<P> The primary regulated metrics are Mechanical Index (MI), a metric associated with the cavitation bio-effect, and Thermal Index (TI) a metric associated with the tissue heating bio-effect . The FDA requires that the machine not exceed established limits, which are reasonably conservative so as to maintain diagnostic ultrasound as a safe imaging modality . This requires self - regulation on the part of the manufacturer in terms of the machine's calibration . </P> <P> Ultrasound - based pre-natal care and sex screening technologies were launched in India in the 1980s . With concerns about its misuse for sex - selective abortion, the Government of India passed the Pre-natal Diagnostic Techniques Act (PNDT) in 1994 to regulate legal and illegal uses of ultrasound equipment . The law was further amended into the Pre-Conception and Pre-natal Diagnostic Techniques (Regulation and Prevention of Misuse) (PCPNDT) Act in 2004 to deter and punish prenatal sex screening and sex selective abortion . It is currently illegal and a punishable crime in India to determine or disclose the sex of a fetus using ultrasound equipment . </P> <P> After the French physicist Pierre Curie's discovery of piezoelectricity in 1880, ultrasonic waves could be deliberately generated for industry . Thereafter, in 1940, the American acoustical physicist Floyd Firestone devised the first ultrasonic echo imaging device, the Supersonic Reflectoscope, to detect internal flaws in metal castings . In 1941, the Austrian neurologist Karl Theo Dussik was in collaboration with his brother, Friedreich, a physicist, likely, the first person to ultrasonically echo image the human body, outlining thereby the ventricles of a human brain . Ultrasonic energy was first applied to the human body for medical purposes by Dr George Ludwig at the Naval Medical Research Institute, Bethesda, Maryland in the late 1940s . English - born physicist John Wild (1914--2009) first used ultrasound to assess the thickness of bowel tissue as early as 1949; he has been described as the "father of medical ultrasound". Subsequent advances in the field took place concurrently in several countries . But it was not until 1963 when Meyerdirk & Wright launched production of the first commercial hand - held articulated arm compound contact B - mode scanner that ultrasound became generally available for medical use . </P> <P> In his book "L'investigation vasculaire par ultrasonographie Doppler" (Ed Masson, 1977) Dr Claude Franceschi laid down the Doppler Ultrasound fundamentals of the hemodynamics semiotics, which are still in use in current Doppler arterial and venous Duplex Ultrasound investigations . </P>

When was ultrasound first used for medical purposes