SummaryThe purpose of this study was to evaluate the effect of an iterative reconstruction method (IR) on shape reproducibility in three-dimensional (3D) computed tomography images. We used an IR (sinogram-affirmed iterative reconstruction: SAFIRE) implemented in a 64-channel multi slice computed tomography system (Siemens, SOMATOM Definition AS). We scanned a simulated vessel phantom with 180-HU vessel contrast at various radiation doses and reconstructed axial images of filtered back projection (FBP) and SAFIRE. Then we reconstructed multi-planar reconstruction (MPR) and volume rendering (VR) images from the axial images. Roundness was evaluated from MPR images and vessel surface roughness was evaluated from pixel value profiles of a vessel in VR images and visual evaluation by radiological technologists. In comparison on equivalent dose, the roundness and roughness were improved with increase of SAFIRE strength level. However, in comparison on equivalent noise (standard deviation: SD) of axial images, SAFIRE strength levels of 2 to 5 were significantly inferior to FBP (p<0.05). SAFIRE strength of 1 with a dose reduction of 19% maintained the shape reproducibility in all evaluations. Therefore, it would be not appropriate to use the SD of axial image as index for the dose reduction rate determination of 3D-CT images.
SummaryIterative reconstruction methods can reduce the noise of computed tomography (CT) images, which are expected to contribute to the reduction of patient dose CT examinations. The purpose of this study was to investigate impact of an iterative reconstruction method (iDose 4 , Philips Healthcare) on vessel visibility in coronary CT angiography (CTA) by using phantom studies. A simulated phantom was scanned by a CT system (iCT, Philips Healthcare), and the axial images were reconstructed by filtered back projection (FBP) and given a level of 1 to 7 (L1-L7) of the iterative reconstruction (IR). The vessel visibility was evaluated by a quantitative analysis using profiles across a 1.5-mm diameter simulated vessel as well as visual evaluation for multi planar reformation (MPR) images and volume rendering (VR) images in terms of the normalized-rank method with analysis of variance. The peak CT value of the profiles decreased with IR level and full width at half maximum of the profile also decreased with the IR level. For normalized-rank method, there was no statistical difference between FBP and L1 (20% dose reduction) for both MPR and VR images. The IR levels higher than L1 sacrificed the spatial resolution for the 1.5-mm simulated vessel, and their visual vessel visibilities were significantly inferior to that of the FBP.
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