• Investigative Magnetic Resonance Imaging
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• v.20 no.4
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• pp.207-214
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• 2016

Purpose: The purpose of this study was to investigate the effect of the number of measurement points on the calculation of transverse relaxation time (T2) with a focus on muscle T2. Materials and Methods: This study assumed that muscle T2 was comprised of a single component. Two phantom types were measured, 1 each for long ("phantom") and short T2 ("polyvinyl alcohol gel"). Right calf muscle T2 measurements were conducted in 9 healthy male volunteers using multiple-spin-echo magnetic resonance imaging. For phantoms and muscle (medial gastrocnemius), 5 regions of interests were selected. All region of interest values were expressed as the mean ${\pm}$ standard deviation. The T2 effective signal-ratio characteristics were used as an index to evaluate the magnetic resonance image quality for the calculation of T2 from T2-weighted images. The T2 accuracy was evaluated to determine the T2 reproducibility and the goodness-of-fit from the probability Q. Results: For the phantom and polyvinyl alcohol gel, the standard deviation of the magnetic resonance image signal at each echo time was narrow and mono-exponential, which caused large variations in the muscle T2 decay curves. The T2 effective signal-ratio change varied with T2, with the greatest decreases apparent for a short T2. There were no significant differences in T2 reproducibility when > 3 measurement points were used. There were no significant differences in goodness-of-fit when > 6 measurement points were used. Although the measurement point evaluations were stable when > 3 measurement points were used, calculation of T2 using 4 measurement points had the highest accuracy according to the goodness-of-fit. Even if the number of measurement points was increased, there was little improvement in the probability Q. Conclusion: Four measurement points gave excellent reproducibility and goodness-of-fit when muscle T2 was considered mono-exponential.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.6
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• pp.153-157
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• 2008

Recently, electronic devices is produced by multilayer structure, therefore analysis for hidden layers is important nondestructive inspection. This paper presents visibility enhancement methods for the ultrasonic multiple echoes reflected from adhesive layer in the multilayers using digital signal processing. The reflected signals from the multilayers come out interval of the peaks in the power cepstrum. In the experiment, the adhesive layers of settled thickness using epoxy were formed. The reflected signals from the multilayer is detected by pulse-echo method and power cepstrum is processed for enhancement of visibility.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.05b
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• pp.1485-1488
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• 2003

IEEE 802.11 무선 랜 환경에서 멀티미디어 트래픽이 효과적으로 전송퇴기 위해서는 정해진 딜레이 바운드내에서 전송이 완료되어야 한다 대표적인 멀티미디어 트래픽인 음성신호를 전송할 때의 단방향 딜레이 바운드는 echo canceller를 쓰지 않았을 경우 $25ms{\sim}30ms$ 이다. 딜레이 바운드를 지키지 못하고 전송된다면 시간에 민감한 음성신호의 특성 때문에 음성품질이 유지되지 않을 뿐만 아니라 채널의 혼잡을 유발하게 된다. 본 논문에서는 음성의 품질이 보장되는 기준을 95%이상의 패킷이 성공적으로 전달되는 경우로 제한하여 음성의 딜레이 바운드에 관한 분석을 시도하였다. 이를 위해 음성패킷이 drop될 확률을 수학적인 분석을 통해 유도하고 시뮬레이션을 통한 검증을 시도하였다. 시뮬레이션에서는 IEEE 802.11의 두 가지 기본적인 MAC(Multiple Access Control) 프로토콜인 DCF와 PCF를 사용해서 음성신호를 전송할 때 딜레이 바운드를 지키지 못하는 음성 패킷을 사전에 drop 시킴으로써 몇 개의 음성 노드가 손실율 5% 이내 (음성의 품질이 유지되는 한계)를 만족시키는지를 음성신호를 발생시키는 STA 수와 손실율의 관계를 통해 알아보았다.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.166-166
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• 2001

목적： 척수의 질환에 대한 확산강조영상 소견에 대하여 알아본다. 대상 및 방법： 임상적으로 진단된 척수질환 환자 8명을 (acute transverse myelitis (n=3), spinal dural AV fistula (n=2), multiple sclerosis (n=1), spinal cord tumor (n=2)) 대상으로 하였다. 영상은 Philips Intera 1.5 T system을 이용하였고, multishot spin echo EPI 펄스열 및 EKG gating을 이용하여 영상을 얻었다. 3R-R 간격으로 영상을 얻었으며 TE=72msec, FOV=25cm, 256 matrix, 5mm thickness, b value=400으로 영상매개변수를 정하였다. 척수 중심으로 3개의 절편을 얻었으며 T2 강조 영상과 겉보기확산계수 영상을 같이 구하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.242-247
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• 2009

The ability of time reversal techniques to focus ultrasonic beams on the source location is important in many aspects of ultrasonic nondestructive evaluation. In this paper, we investigate the time reversal beam focusing of ultrasonic array sensors on a defect in layered media. Numerical modeling is performed using the commercially available software which employs a time domain finite difference method. Two different time reversal approaches are considered - the through transmission and the pulse-echo. Linear array sensors composed of N elements of line sources are used for signal reception/excitation, time reversal, and reemission in time reversal processes associated with the scattering source of a side-drilled hole located in the second layer of two layer structure. The simulation results demonstrate the time reversal focusing even with multiple reflections from the interface of layered structure. We examine the focusing resolution that is related to the propagation distance, the size of array sensor and the wavelength.

• Journal of Veterinary Clinics
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• v.13 no.1
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• pp.87-92
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• 1996

A hemangiosarcoma in a 30 kg, 6-year-old German Shepherd dog showing signs of abdominal distension, anorexia and depression was diagnosed with clinicopathologic examination, abdominal radiographs and ultrasonographic assessmint. In abdominal radiographs, overall abdominal distension was seen. Stomach and some parts of small intestines were deviated caudo-ventrally by enlarged liver. The splenomegaly was also identified and descending colon was dislocated laterally by splenic mass. In ultrasonographic findings, abdominal fluid was identified. Hepatomegaly was seen and it was consisted of multiple, anechoic cysts. The spleen was enlarged and a large round mass with mixed echo pattern at the mid to tail portion of spleen was identified. Grossly, at necropsy, multi-sized cysts in which contained blood and fibrpus materials and some blood were seen in the cross section and it showed hard consistency. Also, lots of small red tumor nodules were dispersed on the serosal surface of the bladder, omentum, mesentery, diaphragm and peritoneum. In abdominal paracentesis, fluid having almost the same properties as circulating blood was identified. The hemoperitoneum was thought to be resulted from the bleeding into peritoneum owing to the rupture of cystic lesions located on the superficial liver area.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.819-830
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• 2017

An FM radio based PCL system is a passive radar technique for detecting the multiple moving targets from FM radio signals and tracking the trajectories of the targets by calculating the cross-correlation function of direct-path signal and target echo signals. However, the interference signals are received from a surveillance channel, which is designed to receive the target echo signals. Because of this problem, the target echo signals are masked by the strong interference signals and this makes it difficult to detect the true targets from the cross-correlation function. Adaptive filters are known as effective methods for suppressing the interference signals but there is a problem to present their accurate performances in the PCL system because many literatures used the cross-correlation function and the ratio of input and output power as a measure of the performance analysis. In this paper, a performance analysis method is proposed to evaluate the performance of interference cancellation algorithms. By using the property that each component of the filter weight vector is adjusted to suppress the specific interference signal, a performance measure of the interference signal suppression is defined by a function of adaptive filter weights. Based on the proposed method, we compare the performance of the adaptive filters used in the PCL system. Simulation results show that the proposed method can be very effective for evaluating the performance of interference cancellation algorithms.

• Journal of the Korean Society of Radiology
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• v.84 no.6
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• pp.1309-1323
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• 2023

Purpose To assess the quality of four images obtained using single-breath-hold (SBH), single-shot fast spin-echo (SSFSE) and multiple-breath-hold (MBH) SSFSE with and without deep-learning based reconstruction (DLR) in patients with Crohn's disease. Materials and Methods This study included 61 patients who underwent MR enterography (MRE) for Crohn's disease. The following images were compared: SBH-SSFSE with (SBH-DLR) and without (SBH-conventional reconstruction [CR]) DLR and MBH-SSFSE with (MBH-DLR) and without (MBH-CR) DLR. Two radiologists independently reviewed the overall image quality, artifacts, sharpness, and motion-related signal loss using a 5-point scale. Three inflammatory parameters were evaluated in the ileum, the terminal ileum, and the colon. Moreover, the presence of a spatial misalignment was evaluated. Signal-to-noise ratio (SNR) was calculated at two locations for each sequence. Results DLR significantly improved the image quality, artifacts, and sharpness of the SBH images. No significant differences in scores between MBH-CR and SBH-DLR were detected. SBH-DLR had the highest SNR (p < 0.001). The inter-reader agreement for inflammatory parameters was good to excellent (κ = 0.76-0.95) and the inter-sequence agreement was nearly perfect (κ = 0.92-0.94). Misalignment artifacts were observed more frequently in the MBH images than in the SBH images (p < 0.001). Conclusion SBH-DLR demonstrated equivalent quality and performance compared to MBH-CR. Furthermore, it can be acquired in less than half the time, without multiple BHs and reduce slice misalignments.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10a
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• pp.409-412
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• 1996

Ultrasonic sensors are widely used in various applications due to advantages of low cost, simplicity in construction, mechanical robustness, and little environmental restriction in usage. But the main purposes of the noncontact sensing are rather narrowly confined within object detection and distance measurement. For the application of object recognition, ultrasonic sensors exhibit several shortcomings of poor directionality which results in low spatial resolution of objects, and specularity which gives frequent erroneous range readings. To resolve these problems in object recognition, an array of the sensor has been used. To improve the spatial resolution, more number of sensors are used in essence throughout the various devices of the sensor arrays. Under the disguise of a fixed number of the sensors, the array can be shifted mechanically in several steps. In this paper we propose a practical sensor resolution enhancement method using an electronic circuit accompanying the sensor array. The circuit changes the transmitter output voltage in several steps. Using the known sensor characteristics, a set of different return echo signals provide enhanced spatial resolution. The improvement is obtained with neither the cost of the increased number of the sensors nor extra mechanical devices.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.9
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• pp.172-180
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• 2012

In multi-static sonar for detecting an underwater target, received signals contain the target echo, reverberation and clutter. Clutter and reverberation are main causes of increasing the false alarm rate. MRAL classifies received signals according to the spatial similarity, and it regards classified signal as reflected signals from a reflector. MRAL reduces the false alarm rate this way. However, the results of MRAL can have localization errors. In this paper, an MRAL post processing algorithm is proposed to reduce the localization errors with the least square (LS) method.