• The Korean Journal of Nuclear Medicine Technology
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• v.17 no.2
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• pp.72-77
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• 2013

Purpose: Whole-body PET using radiopharmaceutical is one of the imaging study methods for physiological changes of body. High specificity of the PET-CT examination is used to detect an early stages of cancer and metastatic cancer by imaging a physiological changes. During the imaging process, PET image has been characterized by a relatively low image quality due to its low sensitivity and the acquisition of random and scatter coincidences as well as patients figure. Therefore, the image quality as the changes of the acquisition times of patient weight was evaluated in this study. Materials and Methods: Thirty patients who presented to our hospital were enrolled. They were divided to normal, overweight, and obese group using BMI index, respectively. The patients with a liver disease and diabetes were excluded. $^{18}F-FDG$ was administered to the patients as 5.2 MBq per kg. After an hour from an injection, image acquisition was obtained as List mode in a part of liver in 1 bed. SNR (signal-to-noise ratio) of each groups acquisition times were confirmed from the calculated radiation counts and random fractions. The statistical significance of three groups was confirmed through one-way ANOVA test. On the basis of the counts of 2 minutes on normal group, the SNR of overweight group and obese group were compared. Results: The SNR were increased with loger aquisition time in 3 groups. In the condition of same acquisition time, the SNR had a statistical significance (P<0.05). The SNR were decreased to the normal, overweight, and obese, respectively. Liver activity had no significance difference on each group and RF had the significance differences (P<0.05). On the basis of the counts of 2 minutes on normal group, there were no statistical significance in a three minute acquisitions of overweight group and two minute acquisitions of obese group (P=0.150). Conclusion: In this study, the administrated amount of radiation dose did not adjust as the change of the patients weight. Increasing the acquisition time when the administration of the same amount of dose was able to get a good result of SNR. When the Based 2 minute on normal group, if overweight and obese case the increased acquisition time of 3 minute was able to obtain a similar SNR. On the basis of the normal group, the acquisition times of overweight and obese group were increased to 3 minutes per bed and the SNR were similar to the normal group.

• Progress in Medical Physics
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• v.15 no.1
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• pp.54-58
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• 2004

The aim of this study was to develop special birdcage resonators for small objects including the human wrist, hand and small animals, using 3T MRI/MRS. Before substantial development, different types of parameters were arranged, based on theoretical analysis, through lumped element transmission line theory. The primary analysis was peformed with a network analyzer (HP 4195A) and the final experimental analysis was carried out with 3T MRI (Medinus, Korea). The manufactured birdcage resonator is typically composed of 12-element structures to which a low-pass filter is fundamentally applied. The diameter and length of each element of the birdcage resonator were as follows: (1) diameter 12 cm, length of element 22 cm, (2) diameter 15 cm, length of element 22 cm, and (2) diameter 17 cm, length of element 25 cm. Copper tape with a width of 1 cm was used for the coils. MRI acquisition parameters were TR=500 ms, TE=17 ms, and Ave=2 for T1-WT images, and TR=4,000 ms, TE=96 ms, and Ave=2 for T2-WT images. The ratio of the samples diameter to the birdcage resonators diameter was approximately 55%, 63% and 70%, respectively, for the three elements. This study determined that the best image quality and S/N ratio were obtained when the ratio of the object's diameter was approximately 50∼80%. A general theoretical analysis of the birdcage coil differs in many respects from the experimental results which were influenced by many factors that were not considering when the general theoretical analysis of the birdcage coil was peformed. The induced resistance may be considered as part of the resistive loss if the quantitative value can be determined using a radiation resistance approach.

• Journal of radiological science and technology
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• v.40 no.3
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• pp.393-400
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• 2017

The purpose of this study is to suggest a method to reduce the dose by Analyzing the dose area product (DAP) and image quality according to the change of tube current using NEMA Phantom. The spatial resolution and low contrast resolution were used as evaluation criteria in addition to signal to noise ratio (SNR) and contrast to noise ratio (CNR), which are important image quality parameters of intervention. Tube voltage was fixed at 80 kVp and the amount of tube current was changed to 20, 30, 40, and 50 mAs, and the dose area product and image quality were compared and analyzed. As a result, the dose area product increased from $1066mGycm^2$ to $6160mGycm^2$ to 6 times as the condition increased, while the spatial resolution and low contrast resolution were higher than 20 mAs and 30 mAs, Spatial resolution and low contrast resolution were observed below the evaluation criteria. In addition, the SNR and CNR increased up to 30 mAs, slightly increased at 40 mAs, but not significantly different from the previous one, and decreased at 50 mAs. As a result, the exposure dose significantly increased due to overexposure of the test conditions and the image quality deteriorated in all areas of spatial resolution, low contrast resolution, SNR and CNR.

• The Journal of the Acoustical Society of Korea
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• v.8 no.4
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• pp.44-52
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• 1989

The UCERSS (Unit Circle Eigendecomposition Rational Signal Subspace) algorithm has extended MUSIC (MUltiple Signal Classification ) by using eigendecomposition on the unit circle in order to estimate incident angles of multiple wide band signals. The purpose of this thesis is to further extend the UCERSS to be able to estimate the direction of arrivals of multiple wide band signals in very low SNR . The wide band ESPRIT (Estimation of Signal Parameter via Rotational Invariance Technique) uses covariance difference matrices to reduce noise components. In this paper the wide band ESPRIT which combines the ideas of UCERSS and ESPRIT Is proposed. Computer simulation results Indicate that the performances of the proposed approaches are superior to those of the UCERSS in very low SNR.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2
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• pp.50-59
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• 1994

This paper presents a speech recognition method utilizing third-order cumulants as a feature vector and a neural network for recognition. The use of higher-order cumulants provides desirable uncoupling between the gaussian noise and speech, which enables us to estimate the coefficients of AR model without bias. Unlike the conventional method using second-order statistics, the proposed one exhibits low bias even in SNR as low as 0 dB at the expense of higher variance. It is confirmed through computer simulation that recognition rate of korean single-vowels with the cumulant-based method is much higher than the results with the conventional method even in low SNR.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.11-19
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• 2021

In this paper, we propose a non-orthogonal multiple access (NOMA) method based on channel alignment to simultaneously transmit multiple unicast and multicast streams in frequency-efficient manner. In this method, all receivers in a multicast cluster use the receive beamforming vectors that align their channels, and the base station uses the aligned channel information to design the transmit beamforming vectors that eliminate interference between multicast clusters. Using the effective receive channel information combined with the transmit beamforming vectors, unicast receivers design their own receive beamforming vectors that eliminate interference between unicast receivers. Since the proposed method effectively eliminates the interference, it achieves a higher sum rate than the existing orthogonal multiple access (OMA) method in high SNR regions. In addition, we present a hybrid method that exploits the benefits of the proposed NOMA method and the existing OMA method. Depending on the channel state, the hybrid method adaptively employs the existing OMA method, which improves the received signal power, in low SNR regions and the proposed NOMA method, which effectively eliminates the interference, in high SNR regions, thereby achieving a good sum rate over the entire SNR region.

• Journal of Korea Multimedia Society
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• v.20 no.8
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• pp.1258-1270
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• 2017

'Semantic gap' has been a year-old problem in automatic video summarization, which refers to the gap between semantics implied in video summarization algorithms and what people actually infer from watching videos. Using the external EEG bio-feedback obtained from video watchers as a solution of this semantic gap problem has several another issues: First, how to define and measure noises against ERP waveforms as signals. Second, whether individual differences among subjects in terms of noise and SNR for conventional ERP studies using still images captured from videos are the same with those differently conceptualized and measured from videos. Third, whether individual differences of subjects by noise and SNR levels help to detect topic-irrelevant shots as signals which are not matched with subject's own semantic topical expectations (mis-match negativity at around 400m after stimulus on-sets). The result of repeated measures ANOVA test clearly shows a 2-way interaction effect between topic-relevance and noise level, implying that subjects of low noise level for video watching session are sensitive to topic-irrelevant visual shots, while showing another 3-way interaction among topic-relevance, noise and SNR levels, implying that subjects of high noise level are sensitive to topic-irrelevant visual shots only if they are of low SNR level.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.465-468
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• 2005

MMA(Multi-Modulus Algorithm) is inferior at a initial equalization in high ISI(intersymbol interference), because it is the inaccurate decision. To improve this probel SMMA(Sliced Multi-Modulus Algorithm) is based on using the MCMA(Modified Constant Modulus Algorithm). SMMA is a improved capability than MMA in high SNR but is inaccurate decision in low SNR. In this paper, We propose some multi-modulus blind equalization algorithm scheme. It is a method of operation in some multi-modulus algorithm which does no obstruct a convergence property at the initial equalization in the low SNR. Proposed algorithm improves the steady-state performance. And it uses residual ISI of the equalizer output in order to decide the optimum switching time between the single modulus and the multi-modulus algorithm.

• IEMEK Journal of Embedded Systems and Applications
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• v.4 no.4
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• pp.195-200
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• 2009

As 4G mobile communication systems require high transmission rates with reliability, the need for efficient error correcting code is increasing. In this paper, a novel LDPC (Low Density Parity Check) decoder is introduced. The LDPC code is one of the most popular error correcting codes. In order to improve performance of the LDPC decoder, we use SNR (Signal-to-Noise Ratio) estimation results to adjust coefficients of modified UMP-BP (Uniformly Most Probable Belief Propagation) algorithm which is one of widely-used LDPC decoding algorithms. An advantage of Modified UMP-BP is that it is amenable to implement in hardware. We generate the optimal values by simulation for various SNRs and coefficients, and the values are stored in a look-up table. The proposed decoder decides coefficients of the modified UMP-BP based on SNR information. The simulation results show that the BER (Bit Error Rate) performance of the proposed LDPC decoder is better than an LDPC decoder using a conventional modified UMP-BP.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.8A
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• pp.1259-1264
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• 1999

In this paper, the High-speed, Low-power Analog-Digital Conversion Archecture is porposed using the Pipelined archecture for High-speed conversion rate and the Successive-Approximation archecture for Low-power consumption. This archecture is the Successive-Approximation archecture using Pipelined Comparator array to change reference voltage during Holding Time. The Analog-to-Digital Converter for video processing is designed using 0.8${\mu}{\textrm}{m}$ CMOS tchnology. When an 6-bit 10MS/s Analog-to-Digital Converter is simulatined, the INL/DNL errors are $\pm$0.5/$\pm$1, respectively. The SNR is 37dB at a sampling rate of 10MHz with 100KHz sine input signal. The power consumption is 1.46mW at 10MS/s. When an 8-bit 10MS/s Analog-to Digital Converter is simulatined, the INL/DNL errors are $\pm$0.5/$\pm$1, respectively. The SNR is 41dB at a sampling rate of 100MHz with 100KHz sine input signal. The power consumption is 4.14m W at 10MS/s.