Further work on improving the technique and development of safer more effective sclerosants continued through the 1940s and 1950s. Of particular importance was the development of sodium tetradecyl sulfate (STS) in 1946, a product still widely used to this day. George Fegan in the 1960s reported treating over 13,000 patients with sclerotherapy, significantly advancing the technique by focussing on fibrosis of the vein rather than thrombosis, concentrating on controlling significant points of reflux, and emphasizing the importance of compression of the treated leg. The procedure became medically accepted in mainland Europe during that time. However, it was poorly understood or accepted in England or the United States, a situation that continues to this day amongst some sections of the medical community.