  We report on 8.4GHz Very Long Baseline Interferometry (VLBI) observations of
the type II-P supernova SN2004et in the spiral galaxy NGC 6946, made on 20
February 2005 (151 days after explosion). The Very Large Array (VLA) flux
density was 1.23$\pm$0.07 mJy, corresponding to an isotropic luminosity at
8.4GHz of (4.45$\pm$0.3)$\times10^{25}$ erg s$^{-1}$ Hz$^{-1}$ and a brightness
temperature of (1.3$\pm$0.3)$\times10^{8}$ K. We also provide an improved
source position, accurate to about 0.5 mas in each coordinate. The VLBI image
shows a clear asymmetry. From model fitting of the size of the radio emission,
we estimate a minimum expansion velocity of 15,700$\pm$2,000 km s$^{-1}$. This
velocity is more than twice the expected mean expansion velocity estimated from
a synchrotron self-absorbed emission model, thus suggesting that synchrotron
self-absorption is not relevant for this supernova. With the benefit of an
optical spectrum obtained 12 days after explosion, we favor an emission model
which consists of two hot spots on an underlying expanding shell of width
comparable to that of SN 1993J.
