High resolution PET detector using wavelength shifting optical fibers and microchannel plate PMT with delay line readout

We are developing a PET detector with depth of interaction (DOI) sensitivity for breast and small animal imaging. The detector uses layers of high density scintillators sandwiched between orthogonal ribbons of wavelength shifting optical fibers. Fibers are coupled to microchannel plate (MCP) based, position sensitive photomultiplier tubes (PSPMTs) containing a crossed delay line readout anode. Preliminary measurements have been made using blue-green waveshifting fiber ribbons coupled to LSO. The measured photoelectron yield due to wavelength shifted light from the fibers is sufficient to ensure a Poisson probability of only 1.0% that no photoelectron is generated in a given MCP PSPMT. Measurement of internally reflected scintillation light permits energy resolution of better than 25% at 511 keV. Optical fiber readout of high density inorganic crystals provides significantly larger detective area per unit phototube area than do one-to-one coupling schemes using PSPMTs. The use of the MCP PSPMT solves problems that have prevented other types of PSPMTs from being used in such a configuration, namely poor resolution at the low light output level of the optical fibers.