• Journal of the Korean Society of Radiology
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• v.16 no.3
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• pp.203-209
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• 2022

One of the typical methods for lowering radiation dose while maintaining image quality of computed tomography (CT) is the use of model-based iterative reconstruction (MBIR). This study is to evaluate the image quality by adjusting the strength of the advanced modeled iterative reconstruction (ADMIRE), which is well known as a representative model of MBIR. The study was conducted using phantom, and CT images were obtained while adjusting the strength of ADMIRE in units of 1 to 5. Quantitative evaluation includes noise levels using coefficient of variation (COV) and contrast to noise ratio (CNR), as well as natural image quality evaluation (NIQE) and blind/referenceless image spatial quality evaluator (BRISQUE). As a result, in both noise level and blind quality evaluation results, the higher the strength of ADMIRE, the better the results were derived. In particular, it was confirmed that COV and CNR were improved 1.89 and 1.75 times at ADMIRE 5 compared to ADMIRE 1, respectively, and NIQE and BRISQUE were proved to be improved 1.35 and 1.22 times at ADMIRE 5 compared to ADMIRE 1, respectively. In conclusion, this study was proved that the reconstruction strength of ADMIRE had a great influence on the noise level and overall image quality evaluation of CT images.

• KIPS Transactions on Computer and Communication Systems
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• v.12 no.1
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• pp.41-46
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• 2023

Iterative reconstruction of CT takes a long time because projection and back-projection are alternatively repeated until taking a good image. To reduce the reconstruction time, we need a fast algorithm for calculating the projection which is a time-consuming step. In this paper, we proposed a new algorithm to calculate the line integral and the algorithm is approximately 10% faster than the well-known Siddon method (Jacobs version) and has a good image quality. Although the algorithm has been investigated for the case of parallel beams, it can be extended to the case of fan and cone beam geometries in the future.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3153-3155
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• 1999

최근 수년간 의료영상분야는 국내외적으로 급격한 발전을 거듭하고 있다. 특히 자기공명영상장치 (Magnetic Resonance Imaging), X-ray CT(Computed Tomography)와 단층촬영장치는 인체내부를 비침습적(non-invasive)으로 영상화함으로써 해부학적인 질병진단에 많은 장점을 가지고 있다. 이와같은 단층영상 재구성에는 역매트릭스법(matrix inversion). 반복재구성법(interative method), 역투영 법(back-projection), 2차원 Fourier 변환법(2D FFT), 중첩재구성법(Filtered back-projection) 등의 다양한 알고리즘을 사용하고 있다. 본 연구에서는 X-ray CT에서의 단층영상재구성 기법 중 널리 사용되고 있는 Filtered Back Projection 기법의 연산순서도와 연산량을 분석하고 이를 시뮬레이션을 통하여 확인하고 실시간 영상재구성을 위하여 범용 Digital Signal Processor의 병렬처리시스템 구성에 기반된 최적 Architecture를 선정하고자 한다.

• Journal of the Korean Society of Radiology
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• v.13 no.3
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• pp.465-472
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• 2019

To investigate the effects of iterative reconstruction algorithms on fat measurements using computed tomography (CT), we comparatively and quantitatively analyzed the ratios of visceral, subcutaneous, and visceral-subcutaneous fat areas as well as the variations of HU and noise of visceral and subcutaneous fat using ADMIRE strength and attempted to identify any difference between them. Experimental results showed that no statistically significant difference existed among the visceral, subcutaneous, and visceral-subcutaneous fat area ratios HU of visceral fat area and HU of subcutaneous fat area when applying ADMIRE as compared with existing conventional filtered back projection algorithms. However, as the ADMIRE strength increases, the noise of visceral and subcutaneous fat decreases by up to 12.1% and 19.2%, respectively. In conclusion, iterative reconstruction algorithms have no effect on the visceral, subcutaneous, and visceral-subcutaneous fat area ratios, which are indicators of fat measurement using CT.

• Journal of Biomedical Engineering Research
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• v.24 no.5
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• pp.473-480
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• 2003

Iterative reconstruction methods have played a prominent role in emission computed tomography due to their remarkable advantages over the conventional filtered backprojection method. However, since iterative reconstructions typically are comprised of repeatedly projecting and backprojecting the data, the computational load required for reconstructing an image depends highly on the performance of the projector-backprojector pair used in the algorithm. In this work we compare quantitative performance of representative methods for implementing projector-backprojector pairs. To reduce the overall cost for the projection-backprojection operations for each method, we investigate how previously computed results can be reused so that the number of redundant calculations can be minimized. Our experimental results demonstrate that the ray tracing method not only outperforms other methods in computation time, but also provides improved reconstructions with good accuracy.

• Journal of radiological science and technology
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• v.37 no.4
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• pp.323-330
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• 2014

Image reconstruction is one of the most important processes in CT (Computed tomography) technology. For fast scanning and low dose to the objects, iterative reconstruction is becoming more and more important. In the implementation of iterative reconstruction, projection and backprojection processes are considered to be indispensable parts. However, many approaches for projection and backprojection may result severe image artifacts due to their discrete characteristics and affects the reconstructed image quality. Thus, new approaches for projection and backprojection are highly demanded these days. In this paper, distance-driven approach was evaluated and compared with other conventional methods. The numerical simulator was developed to make the phantoms, and projection and backprojection images were compared using these approaches. As a result, it turned out that there are less artifacts during projection and backprojection in parallel and fan beam geometry.

• Journal of the Korean Society of Radiology
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• v.13 no.2
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• pp.159-168
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• 2019

We examined the effect of Siemens ADMIRE (Advanced Modeled Iterative Reconstruction) on image quality by measuring changes in HU, noise, and SNR of background air, fat, muscle, and background signals on a chest CT scan. Experimental results show that as the ADMIRE Strength increases, the noise decreases and the signal increases, consequently the signal-to-noise ratio increases. ADMIRE can reduce noise by 28 ~ 61% compared to FBP, which is a conventional image reconstruction algorithm, and improves SNR by 16 ~ 100%.

• The Korean Journal of Nuclear Medicine Technology
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• v.14 no.1
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• pp.13-17
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• 2010

Purpose: Partial volume effect (PVE) is the phenomenon to lower the accuracy of image due to low estimate, which is to occur from PET/CT 3D image acquisition. The more resolution is declined and the lesion is small, the more it causes a big error. So that it can influence the test result. Studied the optimum image reconstruction method by using variation of parameter, which can influence the PVE. Materials and Methods: It acquires the image in each size spheres which is injected $^{18}F$-FDG to hot site and background in the ratio 4:1 for 10 minutes by using NEMA 2001 IEC phantom in GE Discovey STE 16. The iterative reconstruction is used and gives variety to iteration 2-50 times, subset number 1-56. The analysis's fixed region of interest in detail part of image and compute % difference and signal to noise ratio (SNR) using $SUV_{max}$. Results: It's measured that $SUV_{max}$ of 10 mm spheres, which is changed subset number to 2, 5, 8, 20, 56 in fixed iteration to times, SNR is indicated 0.19, 0.30, 0.40, 0.48, 0.45. As well as each sphere's of total SNR is measured 2.73, 3.38, 3.64, 3.63, 3.38. Conclusion: In iteration 6th to 20th, it indicates similar value in % difference and SNR ($3.47{\pm}0.09$). Over 20th, it increases the phenomenon, which is placed low value on $SUV_{max}$ through the influence of noise. In addition, the identical iteration, it indicates that SNR is high value in 8th to 20th in variation of subset number. Therefore, to reduce partial volume effect of small lesion, it can be declined the partial volume effect in iteration 6 times, subset number 8~20 times, considering reconstruction time.

• Progress in Medical Physics
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• v.26 no.1
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• pp.28-35
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• 2015

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.

• Journal of Korea Multimedia Society
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• v.12 no.3
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• pp.372-382
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• 2009

When the range of projection angles is limited, tomographic reconstruction suffers from artifacts caused by incomplete data. One can consider a data completion technique, which estimates projection data at unobserved angles using a prior knowledge or mathematical exploration, but the result is often not improved; the improvement by the data completion often undermined by the artifacts by inaccurate estimation, In this paper, we propose an iterative method, which computes projection data at unobserved angles by using the current estimate on the image, links the computed projection data to the observed ones by using the consistence condition of Radon transform, and reconstruct the next estimate on the image by filtered backprojection. The proposed method does not require a prior knowledge on the image, and has much faster approximation rate than the expectation maximization method. The performance of the proposed method was tested through several simulation studies.