First Digital PET (2016)
2014–2016 — Philips Vereos ships, the first commercial PET / CT with silicon photomultipliers (SiPM) replacing photomultiplier tubes (PMTs) at the detector readout. GE Discovery MI follows in 2017 with a similar SiPM digital architecture; Siemens Biograph Vision in 2018 completes the Big-Three transition. Within ~5 years, digital PET defines the new premium tier and PMT-era PET / CT moves to the value / refurb segment.
Why SiPM matters
PMTs are vacuum-tube photodetectors — a 50+ year-old technology, bulky, fragile, and limited in count-rate handling. SiPMs are silicon semiconductor arrays that match or exceed PMT photon detection while:
- Tolerating higher count rates without saturation, enabling shorter scans and lower injected activity.
- Tighter time-of-flight timing resolution — modern SiPM platforms reach 178–250 ps, vs ~500 ps on the best PMT-era systems. Better ToF = better small-lesion conspicuity.
- Smaller per-pixel footprint — finer crystal granularity, better spatial resolution.
- No high-voltage divider chain — different (and generally simpler) service model.
- Magnetic-field tolerance — PMTs do not work in MR fields; SiPMs (and their predecessor APDs) do, enabling PET / MR hybrid imaging.
Clinical impact
- Sensitivity gain translates to either shorter scan times at matched dose, or lower injected dose at matched scan time. Pediatric and dose-sensitive populations benefit directly.
- Small-lesion conspicuity improves at the same injected activity; subcentimeter nodes and lesions become more reliable.
- Theranostic dosimetry — Lu-177 / Ac-225 follow-up imaging benefits from better quantitation.
- Cardiac PET — short Rb-82 acquisitions tolerate higher count rates cleanly.
The TOF arms race
ToF resolution improvement after digital PET became the clinical positioning lever:
- Vereos (2014) — ~325 ps timing, defining the digital-PET category.
- Discovery MI (2017) — ~375–390 ps depending on configuration.
- Biograph Vision (2018) — 215 ps timing.
- Biograph Vision.X (2023) — ~178 ps timing.
- uEXPLORER (2018) — total-body PET / CT (~194 cm axial FOV) with sensitivity ~40× legacy systems.
Refurb and lifecycle implications
- PMT-era LSO / LYSO PET (Discovery 690, Biograph 64 / mCT, Gemini TF) is now the value-tier refurb category.
- Digital PET is current generation; refurb supply is small but growing.
- Service models diverge — channel-dropout diagnostics on SiPM platforms is fundamentally different from PMT-base troubleshooting.
Descends to
- Philips Vereos
- GE Discovery MI
- Siemens Biograph Vision
- Siemens Biograph Vision.X
- PET / CT (current generation)
- PET / MR (SiPM enables it)