PET is a molecular imaging technique that produces three-dimensional images of functional processes in the body, e.g. the uptake of glucose that fuels metabolic activity. The PET system detects pairs of gamma rays (high energy electromagnetic radiation) originating from a radioactive tracer, a small amount of which is injected into the patient prior to the scan. To image metabolic activity, PET typically uses a radioactive derivative of glucose called fluorodeoxyglucose (FDG). This compound mimics the behavior of glucose in the body and can be detected by the PET system.
Modern PET scanners require photon detector areas of around 0.5 m². Philips’ digital silicon photomultipliers are designed so that they can be tiled to arrive at this area. Theoretically, a 0.5 m² array constructed from the Philips devices would only consume around 100 W of power, eliminating the need for complex cooling arrangements.
For ‘time-of-flight’ PET scanners (originally introduced by Philips), accurately determining the time at which the first photon arrives is also extremely important. Philips’ new digital silicon photomultiplier prototypes achieve a timing accuracy for detection of the first photon of around 190 ps (full-width, half-maximum using a standard scintillator crystal (LYSO) at 511 keV for two detectors in coincidence) and an intrinsic timing resolution for the chip of 20 ps.
High-energy nuclear physics
High-energy physics experiments frequently require large-area scintillator detectors that are immune to both static and changing magnetic fields. In most cases, this precludes the use of photomultiplier tubes. Philips’ digital silicon photomultipliers provide the required immunity to magnetic disturbances plus the extremely high photon sensitivity and speed required to capture the decay-chain characteristics of nuclear disintegrations and high-energy particle collisions.