Concept Verification of Three-Layer DOI Detectors for Small Animal PET

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Improved spatial resolution without sacrificing sensitivity is one of the most challenging developmental goals for small animal PET scanners. The 3-layer configuration that we propose here utilizes relative offsets of half a crystal pitch in x- and y-directions, and pulse shape discrimination to obtain depth of interaction (DOI). Three layers of crystals with a dimension 1.5<formula formulatype="inline"><tex>$\,\times\,$</tex></formula>1.5<formula formulatype="inline"><tex>$\,\times\,$</tex></formula>7.0mm<formula formulatype="inline"> <tex>$^{3}$</tex></formula> were composed of a L<formula formulatype="inline"> <tex>$_{0.2}$</tex></formula> GSO (Lu<formula formulatype="inline"><tex>$_{0.4}$</tex> </formula> Gd<formula formulatype="inline"><tex>$_{1.6}$</tex></formula> SiO<formula formulatype="inline"><tex>$_{4}$</tex></formula>: Ce) crystal layer and a L<formula formulatype="inline"><tex>$_{0.9}$</tex></formula> GSO (Lu<formula formulatype="inline"><tex>$_{1.8}$</tex></formula> Gd<formula formulatype="inline"> <tex>$_{0.2}$</tex></formula> SiO<formula formulatype="inline"><tex>$_{4}$</tex> </formula>: Ce) crystal layer aligned with each other, and a L<formula formulatype="inline"> <tex>$_{0.9}$</tex></formula> GSO crystal layer offset at half a crystal pitch in x- and y-directions. The L<formula formulatype="inline"><tex>$_{0.9}$</tex> </formula> GSO crystal layer was attached to a Hamamatsu H9500 flat-panel PMT. The devised small animal PET scanner has a diameter of 84 mm with one detector ring, and can be upgraded to two detector rings. GEANT4 Monte-Carlo simulation was used to estimate sensitivities of <formula formulatype="inline"> <tex>$\sim 12\hbox{\%}$</tex></formula> and <formula formulatype="inline"> <tex>$\sim 20\hbox{\%}$</tex></formula>, respectively, at the center of one and two PMT ring system with an energy window of 350 <formula formulatype="inline"> <tex>$\sim$</tex></formula> 750 keV. We present flood images with peak-to-valley ratios of about 5–6 obtained using <formula formulatype="inline"><tex>$^{22}$</tex> </formula> Na and layer identification capability of <formula formulatype="inline"> <tex>$\sim 99\hbox{\%}$</tex></formula> with pulse shape analysis, and verified the basic concepts of multi-layer small animal PET. </para>