Sensitivity and resolution study of a small-field γ-Camera system on a tomographic level

The sensitivity and the spatial resolution of a small-field γ-Camera system based on a Position Sensitive PhotoMultiplier Tube (PSPMT) on a tomographic level are examined in this study. A cylindrical Gel-Phantom (d=40 mm, h=50 mm) with cylindro-conoidal tubes and capillaries (from 64 to 640 mm³) containing water solution of ^99mTc is used as a test phantom in the present work. A total of 24 projections covering the full angle region (0°-360°) are obtained with the γ-Camera system under examination. The planar information is further analyzed to reconstruct the tomographic images taking into account all off-line corrections needed to remove barreloid deformations appearing at the edges of the field-of-view. The reconstruction procedure is performed with iterative algorithms and for comparison reasons two different techniques (MLEM and accelerated ART) are used. The variety of the ^99mTc-volumes in the phantom with the given specific radioactivity and the phantom axial asymmetry, due to the different radial distances of the tubes in the gel environment, allow a realistic characterization of the system´s performance on a tomographic level. Obtained experimental results for the system sensitivity and spatial resolution are presented and discussed in this work; they are also directly compared with ideal tomographic results acquired from the fully simulated γ-Camera system through GATE.