To further the above, the call for abstracts page (https://www.ismrm.org/19m/call/) had a few details:
“The meeting also includes poster presentations. New for the 2019 Annual Meeting, ALL POSTERS will be presented in an electronic format on a large 43-inch diagonal flat-panel monitor (similar to those used for Power Pitch presentations).”
…so that’s the size essentially. If I understand it correctly, these are now supposed to replace both the traditional posters as well as the old format e-posters from previous years.