Objective assessment of low-contrast computed tomography images with iterative reconstruction

• Iterative reconstruction (IR) allows noise reduction in images.
• Object-specific contrast-to-noise ratio (CNRobject) is useful for IR assessment.
• CNRobject could serve as an objective index for IR images.

ObjectiveThis study aims to assess low-contrast image quality using a low-contrast object specific contrast-to-noise ratio (CNRLO) analysis for iterative reconstruction (IR) computed tomography (CT) images.MethodsA phantom composed of low-contrast rods placed in a uniform material was used in this study. Images were reconstructed using filtered back projection (FBP) and IR (Adaptive Iterative Dose Reduction 3D). Scans were performed at six dose levels: 1.0, 1.8, 3.1, 4.6, 7.1 and 13.3 mGy. Objective image quality was assessed by comparing CNRLO with CNR using a human observer test.ResultsCompared with FBP, IR yielded increased CNR at the same dose levels. The results of CNRLO and observer tests showed similarities or only marginal differences between FBP and IR at the same dose levels. The coefficient of determination for CNRLO was significantly better (R2 = 0.86) than that of CNR (R2 = 0.47).ConclusionFor IR, CNRLO could potentially serve as an objective index reflective of a human observer assessment. The results of CNRLO test indicated that the IR algorithm was not superior to FBP in terms of low-contrast detectability at the same radiation doses.