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NOTE: No further updates or changes will be made to this repository. I am currently in the process of migrating the entirety of the FreeCT project into one project: This should simplify building and installing in every single way, however in the mean time there are going to be some growing pains and the project will be non-functional. If you have any questions or comments please reach out to

What is FreeCT_ICD?

FreeCT_ICD is the model-based iterative reconstruction companion software to FreeCT_wFBP. It is free software (released under the GNU GPLv2) intended for use in research and education. Modification and contributions are encouraged.

Quick (Science) Facts:


  • Reconstructs third-generation, helical, diagnostic, multidector CT data (without gantry tilt)
  • Uses iterative coordinate descent as an optimizer
  • Employs a stored system matrix (SSM)
  • Employs a rotating slice geometry to keep the stored system matrix sizes small (J. Xu and B. M. W. Tsui, “Iterative image reconstruction in helical cone-beam x-ray CT using a stored system matrix approach.,” Phys. Med. Biol., vol. 57, no. 11, pp. 3477–97, 2012.)
  • Uses a modified Joseph's method approach for the projector
  • Supports flying focal spots (Note: at present, only an in-plane flying focal spot is supported, however support for Z and Z+in-plane are under active development)

Quick (Computing) Facts:

What it is not

FreeCT_ICD is not what the manufacturers use

While our algorithms are based off of publications that are perhaps relevant to some of the current algorithms used in industry, they are not the algorithms used on clinical CT scanners and we make no claims to the similarity between our reconstructed images and what is arrived at clinically. In fact, moreso than FreeCT_wFBP, FreeCT_ICD employs a unique forward projector that has not been previously published.

Work has been done to objectively evaluate the quality of our reconstructions. This can be found here:

(insert link to technical note and/or whitepaper) (Coming soon)

FreeCT_ICD is not a library

There are many great reconstruction libraries out there (, to name two), and perhaps one day FreeCT_ICD will be recast as a library. Currently however, it is not a library, it is a program.

It is structured modularly, so that major subsections of the reconstruction process are easy to identify/customize/edit/etc. so there are library-like qualities to the project to make it easy to use.

FreeCT_ICD is designed to be compiled and run to reconstruct projection data from start to finish.


The latest working version can be found on GitHub at

Bleeding edge updates can be found at


(to be added later)


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(more info to be added later)

Copyright 2018 John Hoffman, Stefano Young, Frédéric Noo


Iterative Coordinate Descent CT MBIR







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