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Inventor Robert Ledley
Robert Ledley Papers,
1972-1981 (bulk 1973-1975)

Extent and Forms of Material: 3 cubic feet, including photographs, slides, and videotape (6 boxes, 2 oversize folders, 1 reel)
Creator: Robert Ledley
Abstract: The Robert Ledley Papers document the development of the first whole-body diagnostic imaging system, the Automatic Computerized Transverse Axial (ACTA) X-ray Scanner by Ledley in 1973. Also included is material relating to Ledley’s company, Digital Science Information Corporation (DISCO), as well as the public and medical communities’ reactions to the scanner.
Repository: Archives Center, National Museum of American History, Smithsonian Institution, Washington, D.C.;; 202-633-3270;
Collection Number: AC1135
Processing Note: Processed by Elizabeth Garber (intern), June 2009; supervised by Alison Oswald, archivist.
© 2009 by the Smithsonian Institution. All rights reserved.


Information for users of the collection

Conditions Governing Access: The collection is open for research use.
Physical Access: Researchers must use reference copies of audio-visual materials.  When no reference copy exists, the Archives Center staff will produce reference copies on an “as needed” basis, as resources allow.
Technical Access: Viewing the film portion of the collection without reference copies requires special appointment. Please inquire for details.
Conditions Governing Reproduction and Use: Copyright held by the Smithsonian Institution.  Collection items available for reproduction, but the Archives Center makes no guarantees concerning copyright restrictions. Other intellectual property rights may apply. Reproduction permission from Archives Center: reproduction fees may apply.
Preferred Citation: Title and date of item, Robert Ledley Papers, 1972-1981, Archives Center, National Museum of American History, box number X, folder number XX, digital file number XXXXXXXX


In-depth information about the collection

Administrative/biographical history
Scope and content
System of arrangement
Acquisition information
Custodial history
Related archival materials
Related artifacts
Access points
Container listing

Administrative/biographical history

Robert Steven Ledley was born in Flushing Meadows, New York in 1926. He received a D.D.S. degree from New York University College in 1948. While attending dental school, he simultaneously studied at Columbia University; he earned a M.A. in Theoretical Physics in 1949. He volunteered for the army and was sent to the U.S. Army Medical Field Service School in Fort Sam Houston, Texas.1 After completing his service, Ledley held a wide variety of research and academic positions in physics, electrical engineering, and medicine.

Ledley was a physicist within the External Control Group of the Electronic Computer Laboratory of the National Bureau of Standards from 1953-1954. He was an operations research analyst within the Strategic Division of the Operations Research Office at Johns Hopkins University from 1954-1956. Ledley went on to become an associate professor in the Department of Electrical Engineering at The George Washington University from 1956-1960 while also serving as a consultant mathematician at the National Bureau of Standards Data Processing Systems Division, 1957-1960. At this time, Ledley also worked part time at the National Research Council’s National Academy of Sciences from 1957-1961. Ledley became the president of the National Biomedical Research Foundation in 1960, a position he still holds today. He was an instructor of pediatrics at the Johns Hopkins University School of Medicine from 1960-1963. He returned to The George Washington University’s Department of Electrical Engineering in 1968  where he was a professor until 1970. He then became a professor in the Department of Physiology and Biophysics at the Georgetown University School of Medicine in 1970. In 1974, Ledley also became a professor in the Radiology Department at the Georgetown University Medical Center. In 1975, he became the director of the Medical Computing and Biophysics Division at Georgetown University Medical Center.

In 1972, the British company Electric and Musical Industries Limited (EMI) released a medical imaging machine for use on smaller areas of the body that were positioned under a water tank. In 1973, Ledley developed the Automatic Computerized Transverse Axial (ACTA) X-ray Scanner (US Patent #3,922,552). This machine was the first whole-body diagnostic medical imaging system. He was awarded a grant from the National Institutes of Health for an engineering equipment project, but the money was never received due to budget cuts. Ledley looked elsewhere for funding. He consulted with Georgetown staff and discovered a neurosurgeon had asked to buy a head scanning machine from EMI. Ledley did not think the images in EMI’s brochure appeared clear, and he offered to create a similar machine for half the price. Georgetown agreed to fund this project for $250,000. Ledley secured the services of a machinist at a local machine shop, an electronic engineer, and a programmer/mathematician to assist in the project.2 The ACTA Scanner debuted in February, 1974 and did not require the use of a water tank.

Following the creation of the ACTA Scanner, Ledley organized Digital Information Science Corporation (DISCO) in order to manufacture the system. DISCO began producing scanners as orders were received. Due to financial constraints, DISCO was forced to request $100,000 upon receipt of the order, $100,000 when the scanner was halfway completed, and the final $100,000 payment upon delivery3. In 1975, Pfizer purchased the rights to manufacture the ACTA Scanner from DISCO for $1.5 million.

Ledley is a Fellow of the American Association for the Advancement of Science and a senior member of the Institute of Electrical and Electronics Engineers. He has earned  numerous awards and honors for his work. In 1997, he received the National Medal of Technology from President William Jefferson Clinton for his pioneering work on the whole-body CT diagnostic X-ray scanner. He also founded the Pattern Recognition Society and Computerized Tomography Society.

1 Ash, J., D. Sittig, and R. Ledley. “The Story Behind the Development of the First Whole-body Computerized Tomography Scanner as Told by Robert S. Ledley.” Journal of the American Medical Informatics Association, 2006 Sep-Oct (2006), 465-469, (accessed June 24, 2009).
2 Ibid.
3 Ibid.

Scope and content

The Robert Ledley Papers document the development of the Automatic Computerized Transverse Axial (ACTA) X-ray Scanner, Ledley’s company Digital Science Information Corporation (DISCO), as well as the public and medical communities’ reactions to the scanner. The collection is arranged into nine series.

Series 1, ACTA Scanner I Schematics, 1973-1975; Series 2, ACTA Scanner I [Computer and Electronics], 1973; and Series 3, ACTA Scanner Tomograph Mechanics, 1973-1974 document the development and design of the ACTA scanner through drawings, notes, memoranda, and product information. More detailed information about these materials is located in the control file. All oversize drawings have been moved to flat storage for preservation concerns.

Series 4, ACTA Scanner Operating Instructions, 1975, is the operating manual created for the scanner used in Ledley’s Georgetown lab.

Series 5, ACTA Articles, Clippings, and Press Releases, 1973-1979, is comprised of the aforementioned materials relating to the ACTA Scanner. Newspaper clippings illuminate the public’s perception of the scanner, and scientific pieces highlight the medical community’s reaction. Ledley’s published articles on the scanner and related topics are included.

Series 6, Digital Information Science Corporation (DISCO) material, 1973-1981, documents Ledley’s career and his company. A biographical sketch, list of articles, textbooks, and patents highlight Ledley’s achievements. Invoices, receipts, contracts, and correspondence illuminate the financial situation at DISCO and the relationship between the company and Pfizer.

Series 7, Computer manuals, 1972-1975, documents the computer systems and software that were used with the ACTA Scanner.

Series 8, Photographic material, 1973-1978, includes an album of photographs depicting the ACTA Scanner and images of the scans it created. This album was disassembled due to preservation concerns. This series also includes a collection of slides featuring the scanner and related equipment in use and images of the scans it created. A detailed description of each photograph and slide is included in the control file.

Series 9, ACTA Scanner film, [1974?], is a 16mm narrated film describing the creation of the scanner, its components, the way they work, the scanner in use, and images of the scans produced.

System of arrangement

Series 1, ACTA Scanner I Schematics, 1973-1975, undated
Series 2, ACTA Scanner I [Computer and Electronics], 1973, undated
Series 3, ACTA Scanner Tomograph Mechanics, 1973-1974, undated
Series 4, ACTA Scanner Operating Instructions, 1975
Series 5, ACTA Articles, Clippings, and Press Releases, 1973-1979
Series 6, Digital Information Science Corporation (DISCO) material, 1973-1981, undated
Series 7, Computer manuals, 1972-1975, undated
Series 8, Photographic material, 1973-1978
Subseries 1, Photographs, 1973-1978
Subseries 2, Slides, 1974
Series 9, ACTA Scanner film, [1974?]


Some articles are in Japanese and Hungarian.

Acquisition information

This collection was donated by Robert Ledley, 1984.

Custodial history

Transferred to the Archives Center from the Division of Medicine and Science in 2008.

Related archival materials

The Smithsonian Institution Archives holds video tapes, audio tapes, and transcripts entitled Medical Imaging Videohistory Collection 1989. These feature Ramunas Kondratas’s interviews with Ledley and his associates during which they discuss the history of X-ray CT imaging and the development of the ACTA Scanner. Ledley also discusses other research projects at the National Biomedical Research Foundation (NBRF) at Georgetown University and his background and career. Visual documentation includes group interaction, two documentary films, components of early models of the ACTA scanner, facilities and equipment of the NBRF, and a complete CT scanning session with a patient. This collection is restricted.

Related artifacts

The Division of Medicine and Science holds the ACTA Model 0100 CT Scanner and a balsa wood miniature model of the scanner. (Accession number: 1984.0680).

Access points

ACTA Scanner
Diagnostic imaging
Digital Information Science Corporation
Georgetown University
Ledley, Robert Steven
Medical innovations
Medical technology
National Biomedical Research Foundation
Whole body imaging


Washington (D.C.)

Articles -- 20th century
Color slides
Conceptual drawings
Electrical drawings
Operating manuals
Technical drawings
Technical manuals


Container listing

Box Folder  
1 1 Video Amp Design (ACTAT) A1, 1973-1974, undated
  2 Video Amp #2 A2, 1974, undated
  3 Analog Signal Generator A8, 1973, undated
  4 A/D Convertor #1 Card A3, 1973-1974, undated
  5 A/D Convertor #2 A4, 1973-1974, undated
  6 Miscellaneous Analog (A & B) A9, 1973, undated
  7 Translate Accel Pulses A10, 1973-1975, undated
  8 Miscellaneous AN-2 A11, undated
  9 Shutter & [Lights] L2, 1973-1974, undated
  10 X-X-X Logic L0, 1974, undated
  11 Translation Card L3, 1974, undated
  12 Rotation Card L4, undated
  13 Miscellaneous Logic L5, 1973, undated
  14 [Light] Pulse control & 161 L6, 1974, undated
  15 L7 (Ramp & Sample), 1973-1974, undated
  16 Extra Logic L8, 1974, undated
  17 Ex-Ex Logic L9, undated
  18 L10, undated
  19 Back Panel Wiring List, undated
  20 To Do's for L7 & L8, 1974, undated
  21 Bed Control ACTA #1, 1974, undated
  22 Horizontal Bed Logic ACTA 1 BC0, undated
  23 Bed Control Logic ACTA 1 BC1, 1975, undated
  24 Bed Control Analog Card BC2, undated
  25 Bed Power Driver BC3, undated
  26 ACTAT Checkout, 1973
  27 X-ray tests, 1973-1974, undated
  28 Interface Card MD4, undated
  29 Clutch Card (#2) MD5, 1974-1975, undated
  30 L Rack [Modifications], undated
  31 Shutter Electronics, 1973-1974, undated
  3 ACTA Scanner Operating Instructions, 1975
4   ACTA Scanner Operating Instructions (decorative binder), 1975
  O/S Fldr. 1 ACTA Scanner instructional guide, undated
2 4-5 ACTA Articles and press releases, 1973-1979
  6-7 Articles and clippings, 1973-1979
3 1 Texas Instruments 960A, 1972
  2 Texas Instruments 960A/980A, 1972-1974
  3 Texas Instruments 979 Tape Transport, 1974
  4-11 Texas Instruments 980, 1974-1975, undated
  12-17 Texas Instruments 980A, 1972-1973
4 1-2 Texas Instruments 980A, 1973-1974
  3 Texas Instruments 980B, 1974
  4 GX-100B, undated
  5-7 Texas Instruments DX980, 1975
  8 Texas Instruments Direct Memory Access Point Expander, 1974
5   Photographs, 1973-1978
4 9 Copies of photograph album pages, 1973-1978
6   Slides, 1974
  OF 1135.1 16mm color composite optical track print, 252 feet
4 11 ACTA Scanner film documentation (photocopies of labels from original enclosure), [1974?]
  O/S Fldrs.1-2 Materials separated for preservation concerns



Last Update: 4 Nov 2009

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