Comparison of adaptive statistical iterative and filtered back projection reconstruction techniques in brain CT☆
Introduction
There has been several image reconstruction algorithms developed since the introduction of computed tomography (CT) technique. Until recently, the Filtered Back Projection (FBP) reconstruction technique was considered as the standard CT imaging reconstruction algorithm due to its short reconstruction times that despite some disadvantages most noticeably the image noise. This reconstruction technique is based on direct inversion of Radon transform [1]. Although the use of ramp filter in FBP removes blurring from the back projection step [2], the limited number of projection sets introduces streak artifacts [3] in the image reconstructions. A different algorithm, namely, the iterative reconstruction algorithm was investigated in order to reduce image noise among other things. The Algebraic Reconstruction Technique (ART) was one of the first iterative reconstruction algorithm used in the commercial clinical CT scanner [1]. However, earlier versions of iterative reconstruction algorithms were complex and required a lot of computational power, and were not widely used in clinical applications.
Adaptive statistical iterative reconstruction (ASIR) algorithm which was introduced in 2009 has caught more and more radiologists’ attention as a newly developed technique with its ability to produce real time images in clinical practice. In contrast to FBP, ASIR takes into account precise modeling of the X-ray photon statistics and electronic noise, all of which are less accurate in FBP [4]. To decrease reconstruction time, ASIR utilizes the information contained in the FBP-reconstruction image as an initial ‘building block’ in the reconstruction process [5]. By partially correcting for the fluctuations in projection measurement due to limited photon statistics, ASIR enables a time-efficient reduction in the pixel variance that is statistically unlikely to be representative of anatomic features, with essentially no trade-off in spatial resolution. In a recent study, Hara et al. thought ASIR was similar to the FBP in terms of spatial resolution [6].
It was reported that ASIR can better reduce image noise, radiation dose and improve diagnostic confidence than FBP reconstruction technique in abdominal, lung, coronary artery and colon CT studies [4], [7], [8], [9], but no articles were found in brain CT about ASIR. For this purpose, we conducted this study to investigate whether ASIR algorithm can improve the image quality and reduce radiation dose in brain CT scanning.
Section snippets
Patient selection
This prospective clinical study was compliant with the guidelines of the Health Insurance Portability and Accountability Act (HIPAA). All patients received written informed consent.
The study included forty patients who underwent brain CT examinations between April 2011 and June 2011. The forty patients were divided into four groups according to their ages (group A, 50–59; group B, 60–69; group C, 70–79; group D, 80–). Brain CT examinations were ordered by attending physicians for patients with
Objective image quality measurements
Statistical results of the objective image quality measurements were summarized in Table 1. There were no statistically significant differences between the MSD of the four age groups with same reconstruction technique (p > .05). The MSD decreased with increasing percentage of ASIR at each level of tube current–time product (mAs); the difference between FBP and 30% ASIR blending at each level of mAs had no statistical significance (p > .05). In addition, there was no statistically significant
Discussion
Since the first commercial clinical computer tomographic (CT) scanner was born, it has played a more and more important role in clinical practice, especially nowadays with its substantial improvements over the recent decades. But the average medical radiation effective dose (ED) to the U.S. population in 2006 was estimated at approximately 3.0 mSv, an increase of 600% in a single generation [12]. The growing use of imaging procedures in the United States has raised concerns about exposure to
Conflict of interest
We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript.
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Sources of funding: Supported by Science and Technology Commission Foundation of Shanghai (No. 10411952600).