prevent page break while returning to twocolumn

You can put a wide image that spans both columns at the top of the page, either by using a two column float (figure*) or by using the optional argument of twocolumn which specifies a spanning text to be put over the columns, so

documentclass[conference]{IEEEtran}
usepackage{graphicx}
begin{document}

twocolumn[%
{includegraphics[width=textwidth]{example-image}}%
]

loop
stepcounter{enumi}
ifnumvalue{enumi}<1000
roman{enumi}
repeat



end{document}