Foot reflexology works on the theory that all parts of the body, its organs and systems, are 'reflected' on specific points on the feet.
Colour Doppler sonography (similar to ultrasound) can be used to measure bloodflow.
The article linked below features a study carried out in Germany to observe blood flow changes in the right kidney during foot reflexology:
Sudmeier, I.; Bodner, G.; Egger, I.; Mur, E.; Ulmer, H.; Herold, M.
Forsch Komplementarmed 1999 3 6 129-134