• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 춘계학술대회
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• pp.471-474
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• 1997

Several selective excitation pulses are used in MRI. Because of the nonlinearity of the Block equation, the pulse problem is nonlinear generally. Recently, Shinnar & Le Roux have proposed a direct solution of this problem. In this paper, we introduce the SLR algorithm and design pulses using SLR algorithm. This SLR pulse produces a specified slice profile. For example, we demonstrate the sinc function pulse with piece wise constant duration ${\Delta}t$. Further, we will design $\pi/2$ pulse and slice profile.

• The Journal of Korean Physical Therapy
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• 제4권1호
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• pp.43-57
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• 1992

This study was conducted from August, 1980 to March, 9991 to the 40 subjects who were admitted to Kosin Medical Center and received rehabilitation treatment and discharged under the impression of stroke. The objectives are to evaluate the function of the activites of daily living and comprehensive function and find the status of rehabilitation treatment by Modified Barthel Index and PULSES Profile when first requested or rehabilitation treatment(T1), at 2 weeks after rehabilitation treatment(T2), at discharge(T3) and at the time of ambulatory treatment after 2 weeks(T4). The study materials were clinical charts and functional evaluation sheets, and the results are as follows : 21 subject$(52.5\%)$ were male, 19 subjects$(47.5\%)$ were female, and the age distribution was from 19 to 70 in age, the average age was 52.7. By the classification of diagnosis, 21 subjects$(52.5\%)$ were cerebral hemorrhage, 8 subjects$(20.2\%)$ were cerebral thrombosis, 6 subjects$(15.0\%)$ were cerebral embolism, and 5 subjects$(12.5\%)$ were cerebral infarction. The Barthel Index scores were 35.7, 54.5, 71.8, 88.7 on the average at T1, T2, T3, T4 respectively. The PULSES scores were 16.4, 13.7, 11.4, 8.7 on the average at T1, T2, T3, T4 respectively. Regarding the Pearson's correlation coefficient between the Barthel Index scores and the PULSES scores, it was -0.7991(P>0.001) at T1 and -0.8986(P>0.001) at T3, then beth of correlations were very high.

• Investigative Magnetic Resonance Imaging
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• 제20권1호
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• pp.27-35
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• 2016

Purpose: Among RF pulses, a sinc pulse is typically used for slice selection due to its frequency-selective feature. When a sinc pulse is implemented in practice, it needs to be apodized to avoid truncation artifacts at the expense of broadening the transition region of the excited-band profile. Here a sinc pulse tailored by a new apodization function is proposed that produces a sharper transition region with well suppression of truncation artifacts in comparison with conventional tailored sinc pulses. A multiband pulse designed using this newly apodized sinc pulse is also suggested inheriting the better performance of the newly apodized sinc pulse. Materials and Methods: A new apodization function is introduced to taper a sinc pulse, playing a role to slightly shift the first zero-crossing of a tailored sinc pulse from the peak of the main lobe and thereby producing a narrower bandwidth as well as a sharper pass-band in the excitation profile. The newly apodized sinc pulse was also utilized to design a multiband pulse which inherits the performance of its constituent. Performances of the proposed sinc pulse and the multiband pulse generated with it were demonstrated by Bloch simulation and phantom imaging. Results: In both simulations and experiments, the newly apodized sinc pulse yielded a narrower bandwidth and a sharper transition of the pass-band profile with a desirable degree of side-lobe suppression than the commonly used Hanning-windowed sinc pulse. The multiband pulse designed using the newly apodized sinc pulse also showed the better performance in multi-slice excitation than the one designed with the Hanning-windowed sinc pulse. Conclusion: The new tailored sinc pulse proposed here provides a better performance in slice (or slab) selection than conventional tailored sinc pulses. Thanks to the availability of analytical expression, it can also be utilized for multiband pulse design with great flexibility and readiness in implementation, transferring its better performance.

• Journal of the Optical Society of Korea
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• 제7권3호
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• pp.139-144
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• 2003

We have characterized the optical parametric chirped-pulse amplification of femtosecond Ti:sapphire laser pulses by using a BBO crystal. It is numerically verified that a high gain and a broad gain bandwidth can be obtained with a 532-nm pump laser. The dependence of the gain profile of OPA on phase matching angles, pump intensity, and crystal length is numerically investigated. Experimental results shows that the temporal fluctuation of a pump laser causes the modulation of an amplified spectrum in OPCPA.

• 한국의학물리학회지:의학물리
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• 제18권1호
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• pp.35-41
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• 2007

본 연구의 목적은 비침습적 동맥스핀라벨링(arterial spin labeling) 자기공명영상을 이용하여 다편(multislice) 뇌 관류영상(perfusion-weighted Images)을 얻을 수 있는 최적화 방법을 연구하는 데 목적이 있다. 본 연구에서는 세 가지 인자를 최적화하는 데 초점을 두었다. 첫째, 뇌로 흘러 들어오는 혈액을 최적으로 라벨링할 수 있는 펄스를 만드는 것이다. 시뮬레이션 결과 900도의 각을 이루는 반전펄스(adiabatic hyperbolic secant Inversion pulse)는 반전을 효과적으로 할 수 있고 반전을 이루는 형태가 직각에 가깝게 할 수 있는 최적이었다. 둘째, 영상을 얻고 난 후에 계속하여 남아 있는 자화(residual magnetization)을 최소화하는 것이다. 이를 최소화하기 위해서는 포화 펄스(saturation pulses)와 자화를 손상시키는 자장(speller gradients)을 동시에 사용하는 것이 최상의 방법임을 알았다. 마지막으로, 라벨링하는 영역과 영상을 얻는 영역 사이의 거리를 최소화할 수 있는 방법을 연구하였다. 두 영역 간의 최소 거리는 약 20 mm 정도가 최적임을 발견하였다. 위에서 얻은 최적화된 인자들을 바탕으로 13명의 정상인의 뇌에서 관류 영상을 얻은 결과 매우 좋은 대조도의 영상을 얻을 수 있었다.

• 한국정밀공학회지
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• 제23권9호
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• pp.102-110
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• 2006

We discuss two possibilities of using femtosecond pulse lasers as a new interferometric light source for enhanced precision surface-profile metrology. First, a train of ultra-fast laser pulses yields repeated low temporal coherence, which allows unequal-path scanning interferometry, which is not feasible with white light. Second, the high spatial coherence of femtosecond pulse lasers enables large-sized optics to be tested in nonsymmetric configurations with relatively small-sized reference surfaces. These two advantages are verified experimentally using Fizeau and Twyman-Green type scanning interferometers.

• 전자공학회논문지D
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• 제34D권3호
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• pp.123-130
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• 1997

We determine the dispersion profile of a dispersion decreasing fiber(DDF) for optimum pulse compression from a trade-off between high pulse compression and low pedestal power/short DDF length. We find that the optimum vlaue of the exponential dispersion decreasing factor .alpha. is 0.95 and that the corresponding optimum fiber length is 1.5 times of the initial soliton period. Passing through the dDF, ~10 times of pulse comparession ratio can be achieved without significant increase in pedestal power. To compress relatively broad pulses using a given DDF optimized at a specific pulse width, we also detemrine the optimum input pulse amplitude, as a function of input pulse width.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1995년도 춘계학술대회
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• pp.42-44
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• 1995

The original DANTE sequence and its variations have limitation in excitation profile (a sinc function-like excitation) due to the finite duration of the DANTE pulsetrain. This sinc function-like selection profile excites only a small fraction of the spins in the pixel thereby results in poor signal to noise ratio (only about ${\sim}1%$ of normal MR imaging sequence). Therefore, this poor signal to noise ratio (SNR) has been the main drawback of the original DANTE sequence. To improve the signal to noise ratio, phases of individual RF pulses in the DANTE pulse train were modulated so that more spins in the object were excited ($1{\sim}3$). We have introduced a new FM (Frequency Modulation) DANTE sequence and analyzed the signal intensity and excitation profiles.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2482-2487
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• 2007

Numerical simulations are conducted for the analysis of a thermal mass air flow sensor with periodic heating pulses on silicon-nitride ($Si_3N_4$) thin membrane structure. This study aims to find the locations of temperature sensors on the thin membrane and the heating pulse conditions, that the higher sensitivity can be achieved, for the development of a MEMS fabricated mass air flow sensor which is driven in periodic heating pulse. The simulations, thus, focus on the membrane temperature profile according to variation of the flow velocity, heating duration time and imposed power. The flow velocity of the simulations is ranging from 3 m/s to 35 m/s, heating duration time from 1 ms to 3 ms and imposed power from 50 mW to 90 mW. The corresponding Reynolds numbers vary from 1000 to 10000.

• 한국광학회지
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• 제12권3호
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• pp.219-224
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• 2001

주파수 위상 간섭계를 이용한 전기장 재구성 방법(SPIDER)을 이용하여 Kerr 렌즈 모드록킹된 티타늄 사파이어 레이저 공진기에서 생성된 펨토초 영역의 극초단 펄스의 펄스폭과 위상을 측정하였다. 8cm 길이의 SF10 매질과 마이켈슨형의 시간지연암(arm)을사용하여 주파수 층밀림(shearing)을 구현하고 제2종 BBO결정으로 합주파수 발생을 시켜 SPIDER 장치를 구성 하였다 얻어진 층밀림 주파수 간섭 신호로부터 SPIDER 알고리즘을 이용하여 펄스의 전기장을 복원하였다 SPIDER의 정확도를 확인하기 위해 SPIDER에서 얻은 펄스로 재구성한 간섭형 자체상솬신호를 직접 측정한 간섭형 자체상관 신호와 비교하였다. SPIDER를 티타늄 사파이어 레이저 공진기에 적용하여 19fs의 펄스폭을 얻었으며 sech$^2$나 가우시안으로 가정한 간섭형 자체상관의 결과는 이보다 작은 값으로 나타나서 펨토초 레이저의 정확한 펄스폭 측정을 위해서는 펄스모양의 가정이 필요없는 SPIDER 방법이 필요함을 알 수 있었다.