Image quantification with a large area multiwire proportional chamber positron camera (MUP-PET)

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Abstract
A large area multi wire proportional chamber positron camera system is under evaluation for clinical Nuclear Medicine investigation using isotopes both from in house generators (68Ga) and from remote cyclotrons (18F,124I,64Cu and81Rb). Images are reconstructed using a fully three dimensional (3D) algorithm and exhibit equal resolution in all three orthogonal directions. The axial field of view of 15 cm is large enough to allow coverage of the whole brain. This paper discusses the performance of the MUP-PET system with particular emphasis on quantification and the development of an attenuation correction scheme for a large area detector system. The distribution of scattered and accidental events is investigated and observed to contribute a fairly uniform background to the image. Dead time correction factors are calculated from an analytical expression obtained by considering the various sources of dead time present in the system. Following correction for atternuation, accidentals, scattered events and dead time, reconstructed phantom images show a strong linear correlation (r=0.998) between count density and regional isotope concentration. The extension of the methods to clinical studies is discussed.