US Patent 7998115 Dialysis system having optical flowrate detection

A medical fluid machine includes an enclosure; a disposable unit accepted by the enclosure, the disposable unit including a conduit through which a medical fluid can flow, the conduit including a viewing portion; a light source configured and arranged to emit light onto the viewing portion of the conduit; a camera focused on the viewing portion of the conduit; and a processor configured to determine a speed of a particle entrained in the medical fluid based on at least two images of the particle in the viewing area taken by the camera.