I am a new user of cisTEM (and a novice to SPR cryoEM in general). I recently generated ab initio 3D volumes of my molecule of interest. These volumes have several features where a central spike is surrounded by a protruding ring, in a shape resembling a tulip. (see attached png file depicting two such features shown at center top)
Does anyone know what might cause this? I assume it is an artifact of the volume building process, possibly due to poor image or particle picking. And, more generally, is there a reference that I may use in the future to investigate unusual features that I might observe in the future?
Thank you for your help.