Quality evaluation of image‐based iterative reconstruction for CT: Comparison with hybrid iterative reconstruction

: The purpose of this study is to evaluate the physical image quality of a commercially available image-based iterative reconstruction (IIR) system for two object contrasts to resemble a soft tissue (60 HU) and an enhanced vessel (270 HU), and compare the results with those of filtered back projection (FBP) and iterative reconstruction (IR). A 192-slice computed tomography (CT) scanner was used for data acquisitions. IIR images were processed from the FBP images. Task-based in-plane transfer function (TTF) and slice sensitivity profile (SSPtask ) were measured from rod objects inside of a 25-cm diameter water phantom at four dose levels (2.5, 5, 10, and 20 mGy). Noise power spectrum (NPS) was measured from the water-only part. System performance (SP) function was calculated as TTF2 /NPS over FBP, IR, and IIR for comparison. In addition, an image subtraction was performed using images of rod objects, a bar-pattern phantom, and a clinical abdomen case to observe the noise reduction performance of IIR. As a results, IIR mostly preserved TTF and SSPtask of FBP, whereas IR exhibited enhanced TTF at 10 and 20 mGy for 60 HU contrast and at all doses for 270 HU contrast. SP of IIR at 2.5, 5, 10 mGy (half doses) were similar to those of FBP at 5, 10, 20 mGy, respectively. IR exhibited enhanced SP at medium to high frequencies. The subtracted images showed weak remained edge signals in the bar-pattern and abdominal images. In conclusion, IIR uniformly improved the task-based image quality of FBP over the entire frequency range, whereas IR improved the characteristics over medium to high frequencies. The dose reduction potential of IIR estimated from SP is approximately 50%, when allowing the slight signal reductions.