• Journal of Korean Neurosurgical Society
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• 제63권3호
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• pp.386-396
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• 2020

Objective : To generate synthetic spine magnetic resonance (MR) images from spine computed tomography (CT) using generative adversarial networks (GANs), as well as to determine the similarities between synthesized and real MR images. Methods : GANs were trained to transform spine CT image slices into spine magnetic resonance T2 weighted (MRT2) axial image slices by combining adversarial loss and voxel-wise loss. Experiments were performed using 280 pairs of lumbar spine CT scans and MRT2 images. The MRT2 images were then synthesized from 15 other spine CT scans. To evaluate whether the synthetic MR images were realistic, two radiologists, two spine surgeons, and two residents blindly classified the real and synthetic MRT2 images. Two experienced radiologists then evaluated the similarities between subdivisions of the real and synthetic MRT2 images. Quantitative analysis of the synthetic MRT2 images was performed using the mean absolute error (MAE) and peak signal-to-noise ratio (PSNR). Results : The mean overall similarity of the synthetic MRT2 images evaluated by radiologists was 80.2%. In the blind classification of the real MRT2 images, the failure rate ranged from 0% to 40%. The MAE value of each image ranged from 13.75 to 34.24 pixels (mean, 21.19 pixels), and the PSNR of each image ranged from 61.96 to 68.16 dB (mean, 64.92 dB). Conclusion : This was the first study to apply GANs to synthesize spine MR images from CT images. Despite the small dataset of 280 pairs, the synthetic MR images were relatively well implemented. Synthesis of medical images using GANs is a new paradigm of artificial intelligence application in medical imaging. We expect that synthesis of MR images from spine CT images using GANs will improve the diagnostic usefulness of CT. To better inform the clinical applications of this technique, further studies are needed involving a large dataset, a variety of pathologies, and other MR sequence of the lumbar spine.

• 디지털콘텐츠학회 논문지
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• 제11권3호
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• pp.283-290
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• 2010

1.5T에서 경직장 코일과 3.0T의 위상 배열 코일을 이용하여 신호대 잡음비를 비교하여 3.0T의 위상 배열 코일의 유용성을 제시한다. 전립선암으로 진단받은 환자 40명을 대상으로 1.5T MR scanner에서는 경직장 표면 코일과 3.0T MR scanner에서는 위상 배열 코일을 이용하여 T2 강조 영상, T1 강조영상, 확산 강조 영상을 각각 획득 후 전립선의 Central Zone(CZ)과 Peripheral Zone(PZ)에서 Right Peripheral Zone(PZ)과 Left Peripheral Zone(PZ) 세 부위에서 신호 강도(signal intensity)측정을 하였다. 정량적 분석방법으로 관심영역의 신호대 잡음비(signal to noise ratio)를 구하고 평균화 하여 1.5T MR scanner로 획득한 그룹과 3.0T MR scanner로 획득한 그룹에서의 신호대 잡음비를 비교하였다. 3.0T MR scanner에서 위상 배열 코일을 사용한 경우 1.5T MR scanner에서 경직장 코일을 사용한 경우보다 신호대 잡음비가 증가됨을 알 수 있었다.

• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 2001년도 제6차 학술대회 초록집
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• pp.140-140
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• 2001

We present two cases of surgically proven focal nodular hyperplasia whou underwent tri contrast-enhance MR imaging using gadolinium chelates, mangafodipir trisodium, and ferumoxides After the unehanced MR images were obtained, dynamic gadolinium-enhanced T1-weighted imagi were performed, then mangafodipir enhanced and ferumoxides-enhanced images were obtained. In one case, the mass was isointense on both T1- and T2-weighted images on the unehanced M images, iso and slightly hyperintense on ferumoxides-enhanced FSE and GRE images, strong hyperintense on the mangafodipir enhanced and gadolinium enhanced arterial phase images. In th other case, the mass was isointense on T2-weighted and hypointense on T1-weighted image isointense on ferumoxides-enhanced images, and hyperintense on mangafodipir enhanced an gadolinium enhanced arterial phase images. Triple contrast enhanced MR images were useful correctly diagnose these two cases preoperatively.

• Imaging Science in Dentistry
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• 제35권3호
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• pp.157-165
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• 2005

Purpose : To find out the proper compression ratios without degrading image quality and affecting lesion detectability on diagnostic images used in dentistry compressed with JPEG 2000 algorithm. Materials and Methods : Sixty Digora periapical images, sixty panoramic computed radiographic (CR) images, sixty computed tomographic (CT) images, and sixty magnetic resonance (MR) images were compressed into JPEG 2000 with ratios of 10 levels from 5:1 to 50:1. To evaluate the lesion detectability, the images were graded with 5 levels (1 : definitely absent; 2: probably absent; 3: equivocal; 4: probably present; 5: definitely present), and then receiver operating characteristic analysis was performed using the original image as a gold standard. Also to evaluate subjectively the image quality, the images were graded with 5 levels (1 definitely unacceptable; 2: probably unacceptable; 3: equivocal, 4: probably acceptable; 5· definitely acceptable), and then paired t-test was performed. Results : In Digora, CR panoramic and CT images, compressed images up to ratios of 15 : 1 showed nearly the same lesion detectability as original images, and in MR images, compressed images did up to ratios of 25 : 1. In Digora and CR panoramic Images, compressed images up to ratios of 5 : 1 showed little difference between the original and reconstructed images in subjective assessment of image quality In CT images, compressed images did up to ratios of 10: 1 and in MR images up to ratios of 15 : 1 Conclusion : We considered compression ratios up to 5 : 1 in Digora and CR panoramic images, up to 10 : 1 in CT images, up to 15 : 1 in MR images as clinically applicable compression ratios.

• Journal of Korean Neurosurgical Society
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• 제54권4호
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• pp.302-308
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• 2013

Objective : MR perfusion and single photon emission computerized tomography (SPECT) are well known imaging studies to evaluate hemodynamic change between prior to and following superficial temporal artery (STA)-middle cerebral artery (MCA) anastomosis in moyamoya disease. But their side effects and invasiveness make discomfort to patients. We evaluated the ivy sign on MR fluid attenuated inversion recovery (FLAIR) images in adult patients with moyamoya disease and compared it with result of SPECT and MR perfusion images. Methods : We enrolled twelve patients (thirteen cases) who were diagnosed with moyamoya disease and underwent STA-MCA anastomosis at our medical institution during a period ranging from September of 2010 to December of 2012. The presence of the ivy sign on MR FLAIR images was classified as Negative (0), Minimal (1), and Positive (2). Regions were classified into four territories: the anterior cerebral artery (ACA), the anterior MCA, the posterior MCA and the posterior cerebral artery. Results : Ivy signs on preoperative and postoperative MR FLAIR were improved (8 and 4 in the ACA regions, 13 and 4 in the anterior MCA regions and 19 and 9 in the posterior MCA regions). Like this result, the cerebrovascular reserve (CVR) on SPECT was significantly increased in the sum of CVR in same regions after STA-MCA anastomosis. Conclusion : After STA-MCA anastomosis, ivy signs were decreased in the cerebral hemisphere. As compared with conventional diagnostic modalities such as SPECT and MR perfusion images, the ivy sign on MR FLAIR is considered as a useful indicator in detecting brain hemodynamic changes between preoperatively and postoperatively in adult moyamoya patients.

• Investigative Magnetic Resonance Imaging
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• 제22권4호
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• pp.218-228
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• 2018

Purpose: The objective of this study is to determine the effect of physical changes on MR temperature imaging at 7.0T and to examine proton-resonance-frequency related changes of MR phase images and T1 related changes of MR magnitude images, which are obtained for MR thermometry at various magnetic field strengths. Materials and Methods: An MR-compatible capacitive-coupled radio-frequency hyperthermia system was implemented for heating a phantom and swine muscle tissue, which can be used for both 7.0T and 3.0T MRI. To determine the effect of flip angle correction on T1-based MR thermometry, proton resonance frequency, apparent T1, actual flip angle, and T1 images were obtained. For this purpose, three types of imaging sequences are used, namely, T1-weighted fast field echo with variable flip angle method, dual repetition time method, and variable flip angle method with radio-frequency field nonuniformity correction. Results: Signal-to-noise ratio of the proton resonance frequency shift-based temperature images obtained at 7.0T was five-fold higher than that at 3.0T. The T1 value increases with increasing temperature at both 3.0T and 7.0T. However, temperature measurement using apparent T1-based MR thermometry results in bias and error because B1 varies with temperature. After correcting for the effect of B1 changes, our experimental results confirmed that the calculated T1 increases with increasing temperature both at 3.0T and 7.0T. Conclusion: This study suggests that the temperature-induced flip angle variations need to be considered for accurate temperature measurements in T1-based MR thermometry.

• Nuclear Engineering and Technology
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• 제55권1호
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• pp.222-228
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• 2023

This study aimed to analyze the applicability of the improved median filter in positron emission tomography (PET)/magnetic resonance (MR) fusion images based on parallel imaging using generalized autocalibrating partially parallel acquisition (GRAPPA). In this study, a PET/MR fusion imaging system based on a 3.0T magnetic field and ¹⁸F radioisotope were used. An improved median filter that can set a mask of the median value more efficiently than before was modeled and applied to the acquired image. As quantitative evaluation parameters of the noise level, the contrast to noise ratio (CNR) and coefficient of variation (COV) were calculated. Additionally, no-reference-based evaluation parameters were used to analyze the overall image quality. We confirmed that the CNR and COV values of the PET/MR fusion images to which the improved median filter was applied improved by approximately 3.32 and 2.19 times on average, respectively, compared to the noisy image. In addition, the no-reference-based evaluation results showed a similar trend for the noise-level results. In conclusion, we demonstrated that it can be supplemented by using an improved median filter, which suggests the problem of image quality degradation of PET/MR fusion images that shortens scan time using GRAPPA.

• Investigative Magnetic Resonance Imaging
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• 제10권2호
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• pp.117-120
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• 2006

위축뇌탈출증(atrectic cephalocele)은 중앙의 두피하부에 있는 피부로 덮힌 병변으로서 수막과 아교세포나 중추신경계 조직의 잔유물들을 포함한다. 수직동이 없거나 잔유물로 남아있는 경우 낫형동(falcin sinus)이 다시 관류하게 되어 정맥의 배출이 가능하게 된다. 위축된 뇌탈출증 또는 지속적인 낫형동은 소아에서 주로 기술되어 왔으며, 성인에서는 매우 드문 병변이다. 저자들은 성인에서 자연퇴화된 위축뇌탈출증이 지속적인 낫형동을 동반한 매우 드문증례를 보고하고자 하며 MR영상과 MR정맥조영술은 정확한 해부학적 묘사와 진단에 유용하였다.

• International Journal of CAD/CAM
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• 제3권1_2호
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• pp.61-66
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• 2003

This paper describes a novel experiment that measures skin movement with respect to the flexional motion of a hand. The study was based on MR images in conjunction with CAD techniques. The MR images of the hand were captured in 3 different postures with surface markers. The surface markers attached to the skin where employed to trace skin movement during the flexional motion of the hand. After reconstructing 3D isosurfaces from the segmented MR images, the global registration was applied to the 3D models based on the particular bone shape of different postures. Skin movement was interpreted by measuring the centers of the surface markers in the registered models.

• Investigative Magnetic Resonance Imaging
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• 제13권2호
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• pp.183-189
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• 2009

목적 : 유방자기공명영상에서 3 차원 최대 강도 투사 (3D MIP) 재건 영상의 유용성을 알아보고자 하였다. 대상 및 방법 : 유방암으로 진단받고 유방자기공명영상을 시행한 27명의 환자의 54개의 유방을 대상으로 하였다. GE Signa Excite Twin speed (GE medical system, Wisconsin, USA) 1.5 T 기기를 이용하여 기본 영상으로 축면 T2 강조 T1 강조 영상과 시상면 T1 강조 지방 억제 영상, 역동적 조영 증강 영상과 감산 영상을 얻었다. 이후 초기 역동적 조영증강 영상의 감산영상으로 워크스테이견 (GE Medical system)을 이용하여 3D MIP 영상을 얻었다. 3D MIP 영상과 기본 유방자기공명영상에서 발견된 병변을 ACR BI-$RADS^{(R)}$ MRI lexicon에 따라 분석하였다. 각각의 영상에서 발견된 병변의 소견들을 비교하고 3D MIP에서 기본자기공명영상에서 보다 추가적인 정보를 얻을 수 있는지 알아보았다. 결과 : 종괴의 경우 기본 유방자기공명영상에서 보이는 56개 중 43개가 3D MIP 영상에서 발견되었다 (76.8%). 비종괴성 조영 증강의 경우 20개 중 17개가 발견되었다 (85%). 169개의 초점성 조영증강 병변이 3D MIP 영상에서, 109개가 기본 유방자기공명영상에서 확인되었다. 3D MIP 영상에서 60.9%의 category 3병변이 발견되었고(14/23), 68.87%의 category 4 병변 (11/16), 100%의 category 5병변 (28/28)이 발견되었다. 3D MIP 영상에서 분석된 조영증강 병변들의 category가 기본 유방 자기공명 영상의 결과들과 통계적으로 일치하였다(p-value < 0.0001). 기본 유방 자기공명 영상에서 초점으로 분석된 2개의 병변들이 3D MIP 영상에서는 다초점성의 악성 병변으로 발견되었고, 1개의 추가적 병변이 3D MIP 영상에서만 발견되었다. 결론 : 3D MIP 영상은 한계점들을 갖고 있으나, 기본 유방자기공명영상의 분석에 있어 추가적으로 이용 시 유용하다.