First Clinical CT (1972)

October 1, 1971 — first clinical CT scan, performed at Atkinson Morley Hospital, London, on a 41-year-old woman with a suspected brain tumor. The scanner was the EMI Mark I, designed by Godfrey Hounsfield at EMI Laboratories in Hayes, Middlesex. The first scan demonstrated a frontal-lobe cyst, immediately changing surgical planning.

Commercial installations began in 1972; the EMI scanner was head-only, used translate-rotate motion (Hounsfield's "first generation" geometry), produced an 80×80 pixel image, and required ~5 minutes per slice. Hounsfield received the 1979 Nobel Prize in Physiology or Medicine, shared with Allan Cormack, who had independently developed the reconstruction mathematics in the 1960s.

What made CT possible

• Computational power — image reconstruction from projection data requires solving a large linear system. CT became practical only when minicomputers (the EMI Mark I used a Data General Nova) could perform the math in clinically reasonable time.
• Reconstruction algorithms — filtered back projection (FBP), the mathematical technique that took analog projection data into a 2D image, traces to Cormack's earlier theoretical work on tomography.
• Detector physics — early scanners used scintillation detectors paired with photomultiplier tubes; later generations moved to xenon ionization chambers and then solid-state scintillators.

Generations and architectural evolution

• 1st generation (1972) — translate-rotate, single detector, head-only, ~5 min / slice.
• 2nd generation — translate-rotate with a small fan beam and a few detectors.
• 3rd generation (mid-1970s) — full fan beam, rotating tube and detector arc together. The geometry of every modern CT scanner.
• 4th generation — stationary detector ring with rotating tube; commercially deprecated.
• Helical (1989) — continuous gantry rotation with continuous patient translation; eliminates step-and-shoot acquisition.
• Multi-detector (1998) — 4-slice, then 16, 64, 128, 256, 320-row.
• Dual-source (2006) — Siemens SOMATOM Definition; two tubes, two detectors at 90° offset.
• Photon-counting (2021) — Siemens NAEOTOM Alpha; direct photon counting replaces energy-integrating detectors.

Why CT changed medicine

• Cross-sectional anatomy at clinical scale, in living patients, for the first time. Stroke, intracranial hemorrhage, tumor staging, trauma — all transformed within years of clinical adoption.
• Trauma imaging — pan-scan CT redefined ED workflow; whole-body CT in stable blunt trauma reduces missed injury and (in Level 1 trauma populations) reduces mortality.
• Oncology — staging, restaging, and response assessment depend on serial CT.

Descends to

• Every CT scanner modern and legacy
• Intraoperative CT
• Dental CBCT
• PET / CT (hybrid sibling)
• GE LightSpeed family
• GE Revolution CT
• Siemens SOMATOM Definition
• Siemens NAEOTOM Alpha (photon-counting)
• Canon Aquilion ONE

Related

• Röntgen Discovers X-rays (1895) — predecessor inflection
• First 64-slice CT (2004) — multi-detector inflection
• First Commercial PET / CT (2001) — hybrid descendant
• CT Trauma