In this paper, we brie y compare the performance of the proposed model-based scheme with the universal back-projection and model back-projection reconstructions obtained for full- and limited view test-cases in spherical detection geometry for noisy acoustic measurements. The algorithm has also been validated for experimental ring-array XACT data.
Most cervical cancers originate from the epithelial layer by an uncontrolled growth of abnormal squamous cells and are known as carcinomas. Early stages of this disease manifest as biochemical and morphological changes in the superficial layer. Such changes can be captured from the spectral behavior of intrinsic fluorophores present in the layered cervical tissue. Fluorescence spectroscopy is thus widely used for detection of pre-cancers, also due to its capability as a fast, non-invasive and quantitative probe. This study focuses on analysis of the spectral information of the fluorophores using spatially resolved fluorescence spectroscopy for diagnosis of cervical cancer at an early stage. An in-house fabricated fiber-optic probe of diameter 1mm, consisting of 77 fibers in approximately five circular rings with very high sensitivity for superficial layer changes, has been used to collect fluorescence spectra from different spatially resolved positions of two layered solid phantoms. The phantoms are prepared by varying the thickness and fluorophore concentration of the upper layer. Optical properties of these layered phantoms have been kept similar to cervical tissue to replicate the subtle changes that occur in the tissue with the growth of abnormality. A 405 nm laser diode source is used to excite the samples with two different fluorophores in the two layers, Flavin Adenine Dinucleotide (FAD) in upper layer and Proto-porphyrin (PpIX) in bottom layer. A `Look-up Table' method is used to finally reconstruct thickness and fluorophore concentrations of upper layer of an unknown phantom by evaluating the peak ratios of fluorophores from spectra obtained at different spatially resolved positions.
Photo-acoustic tomography is a hybrid imaging modality that combines the advantages of optical as well as ultrasound imaging techniques to produce images with high resolution and good contrast at high penetration depths. Choice of reconstruction algorithm as well as experimental and computational parameters plays a major role in governing the accuracy of a tomographic technique. Therefore error estimates with the variation of these parameters have extreme importance. Due to the finite support, that photo-acoustic source has, the pressure signals are not band-limited, but in practice, our detection system is. Hence the reconstructed image from ideal, noiseless band-limited forward data (for future references we will call this band-limited reconstruction) is the best approximation that we have for the unknown object. In the present study, we report the error that arises in the universal back-projection (UBP) based photo-acoustic reconstruction for planer detection geometry due to sampling and filtering of forward data (pressure signals).Computational validation of the error estimates have been carried out for synthetic phantoms. Validation with noisy forward data has also been carried out, to study the effect of noise on the error estimates derived in our work. Although here we have derived the estimates for planar detection geometry, the derivations for spherical and cylindrical geometries follow accordingly.
Under the assumption of high scattering and weak absorbing media, diffusion approximation holds in the radiative transport equation to model propagation of light. Diffusion approximation is valid deep inside the medium, not near the boundary. So, we need to implement accurate boundary conditions. Diffuse reflectance close to the source, majorly, depends on the source model inside the medium and boundary conditions used to derive the analytical solution. We have implemented partial current boundary condition and extrapolated boundary condition with extended isotropic source (exponentially decaying) model. Our model predicts diffuse reflectance close to the source at distance less than one mean free path is more accurate than the other methods. Monte-carlo simulation is the standard model to provide diffuse reflectance close to source most accurately. In this report, partial current, extrapolated boundary condition and a unified boundary condition have been compared for accuracy at different regions from the source. It is found that different boundary conditions work in different regimes and the relative error is less with extended source compared to point source.
Mueller matrix has a vast application regarding information of any scattering (turbid) media such as fog, sea water, and biological tissues. It can extract information from scattering properties of the medium. Recently, information from Mueller images and their interpretation are being used for diagnostic purposes in biological tissues. Polar decomposition of Mueller matrices for scattering medium have also been developed, which could be a very powerful and sensitive tool for mapping the morphology of human tissue sections. On the basis of such decomposition, we report here the variation of diattenuation, depolarization and retardance from normal to dysplasia state in cervix tissue.
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