2008 IEEE Nuclear Science Symposium Conference Record Study of compatibility of a Silicon Drift Detector with a MRI system C. Fiorini, member, IEEE, A. Laratta ,R. Peloso, A. Longoni, T. Mennini, E. Micotti M10-62 Abstract-A Gamma Camera based on Silicon Drift Detectors (SDDs) represents a gamma-ray imaging device with several potentialities in the field of medical imaging. The potential intrinsic insensitivity to magnetic fields of SDDs provides the important capability to use this device in combination with MRI. The possibility of simultaneous data acquisition with scintigraphicJSPECT and MRI systems plays in fact a topic role in the field of medical research and clinical diagnosis. The main effect in a SDD due to the presence of a constant magnetic field was simulated and tested and the preliminary results are presented in this work. Simulations and tests were also made to verify that the presence of the detection system doesn't significantly perturb magnetic force lines in the MRI system. The results are here presented and discussed. Experimental characterization was made with a simplified gamma-ray detection system in order to verify the possibility of simultaneous data acquisition with a MRI system operating with a magnetic field up t07T. I. INTRODUCTION D iagnostic imaging techniques are nowadays tools of great importance in medical research. Two kinds of modalities can be outlined: on one side the anatomical imaging, providing a very accurate image of the structures of the human body (bones, tissues, organs... ), that are investigated through the use of Radiography and MRI (Nuclear Magnetic Imaging), and on the other side the functional imaging, which is aimed to quantify the physiological processes taking place inside the human body without influencing them. Functional imaging allows recognizing pathologies and different techniques are used for this purpose, like SPECT (Single Photon Emission Computed Tomography) and PET (Positron Emission Tomography). The combination of different imaging processes will of course enable the possibility to improve medical diagnostic. As SPECT and MRI occupy quite different positions in resolution/sensitivity space they are often used in combination. The need to joint the information on metabolism and on anatomy is at the basis of the current efforts towards the integration between the two imaging modalities [1]. Nowadays, most of the integration relies on two separate acquisitions in different times and places but during the last years efforts were made to obtain a simultaneous multimodal acquisition. The development of a SPECTIMRI system is in fact motivated by several diagnostic potentials. Manuscript received November 14, 2008. This work is supported by EC under contract LSHC-CT-2006-037737. C. Fiorini. R. Peloso, A. Laratta and A. Longoni are with Politecnico di Milano. Oipartimento di Elettronica e Informazione, Milan, Italy and with INFN, Sezione di Milano, Milan, Italy. T. Mennini and E. Micotti are with Istituto Mario Negri, Milan, Italy.. As Silicon Drift Detectors (SDDs) have recently shown to be a competitive device for the readout of scintillator they are valid alternative to photomultiplier tubes in new Gamma cameras, thanks to their high quantum efficiency and low electronics noise [2]. The potential intrinsic insensitivity of SDDs to magnetic fields provides also an important capability in view of the use of a gamma camera in combination with MRI. Aim of this study is to evaluate the compatibility of the detection modules based on SDDs developed in our laboratories with a MRI system. In this section will be presented experimental results obtained combining our SDD-based system with a Bruker magnetic resonance instrument, operating at 7 T. The effects of high magnetic fields on semiconductor devices and the impact of the experimental set-up on nuclear magnetic resonance images are presented in this paper. Comparison and confirmation of theoretical and simulated results were achieved, providing a proof of the possibility to integrate an SDD-based gamma camera with a MRI system. No significant problems with static magnetic fields and gradients were found, but further improvements are required. II. SILICON DRIFT DETECTORS The presence of a constant field produces main effects on the charge drift when the magnetic field is parallel to the surface of the SDD and is orthogonally directed with respect to the electron velocity [3]. __ rightpath -- wrong path with mIIgnetlc field In -- wrong path with mugneUcfield out Fig. 1. In the upper part a section of a SOD is shown. In the lower part it is possible to see the path of the electrons in the region near the anode. A magnetic field, parallel to the surface of the SOD can cause deviations from the right path depending on its versus. 978-1-4244-2715-4/08/$25.00 ©2008 IEEE 4667 Authorized licensed use limited to: Politecnico di Milano. Downloaded on February 9, 2009 at 03:48 from IEEE Xplore. Restrictions apply.