BGO
Bismuth germanate (Bi₄Ge₃O₁₂) scintillator. Used in pre-ToF PET (Discovery VCT, Discovery STE). High light yield but slow decay (~300 ns) — not ToF-capable.
Why it matters to buyers: Legacy scintillator. BGO PET / CT systems are the entry-tier refurb category today — value-tier capability without ToF performance.
Why it matters to engineers: Not upgradeable to ToF — requires crystal + electronics swap, effectively a new scanner. The scintillator-physics inflection from BGO to LYSO / LSO is the generational divide between ToF and non-ToF PET.