Task-Based Image Quality Assessment Comparing Classical and Iterative Cone Beam CT Images on Halcyon®

Abstract

Background: Despite the development of iterative reconstruction (IR) in diagnostic imaging, CBCT are generally reconstructed with filtered back projection (FBP) in radiotherapy. Varian medical systems, recently released with their latest Halcyon® V2.0 accelerator, a new IR algorithm for CBCT reconstruction. Purpose: To assess the image quality of radiotherapy CBCT images reconstructed with FBP and an IR algorithm. Methods: Three CBCT acquisition modes (head, thorax and pelvis large) available on a Halcyon® were assessed. Five acquisitions were performed for all modes on an image quality phantom and reconstructed with FBP and IR. Task-based image quality assessment was performed with noise power spectrum (NPS), task-based transfer function (TTF) and detectability index (d’). To illustrate the image quality obtained with both reconstruction types, CBCT acquisitions were made on 6 patients. Results: The noise magnitude and the spatial frequency of the NPS peak was lower with IR than with FBP for all modes. For all low and high-contrast inserts, the values for TTF at 50% were higher with IR than with FBP. For all inserts and all modes, the contrast values were similar with FBP and IR. For all low and high-contrast simulated lesions, d’ values were higher with IR than with FBP for all modes. These results were also found on the 6 patients where the images were less noisy but smoother with IR-CBCT. Conclusions: Using the IR algorithm for CBCT images in radiotherapy improve image quality and thus could increase the accuracy of online registration and limit positioning errors during processing.

Novel Detector Configurations in Cone-Beam CT Systems: A Simulation Study

“…On the other hand, OSEM represents a speedup version of the expectation-maximization maximum likelihood (EMML) algorithm [39] that assumes that acquired data follow a Poisson statistic. Iterative algorithms in general produce images with better CNR or SNR values and with improved spatial resolution, free from the artifacts of analytical reconstruction [40]. To succeed with this, iterative methods usually rely on a linear relation between acquired data y and image x, according to the following equation:…”