Deep learning enabled ultra-fast-pitch acquisition in clinical X-ray Computed Tomography.

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Abstract

In x-ray Computed Tomography (CT), many important clinical applications may benefit from a fast acquisition speed. Helical scan is the most widely used acquisition mode in clinical CT, where a fast helical pitch can improve the acquisition speed. However, on a typical single-source CT (SSCT) system, the helical pitch p typically cannot exceed 1.5; otherwise, reconstruction artifacts will result from data insufficiency. The purpose of this work is to develop a deep convolutional neural network to correct for artifacts caused by an ultra-fast pitch, which can enable faster acquisition speed than what is currently achievable.A customized convolutional neural network (denoted as UFP-net) was developed to restore the underlying anatomical structure from the artifact-corrupted post-reconstruction data acquired from SSCT with ultra-fast pitch (i.e. p ≥ 2). UFP-net employed residual learning to capture the features of image artifacts. UFP-net further deployed in-house-customized functional blocks with spatial-domain local operators and frequency-domain non-local operators, to explore multi-scale feature representation. Images of contrast-enhanced patient exams (n = 83) with routine pitch setting (i.e. p < 1) were retrospectively collected, which were used as training and testing datasets. This patient cohort involved CT exams over different scan range of anatomy (chest, abdomen and pelvis) and CT systems (Siemens Definition, Definition Flash, Definition AS+, Siemens Healthcare, Inc.), and the corresponding base CT scanning protocols used consistent settings of major scan parameters (e.g. collimation and pitch). Forward projection of the original images was calculated to synthesize helical CT scans with one regular pitch setting (p = 1) and two ultra-fast-pitch setting (p = 2, and 3). All patient images were reconstructed using standard filtered-back-projection (FBP) algorithm. A customized multi-stage training scheme was developed to incrementally optimize the parameters of UFP-net, using ultra-fast-pitch images as network inputs and regular pitch images as labels. Visual inspection was conducted to evaluate image quality. Structural similarity index (SSIM) and relative root-mean-square-error (rRMSE) were used as quantitative quality metrics.The UFP-net dramatically improved image quality over standard FBP at both ultra-fast-pitch settings. At p = 2, UFP-net yielded higher mean SSIM (>0.98) with lower mean rRMSE (<2.9%), compared to FBP (mean SSIM <0.93; mean rRMSE > 9.1%). Quantitative metrics at p = 3: UFP-net – mean SSIM [0.86, 0.94], and mean rRMSE [5.0%, 8.2%]; FBP – mean SSIM [0.36, 0.61], and mean rRMSE [36.0%, 58.6%].The proposed UFP-net has the potential to enable ultra-fast data acquisition in clinical CT without sacrificing image quality. This method has demonstrated reasonable generalizability over different body parts, when the corresponding CT exams involved consistent base scan parameters. This article is protected by copyright. All rights reserved.This article is protected by copyright. All rights reserved.