Low Dose CT Perfusion With K-Space Weighted Image Average (KWIA).

Chenyang Zhao,Xingfeng Shao,Vinay Duddalwar,Jeffry R Alger,Danny J J Wang,Thomas Martin

doi:10.1109/tmi.2020.3006461

Abstract

CTP (Computed Tomography Perfusion) is widely used in clinical practice for the evaluation of cerebrovascular disorders. However, CTP involves high radiation dose (≥ ~200mGy) as the X-ray source remains continuously on during the passage of contrast media. The purpose of this study is to present a low dose CTP technique termed K-space Weighted Image Average (KWIA) using a novel projection view-shared averaging algorithm with reduced tube current. KWIA takes advantage of k-space signal property that the image contrast is primarily determined by the k-space center with low spatial frequencies and over-sampled projections. KWIA divides each 2D Fourier transform (FT) or k-space CTP data into multiple rings. The outer rings are averaged with neighboring time frames to achieve adequate signal-to-noiseratio (SNR), while the center region of k-space remains unchanged to preserve high temporal resolution. Reduced dose sinogram data were simulated by adding Poisson distributed noise with zero mean on digital phantom and clinical CTP scans. A physical CTP phantom study was also performed with different X-ray tube currents. The sinogram data with simulated and real low doses were then reconstructed with KWIA, and compared with those reconstructed by standard filtered back projection (FBP) and simultaneous algebraic reconstruction with regularization of total variation (SART-TV). Evaluation of image quality and perfusion metrics using parameters including SNR, CNR (contrast-to-noise ratio), AUC (area-under-the-curve), and CBF (cerebral blood flow) demonstrated that KWIA is able to preserve the image quality, spatial and temporal resolution, as well as the accuracy of perfusion quantification of CTP scans with considerable (50–75%) dose-savings.

Highlights

C OMPUTED Tomography Perfusion (CTP) of the brain is a widely used imaging technique that provides assessments of regional blood supply, and hemodynamic information to distinguish the ischemic core from penumbral tissue, helping with decision making for recanalization therapy in cerebral ischemia [1]–[4]
The purpose of this study is to introduce a variant of the K-space Weighted Image Contrast (KWIC) algorithm termed k-space weighted image average (KWIA) that preserves high spatial and temporal resolutions as well as image quality of low-dose CTP data (50-75% dose reduction), yielding images comparable to those of standard CTP scans
The insets show two zoomed ROIs to highlight the signal-to-noise ratio (SNR) changes. In these two ROIs, it can be seen that the SNR was degraded in 50% and 25% dose images compared to full dose images, which was recovered by K-space Weighted Image Average (KWIA) reconstruction

Summary

Introduction

C OMPUTED Tomography Perfusion (CTP) of the brain is a widely used imaging technique that provides assessments of regional blood supply, and hemodynamic information to distinguish the ischemic core from penumbral tissue, helping with decision making for recanalization therapy in cerebral ischemia [1]–[4]. In a typical CTP scan, a dataset of time-resolved CT images is acquired over the scan duration (∼ 1 min) to track the passage of the contrast bolus through the intracranial vasculature. The repeated CT scans that are performed on the same brain region during the passage of a contrast bolus resulting in a high radiation dose to patients. With a typical clinical setting of CTP scan acquisition parameters using a tube voltage of 80 keV, tube current of 150 mAs, and temporal sampling rate of 1 image/2s according to the ALARA (As Low As Reasonably Achievable) principle, the resultant dose can be about 200 mGy which is approximately 3 times higher than that of a standard head CT [6].

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