Viviana Fanti

Towards breast tomography with synchrotron radiation at Elettra: First images

The aim of the SYRMA-CT collaboration is to set-up the first clinical trial of phase-contrast breast CT with synchrotron radiation (SR). In order to combine high image quality and low delivered dose a number of innovative elements are merged: a CdTe single photon counting detector, state-of-the-art CT reconstruction and phase retrieval algorithms. To facilitate an accurate exam optimization, a Monte Carlo model was developed for dose calculation using GEANT4. In this study, high isotropic spatial resolution (120 μm)(3) CT scans of objects with dimensions and attenuation similar to a human breast were acquired, delivering mean glandular doses in the range of those delivered in clinical breast CT (5-25 mGy). Due to the spatial coherence of the SR beam and the long distance between sample and detector, the images contain, not only absorption, but also phase information from the samples. The application of a phase-retrieval procedure increases the contrast-to-noise ratio of the tomographic images, while the contrast remains almost constant. After applying the simultaneous algebraic reconstruction technique to low-dose phase-retrieved data sets (about 5 mGy) with a reduced number of projections, the spatial resolution was found to be equal to filtered back projection utilizing a four fold higher dose, while the contrast-to-noise ratio was reduced by 30%. These first results indicate the feasibility of clinical breast CT with SR.

Medipix2 parallel readout system

A fast parallel readout system based on a PCI board has been developed in the framework of the Medipix collaboration. 1 The readout electronics consists of two boards: the motherboard directly interfacing the Medipix2 chip, and the PCI board with digital I/O ports 32 bits wide. The device driver and readout software have been developed at low level in Assembler to allow fast data transfer and image reconstruction. The parallel readout permits a transfer rate up to 64 Mbytes/s. r 2003 Elsevier Science B.V. All rights reserved. PACS: 07.05.Hd; 87.59.Hd

MPRS: Medipix parallel readout system for angiography digital imaging

A fast readout system for a low noise CMOS pixel chip, working in single photon counting mode (Medipix2) has been developed for digital angiography applications. Each chip has an active area of about 2 cm/sup 2/, with 256/spl times/256 square pixels 55 /spl mu/m side size, and can be bump bonded to Si or GaAs for direct charge conversion of incoming photons. The system permits the parallel readout of up to 8 chips at a rate of at least 25 frames/s, to allow real time X-ray imaging of contrast medium flowing in blood vessels. The readout electronics is PCI bus-based and consists of two boards, the motherboard directly interfacing the chip for settings and data flow, and the PCI board linking the motherboard to the bus. Dedicated software has been developed to test each single pixel, set configuration patterns and perform data transfer. With parallel readout transfer rate up to 64 MByte/s has been achieved.

Monte Carlo Computations for Radiotherapy with the use of Dedicated Processors

The project we present foresees the development of a hardware processor dedicated to real time Monte Carlo computations for radiotherapy treatment planning. Treatment planning systems are nowadays based on empirical methods which can lead to errors in the localization of the area to be irradiated of the order of centimeters. The use of Monte Carlo techniques permits to reach a more adequate precision but with the drawback of a computing time which is too high with respect to the requirements of a radiotherapy center. We propose to implement time consuming algorithms directly in hardware circuits based on programmable logic devices in order to speed up the computation. The hardware is based on a Configurable Computer, a PCI master board housing one or more high performance fPGA and a RAM large enough for the application.

A Portable Acquisition System Based on USB Standard for the Medipix2 X-Ray Detector

We describe a portable readout system for an X-ray hybrid detector based on the Medipix2 pixel readout chip. The Medipix2 chip (256times256 square pixels with 55 mum pitch) is bump-bonded with a pixellated Silicon sensor 300-micron thick. The readout system consists of a simple small size electronic card based on a single powerful microcontroller and can be connected to a PC through the widespread Universal Serial Bus (USB) interface. The reduced size of the final card (3.8 cmtimes4.8 cm) makes it suitable for special applications like dental radiology

Operation of silicon photomultipliers at liquid helium temperature

We have investigated the performance of a few silicon photomultipliers to readout inorganic scintillators operated at cryogenic temperatures. Such detectors, that would need to operate close to liquid helium (LHe) temperatures and in a magnetic field of a few Tesla, have been proposed by our group as a way to build an active polarized target to be used for neutrino physics, for the search of axions and CP violation, as suggested by some theoretical papers. In the present work we investigate in some details the performance of a few different silicon photomultipliers produced by Hamamatsu and Advansid down to liquid helium temperature, to verify the temperature range of usability of these devices and their performance at cryogenic temperatures.

Operation of Multi-Pixel Photon Counters Down to Liquid Helium Temperatures

We are investigating the possibility of using Silicon Avalanche Photo Detectors (APD), both in proportional and in Geiger mode, to readout inorganic scintillators operated at cryogenic temperatures. Such detectors, that need to operate close to liquid helium (LHe) temperatures and in a magnetic field of a few Tesla, have been proposed by our group as a way to build an active polarized target to be used for neutrino physics, for the search of axions and CP violation, as suggested by some theoretical papers. In the present work we investigate in some details the performance of Hamamatsu Multi-Pixel Photon Counters (MPPCs) down to LHe temperature to verify the temperature range of usability of these devices.

AX-PET: Concept, proof of principle and first results with phantoms

AX-PET is a novel PET concept based on long crystals axially arranged and orthogonal Wavelength shifter (WLS) strips, both individually readout by Geiger-mode Avalanche Photo Diodes (G-APD). Its design was conceived in order to reduce the parallax error and simultaneously improve spatial resolution and sensitivity. The assessment of the AX-PET concept and potential was carried out through a set of measurements comprising individual module characterizations and scans in coincidence mode of point-like and extended sources. The estimated energy and spatial resolutions from point-like measurements are RFWHM=11.6% (at 511 keV) and 1.7–1.9 mm (FWHM) respectively as measured with point-like sources placed in different positions of the FOV. First results from scans of extended phantoms confirmed our expectations.