title: Cherenkov luminescence measurements with digital silicon photomultipliers: a feasibility study.
abstract: BACKGROUND
  A feasibility study was done to assess the capability of digital silicon photomultipliers to measure the Cherenkov luminescence emitted by a β source. Cherenkov luminescence imaging (CLI) is possible with a charge coupled device (CCD) based technology, but a stand-alone technique for quantitative activity measurements based on Cherenkov luminescence has not yet been developed. Silicon photomultipliers (SiPMs) are photon counting devices with a fast impulse response and can potentially be used to quantify β-emitting radiotracer distributions by CLI.
  
  
  METHODS
  In this study, a Philips digital photon counting (PDPC) silicon photomultiplier detector was evaluated for measuring Cherenkov luminescence. The PDPC detector is a matrix of avalanche photodiodes, which were read one at a time in a dark count map (DCM) measurement mode (much like a CCD). This reduces the device active area but allows the information from a single avalanche photodiode to be preserved, which is not possible with analog SiPMs. An algorithm to reject the noisiest photodiodes and to correct the measured count rate for the dark current was developed.
  
  
  RESULTS
  The results show that, in DCM mode and at (10-13) °C, the PDPC has a dynamic response to different levels of Cherenkov luminescence emitted by a β source and transmitted through an opaque medium. This suggests the potential for this approach to provide quantitative activity measurements. Interestingly, the potential use of the PDPC in DCM mode for direct imaging of Cherenkov luminescence, as a opposed to a scalar measurement device, was also apparent.
  
  
  CONCLUSIONS
  We showed that a PDPC tile in DCM mode is able to detect and image a β source through its Cherenkov radiation emission. The detector's dynamic response to different levels of radiation suggests its potential quantitative capabilities, and the DCM mode allows imaging with a better spatial resolution than the conventional event-triggered mode. Finally, the same acquisition procedure and data processing could be employed also for other low light levels applications, such as bioluminescence.
authors.affiliation: Department of Physics, University of Pisa, Pisa, Italy. esther.ciarrocchi@pi.infn.it.|INFN, section of Pisa, Pisa, Italy. esther.ciarrocchi@pi.infn.it.
authors.forename: Esther
authors.initials: E
authors.lastname: Ciarrocchi
authors.affiliation: Department of Physics, University of Pisa, Pisa, Italy. nicola.belcari@unipi.it.|INFN, section of Pisa, Pisa, Italy. nicola.belcari@unipi.it.
authors.forename: Nicola
authors.initials: N
authors.lastname: Belcari
authors.affiliation: Department of Physics, University of Pisa, Pisa, Italy. alberto.del.guerra@unipi.it.|INFN, section of Pisa, Pisa, Italy. alberto.del.guerra@unipi.it.
authors.forename: Alberto Del
authors.initials: AD
authors.lastname: Guerra
authors.affiliation: Department of Biomedical Engineering, University of California, Davis, CA, USA. srcherry@ucdavis.edu.
authors.forename: Simon R
authors.initials: SR
authors.lastname: Cherry
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA, USA. alehnert@uw.edu.
authors.forename: Adrienne
authors.initials: A
authors.lastname: Lehnert
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA, USA. wcjh@uw.edu.
authors.forename: William C J
authors.initials: WC
authors.lastname: Hunter
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA, USA. wam2@u.washington.edu.
authors.forename: Wendy
authors.initials: W
authors.lastname: McDougald
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA, USA. rmiyaoka@uw.edu.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Miyaoka
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA, USA. kinahan@uw.edu.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Kinahan
keywords: Cerenkov radiation; Cherenkov luminescence imaging; Cherenkov radiation; Digital silicon photomultipliers; Silicon photomultipliers