A CT scanner builds body slices from thousands of X-ray angles
A CT scanner spins an X-ray tube around the body, measures how much each tissue absorbs, then lets a computer reconstruct virtual slices. The idea earned Godfrey Hounsfield and Allan Cormack the 1979 Nobel Prize, and by 2015 Americans were undergoing more than 80 million scans a year.
Inside the ring, or gantry, a rotating tube fires X-rays while detectors opposite record how strongly different tissues weaken the beam. Readings gathered from many angles feed reconstruction algorithms that produce cross-sections. Early step-and-shoot machines paused the table for each slice, which made scans slow. Spiral scanners, now dominant because they are cheaper, rotate continuously, though the heavy tube and detectors limit how fast they can turn. Dual-source designs mount two tubes at 90 degrees and capture a slice in half a rotation, cutting blur from a fast heartbeat; electron-beam versions sweep only the electron path for speed but cost more to build.
Uses span the whole body. Head scans reveal strokes, bleeding and fractures: dark areas can mean swelling or infarction, bright ones calcification or blood. Non-contrast scans are the standard for kidney stones, sizing them to predict whether they will pass. CT picks up lung damage that ordinary X-rays miss, maps clots in the pulmonary arteries with iodine contrast, and resolves fractures around joints at 0.2 mm. Dual-energy machines have even helped diagnose gout. Unlike MRI, CT can be used on people with pacemakers or metal implants.
Hybrids add function to anatomy. PET–CT merges metabolic activity with structural images in one session, which helps in finding cancers, while perfusion CT tracks contrast through blood vessels and can reveal poor blood flow in the brain earlier than a standard spiral scan. Cardiac CT increasingly guides valve repairs through catheters, sometimes with 3D prints made from the scan data.
Radiation is the catch. Many professional bodies oppose full-body scans for healthy people because of the dose, and guidelines warn against scanning small incidental lung nodules more often than recommended, since solid nodules unchanged for two years in people without prior cancer are unlikely to be malignant. A study counting chromosome damage found higher baseline levels in liver cancer patients than in others, supporting careful tracking of cumulative imaging exposure.
Source: CT scan
