How to access material thumbnail images in other windows?

I'm trying to access the thumbnail images used to render previews for materials in the example Layered Shader custom UI. The path to these images is formatted like so: "image://resources/resource://texture_source_painter/3d_printed_mesh_lattice/3d_printed_mesh_lattice?version=bad26bc3263a81f1fd8010e8e7d64375c4eb096c.sbsar" I can't get that same path to load in any window (QML or Python) other than the Shader Settings window, even when using the same code from MaterialPreview.qml in a second QML window. Is there anything else I need to do to be able to load these images? The same path returns success loading in Image QML widget in Shader Settings window and returns error in any other one.