Detection and measurement of breathing using an optical camera and projected shadows

A respiratory monitoring device comprises: a light source (30) arranged to generate a projected shadow (S) of an imaging subject (P) positioned for imaging by an imaging device (8); a video camera (40) arranged to acquire video of the projected shadow; and an electronic processor (42) programmed to extract a position of an edge of the projected shadow as a function of time from the acquired video. In some embodiments, the light source is arranged to project the shadow onto a bore wall (20) of the imaging device, and the video camera is arranged to acquire video of the projected shadow on the bore wall. The electronic processor may be programmed to extract the position of the edge (E) as a one-dimensional function of time (46) based on the position of the edge in each frame of the acquired video and time stamps of the video frames.