Breast CT

In the framework of the BREAST-CT project funded by INFN (Committee V), the Medical Physics group of INFN Napoli has assembled a Cone-Beam Breast Computed Tomography (CBBCT) experimental scanner dedicated to X-ray CT imaging of the breast. The present system employs a tungsten anode X-ray tube, operated at 35-80 kVp tube voltage, with a maximum tube current of 0.25 mA, and uses as imaging detector a CsI:Tl scintillator CMOS Flat Panel with a sensitive area of 12 cm x 12 cm with 50 micron x 50 micron pixels. The system has been tested for preliminary CT scans of cylindrical and semi-ellipsoidal PMMA objects: PMMA is used as a material with linear attenuation coefficient close to that of soft tissues for diagnostic range X-rays. The PMMA breast phantoms, either homogeneous or containing small holes for contrast and spatial resolution evaluation, have a maximum diameter of 14 cm, thus simulating the average diameter of the female breast at the chest wall. Cone-beam reconstruction is by a Feldkamp filtered-backprojection algorithm developed by the University of Pisa Medical Physics group. Tests have been conducted at varying tube voltage in order to investigate the different performance of the CT scan. Absorbed dose measurements have been carried out with TLD dosimeters placed inside the PMMA phantoms and with an ionization chamber in air. The INFN Cagliari group has developed an imaging system based on the Medipix2, a single photon counting pixel readout ASIC for X-ray hybrid detectors, has been developed for tomography imaging applications. The ‘‘quad assembly’’ houses four Medipix2 chips placed in a 2_2 array with an active area of about 3_3 cm2. The readout system consists of four electronic cards and exploits the Medipix2 parallel readout mode and a fast optical link based on the Glink standard, giving high flexibility and EM interference immunity over long distance connections. The overall DAQ system consists of four electronic cards. Two cards (Chipboard_4C and Motherboard) form the detector stage, the third (Opt-Hub) acts as the optical link interface, while the remaining one (PCI9054) is the PC acquisition board. Detector and PC are linked by an optical fibre channel