Photon-counting CT

Conventional CT detectors convert X-rays to light in a scintillator and measure the summed glow, losing the energy of each photon and adding electronic noise. A photon-counting detector made of cadmium telluride or silicon converts each X-ray directly into an electrical pulse whose height gives its energy, so the scanner records how many photons arrived in each energy bin. That removes electronic noise, allows much smaller detector pixels for sharper images, and delivers spectral information (iodine maps, virtual non-contrast images, material separation) on every scan without a dedicated dual-energy protocol. The first clinical system, the Siemens Healthineers NAEOTOM Alpha, was cleared in the United States in 2021; GE HealthCare and Canon Medical have their own detector programmes.

For cancer the early gains are in lung nodules and small vessels, bone and marrow lesions in myeloma, sharper liver and pancreatic imaging with less contrast, and lower dose in children and in patients who are scanned many times for follow-up. The limits are price, a small installed base, very large datasets and the need to relearn what normal looks like at the new resolution.