Correct spelling for the English word "orthodiagraph" is [ɔːθˈə͡ʊdɪˌaɡɹaf], [ɔːθˈəʊdɪˌaɡɹaf], [ɔː_θ_ˈəʊ_d_ɪ__ˌa_ɡ_ɹ_a_f] (IPA phonetic alphabet).
An instrument by means of which one can determine the true contour and dimensions of any internal organ or other object rendered visible by the x-rays, the latter being so deflected as to be made parallel.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.