title: Optimal section thickness for detection of polyps at MR: resolution phantom study.
abstract: OBJECTIVE
  To determine (1) the sensitivity for detection of small polyps with varying MR slice thicknesses using a resolution phantom; (2) reader confidence in polyp detection; and (3) image acquisition time.
  
  
  METHODS
  A resolution phantom was created using a 3D printer. Polyp morphologies were sessile (height = diameter), flat (height = 1/2 diameter of the base), and pedunculated (stalk length = polyp diameter). Polyp diameters were 5, 7, 10, and 12 mm. Images were acquired with section thicknesses of 5, 3, and 1 mm. Images were independently reviewed by 4 board-certified radiologists who were blinded to phantom design and sequences parameters. Readers recorded maximal polyp diameter and confidence level that a polyp was present on a 1-100 point scale. Image acquisition time was also recorded.
  
  
  RESULTS
  All polyps were detected by all 4 readers in the 5-mm-section thickness series. All polyps were detected by 3 readers in the 3- and 1-mm-section thickness series. The fourth reader identified 11/12 polyps in the 3- and 1-mm-section thickness series. Confidence levels were not statistically significantly different for the different section thicknesses (p = 0.28). Increasing the section thickness from 1 to 5 mm decreased image acquisition time from 3 min 54 s to 41 s.
  
  
  CONCLUSIONS
  Five-millimeter-section thickness was adequate for identification of 5-12 mm polyps regardless of shape. Pending further reduction in acquisition time, this prototype sequence holds promise for segmental imaging of the colon with MR colonography.
authors.affiliation: Department of Radiology & Imaging Sciences, Emory University School of Medicine, 1364 Clifton Road, NE, Atlanta, GA, 30322, USA, courtney.coursey@emoryhealthcare.org.
authors.forename: Courtney C
authors.initials: CC
authors.lastname: Moreno
authors.forename: Pardeep K
authors.initials: PK
authors.lastname: Mittal
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Henson
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Baumgarten
authors.forename: Lauren F
authors.initials: LF
authors.lastname: Alexander
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Hanes
authors.forename: William C
authors.initials: WC
authors.lastname: Small
authors.forename: Hiroumi D
authors.initials: HD
authors.lastname: Kitajima
authors.forename: Jian
authors.initials: J
authors.lastname: Kang
authors.forename: John R
authors.initials: JR
authors.lastname: Votaw
authors.forename: John N
authors.initials: JN
authors.lastname: Oshinski
authors.forename: W Thomas
authors.initials: WT
authors.lastname: Dixon
mesh_terms: D003106:Colon / Q000473:pathology*; D003111:Colonic Polyps / Q000175:diagnosis*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D015588:Observer Variation; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity