The energy resolution is measured for a plastic scintillating fiber detector coupled to position sensitive photomultiplier tubes. A point source (Mn-54) is placed at a distance in front of an xy plastic scintillating fiber stack which is coupled to two Hamamatsu R2486 position sensitive photomultiplier tubes. At some distance behind this detector another plastic scintillating detector coupled to another position sensitive photomultiplier is placed. Gamma rays interacting in the 1st detector are scattered, and interact with the 2nd detector. By the knowledge of the source location, the Compton interaction location in the 1st detector, and the interaction location of the scattered gamma in detector 2, the scattering angle of the Compton interaction in detector 1 can be determined. From this scattering angle and the known primary gamma energy the Compton electron energy can be calculated. The energy resolution of the scintillating fiber stack-photomultiplier unit of detector 1 for different Compton electron energies is determined by plotting the experimentally measured electron energies obtained from the light output of the photomultiplier tubes of detector 1, comparing them with the electron energy calculated above, and expressed in terms of the FWHM.

We are continuing the characterization of a PET module using plastic scintillating fibers coupled to position sensitive photomultipliers. The sensitivity in air and the resolution in air and water are tabulated for a source positioned at nine locations within the detector field ofview. The full width half maximum resolution for a 0.5 mm diameter Na22 source in air and water is approximately 2.5 mm. The sensitivity is 19 c.p.s./tCi. APPARATUSThe detectors are constructed from KyowalKuraray's 1 mm diameter, round SCSF-81 plastic scintillating fiber with extra mural absorber. The fibers are arranged parallel to the detector axis in a 24 cm2 circular Deirin plastic mold. The packing fraction is approximately 80%, and the thickness of the detectors is 2.5 cm. (Figure 1)1 The photon detectors used are the Haniamatsu R2486 position sensitive photomultiplier (PMT). The PMT's have 12 mesh dynodes followed by (16X) x (16Y) crossed wire anodes (pitch 3.75 mm). The PMT preamps are a University ofTexas at Dallas (U'TD) design and are based on Fujitsu's MB43458 and MB43468 preamplifiers. The anodes have a gain of 12V/pC, and the trigger, which is taken from the 1 ith and 12th dynodes, has a gain of 4.6V/pC. The trigger pulse from each PMT must pass a 375 mV (5 photoelectrons at photocathode) discriminator. The coincidence trigger window is 10 ns. The PMT's operate at a voltage to produce a gain of iø5. The A/D cards are also a UTD design and consist of 16 Philips TDA8703 40MHz flash A/D converters. Each converter is accompanied by dual 8k ram buffers. The fiber detector is coupled to the PMT using Dow Corning Q2-3067 optical couplant. EXPERIMENTAL ARRANGEMENTThe detectors are separated by a distance of 20 cm. To simulate a patient's head we use a 15 cm diameter 4 liter glass beaker filled to a depth of 15 cm. The source is Na-22 and is manufactured by Amersham. It is a 0.5 mm diameter spherical pellet with an activity of 0.75Ci. The source is placed at nine locations within the detector field of view. The locations are: (1) -center, (2 and 6) -1 cm off axis, (3 and 7) -2 cm off axis, (4 and 8) -3 cm from center along the detector axis, and (5 and 9) -5 cm from center along the detector axis. (Figure 2). 132 / SPJE Vol. 2007 Q-8194-1256-2/93/$6.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx