Neural network convolution (NNC) for converting ultra-low-dose to “virtual” high-dose CT images

Abstract

To reduce radiation dose in CT, we developed a novel deep-learning technique, neural network convolution (NNC), for converting ultra-low-dose (ULD) to “virtual” high-dose (HD) CT images with less noise or artifact. NNC is a supervised image-based machine-learning (ML) technique consisting of a neural network regression model. Unlike other typical deep learning, NNC can learn thus output desired images, as opposed to class labels. We trained our NNC with ULDCT (0.1 mSv) and corresponding “teaching” HDCT (5.7 mSv) of an anthropomorphic chest phantom. Once trained, our NNC no longer require HDCT, and it provides “virtual” HDCT where noise and artifact are substantially reduced. To test our NNC, we collected ULDCT (0.1 mSv) of 12 patients with 3 different vendor CT scanners. To determine a dose reduction rate of our NNC, we acquired 6 CT scans of the anthropomorphic chest phantom at 6 different radiation doses (0.1–3.0 mSv). Our NNC reduced noise and streak artifacts in ULDCT substantially, while maintaining anatomic structures and pathologies such as vessels and nodules. With our NNC, the image quality of ULDCT (0.1 mSv) images was improved at the level equivalent to 1.1 mSv CT images, which corresponds to 91% dose reduction.