CT (Computed Tomography)

Rotating X-ray source and detector array reconstruct cross-sectional images from hundreds of projections per rotation. The detector-row count drives clinical capability — "16-slice", "64-slice", "320-slice" refers to the number of parallel detector rows.

Physics

X-ray tube and detector rotate around the patient on a gantry. Patient couch translates through the gantry during helical acquisition. Reconstruction algorithms (filtered back projection historically; iterative reconstruction since the 2010s) convert projection data into cross-sectional images expressed in Hounsfield units.

History

1972 — Godfrey Hounsfield (EMI) builds the first commercial CT (EMI Mark I).
1979 — Hounsfield + Cormack share Nobel Prize in Physiology or Medicine.
1989 — single-slice helical (spiral) CT.
1998 — 4-slice CT (multi-detector era).
2004 — 64-slice CT becomes clinical standard (GE LightSpeed VCT, Siemens Definition).
2007 — Canon (Toshiba) Aquilion ONE ships 320-slice (160 mm Z-axis).
2013+ — iterative reconstruction (ASiR, SAFIRE, iDose) becomes standard.

Key specs buyers evaluate

Slice count — 16 / 32 / 64 / 128 / 256 / 320
Rotation time — 0.35 sec fast, 2.0 sec slow
Gantry aperture — 70 cm standard, 80 cm wide-bore
Tube — heat capacity (MHU), focal spot size, wear indicators
Dose reduction — ASiR, SAFIRE, iDose, AIDR
Cardiac capability — gating, SnapShot Pulse, dual-source
Dual-energy — TwinBeam, GSI

Systems

Service reality

The X-ray tube is the dominant cost of ownership. A Performix Pro VCT 100 tube is $80k–$180k refurbished. Duty cycle determines tube lifespan more than anything else. Chronically pushing mA limits = shorter tube life. Plan capital around tube replacement cycles, not scanner lifespan.

Regulatory

ACR CT accreditation. Dose monitoring (CTDI / DLP tracked and reported via structured dose reports). State fluoroscopy / radiography registration.