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Han Dongyeob,Choi Moon Hyung,Lee Young Joon,Kim Dong-Hyun 대한영상의학회 2021 Korean Journal of Radiology Vol.22 No.8
Objective: To evaluate the feasibility of a new three-dimensional (3D) MR fingerprinting (MRF) technique for the prostate gland by conducting phantom and clinical studies. Materials and Methods: The new 3D MRF technique used in this study enables quick data acquisition and has a high resolution. For the phantom study, the MRF T1 and T2 values in an in-house phantom were compared with those of goldstandard mapping methods using linear regression analysis. For the clinical study, we evaluated 90 patients who underwent prostate imaging with MRF for suspected prostate cancer between September 2019 and February 2020. The mean T1 and T2 values were compared in the peripheral zone, transition zone, and focal lesions using paired t tests. The differences in the T1 and T2 values according to cancer aggressiveness were evaluated using one-way analysis of variance. Results: In the phantom study, the MRF T1 and T2 values showed a perfect correlation with the gold-standard T1 and T2 values (R > 0.99). In the clinical study, the T1 and T2 values in the peripheral zone were significantly higher than those in the transitional zone (p < 0.001, both). The T1 and T2 values in prostate cancer were significantly lower than those in the peripheral and transitional zones. The higher the grade of cancer, the lower the T2 values. Conclusion: The T1 and T2 values obtained from the 3D MRF showed a perfect correlation with the gold standard values in the phantom study. Differences in the T1 and T2 values among the different zones of the prostate gland were identified using 3D MRF in patients.
Han, Dongyeob,Hong, Taehwa,Lee, Yonghan,Kim, Dong-Hyun Korean Society of Magnetic Resonance in Medicine 2021 Investigative Magnetic Resonance Imaging Vol.25 No.3
Purpose: To develop a 3D magnetic resonance fingerprinting (MRF) method for application in high resolution knee cartilage PD, T<sub>1</sub>, T<sub>2</sub> mapping. Materials and Methods: A novel 3D acquisition trajectory with golden-angle rotating radial in k<sub>xy</sub> direction and interleaved echo planar imaging (EPI) acquisition in the k<sub>z</sub> direction was implemented in the MRF framework. A centric order was applied to the interleaved EPI acquisition to reduce Nyquist ghosting artifact due to field inhomogeneity. For the reconstruction, singular value decomposition (SVD) compression method was used to accelerate reconstruction time and conjugate gradient sensitivity-encoding (CG-SENSE) was performed to overcome low SNR of the high resolution data. Phantom experiments were performed to verify the proposed method. In vivo experiments were performed on 6 healthy volunteers and 2 early osteoarthritis (OA) patients. Results: In the phantom experiments, the T<sub>1</sub> and T<sub>2</sub> values of the proposed method were in good agreement with the spin-echo references. The results from the in vivo scans showed high quality proton density (PD), T<sub>1</sub>, T<sub>2</sub> map with EPI echo train length (N<sub>ETL</sub> = 4), acceleration factor in through plane (R<sub>z</sub> = 5), and number of radial spokes (N<sub>spk</sub> = 4). In patients, high T<sub>2</sub> values (50-60 ms) were seen in all transverse, sagittal, and coronal views and the damaged cartilage regions were in agreement with the hyper-intensity regions shown on conventional turbo spin-echo (TSE) images. Conclusion: The proposed 3D MRF method can acquire high resolution (0.5 mm<sup>3</sup>) quantitative maps in practical scan time (~ 7 min and 10 sec) with full coverage of the knee (FOV: 160 × 160 × 120 mm<sup>3</sup>).
RTK 무인기로 취득한 하천 경계 영상의 직접 지오레퍼런싱
한수희(Han, Soohee),한동엽(Han Dongyeob) 한국측량학회 2023 한국측량학회지 Vol.41 No.6
This study aims to implement direct georeferencing using RTK (Real-Time Kinematic) UAV (Unmanned Aerial Vehicle) images acquired along river boundaries. It is difficult to accurately calculate EOPs (Exterior Orientation Parameters) based on SfM (Structure from Motion) in river boundary images because extracting and matching feature points is not affordable for water bodies. Three weights were applied to the constraint equations of SfM to adjust the amount of adjustment of the 3D coordinates among the EOPs. An experiment was conducted using RTK UAV images acquired in the form of a strip along the boundary on both sides of a river approximately 2.4 km long, and additional strip images taken at a distance were also applied individually or in combination. As a result of the accuracy assessment using 13 checkpoints on ortho mosaic images, the horizontal RMSE (Root Mean Square Error) was estimated from about 2cm to 4cm and the vertical RMSE from about 5cm to 7cm when large amounts of weight were applied. In conclusion, direct georeferencing was successfully implemented by applying large weights to the 3D coordinates of the EOPs, and it can be expected that RTK UAVs can be efficiently utilized for aerial triangulation and ortho mosaic image production for long-distance rivers and coastlines.
Lee, Hyoseong,Han, Dongyeob Hindawi Limited 2018 Journal of sensors Vol.2018 No.-
<P>We propose a photogrammetric board to measure the deformation of a railroad bridge using close-range photogrammetry. The method can be used to compute the exterior orientation parameters and determine three-dimensional (3D) coordinates from images without measuring the control points. The bridge deformation measured using the proposed method was compared to that measured with a 3D laser tracker. The measurement error was within 1 mm, and the proposed method can measure the deformation of an I-plate girder of a railroad bridge. This method may be an alternative to precise stability inspections and bridge inspections.</P>