Image quality evaluation of a LightSpeed CT750 HD computed tomography system

Abstract

ABSTRACT With the advancement of Computed Tomography technology, improving image quality while reducing patient dose has been a big technical challenge. The recent CT750 HD system from GE Healthcare provides significantly improved spatial resolution and the capability to reduce dose during routine clinical imaging. This paper evaluates the image quality of this system. Spatial resolution, dose reduction, noise, and low contrast detectability have been quantitatively characterized. Results show a quantifiable and visually discernable higher spatial resolution for both body and cardiac scanning modes without compromise of image noise. Further, equivalent image quality performance with up to 50% lower dose has been achieved. Keywords: Computed Tomography (CT), image quality, spatial resolution, MTF, dose, ASIR, noise 1. INTRODUCTION Improving image quality has historically had a big impact on the applications and use of CT imaging. As a medical imaging device, the image quality of the clinical images generated determines the quality of a CT system. Recent advancements in technology have enabled the development of a new generation CT system (LightSpeed CT750 HD - GE Healthcare), which provides significantly improved spatial resolution and the capability to reduce patient radiation dose during routine clinical imaging. It also provides the capability of spectral imaging. Image quality is the key figure of merit to study for an imaging system. This paper evaluates the image quality of a CT750 HD CT system (Fig. 1), with emphasis on the spatial resolution, noise, and low contrast detectability (LCD). The study includes the measurement of high contrast spatial resolution in terms of modulation transfer function (MTF) via the imaging of phantoms and the evaluation of different reconstruction algorithms. It should be noted that not like other approaches, this higher resolution has been achieved without the utilization of post-patient collimation, which is usually associated with large radiation dose penalty. What’s more, this higher resolution can be achieved on whole body scan modes as well as Cardiac scan modes. The Advanced Statistical Iterative Reconstruction (ASIR) technique reduces noise, which allows for higher resolution imaging without the traditional noise increase. The performance of ASIR is evaluated and its effect on image noise and dose reduction is studied, in addition to the analysis of the LCD improvement. Results of the image quality analysis shows a quantifiable and visually discernable higher spatial resolution for both body scanning modes and cardiac scanning modes without compromise of image noise. Further, the image quality results from the study of the ASIR algorithm show equivalent imaging performance with up to 50% lower radiation dose. Note the study of spectral imaging of CT750 HD is not in the scope of this paper, which will be addressed in later publications. This paper is outlined as following. Section 2 describes the methodology used in this study for physical evaluation of key image quality parameters. Section 3 provides the results from different phantoms as well as actual clinical images. Section 4 summarizes the paper with conclusions and discussions.