Anatomical background and generalized detectability in tomosynthesis and cone-beam CT

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Abstract

Purpose: Anatomical background presents a major impediment to detectability in 2D radiography as well as 3D tomosynthesis and cone-beam CT (CBCT). This article incorporates theoretical and experimental analysis of anatomical background "noise" in cascaded systems analysis of 2D and 3D imaging performance to yield "generalized" metrics of noise-equivalent quanta (NEQ) and detectability index as a function of the orbital extent of the (circular arc) source-detector orbit. Methods: A physical phantom was designed based on principles of fractal self-similarity to exhibit power-law spectral density (κ/ fΒ) comparable to various anatomical sites (e.g., breast and lung). Background power spectra [SB (f)] were computed as a function of source-detector orbital extent, including tomosynthesis (∼10°-180°) and CBCT (180°+fan to 360°) under two acquisition schemes: (1) Constant angular separation between projections (variable dose) and (2) constant total number of projections (constant dose). The resulting SB was incorporated in the generalized NEQ, and detectability index was computed from 3D cascaded systems analysis for a variety of imaging tasks. Results: The phantom yielded power-law spectra within the expected spatial frequency range, quantifying the dependence of clutter magnitude (κ) and correlation (Β) with increasing tomosynthesis angle. Incorporation of SB in the 3D NEQ provided a useful framework for analyzing the tradeoffs among anatomical, quantum, and electronic noise with dose and orbital extent. Distinct implications are posed for breast and chest tomosynthesis imaging system design-applications varying significantly in κ and Β, and imaging task and, therefore, in optimal selection of orbital extent, number of projections, and dose. For example, low-frequency tasks (e.g., soft-tissue masses or nodules) tend to benefit from larger orbital extent and more fully 3D tomographic imaging, whereas high-frequency tasks (e.g., microcalcifications) require careful, application-specific selection of orbital extent and number of projections to minimize negative effects of quantum and electronic noise. Conclusions: The complex tradeoffs among anatomical background, quantum noise, and electronic noise in projection imaging, tomosynthesis, and CBCT can be described by generalized cascaded systems analysis, providing a useful framework for system design and optimization.

Original languageEnglish (US)
Pages (from-to)1948-1965
Number of pages18
JournalMedical Physics
Volume37
Issue number5
DOIs
Publication statusPublished - May 2010

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Keywords

  • Anatomical background
  • Anatomical clutter
  • Anatomical noise
  • Cascaded systems analysis
  • Cone-beam CT
  • Detectability index
  • Imaging task
  • Noise-equivalent quanta
  • Noise-power spectrum
  • Tomosynthesis

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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