• 한국자기학회지
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• 제26권3호
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• pp.105-114
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• 2016

삼각 섬유성 연골(TFCC) 손상 환자의 평가를 위하여 fat suppressed 3D fast spoiled gradient recalled T1 기법과 fat suppressed Isotropic 3D fast spin echo T1 기법을 이용하여 영상을 획득하였다. 정량적 평가를 위해 각각의 영상에서 signal to noise ratio 및 contrast to noise ratio 값을 측정하고, Mann-Whitney U 검정으로 두 기법 간의 통계적 유의성을 검증하였다. 또한 정성적 평가를 위해 영상의학의 2명이 각각의 영상을 관찰하여, TFCC의 형태, 영상 내 인공음영, 병변의 묘사 정도의 3가지 항목을 선정한 후 이를 4점 척도(0: 진단 불가, 1: 부족함, 2: 충분함, 3: 좋음)로 평가하였고, Kappa-value 검정을 이용하여 두 관찰자 간의 일치도 검증을 하였다. 영상획득에는 3.0 Tesla MR 장비와 8-channel RF coil을 사용하였다. 정량적 평가 결과, 모든 영상 단면에서 signal to noise ratio 및 contrast to noise ratio 값이 Isotropic 3D fast spin echo T1 기법이 높게 나타났으며, Mann-Whitney U 검정을 이용한 두 영상기법 간의 검증도 통계적으로도 유의하였다(p < 0.05). 정성적 평가 결과, 관찰자 1, 2 모두에서 Isotropic 3D fast spin echo T1 기법의 평가 결과가 더 높게 나타났으며, Kappa-value 검증을 이용한 두 관찰자 간 평가 결과의 일치도 검증도 통계적으로 유의하였다(p < 0.05). 결론적으로 TFCC 손상 환자의 자기공명영상 검사 시 fat suppressed Isotropic 3D fast spin echo T1 기법의 적용은 TFCC 병변의 감별에 보다 유용한 진단적 정보를 제공 할 수 있을 것이라 생각된다.

• 정보처리학회논문지B
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• 제15B권6호
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• pp.507-516
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• 2008

최근 연구 결과에 따르면 여러가지 질환 중에 심장 질환으로 인한 사망률이 가장 높은 것으로 나타났다. 임상 실습에서 심장 기능은 좌심실을 수동윤곽검출하여 혈류량이나 심박구출률을 계산하여 분석하지만, 많은 시간과 비용을 필요로 한다. 본 연구에서는 심장을 촬영한 단축 자기공명영상을 사용하여 자동 좌심실 분할 알고리즘을 제안한다. 코일 위치에 따른 왜곡을 보상하고, 에지 정보를 검출하고 특성에 따라 분류한후에, 영역 확장 기법을 사용하여 좌심실을 분할하였다. 또한 부분 복셀소(voxel)의 영향을 고려하였다. 코넬대학교 IRB의 승인하에 38 명의 심장 자기공명영상을 사용하여 제안한 알고리즘을 수동윤곽검출 및 GE MASS 소프트웨어와 비교하였다. 심장의 이완기와 수축기에 혈류량은 부분 복셀소 영향을 고려하지 않을 경우 각각 $3.3mL{\pm}5.8$(표준편차)와 $3.2mL{\pm}4.3$, 부분 복셀소 영향을 고려한 경우 각각 $19.1mL{\pm}8.8$와 $10.3mL{\pm}6.1$의 정확도를 보였다. 심박구출률은 부분 복셀소 영향을 고려하지 않은 경우와 고려한 경우에 대해서 각각 $-1.3%{\pm}2.6$ 와 $-2.1%{\pm}2.4$의 정확도를 보였다. 이를 통해 제안한 알고리즘이 정확하고 정기적인 임상 실습에 유용함을 확인할 수 있다.

• 한국전문물리치료학회지
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• 제10권3호
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• pp.17-27
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• 2003

Repetitive transcranial magnetic stimulation (rTMS) modulates cortical excitability beyond the duration of the rTMS trains themselves. Depending on rTMS parameters, a lasting inhibition or facilitation of cortical excitability can be induced. Therefore, rTMS of high or low frequency over motor cortex may change certain aspects of motor learning performance and cortical activation. This study investigated the effect of high and low frequency subthreshold rTMS applied to the motor cortex on motor learning of sequential finger movements and brain activation using functional MRI (fMRI). Three healthy right-handed subjects (mean age 23.3) were enrolled. All subjects were trained with sequences of seven-digit rapid sequential finger movements, 30 minutes per day for 5 consecutive days using their left hand. 10 Hz (high frequency) and 1 Hz (low frequency) trains of rTMS with 80% of resting motor threshold and sham stimulation were applied for each subject during the period of motor learning. rTMS was delivered on the scalp over the right primary motor cortex using a figure-eight shaped coil and a Rapid(R) stimulator with two Booster Modules (Magstim Co. Ltd, UK). Functional MRI (fMRI) was performed on a 3T ISOL Forte scanner before and after training in all subjects (35 slices per one brain volume TR/TE = 3000/30 ms, Flip angle $60^{\circ}$, FOV 220 mm, $64{\times}64$ matrix, slice thickness 4 mm). Response time (RT) and target scores (TS) of sequential finger movements were monitored during the training period and fMRl scanning. All subjects showed decreased RT and increased TS which reflecting learning effects over the training session. The subject who received high frequency rTMS showed better performance in TS and RT than those of the subjects with low frequency or sham stimulation of rTMS. In fMRI, the subject who received high frequency rTMS showed increased activation of primary motor cortex, premotor, and medial cerebellar areas after the motor sequence learning after the training, but the subject with low frequency rTMS showed decreased activation in above areas. High frequency subthreshold rTMS on the motor cortex may facilitate the excitability of motor cortex and improve the performance of motor sequence learning in normal subject.

• Investigative Magnetic Resonance Imaging
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• 제10권2호
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• pp.89-97
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• 2006

목적 : 자기공명영상 화질을 평가하는 팬텀으로서 코일 장착도구가 내장된 새로운 형태의 팬텀을 개발하였다. 대상 및 방법 : 자기공명영상 화질평가항목인 절편 두께 정확도, 공간 분해능, 대조도 분해능, 기하학적 정확도, 절편 위치 정확도, 영상강도 균일성, 고스트 신호 백분율, 신호대잡음비 등 총 8개의 사양을 가진 팬텀을 고안하였다. 팬텀의 코일 장착을 위한 장치가 팬텀 표면에 설치 되었다. 개발된 팬텀의 임상적용가능성을 알아보기 위하여 6개의 다른 종류의 자기공명영상기기를 사용하여 영상을 습득하였고 이들 화질이 평가되었다. 결과 : 사용된 모든 자기공명영상기기에서 영상평가에 문제가 없는 영상을 보여주었고 그들의 평가결과는 일부 평가항목에서 실측치와 비교하여 적절한 값 범위에 있음을 확인하였다. 코일장착도구를 사용하여 팬텀을 두부용 코일 안에 설치하는 데 문제가 없음을 확인하였다. 결론 : 본 논문에서 개발된 팬텀은 자기공명영상 화질을 평가하는 데 있어 그 임상적용 가능성이 있음을 보여주었다.

• Korean Journal of Radiology
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• 제22권4호
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• pp.559-567
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• 2021

Objective: To evaluate the impact of multiparametric magnetic resonance imaging (mpMRI) before confirmatory prostate biopsy in patients under active surveillance (AS). Materials and Methods: This retrospective study included 170 patients with Gleason grade 6 prostate cancer initially enrolled in an AS program between 2011 and 2019. Prostate mpMRI was performed using a 1.5 tesla (T) magnetic resonance imaging system with a 16-channel phased-array body coil. The protocol included T1-weighted, T2-weighted, diffusion-weighted, and dynamic contrast-enhanced imaging sequences. Uroradiology reports generated by a specialist were based on prostate imaging-reporting and data system (PI-RADS) version 2. Univariate and multivariate analyses were performed based on regression models. Results: The reclassification rate at confirmatory biopsy was higher in patients with suspicious lesions on mpMRI (PI-RADS score ≥ 3) (n = 47) than in patients with non-suspicious mpMRIs (n = 61) and who did not undergo mpMRIs (n = 62) (66%, 26.2%, and 24.2%, respectively; p < 0.001). On multivariate analysis, presence of a suspicious mpMRI finding (PI-RADS score ≥ 3) was associated (adjusted odds ratio: 4.72) with the risk of reclassification at confirmatory biopsy after adjusting for the main variables (age, prostate-specific antigen density, number of positive cores, number of previous biopsies, and clinical stage). Presence of a suspicious mpMRI finding (adjusted hazard ratio: 2.62) was also associated with the risk of progression to active treatment during the follow-up. Conclusion: Inclusion of mpMRI before the confirmatory biopsy is useful to stratify the risk of reclassification during the biopsy as well as to evaluate the risk of progression to active treatment during follow-up.

• Journal of Korean Neurosurgical Society
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• 제45권1호
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• pp.5-10
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• 2009

Objective : Direct surgical clipping of paraclinoid aneurysms poses technical challenges to even very experienced neurosurgeons, making endovascular treatment an alternative treatment modality in many centers. We have therefore retrospectively evaluated the safety and efficacy of endovascular detachable coil embolization of paraclinoid aneurysms. Methods : From June 1997 to June 2007, 65 patients underwent endovascular detachable coiling for 67 paraclinoid aneurysms (of which 9 were ruptured and 58 were unruptured) in our institute. Their medical records, radiological images and readings, and operation records were reviewed retrospectively. Results : After the initial embolization procedure, complete occlusion was achieved in 29 (43.3%) of the aneurysms treated by endovascular detachable coiling. Six aneurysms required retreatment, with two each requiring one, two, or three additional endovascular procedures. Fifty-five (82.1%) aneurysms were measured by three-dimensional time of flight (TOF) magnetic resonance images (MRI) or transfemoral cerebral angiography (TFCA) at a mean follow-up of 29.7 months (range from 4 to 94 months), with 39 aneurysms (70.9%) showing complete occlusion. Thromboembolic events (3.8%) were the most frequent complication. Rupture did not occur during or after any of the procedures. According to the Glasgow Outcome Scale (GOS), 98.4% of the patients treated by coil embolization had a score of 4 or 5. Conclusion : Our results indicate that endovascular detachable coiling is a safe and effective treatment modality in paraclinoid aneurysms.

• Investigative Magnetic Resonance Imaging
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• 제20권4호
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• pp.215-223
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• 2016

Purpose: The management of metal-induced field inhomogeneities is one of the major concerns of distortion-free magnetic resonance images near metallic implants. The recently proposed method called "Slice Encoding for Metal Artifact Correction (SEMAC)" is an effective spin echo pulse sequence of magnetic resonance imaging (MRI) near metallic implants. However, as SEMAC uses the noisy resolved data elements, SEMAC images can have a major problem for improving the signal-to-noise ratio (SNR) without compromising the correction of metal artifacts. To address that issue, this paper presents a novel reconstruction technique for providing an improvement of the SNR in SEMAC images without sacrificing the correction of metal artifacts. Materials and Methods: Low-rank approximation in each coil image is first performed to suppress the noise in the slice direction, because the signal is highly correlated between SEMAC-encoded slices. Secondly, SEMAC images are reconstructed by the best linear unbiased estimator (BLUE), also known as Gauss-Markov or weighted least squares. Noise levels and correlation in the receiver channels are considered for the sake of SNR optimization. To this end, since distorted excitation profiles are sparse, $l_1$ minimization performs well in recovering the sparse distorted excitation profiles and the sparse modeling of our approach offers excellent correction of metal-induced distortions. Results: Three images reconstructed using SEMAC, SEMAC with the conventional two-step noise reduction, and the proposed image denoising for metal MRI exploiting sparsity and low rank approximation algorithm were compared. The proposed algorithm outperformed two methods and produced 119% SNR better than SEMAC and 89% SNR better than SEMAC with the conventional two-step noise reduction. Conclusion: We successfully demonstrated that the proposed, novel algorithm for SEMAC, if compared with conventional de-noising methods, substantially improves SNR and reduces artifacts.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 추계학술대회
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• pp.142-146
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• 1996

In this paper, we present the main research results on the 2 Tesla class - superconducting MRI magnet which we have developed. Multi section type superconducting MRI main coil and various superconducting shims were designed and fabricated for obtaining the high field homogeneity, which is requested in the MR imaging. After assembling the magnet with room temperature bore cryostat field homogenity has been measured and analyzed by NMR field mapping system. According to this, field homogeneity of 22 ppm / 30 cm dsv was confirmed.

• Investigative Magnetic Resonance Imaging
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• 제13권2호
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• pp.137-145
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• 2009

목적: 각각 12개와 32개 요소 표면 코일 어레이를 사용한 가속율이 매우 큰 관상동맥 자기 공명 혈관조영술을 병렬 영상 기법에 적용하고 결과를 비교한다. 방법: 5명의 건강한 지원자에 대하여 1.5T 전신 자기공명영상장치에서 각각 12개와 32개 요소 표면 코일 어레이를 사용한 steady state free precession 자기공명 혈관조영술이 수행되었다. 각 지원자의 좌전하방관상동맥과 우관상동맥을 영상하여 데이터를 얻었다. 데이터는 병렬 영상을 위하여 1에서 6에 이르는 감소율로 부분 추출되었다. 양 코일 어레이 각각에 대하여 지형 인자의 평균, 극대, 그리고 인공물정도가 계산되었다. 결과: 모든 감소율에 있어서, 32개 요소 어레이가 12개 요소 어레이에 비하여 지형인자의 평균과 극대, 그리고 인공물정도가 상당히 줄어들었다 (P << 0.1). 지형인자의 평균은 관상동맥의 영상 방향에 민감한 반면, 지형인자 극대치와 인공물정도는 영상 방향에 독립적이었다. 결론: 가속율이 매우 큰 관상동맥 자기공명 혈관조영술의 병렬 영상 적용에 있어 32개 요소 표면 코일 어레이를 사용함은 인공물과 잡음을 상당히 억제시킨다. 32개 요소 표면 코일 어레이를 사용하여 가속율을 증가시키는 것은 공간 해상도를 향상시키거나 3D관상동맥 자기공명 혈관조영술에 있어서 체적 범위를 증가시킬 수 있는 가능성을 제공한다.

• Korean Journal of Radiology
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• 제23권2호
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• pp.246-255
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• 2022

Objective: To determine the usefulness of Silent MR angiography (MRA) for evaluating intracranial aneurysms treated with stent-assisted coil embolization. Materials and Methods: Ninety-nine patients (101 aneurysms) treated with stent-assisted coil embolization (Neuroform atlas, 71 cases; Enterprise, 17; LVIS Jr, 9; and Solitaire AB, 4 cases) underwent time-of-flight (TOF) MRA and Silent MRA in the same session using a 3T MRI system within 24 hours of embolization. Two radiologists independently interpreted both MRA images retrospectively and rated the image quality using a 5-point Likert scale. The image quality and diagnostic accuracy of the two modalities in the detection of aneurysm occlusion were further compared based on the stent design and the site of aneurysm. Results: The average image quality scores of the Silent MRA and TOF MRA were 4.38 ± 0.83 and 2.78 ± 1.04, respectively (p < 0.001), with an almost perfect interobserver agreement. Silent MRA had a significantly higher image quality score than TOF MRA at the distal internal carotid artery (n = 57, 4.25 ± 0.91 vs. 3.05 ± 1.16, p < 0.001), middle cerebral artery (n = 21, 4.57 ± 0.75 vs. 2.19 ± 0.68, p < 0.001), anterior cerebral artery (n = 13, 4.54 ± 0.66 vs. 2.46 ± 0.66, p < 0.001), and posterior circulation artery (n = 10, 4.50 ± 0.71 vs. 2.90 ± 0.74, p = 0.013). Silent MRA had superior image quality score to TOF MRA in the stented arteries when using Neuroform atlas (4.66 ± 0.53 vs. 3.21 ± 0.84, p < 0.001), Enterprise (3.29 ± 1.59 vs. 1.59 ± 0.51, p = 0.003), LVIS Jr (4.33 ± 1.89 vs. 1.89 ± 0.78, p = 0.033), and Solitaire AB stents (4.00 ± 2.25 vs. 2.25 ± 0.96, p = 0.356). The interpretation of the status of aneurysm occlusion exhibited significantly higher sensitivity with Silent MRA than with TOF MRA when using the Neuroform Atlas stent (96.4% vs. 14.3%, respectively, p < 0.001) and LVIS Jr stent (100% vs. 20%, respectively, p = 0.046). Conclusion: Silent MRA can be useful to evaluate aneurysms treated with stent-assisted coil embolization, regardless of the aneurysm location and type of stent used.