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. 2016 Feb 9:4:e1680.
doi: 10.7717/peerj.1680. eCollection 2016.

Four-dimensional noise reduction using the time series of medical computed tomography datasets with short interval times: a static-phantom study

Tatsuya Nishii  1 , Atsushi K Kono  1 , Wakiko Tani  2 , Erina Suehiro  2 , Noriyuki Negi  2 , Satoru Takahashi  1 , Kazuro Sugimura  1
Affiliations

Four-dimensional noise reduction using the time series of medical computed tomography datasets with short interval times: a static-phantom study

Tatsuya Nishii et al. PeerJ. .

Abstract

Backgrounds. This study examines the hypothesis that four-dimensional noise reduction (4DNR) with short interval times reduces noise in cardiac computed tomography (CCT) using "padding" phases. Furthermore, the capability of reducing the reduction dose in CCT using this post-processing technique was assessed. Methods. Using base and quarter radiation doses for CCT (456 and 114 mAs/rot with 120 kVp), a static phantom was scanned ten times with retrospective electrocardiogram gating, and 4DNR with short interval times (50 ms) was performed using a post-processing technique. Differences in the computed tomography (CT) attenuation, contrast-to-noise ratio (CNR) and spatial resolution with modulation transfer function in each dose image obtained with and without 4DNR were assessed by conducting a Tukey-Kramer's test and non-inferiority test. Results. For the base dose, by using 4DNR, the CNR was improved from 1.18 ± 0.15 to 2.08 ± 0.20 (P = 0.001), while the CT attenuation and spatial resolution of the image of 4DNR did not were significantly inferior to those of reference image (P < 0.001). CNRs of the quarter-dose image in 4DNR also improved to 1.28 ± 0.11, and were not inferior to those of the non-4DNR images of the base dose (P < 0.001). Conclusions. 4DNR with short interval times significantly reduced noise. Furthermore, applying this method to CCT would have the potential of reducing the radiation dose by 75%, while maintaining a similar image noise level.

Keywords: Cardiac CT; Computed tomography; Image quality; Radiation dose; Temporal noise reduction.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. The relationship with contrast noise ratio and interval times for legato.
Legato, the method of obtaining a noisele ss imag e by a daptive phase-shifted to pological coherence analysis.
Figure 2
Figure 2. Reference and legato images.
The original images obtained by filtered back projection (FBP) with reference dose (A), iterative reconstruction (IR) with reference dose (B), and IR with quarter radiation dose (C) are shown in upper column. By using legato, the image noise levels are significantly improved in images of FBP with reference dose (D), IR with reference dose (E), and IR with quarter radiation dose (F). Legato, the method of obtaining a noisele ss imag e by a daptive phase-shifted to pological coherence analysis.
Figure 3
Figure 3. Box plots of the contrast-noise ratio (CNR) and image noise.
Significant improvements in the CNRs of the images obtained by filtered back projection (FBP) (A), iterative reconstruction (IR) (B), quarter dose image-acquisition (C), were achieved using legato. Significant noise reduction of the in-vivo image with quarter dose (D), were also achieved using legato. Legato, the method of obtaining a noisele ss imag e by a daptive phase-shifted to pological coherence analysis.
Figure 4
Figure 4. Results of modulation transfer function (MTF) analyses and noise power spectrum (NPS) analysis.
The MTF curve (A) was almost the same for the image processed with legato (black line) and the reference image not processed with legato (gray dot line). The NPS curve (B) of the legato image (black line) shows the uniform reduction in noise throughout the frequency band relative to the noise level in the reference image (gray dot line). Legato, the method of obtaining a noisele ss imag e by a daptive phase-shifted to pological coherence analysis.
Figure 5
Figure 5. Representative images of in-vivo study.
Representative clinical images are shown; from the left, a quarter-radiation-dose image (systolic phase) without legato post processing (A), a quarter-radiation-dose image (systolic phase) with legato post processing (B), and a reference-dose image without legato post processing (C). Legato, the method of obtaining a noisele ss imag e by a daptive phase-shifted to pological coherence analysis.
See this image and copyright information in PMC

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