MRPC-PET: A new technique for high precision time and position measurements K. Doroud a,n , D. Hatzifotiadou b , S. Li a , M.C.S. Williams b , A. Zichichi c,d , R. Zuyeuski a a World Laboratory, Geneva, Switzerland b Sezione INFN, Bologna, Italy c Dipartimento di Fisica dell’Universit  a, Bologna, Italy d PH Dept, CERN, Geneva, Switzerland article info Article history: Received 31 July 2011 Received in revised form 2 September 2011 Accepted 7 September 2011 Available online 22 September 2011 Keywords: Multigap RPC MRPC Timing TOF PET abstract The purpose of this paper is to consider a new technology for medical diagnosis: the MRPC-PET. This technology allows excellent time resolution together with 2-D position information thus providing a fundamental step in this field. The principle of this method is based on the Multigap Resistive Plate Chamber (MRPC) capable of high precision time measurements. We have previously found that the route to precise timing is differential readout (this requires matching anode and cathode strips); thus crossed strip readout schemes traditionally used for 2-D readout cannot be exploited. In this paper we consider the time difference from the two ends of the strip to provide a high precision measurement along the strip; the average time gives precise timing. The MRPC-PET thus provides a basic step in the field of medical technology: excellent time resolution together with 2-D position measurement. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Positron Emission Tomography (PET) is an imaging technique using a positron emitting radio-tracer. This method is based on detecting the two back-to-back gammas emitted when the posi- tron annihilates in the patient’s body. A line is drawn connecting the detected positions of the two gammas; thus an image can be constructed when many such lines have been recorded. If the time of arrival of the gamma in the detector can be measured (with some precision), then the position of the positron annihilation can be localised along this line. This technique is known as TOF-PET and studies have shown that the resultant image becomes much clearer due to the reduction of the background [1]. The Multigap Resistive Plate Chamber (MRPC) is capable of high precision time measurements and has been used for time-of- flight purposes in many experiments [2,3]. The interaction of the gammas with the MRPC resistive plates provides the possibility of their detection. However, the efficiency of the chamber depends on the probability of conversion and the resultant electron emerging into one of the gas gaps [4]. To obtain high precision timing we have found that it is necessary to have differential readout (i.e. both anode and cathode strips) rather than the more commonly used single-ended readout with respect to a common ground. Previously we have tested single-ended readout and showed that noise in the common ground appeared to limit the time resolution to above 150 ps [7]. However, to obtain differential readout, we need to have matching anode and cathode strips and this precludes the use of the more traditional crossed-strip readout scheme to obtain the 2-D position of a detected gamma. In this paper we explore the possibility of using the time difference between the two ends of the strip to obtain the hit position along the strip. The detectors that have been extensively used for PET imaging are based on the scintillators like Bismuth germinate (BGO), Lutetium orthosilicate (LSO) or Lutetium–yttrium oxyorthosili- cate (LYSO) [5]. These crystals have excellent light output and very good energy resolution: these crystals are read out by multi- anode photomultiplier tubes or more recently with silicon photo- multipliers [6] with its associated readout channel that includes a tdc and adc. However, to achieve millimeter spatial resolution there are obviously many difficulties and a high cost. The big difference between a PET scanner based on crystals compared to one based on the MRPC is that the MRPC can have strip readout; this brings a substantial reduction in channels and therefore cost. This will be critically important if a large PET system is envisaged, such as needed for a whole body PET scanner. 2. The detector The MRPC consists of a stack of resistive plates, each separated from its neighbour by very precise spacers (monofilament fishing Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2011.09.008 n Corresponding author. E-mail address: kdoroud@cern.ch (K. Doroud). Nuclear Instruments and Methods in Physics Research A 660 (2011) 73–76