Method for measuring the intensity profile of a CT fan-beam filter

Bruce R. Whiting, Andreea Dohatcu

Research output: Chapter in Book/Report/Conference proceedingConference contribution

3 Scopus citations

Abstract

Research on CT systems often requires knowledge of intensity as a function of angle in the fan-beam, due to the presence of bowtie filters, for studies such as dose reduction simulation, Monte Carlo dose calculations, or statistical reconstruction algorithms. Since manufacturers consider the x-ray bowtie filter design to be proprietary information, several methods have been proposed to measure the beam intensity profile independently: 1) calculate statistical properties of noise in acquired sinograms (requires access to raw data files, which is also vendor proprietary); 2) measure the waveform of a dosimeter located away from the isocenter (requires dosimeter equipment costing > 10K). We present a novel method that is inexpensive (parts costing ~100 from any hardware store, using Gafchromic film at ~3 per measurement), requires no proprietary information, and can be performed in a few minutes. A fixture is built from perforated steel tubing, which forms an aperture that selectively samples the intensity at a particular fan-beam angle in a rotating gantry. Two exposures (1× and 2×) are made and self-developing radiochromic film (Gafchromic XR- Ashland Inc.) is then scanned on an inexpensive PC document scanner. An analysis method is described that linearizes the measurements for relative exposure. The resultant profile is corrected for geometric effects (1/LΛ2 fall-off, gantry dwell time) and background exposure, providing a noninvasive estimate of the CT fan-beam intensity present in an operational CT system. This method will allow researchers to conveniently measure parameters required for modeling the effects of bowtie filters in clinical scanners.

Original languageEnglish (US)
Title of host publicationMedical Imaging 2014
Subtitle of host publicationPhysics of Medical Imaging
PublisherSPIE
Volume9033
ISBN (Print)9780819498267
DOIs
StatePublished - 2014
Externally publishedYes
EventMedical Imaging 2014: Physics of Medical Imaging - San Diego, CA, United States
Duration: Feb 17 2014Feb 20 2014

Other

OtherMedical Imaging 2014: Physics of Medical Imaging
CountryUnited States
CitySan Diego, CA
Period2/17/142/20/14

Keywords

  • bowtie filter
  • CT
  • fanbeam
  • radiochromic

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Radiology Nuclear Medicine and imaging

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  • Cite this

    Whiting, B. R., & Dohatcu, A. (2014). Method for measuring the intensity profile of a CT fan-beam filter. In Medical Imaging 2014: Physics of Medical Imaging (Vol. 9033). [903322] SPIE. https://doi.org/10.1117/12.2043246