title: Effect of iterative reconstruction on image quality in evaluating patients with coronary calcifications or stents during coronary computed tomography angiography: a pilot study.
abstract: OBJECTIVE
  To determine the effect of "Iterative Reconstruction in Image Space" (IRIS) on image quality by comparing reconstructions of both medium and sharp kernels when evaluating coronary calcifications or stents during coronary computed tomography (CT) angiography.
  
  
  METHODS
  Thirty one consecutive patients were scanned with an electrocardiogram-gated helical technique on a dual-source CT system. Image reconstruction was performed using standard filtered back projection (FBP) and IRIS algorithm on both medium and sharp kernels (B26f, I26f, B46f, I46f). Each reconstruction was derived from the same raw data. Two blinded readers graded image quality using a five-point scale. Noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) were obtained. Noise was derived from the ascending aorta and left ventricle. SNR was obtained from sinus Valsalva, interventricular septum, and coronary vessels. CNR was obtained from septum, coronary vessels, and left ventricle. Comparisons of paired results between FBP and IRIS images were analyzed using the repeated measures analysis of variance method. Interreader correlation was assessed using weighted Kappa statistic.
  
  
  RESULTS
  Noise values of the ascending aorta and left ventricle were significantly lower in the images reconstructed with IRIS than those reconstructed with FBP for the evaluation of the same filters. SNR and CNR values were higher in the IRIS images (p<0.05). Interreader agreement for four reconstructions was interpreted as moderate (κ=0.40-0.59).
  
  
  CONCLUSIONS
  IRIS significantly reduced image noise and improved imaging of coronary calcifications or stents. When combined with a sharp kernel, IRIS can improve image quality by reducing the negative effects of decreased signal that may result from using a sharp kernel.
authors.affiliation: Department of Radiology, Faculty of Medicine, Hacettepe University; Ankara-Turkey. gulerezgi@yahoo.com.
authors.forename: Ezgi
authors.initials: E
authors.lastname: Güler
authors.forename: Volkan
authors.initials: V
authors.lastname: Vural
authors.forename: Emre
authors.initials: E
authors.lastname: Ünal
authors.forename: Ilgaz Çağatay
authors.initials: IÇ
authors.lastname: Köse
authors.forename: Deniz
authors.initials: D
authors.lastname: Akata
authors.forename: Muşturay
authors.initials: M
authors.lastname: Karcaaltıncaba
authors.forename: Tuncay
authors.initials: T
authors.lastname: Hazırolan
mesh_terms: D017023:Coronary Angiography; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011237:Predictive Value of Tests; D012720:Severity of Illness Index; D015607:Stents; D014057:Tomography, X-Ray Computed