A high-resolution photon-counting breast CT system with tensor-framelet based iterative image reconstruction for radiation dose reduction

摘要

Both computer simulations and experimental phantom studies were carried out to investigate the radiation dose reduction with tensor framelet based iterative image reconstruction (TFIR) for a dedicated high-resolution spectral breast computed tomography (CT) based on a silicon strip photon-counting detector. The simulation was performed with a 10 cm-diameter water phantom including three contrast materials (polyethylene, 8 mg/ml iodine and B-100 bone-equivalent plastic). In the experimental study, the data were acquired with a 1.3 cm-diameter polymethylmethacrylate (PMMA) phantom containing iodine in three concentrations (8, 16 and 32 mg/ml) at various radiation doses (1.2, 2.4 and 3.6 mGy) and then CT images were reconstructed using filtered-back-projection (FBP) technique and TFIR technique, respectively. The image quality between these two techniques was evaluated by the quantitative analysis on contrast-to-noise ratio (CNR) and spatial resolution that was evaluated using the tasked-based modulation transfer function (MTF). Both simulation and experimental results indicated that the task-based MTF obtained from TFIR reconstruction with one-third of the radiation dose was comparable to that from FBP reconstruction for low contrast target. For high contrast target, TFIR was substantially superior to FBP reconstruction in term of spatial resolution. In addition, TFIR was able to achieve a factor of 1.6 to 1.8 increase in CNR depending on the target contrast level. This study demonstrates that TFIR can reduce the required radiation dose by a factor of two-third for a CT image reconstruction compared to FBP technique. It achieves much better CNR and spatial resolution for high contrast target in addition to retaining similar spatial resolution for low contrast target. This TFIR technique has been implemented with a graphic processing unit (GPU) system and it takes approximately 10 seconds to reconstruct a single-slice CT image, which can be potentially used in a future multi-slit multi-slice (MSMS) spiral CT system.