Lawrence E. Williams, Ph.D., is a professor of radiology and an imaging physicist at City of Hope National Medical Center in Duarte, California. In addition, he is an adjunct professor of radiology at University of California–Los Angeles (UCLA). While in high school, he was one of 40 national winners of the Westinghouse (now Intel) Science Talent Search. Dr. Williams obtained his B.S. from Carnegie Mellon University and his M.S. and Ph.D. degrees (both in physics) from the University of Minnesota, where he was a National Science Foundation (NSF) fellow. His initial graduate training was in nuclear reactions at Minnesota, where he demonstrated excited states of the mass-4 system (4He*). He later extended this work by finding excited levels of mass-3 nuclides while working at the Rutherford High Energy Laboratory in England. Since obtaining the National Institutes of Health (NIH) support to become a medical physicist, Dr. Williams has devoted most of his research to tumor detection and treatment and has written approximately 250 total publications as well as a number of patents in nuclear imaging and radionuclide therapy. He is a coauthor of Biophysical Science (Prentice Hall, 1979) and editor of Nuclear Medicine Physics (CRC Press, 1987). He has been a grant and site reviewer for NIH since the mid-1990s. Dr. Williams is associate editor of Medical Physics and a reviewer for several other journals. He is a member of the American Association of Physicists in Medicine (AAPM), the Society of Nuclear Medicine, the New York Academy of Sciences, Sigma Xi, Society of Imaging Informatics in Medicine (SIIM), and the Society of Breast Imaging. Dr. Williams has received a lifetime service award from the American Board of Radiology. Among Dr. Williams’ most significant biophysical discoveries is the mass-law for tumor uptake as a function of tumor size. He was also codiscoverer (with Richard Proffitt) of tumor targeting with liposomes. This work involved one of the first applications of normal organ blockage by use of an unlabeled agent—that is, a two-step process. Dr. Williams has developed a pair of indices for quantifying the ability of a radiopharmaceutical to permit imaging or therapy of lesions in animals or patients. He has also demonstrated that radioactive decay must be considered inherently as one possible exit route in modeling analysis of radioactive drugs. With his colleagues at City of Hope, Dr. Williams measured and calculated the brake radiation dose result for a source of 90Y in a humanoid phantom. This study remains as one of the few examples of a comparison of dose estimates and measurement in the nuclear medicine literature.