title: Ultra-low peak voltage CT colonography: effect of iterative reconstruction algorithms on performance of radiologists who use anthropomorphic colonic phantoms.
abstract: OBJECTIVE
  To analyze the effect of a decrease in computed tomographic (CT) colonographic voltage, from 100 and 120 kVp to 80 kVp and reconstructed with filtered back projection ( FBP filtered back projection ), on radiation dose, image noise, and diagnostic performance in anthropomorphic phantoms and to assess the effect of iterative reconstruction ( IR iterative reconstruction ) algorithms on radiologists' performance for 80-kVp CT colonography.
  
  
  METHODS
  Seven colon phantoms with 68 simulated polyps (≥6 mm) were scanned at three peak voltage settings (80, 100, 120 kVp) and 10 mAs. Images were reconstructed by using FBP filtered back projection , hybrid statistic-based IR iterative reconstruction , and knowledge-based IR iterative reconstruction algorithms. Effective radiation dose, image noise, and per-polyp sensitivity were recorded and compared by two reviewers with Friedman test, repeated measures analysis of variance, and McNemar test.
  
  
  RESULTS
  Median size-specific dose estimate and effective radiation dose of 80-kVp CT colonography was 0.231 mGy and 0.167 mSv, respectively, which was lower than with 100- and 120-kVp CT colonography, with significant difference between 80 and 120 kVp (P = .0005). Image noise (202.0 HU) at 80-kVp FBP filtered back projection CT colonography was significantly higher than at 100-kVp FBP filtered back projection (139.1 HU) and 120-kVp FBP filtered back projection (120.4 HU) (P < .0001). Per-polyp sensitivity (reviewer 1, 14.7% [10 of 68]; reviewer 2, 7.4% [five of 68]) at 80-kVp FBP filtered back projection was significantly lower than at 100-kVp FBP filtered back projection (reviewer 1, 57.4% [39 of 68]; reviewer 2, 39.7% [27 of 68]) and 120-kVp FBP filtered back projection (reviewer 1, 85.3% [58 of 68]; reviewer 2, 83.8% [57 of 68]) (P < .0001). With statistic-based IR iterative reconstruction , image noise at 80 kVp decreased significantly (52.8% [106.7 HU of 202.0 HU]) compared with that at 80-kVp FBP filtered back projection (P < .0001), but per-polyp sensitivity (reviewer 1, 79.4% [54 of 68]; reviewer 2, 66.2% [45 of 68]) at 80-kVp statistic-based IR iterative reconstruction remained significantly lower than at 100-kVp statistic-based IR iterative reconstruction (reviewer 1, 95.6% [65 of 68]; reviewer 2, 86.8% [59 of 68]) (P = .001) and 120-kVp statistic-based IR iterative reconstruction (reviewer 1, 98.5% [67 of 68]; reviewer 2, 89.7% [61 of 68]) (P < .001). For knowledge-based IR iterative reconstruction , per-polyp sensitivity at 80 kVp was improved to 98.5% (67 of 68) and 94.1% (64 of 68), not significantly different from that at 100 kVp (reviewer 1, 100% [68 of 68]; reviewer 2, 95.6% [65 of 68]) and 120 kVp (reviewer 1, 100% [68 of 68]; reviewer 2, 95.6% [65 of 68]) (P > .999).
  
  
  CONCLUSIONS
  A decrease in tube voltage to 80 kVp caused reduction in radiation dose (0.166 mSv) with deterioration in image noise and per-polyp sensitivity. By using a knowledge-based IR iterative reconstruction algorithm, radiologists' performance of 80-kVp CT colonography was acceptable and on par with that at 100- or 120-kVp CT colonography.
authors.affiliation: From the Department of Radiology (C.I.S., S.H.K., E.S.L., D.H.L., E.J.H., J.M.L., J.K.H., B.I.C.), Institute of Radiation Medicine (S.H.K., J.M.L., J.K.H., B.I.C.), and Healthcare System Gangnam Center (S.Y.C.), Seoul National University Hospital, 101 Daehangno, Jongno-gu, Seoul 110-744, Korea.
authors.forename: Cheong-Il
authors.initials: CI
authors.lastname: Shin
authors.forename: Se Hyung
authors.initials: SH
authors.lastname: Kim
authors.forename: Eun Sun
authors.initials: ES
authors.lastname: Lee
authors.forename: Dong Ho
authors.initials: DH
authors.lastname: Lee
authors.forename: Eui Jin
authors.initials: EJ
authors.lastname: Hwang
authors.forename: Se-Yeong
authors.initials: SY
authors.lastname: Chung
authors.forename: Jeong Min
authors.initials: JM
authors.lastname: Lee
authors.forename: Joon Koo
authors.initials: JK
authors.lastname: Han
authors.forename: Byung Ihn
authors.initials: BI
authors.lastname: Choi
mesh_terms: D000465:Algorithms; D000818:Animals; D002983:Clinical Competence; D003111:Colonic Polyps / Q000000981:diagnostic imaging*; D023881:Colonography, Computed Tomographic / Q000592:standards*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012680:Sensitivity and Specificity; D012984:Software; D013552:Swine