Comparison of four depth-encoding PET detector modules with wavelength shifting (WLS) and optical fiber read-out.

We propose detectors for a laboratory positron emission tomography scanner specific for mouse imaging that utilizes fewer detectors and channels of electronics compared with existing designs. The detectors are based on lutetium oxyorthosilicate arrays, read out by orthogonal optical fibers placed on the top and bottom of the arrays. Depth of interaction (DOI) information is obtained from the ratio of the signals at either end of the array. Four different detector modules were evaluated, using different reflector materials and two types of optical fibers (wavelength shifting (WLS) fibers and clear optical fibers). The modules were compared in terms of flood histograms, energy resolution, DOI resolution and timing resolution. Energy resolution for single crystals at one irradiation depth was around 65% full-width half-maximum (FWHM). A DOI resolution of approximately 6 mm was obtained for the modules. Timing resolution was in the range of 5.1-7.8 ns. An array assembled in the laboratory and coupled with WLS fibers had the best DOI resolution; the same array with clear fibers had the best timing resolution and a commercially manufactured array and coupled with WLS fibers had the best energy resolution.