engleski

Monte Carlo simulations of a convolution cross talk correction technique in the simultaneous Tc-Tl dual-isotope SPECT imaging

Different cross talk correction schemes in dual isotope imaging procedures have been proposed recently. They range from the very basic ones, like a simple spill-down photon correction, use of a SPECT projection-dependent spill-down factor, techniques using multiple energy windows, convolution cross talk correction (CCTC) or eventually very sophisticated correction schemes which could be introduced into iterative reconstruction techniques that are usually unavailable on commercial acquisition/processing systems. The ultimate aim of this study is to find an optimal transformation in a convolution cross-talk correction scheme, which could rapidly, accurately and simply be implemented in majority of processing computer systems. This scheme is based on an assumption that there exists a kernel which transform photopeak images into the scattered ones as seen through other primary energy window. A set of programs based on the EGS4 code has been written for the description of a photon transport through the sources, phantoms and gamma camera. MC simulations offer elegant separation of the scattered from primary photons, distinction of medium of the scattering, and subsequent formation of sets of projections according to the different criterion (e.g. window width, scatter order). Three type of phantoms, of increased level of complexity have been modeled: simple cylindrical (elliptical) with a point (line) source, cylindrical with the spherical sources and finally, elliptical with the heart model, lungs and liver. The simulation results for a FWHM (FWTM) of the reconstructed point sources in water phantoms, respective energy spectra and cross-talk fractions showed good agreement with the measured data. Among four different approaches of the correction: CCTC with the use of either noise reduced scatter functions or with scatter functions fitted to the simulated PSF, CCTC with an addition of the restoration or a triple window scatter correction scheme, the first two show slightly better results of the reconstructed images of both, the phantom with spherical sources and heart phantom, in terms of contrast. This simulation shows results similar to the experimental phantom findings justifying the simulation assumptions. Further investigation with more complicated phantoms and the inclusion of the spatially variant scatter and restoration functions should be completed in order to improve the dual-isotope images.

MC simulations; cross-talk correction

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