Advanced Compton Camera with the ability in electron tracking based on Micro Pixel Gas Detector for Medical Imaging

We have developed the electron tracking Compton camera (ETCC) with reconstructing the 3-D tracks of the scattered electron in Compton process in the range from sub-MeV to several MeV for both gamma-ray astronomy and medical imaging [Bhattacharya, D, et al., 2004; Kanbach, G, et al., 2004]. By measuring both the directions and energies of a recoil gamma ray and a scattered electron, the direction of the incident gamma ray is determined for each individual photon. Furthermore, a residual measured angle between the recoil electron and scattered gamma ray is powerful for the kinematical background-rejection. For the 3-D tracking of the electrons, the micro time projection chamber (mu-TPC) was developed, which consists of a new type of the micro pattern gas detector, or a micro pixel gas chamber (mu-PIC) [Kanbach, G, et al., 2004; Ochi, A, et al., 2001; Nagayoshi, T, et al., 2005]. The ETCC consists of this mu-TPC (10 cm cube) and the 6 times 6 times 3mm GSO crystal pixel arrays with a flat panel photo-multiplier surrounding the base and side of the mu-TPC for detecting the recoil gamma rays. The ETCC provided the gamma ray images of point sources between 120 keV and ~1 MeV with the angular esolution of 6 degree and 5 degree (FWHM) at 364 keV of ¹³¹iodine and 511 keV of ¹⁸F ion, respectively. Also the angle of the scattered electron was measured with the resolution of ~80 degree, by which most backgrounds were removed by the kinematical constraint. A mobile ETCC for medical imaging, which is fabricated in a 1 m cubic box, has been tested since October 2005. Here we present the imaging performances using both a phantom and a rat.