Time-of-flight positron emission tomography

5 problems

• Joint depth-of-interaction and timing measurement

  Open

  Where inside the crystal the gamma ray stops affects both how long the light takes to arrive and the image sharpness at the edges of the scanner. Measuring both at once is unsolved.

• Fast light emission channels in scintillators

  Open

  A crystal that converts a gamma ray into light emits most of it too slowly for very precise timing. Finding or engineering a fast first burst of light is the main limit.

• Imaging without tomographic reconstruction

  Open

  If the timing becomes precise enough, each detected pair marks its own point in space, so the image can be built without reconstruction. The timing and sampling requirements for that are not worked out.

• Fundamental bound on scintillation timing

  Partially resolved

  Light arrives at the sensor at random times, which sets a floor on how precisely the arrival can be timed. The exact floor for realistic detectors is not established.

• Is 10 ps coincidence time resolution reachable

  Open

  Today the best clinical scanners time the two photons to about two hundred trillionths of a second (picoseconds). Getting to ten would place each emission directly, with no image reconstruction.