# Photon-counting CT

Source: https://onco.cc/technologies/photon-counting-ct/  
OnCo record `photon-counting-ct` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A new kind of CT detector that counts every X-ray photon and records its energy, giving sharper pictures at lower dose and colour-like tissue information from every scan.

## Summary

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.

## Fields

- Kind: Technology
- Status: emerging
- Last checked: 2026-09-17
- Tags: machines-wave
- Principle: Direct-conversion semiconductor detectors register individual X-ray photons and their energies, removing electronic noise and giving intrinsic spectral separation with smaller pixels than scintillator detectors allow.
- Since: 2021
- Strengths: Higher spatial resolution at the same or lower dose; Spectral information from every scan; Less blooming from calcium and metal
- Limitations: Expensive and installed in few hospitals; Large data volumes and new reading habits; Evidence of better cancer outcomes still to come

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Photon-counting_computed_tomography
- Siemens Healthineers: NAEOTOM Alpha photon-counting CT: https://www.siemens-healthineers.com/computed-tomography/photon-counting-ct
- Wikipedia: https://en.wikipedia.org/wiki/Photon-counting_computed_tomography

## Connected records

- technologies: [CT (computed tomography)](https://onco.cc/technologies/ct/), [Dual-energy and spectral CT](https://onco.cc/technologies/dual-energy-spectral-ct/), [Low-dose CT lung screening](https://onco.cc/technologies/low-dose-ct-screening/)
- cancers: [Childhood cancers (all types)](https://onco.cc/cancers/childhood-cancers/), [Hepatocellular carcinoma](https://onco.cc/cancers/hcc/), [Multiple myeloma](https://onco.cc/cancers/multiple-myeloma/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Pancreatic ductal adenocarcinoma](https://onco.cc/cancers/pancreatic/)
- fronts: [Imaging](https://onco.cc/fronts/imaging/)
- companies: [Canon Medical Systems](https://onco.cc/companies/canon-medical/), [GE HealthCare](https://onco.cc/companies/ge-healthcare/), [Siemens Healthineers](https://onco.cc/companies/siemens-healthineers/)

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