title: CT colonography at low tube potential: using iterative reconstruction to decrease noise.
abstract: OBJECTIVE
  To determine the level of iterative reconstruction required to reduce increased image noise associated with low tube potential computed tomography (CT).
  
  
  METHODS
  Fifty patients underwent CT colonography with a supine scan at 120 kVp and a prone scan at 100 kVp with other scan parameters unchanged. Both scans were reconstructed with filtered back projection (FBP) and increasing levels of adaptive statistical iterative reconstruction (ASiR) at 30%, 60%, and 90%. Mean noise, soft tissue and tagged fluid attenuation, contrast, and contrast-to-noise ratio (CNR) were collected from reconstructions at both 120 and 100 kVp and compared using a generalised linear mixed model.
  
  
  RESULTS
  Decreasing tube potential from 120 to 100 kVp significantly increased image noise by 30-34% and tagged fluid attenuation by 120 HU at all ASiR levels (p<0.0001, all measures). Increasing ASiR from 0% (FBP) to 30%, 60%, and 90% resulted in significant decreases in noise and increases in CNR at both tube potentials (p<0.001, all comparisons). Compared to 120 kVp FBP, ASiR greater than 30% at 100 kVp yielded similar or lower image noise.
  
  
  CONCLUSIONS
  Iterative reconstruction adequately compensates for increased image noise associated with low tube potential imaging while improving CNR. An ASiR level of approximately 50% at 100 kVp yields similar noise to 120 kVp without ASiR.
authors.affiliation: Department of Diagnostic Imaging, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, 593 Eddy St., Providence, RI 02903, USA. Electronic address: kchang@lifespan.org.
authors.forename: K J
authors.initials: KJ
authors.lastname: Chang
authors.affiliation: Department of Diagnostic Imaging, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, 593 Eddy St., Providence, RI 02903, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Heisler
authors.affiliation: The Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins School of Medicine, 601 N. Caroline St, Room 3140D, Baltimore, MD 21287, USA.
authors.forename: M
authors.initials: M
authors.lastname: Mahesh
authors.affiliation: Department of Diagnostic Imaging, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, 593 Eddy St., Providence, RI 02903, USA.
authors.forename: G L
authors.initials: GL
authors.lastname: Baird
authors.affiliation: Department of Diagnostic Imaging, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, 593 Eddy St., Providence, RI 02903, USA.
authors.forename: W W
authors.initials: WW
authors.lastname: Mayo-Smith
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D023881:Colonography, Computed Tomographic / Q000379:methods*; D003287:Contrast Media; D003974:Diatrizoate Meglumine; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*
chemical_list: D003287:Contrast Media; D003974:Diatrizoate Meglumine