Hasselgren, Per-Olof: - Dr. Per-Olof Hasselgren has practiced surgery for 45 years. During his career, he has performed numerous procedures related to endocrine surgery, including thyroid, parathyroid, and adrenal gland procedures. Dr. Hasselgren recently stepped down from his clinical duties to devote more time to teaching and research. He is a member of the Section of Endocrine Surgery in the Department of Surgery at the Beth Israel Deaconess Medical Center in Boston, and serves as the George H.A. Clowes, Jr. Distinguished Professor of Surgery at Harvard Medical School.