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We report on third epoch VLBI observations of the radio-bright supernova SN2011dh located in the nearby (7.8 Mpc) galaxy M51. The observations took placeat $t=453$ d after the explosion and at a frequency of 8.4 GHz. We obtained afairly well resolved image of the shell of SN 2011dh, making it one of only sixrecent supernovae for which resolved images of the ejecta are available. SN2011dh has a relatively clear shell morphology, being almost circular inoutline, although there may be some asymmetry in brightness around the ridge.By fitting a spherical shell model directly to the visibility measurements wedetermine the angular radius of SN 2011dh's radio emission to be $636 \pm 29$$\mu$as. At a distance of 7.8 Mpc, this angular radius corresponds to a linearradius of $(7.4 \pm 0.3) \times 10^{16}$ cm and an average expansion velocitysince the explosion of $19000^{+2800}_{-2400}$ kms$^{-1}$. We combine our VLBImeasurements of SN 2011dh's radius with values determined from the radiospectral energy distribution under the assumption of asynchrotron-self-absorbed spectrum, and find all the radii are consistent witha power-law evolution, with $R \sim t^{0.97\pm0.01}$, implying almost freeexpansion over the period $t=4$ d to 453 d.

Imaging the Expanding Shell of SN 2011dh