Noise, sampling, and the number of projections in cone-beam CT with a flat-panel detector

Z. Zhao, G. J. Gang, J. H. Siewerdsen

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Purpose: To investigate the effect of the number of projection views on image noise in cone-beam CT (CBCT) with a flat-panel detector. Methods: This fairly fundamental consideration in CBCT system design and operation was addressed experimentally (using a phantom presenting a uniform medium as well as statistically motivated "clutter") and theoretically (using a cascaded systems model describing CBCT noise) to elucidate the contributing factors of quantum noise (σQ), electronic noise (σE), and view aliasing (σview). Analysis included investigation of the noise, noise-power spectrum, and modulation transfer function as a function of the number of projections (Nproj), dose (Dtot), and voxel size (bvox). Results: The results reveal a nonmonotonic relationship between image noise andNproj at fixed total dose: for the CBCT system considered, noise decreased with increasing Nproj due to reduction of view sampling effects in the regime Nproj <∼200, above which noise increased with N proj due to increased electronic noise. View sampling effects were shown to depend on the heterogeneity of the object in a direct analytical relationship to power-law anatomical clutter of the form κ/ β - and a general model of individual noise components (σQ, σE, and σview) demonstrated agreement with measurements over a broad range in Nproj, Dtot, and bvox. Conclusions: The work elucidates fairly basic elements of CBCT noise in a manner that demonstrates the role of distinct noise components (viz., quantum, electronic, and view sampling noise). For configurations fairly typical of CBCT with a flat-panel detector (FPD), the analysis reveals a "sweet spot" (i.e., minimum noise) in the rangeNproj ∼ 250-350, nearly an order of magnitude lower in Nproj than typical of multidetector CT, owing to the relatively high electronic noise in FPDs. The analysis explicitly relates view aliasing and quantum noise in a manner that includes aspects of the object ("clutter") and imaging chain (including nonidealities of detector blur and electronic noise) to provide a more rigorous basis for commonly held intuition and heurism in CBCT system design and operation.

Original languageEnglish (US)
Article number061909
JournalMedical physics
Issue number6
StatePublished - Jun 2014


  • cascaded systems analysis
  • cone-beam CT
  • electronic noise
  • image quality
  • quantum noise
  • view-sampling

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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