Michels KB, Rothman KJ. Update on unethical use of placebos in randomised trials. Bioethics. 2003 Apr;17(2):188-204.
Caso P, Sutherland GR, Fleming A, McDicken WN. Doppler tissue imaging: current status and future prospects. G Ital Cardiol. 1995 May 1;25(5):639-47.