  The SPI instrument on-board the ESA/INTEGRAL satellite is engaged in a
mission-long study of positron annihilation radiation from the Galaxy. Early
results suggest that the disk component is only weakly detected at 511 keV by
SPI. We review CGRO/OSSE, TGRS and SMM studies of 511 keV line and positronium
continuum emission from the Galaxy in light of the early INTEGRAL/SPI findings.
We find that when similar spatial distributions are compared, combined fits to
the OSSE/SMM/TGRS data-sets produce bulge and disk fluxes similar in total flux
and in B/D ratio to the fits reported for SPI observations. We further find
that the 511 keV line width reported by SPI is similar to the values reported
by TGRS, particularly when spectral fits include both narrow-line and
broad-line components. Collectively, the consistency between these four
instruments suggests that all may be providing an accurate view of positron
annihilation in the Galaxy.
