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Standards for x-ray computed tomography

The objective of this project is to create low cost standards for use in x-ray computed tomography (CT) in medicine with emphasis on lung studies. Typically, CT images made of a patient are calibrated daily. However, due to the large variety of vendors with different hardware and software in a rapidly evolving field, it is not always possible to have meaningful time sequences of CT images to show changes in the size of tumors, for example. Moreover, the “CT numbers” as reported show a certain variability due to technical issues such as detector design as well as a lack of precision in the underlying definition.

Major Accomplishments

  • A study showing that volumetric measurements can reduce the variation in size measurements of ideal objects compared to the standard RECIST measurement by a factor of ten

  • Development of a low-cost device capable of reproducing lengths within a CT to better than 0.1 mm with data acquired with 0.6 mm voxels

  • Identification of a commercially available foam for use as a density reference

Selected Publications

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CT standards

A commercially available foam may be suitable as a standard for lung CT imaging.



Zachary Levine
Heather Chen-Mayer
John Lu

Related programs and projects:


Associated products:

Beta-test versions of the density and length standards are available for distribution.


Standards for x-ray computed tomography:
Zachary Levine, Project Leader
301-975-5453 Telephone
301-869-5700 Facsimile

100 Bureau Drive, M/S 8441
Gaithersburg, MD 20899-8441