The ACTA (Automatic Computerized Transverse Axial) scanner was developed in 1973. The introduction of this first full-body CAT--or CT (Computer Assisted Tomography)--scanner lead to advancement in medical imaging and diagnostic medicine, especially for non-invasive viewing of soft tissue inside the body. The machine revolutionized diagnosis in cancer, heart disease, and soft tissue irregularities by transmitting X-ray beams through transverse axial slices of the body, resulting in computerized cross-sectional images of the body part scanned. Robert S. Ledley, of Georgetown University Medical Center, designed the ACTA scanner, and it was first used in clinical operation there in 1973. Ramunas Kondratas, curator at the National Museum of American History (NMAH), interviewed Ledley, Homer Twigg, Robert Zeman, David Greigo and Seong Ki Mun about the history of CAT scanning in general, and the development and operation of the ACTA scanner in particular, as well as Ledley's more recent work in biotechnology instrumentation. Kondratas also visually documented CAT scanning equipment, from the earliest model ACTA scanner to most recent CT (Computerized Tomography) scanners. The project also includes a documentary film, "The ACTA Scanner," that explains the operating principles of the ACTA Scanner, c. 1978.