Development of Electron tracking Compton Camera based on micro pixel gas detector and its application 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 for both gamma-ray astronomy and medical imaging [1–3]. 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 an 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 (μ-TPC) was developed, which consists of a new type of the micro pattern gas detector, or a Micro Pixel Gas Chamber (μ-PIC). The ETCC consists of this μ-TPC and the GSO crystal pixel arrays below the μ̃TPC for detecting the recoil gamma rays. The ETCC provided the gamma ray images of point sources between 120keV and ∼1 MeV with the angular resolution of 6 degree (FWHM) at 511keV of ¹⁸F ion, respectively. Also the angle of the scattered electron was measured with the resolution of ∼80 degree. Two mobile ETCCs with 10cm-cube TPC for small animal and 30cm-cube TPC for human body, are now being operated for Medical Imaging test. We have studied the imaging performances using both phantoms and small animals (rats and mice) for conventional radioisotopes of ¹³¹I and ¹⁸F-FDG. In particular, new ETCC with LaBr3 pixel scintillator provides good images similar to SPECT for ¹³¹I and human PET for 511keV, respectively, where a clear concentration to tumors in a mouse is observed The 30cm-cube ETCC can get an image for 1m-size length objects in one measurement. Thus, we have carried out several comparisons of our images with those of SPECT and PET. Multi-tracer image using I-131 and FDG for small animal and the image for higher energy gamma ray above 511keV for plants using ^{54Mn have been carried out successfully. Also several new biomarkers and new radio nuclides were examined to verify the merits of ETCC for medical imaging.}