Focus on time-of-flight PET: the benefits of improved time resolution

  • Maurizio Conti
Review Article


TOF PET is characterized by a better trade-off between contrast and noise in the image. This property is enhanced in more challenging operating conditions, allowing for example shorter examinations or low counts, successful scanning of larger patients, low uptake, visualization of smaller lesions, and incomplete data sampling. In this paper, the correlation between the time resolution of a TOF PET scanner and the improvement in signal-to-noise in the image is introduced and discussed. A set of performance advantages is presented which include better image quality, shorter scan times, lower dose, higher spatial resolution, lower sensitivity to inconsistent data, and the opportunity for new architectures with missing angles. The recent scientific literature that reports the first experimental evidence of such advantages in oncology clinical data is reviewed. Finally, the directions for possible improvement of the time resolution of the present generation of TOF PET scanners are discussed.


TOF PET Time-of-flight Dose Image quality Signal-to-noise Time resolution Detectability 



I am grateful to Harold Rothfuss for his help with the Geant4 simulation. I also thank David Townsend for providing patient images, Joel Karp and Cristina Lois for Figs. 5 and 6, and Bernard Bendriem for helpful discussions and advice.

Conflicts of interest



  1. 1.
    Lewellen TK. Time-of-flight PET. Semin Nucl Med. 1998;28:268–75.PubMedCrossRefGoogle Scholar
  2. 2.
    Moses WW. Time of flight in PET revisited. IEEE Trans Nucl Sci. 2003;50:1325–30.CrossRefGoogle Scholar
  3. 3.
    Muehllehner G, Karp JS. Positron emission tomography. Phys Med Biol. 2006;51:R117–37.PubMedCrossRefGoogle Scholar
  4. 4.
    Conti M. State of the art and challenges of time-of-flight PET. Phys Med. 2009;25:1–11.PubMedCrossRefGoogle Scholar
  5. 5.
    Gariod R, Allemand R, Carmoreche E, et al. The LETI positron tomograph architecture and time of flight improvements. Proceeding of the Workshop on Time-of-flight tomography, Washington University. IEEE Publication; 1982. p. 25–29.Google Scholar
  6. 6.
    Yamamoto M, Ficke DC, Ter-Pogossian MM. Experimental assessment of the gain achieved by the utilization of time-of-flight information in a positron emission tomograph (Super PETT I). IEEE Trans Med Imaging. 1982;1:187–92.PubMedCrossRefGoogle Scholar
  7. 7.
    Wong WH, Mullani NA, Philippe EA, Hartz RK, Bristow D, Yerian K, et al. Performance characteristics of the University of Texas TOFPET-I PET camera. J Nucl Med. 1984;25:46–7.Google Scholar
  8. 8.
    Lewellen TK, Bice AN, Harrison RL, Pencke MD, Link JM. Performance measurements of the SP3000/UW time-of-flight positron emission tomograph. IEEE Trans Nucl Sci. 1988;35:665–9.CrossRefGoogle Scholar
  9. 9.
    Ishii K, Orihara H, Matsuzawa T, Binkley DM, Nutt R. High resolution time-of-flight positron emission tomograph. Rev Sci Instrum. 1990;61:3755–62.CrossRefGoogle Scholar
  10. 10.
    Jakoby BW, Bercier Y, Conti M, Casey ME, Gremillion T, Hayden C, et al. Performance investigation of a time-of-flight PET/CT scanner. Nuclear Science Symposium Conference Record, 2008. IEEE. p. 3738–3743.Google Scholar
  11. 11.
    Surti S, Kuhn A, Werner ME, Perkins AE, Kolthammer J, Karp JS. Performance of Philips Gemini TF PET/CT scanner with special consideration for its time-of-flight imaging capabilities. J Nucl Med. 2007;48:471–80.PubMedGoogle Scholar
  12. 12.
    Wilson JM and Turkington TG. TOF-PET small-lesion image quality measured over a range of phantom sizes. Nuclear Science Symposium Conference Record, 2009. IEEE. p. 3710–3714.Google Scholar
  13. 13.
    Daube-Witherspoon ME, Surti S, Perkins A, Kyba CCM, Wiener R, Werner ME, et al. The imaging performance of a LaBr3-based PET scanner. Phys Med Biol. 2010;55:45–64.PubMedCrossRefGoogle Scholar
  14. 14.
    Conti M. Effect of random reduction on signal-to-noise-ratio in TOF PET. IEEE Trans Nucl Sci. 2006;53:1188–93.CrossRefGoogle Scholar
  15. 15.
    Budinger TF. Instrumentation trends in nuclear medicine. Semin Nucl Med. 1977;7:285–97.PubMedCrossRefGoogle Scholar
  16. 16.
    Budinger TF. Time-of-flight positron emission tomography: status relative to conventional PET. J Nucl Med. 1983;24:73–8.PubMedGoogle Scholar
  17. 17.
    Mullani NA, Markham J, Ter-Pogossian MM. Feasibility of time-of-flight reconstruction in positron emission tomography. J Nucl Med. 1980;21:1095–97.PubMedGoogle Scholar
  18. 18.
    Wong WH, Mullani NA, Philippe EA, Hartz RK, Gould KL. Image improvement and design optimization of the time-of-flight PET. J Nucl Med. 1983;24:52–60.PubMedGoogle Scholar
  19. 19.
    Tomitani T. Image reconstruction and noise evaluation in photon time-of-flight assisted positron emission tomography. IEEE Trans Nucl Sci. 1981;28:4582–88.CrossRefGoogle Scholar
  20. 20.
    Snyder DL, Thomas LJ, Ter-Pogossian MM. A mathematical model for positron emission tomography systems having time-of-flight measurements. IEEE Trans Nucl Sci. 1981;28:3575–83.CrossRefGoogle Scholar
  21. 21.
    Strother SC, Casey ME, Hoffman EJ. Measuring PET scanner sensitivity: relating count rates to image signal-to-noise ratios using noise equivalent counts. IEEE Trans Nucl Sci. 1990;37:783–8.CrossRefGoogle Scholar
  22. 22.
    Conti M, Bendriem B, Casey ME, Chen M, Kehren F, Michel C, et al. First experimental results of time-of-flight reconstruction on an LSO PET scanner. Phys Med Biol. 2005;50:4507–26.PubMedCrossRefGoogle Scholar
  23. 23.
    Huang B, Law MWM, Khong PL. Whole-body PET/CT scanning: estimation of radiation dose and cancer risk. Radiology. 2009;251:166–74.PubMedCrossRefGoogle Scholar
  24. 24.
    Roberts F, Gunawardana DH, Pathmaraj K, Wallace A, Mi T, Berlangieri SU, et al. Radiation dose to PET technologists and strategies to lower occupational exposure. J Nucl Med Technol. 2005;33:44–7.PubMedGoogle Scholar
  25. 25.
    Murray I, Kalemis A, Glennon J, Hasan S, Quraishi S, Beyer T, et al. Time-of-flight PET/CT using low-activity protocols: potential implications for cancer therapy monitoring. Eur J Nucl Med Mol Imaging. 2010;37:1643–53.PubMedCrossRefGoogle Scholar
  26. 26.
    Lhommel R, van Elmbt L, Goffette P, van den Eynde M, Jamar F, Pauwels S, et al. Feasibility of 90Y TOF PET-based dosimetry in liver metastasis therapy using SIR-Spheres. Eur J Nucl Med Mol Imaging. 2010;37:1654–62.PubMedCrossRefGoogle Scholar
  27. 27.
    Surti S, Karp JS. Design considerations for a limited-angle, dedicated breast, TOF PET scanner. Phys Med Biol. 2009;53:2911–21.CrossRefGoogle Scholar
  28. 28.
    Crespo P, Shakirin G, Fiedler F, Enghardt W, Wagner A. Direct time-of-flight for quantitative, real-time in-beam PET: a concept and feasibility study. Phys Med Biol. 2007;52:6795–811.PubMedCrossRefGoogle Scholar
  29. 29.
    Wang W, Hu Z, Gualtieri EE, Parma MJ, Walsh ES, Sebok D, et al. Systematic and distributed time-of-flight list mode PET reconstruction. Nuclear Science Symposium Conference Record, 2006. IEEE. p. 1715–1722.Google Scholar
  30. 30.
    Werner ME, Surti S, Karp JS. Implementation and evaluation of a 3D PET single scatter simulation with TOF modeling. Nuclear Science Symposium Conference Record, 2006. IEEE. p. 1768–1773.Google Scholar
  31. 31.
    Turkington TG, Wilson JM. Attenuation artifacts and time-of-flight PET. Nuclear Science Symposium Conference Record, 2009. IEEE. p. 2997–2999.Google Scholar
  32. 32.
    National Electrical Manufacturers Association. NEMA Standards Publication NU 2-2001: Performance Measurements of Positron Emission Tomographs. Rosslyn, VA: National Electrical Manufacturers Association; 2001.Google Scholar
  33. 33.
    Karp JS, Surti S, Daube-Witherspoon ME, Muehllehner G. Benefit of time-of-flight in PET: experimental and clinical results. J Nucl Med. 2008;49:462–70.PubMedCrossRefGoogle Scholar
  34. 34.
    Kadrmas DJ, Casey ME, Conti M, Jakoby BW, Lois C, Townsend DW. Impact of time-of-flight on PET tumor detection. J Nucl Med. 2009;50:1315–23.PubMedCrossRefGoogle Scholar
  35. 35.
    Lois C, Jakoby BW, Long MJ, Hubner KF, Barker DW, Casey ME, et al. An assessment of the impact of incorporating time-of-flight (TOF) information into clinical PET/CT imaging. J Nucl Med. 2010;51:237–45.PubMedCrossRefGoogle Scholar
  36. 36.
    Moses WW, Ullisch M. Factors influencing timing resolution in a commercial LSO PET camera. IEEE Trans Nucl Sci. 2006;53:78–85.CrossRefGoogle Scholar
  37. 37.
    Conti M, Eriksson L, Rothfuss H, Melcher C. Comparing fast scintillators with TOF PET potentiality. IEEE Trans Nucl Sci. 2009;56:926–33.CrossRefGoogle Scholar
  38. 38.
    Kyba CCM, Glodo J, van Loef EVD, Karp JS, Shah KS. Energy and time response of six prototype scintillators for TOF-PET. IEEE Trans Nucl Sci. 2008;55:1404–8.CrossRefGoogle Scholar
  39. 39.
    Lewellen TK. Recent development in PET detector technology. Phys Med Biol. 2008;53:R287–317.PubMedCrossRefGoogle Scholar
  40. 40.
    Renker D. New trends of photodetectors. Nucl Instrum Methods Phys Res A. 2007;571:1–6.CrossRefGoogle Scholar
  41. 41.
    Schaart DR, Seifert S, Vinke R, van Dam HT, Dendooven P, Loehner H, et al. LaBr3:Ce and SiPMs for time-of-flight PET: achieving 100 ps coincidence resolving time. Phys Med Biol. 2010;55:N179–89.PubMedCrossRefGoogle Scholar
  42. 42.
    Degenhardt C, Prescher G, Frach T, Thon A, de Gruyter R, Schmitz A, et al. The digital silicon photomultiplier – A novel sensor for the detection of scintillation light. Nuclear Science Symposium Conference Record, 2009. IEEE. p. 2383–2386.Google Scholar

Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Siemens HealthcareMolecular ImagingKnoxvilleUSA

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