Dr. Welch was born and raised in Stoke-on Trent in England in 1939 and earned a bachelor's and master's degree in natural sciences at Cambridge University. He later went on to earn a doctorate in chemistry at the University of London in 1965. He began his career in the US for postdoctoral studies at Brookhaven National Laboratory. In 1976 he moved to Washington University, St. Louis and began working with Dr. Michel Ter-Pogossian where he began his focus on radiochemistry. He was a professor of radiology, of chemistry, of biomedical engineering and of developmental biology at Washington University School of Medicine. Dr. Welch was most notably a pioneer in the use of a technique called Positron Emission Tomography (PET) to create new tools for understanding human physiology and diagnosing important diseases. He contributed to the compounds that allow imaging of brain blood flow and creation of imaging agents for the study of many types of cancer. He also worked to ensure that an adequate supply of radiopharmaceuticals was available for medical treatment. He was the author of multiple books and co-author of 4. Throughout his career, he wrote over 550 papers, 4 books and 73 chapters. He was a mentor to an entire generation of radiochemists who now are leaders in the field.