Prog Med Phys.  2015 Mar;26(1):28-35. 10.14316/pmp.2015.26.1.28.

Effects of Iterative Reconstruction Algorithm, Automatic Exposure Control on Image Quality, and Radiation Dose: Phantom Experiments with Coronary CT Angiography Protocols

• Ha S
• Jung S
• Chang HJ
• Park EA
• Shim H

• KMID: 2315775
• DOI: http://doi.org/10.14316/pmp.2015.26.1.28

Abstract

In this study, we investigated the effects of an iterative reconstruction algorithm and an automatic exposure control (AEC) technique on image quality and radiation dose through phantom experiments with coronary computed tomography (CT) angiography protocols. We scanned the AAPM CT performance phantom using 320 multi-detector-row CT. At the tube voltages of 80, 100, and 120 kVp, the scanning was repeated with two settings of the AEC technique, i.e., with the target standard deviations (SD) values of 33 (the higher tube current) and 44 (the lower tube current). The scanned projection data were reconstructed also in two ways, with the filtered back projection (FBP) and with the iterative reconstruction technique (AIDR-3D). The image quality was evaluated quantitatively with the noise standard deviation, modulation transfer function, and the contrast to noise ratio (CNR). More specifically, we analyzed the influences of selection of a tube voltage and a reconstruction algorithm on tube current modulation and consequently on radiation dose. Reduction of image noise by the iterative reconstruction algorithm compared with the FBP was revealed eminently, especially with the lower tube current protocols, i.e., it was decreased by 46% and 38%, when the AEC was established with the lower dose (the target SD=44) and the higher dose (the target SD=33), respectively. As a side effect of iterative reconstruction, the spatial resolution was decreased by a degree that could not mar the remarkable gains in terms of noise reduction. Consequently, if coronary CT angiogprahy is scanned and reconstructed using both the automatic exposure control and iterative reconstruction techniques, it is anticipated that, in comparison with a conventional acquisition method, image noise can be reduced significantly with slight decrease in spatial resolution, implying clinical advantages of radiation dose reduction, still being faithful to the ALARA principle.

Keyword

Iterative reconstruction; AEC; Low-dose CT; CCTA; Phantom experiment

MeSH Terms

Angiography*
Noise
Tomography, X-Ray Computed

Figure

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  Fig. 1. Region of interest of phantom module. (a) spatial resolution: (a-1) thin wire part, (a-2) qualitative part, (a-3) water part, (b) (b-1) low-contrast part, (b-2) water part.

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  Fig. 2. Comparisons of tube current from AEC was adjusted dose. According to rise 80 kVp to 120 kVp, tube current was increased the tube current in order to adjust the optimal dose.

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  Fig. 3. Tube voltage according to applied AEC was compared with MTF of FBP and AIDR3D algorithm. (a) In MTF of 100% to 50%, the more right side be located, the more image was contained noise. (b) In MTF of 50% to 10%, the more right side be located, the more image was sharp.

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  Fig. 5. Noise rates of automatic exposure control options: (SD44/ SD33, reference: (44/33)≒1.33).

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  Fig. 4. Spatial resolutions of hole pattern with (a). Filtered back projection (FBP) and (b). Iterative reconstruction (AIDR 3D).

Reference

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