Cheol-Pyo Hong

Location of the corticospinal tract at the corona radiata in human brain.

Little is known about the location of the corticospinal tract (CST) at the corona radiata (CR). In the current study we attempted to elucidate the location of the CST for the hand at the CR using diffusion tensor tractography analysis based on functional MRI activation results. Functional MRI was performed at 1.5-T with timed hand grasp-release movements, and diffusion tensor tractography was performed using a Synergy-L Sensitivity Encoding (SENSE) head coil. Probabilistic mapping was obtained for 16 normal subjects using areas of functional MRI activation as the first region of interest (ROI 1) and the CST area in the lower pons as the second region of interest (ROI 2). The authors measured the antero-posterior and medio-lateral locations of pixels in the CST in two areas of the CR (CR 1 - the first axial image to show the septum pellucidum and the body of the fornix from the vertex, and CR 2 - the axial image showing the insular gyrus). The most probable locations in the medio-lateral direction (from the most medial point of the lateral ventricle wall to the most lateral point of the cerebral cortex) were 24.2% in both CR 1 and 2, and the most probable locations in the antero-posterior direction (from the most anterior point of the lateral ventricle to the most posterior point of the lateral ventricle) were 66.7 and 63.6% in CR 1 and 2, respectively. It was found that the CST for the hand descended through about one quarter (medio-lateral direction) and two-thirds (antero-posterior direction) at the CR.

Have You Ever Seen the Impact of Crossing Fiber in DTI?: Demonstration of the Corticospinal Tract Pathway.

Objective The identification of the corticospinal tract (CST) pathway with a deterministic fiber tracking approach is limited because of crossing fibers, especially for the hand fibers of the CST due to the crossing superior longitudinal fasciculus (SLF). We examined a patient with congenital bilateral perisylvian syndrome (CBPS) who did not have the SLF, in order to visualize CST hand fibers that were not affected by crossing fibers. Methods A 10-year-old girl without the SLF due to CBPS and three normal healthy subjects participated in this study. We used a deterministic fiber tracking algorithm, and the regions of interest (ROIs) were drawn in the posterior limb of internal capsule (PLIC) and the primary motor cortex. The apparent diffusion coefficient (ADC), fractional anisotropy (FA), relative anisotropy (RA), and volume ratio (VR) were measured based on the extracted fiber tracts. Results The ADC values were not different between the normal subjects and the patient with CBPS. The FA, RA, and VR values of the normal subjects were similar, but were relatively higher than those of the patient with CBPS. Conclusion Our results clearly show the impact of the crossing fiber for the hand motor fibers of the CST pathway with deterministic tracking algorithms in diffusion tensor tractography.

Characteristics of geometric distortion correction with increasing field-of-view in open-configuration MRI

Open-configuration magnetic resonance imaging (MRI) systems are becoming increasingly desirable for musculoskeletal imaging and image-guided radiotherapy because of their non-claustrophobic configuration. However, geometric image distortion in large fields-of-view (FOV) due to field inhomogeneity and gradient nonlinearity hinders the practical applications of open-type MRI. We demonstrated the use of geometric distortion correction for increasing FOV in open MRI. Geometric distortion was modeled and corrected as a global polynomial function. The appropriate polynomial order was identified as the minimum difference between the coordinates of control points in the distorted MR image space and those predicted by polynomial modeling. The sixth order polynomial function was found to give the optimal value for geometric distortion correction. The area of maximum distortion was<1 pixel with an FOV of 285mm. The correction performance error was increased at most 1.2% and 2.9% for FOVs of 340mm and~400mm compared with the FOV of 285mm. In particular, unresolved distortion was generated by local deformation near the gradient coil center.

Regularization of DT-MR images using a successive Fermat median filtering method

Tractography using diffusion tensor magnetic resonance imaging (DT-MRI) is a method to determine the architecture of axonal fibers in the central nervous system by computing the direction of greatest diffusion in the white matter of the brain. To reduce the noise in DT-MRI measurements, a tensor-valued median filter, which is reported to be denoising and structure preserving in the tractography, is applied. In this paper, we proposed the successive Fermat (SF) method, successively using Fermat point theory for a triangle contained in the two-dimensional plane, as a median filtering method. We discussed the error analysis and numerical study about the SF method for phantom and experimental data. By considering the computing time and the image quality aspects of the numerical study simultaneously, we showed that the SF method is much more efficient than the simple median (SM) and gradient descents (GD) methods.

Diffusion-Tensor Magnetic Resonance Imaging for Hand and Foot Fibers Location at the Corona Radiata: Comparison with Two Lesion Studies

The corticospinal tract is the motor pathway in the human brain, and corona radiata (CR) is an important location to diagnose stroke. We detected hand and foot motor fiber tracts in the CR to investigate accurate locations using diffusion-tensor imaging (DTI) and functional imaging. Ten right-handed normal volunteers participated in this study. We used a probabilistic tracking algorithm, a brain normalization method, and functional imaging results to set out region of interests. Moreover, our results were compared to previous results of lesion studies to confirm their accuracy and usefulness. The location measurements were performed in two index types; anteriority index on the basis of the anterior and posterior location of lateral ventricle and laterality index on the basis of the left and right location. The anteriority indices were 56.40/43.2 (hand/foot) at the upper CR and lower CR 40.72/30.90 at the lower CR. The measurements of anteriority and laterality of motor fibers were represented as anteriority index 0.40/0.31 and laterality index 0.60/0.47 (hand/foot). Our results showed that the hand and foot fibers were in good agreements with previous lesion studies. This study and approaches can be used as a standard for DTI combined with lesion location studies in patients who need rehabilitation or follow-up.

Quantitative volumetric analysis of the optic radiation in the normal human brain using diffusion tensor magnetic resonance imaging-based tractography.

To attain the volumetric information of the optic radiation in normal human brains, we performed diffusion tensor imaging examination in 13 healthy volunteers. Simultaneously, we used a brain normalization method to reduce individual brain variation and increase the accuracy of volumetric information analysis. In addition, tractography-based group mapping method was also used to investigate the probability and distribution of the optic radiation pathways. Our results showed that the measured optic radiation fiber tract volume was a range of about 0.16% and that the fractional anisotropy value was about 0.53. Moreover, the optic radiation probability fiber pathway that was determined with diffusion tensor tractography-based group mapping was able to detect the location relatively accurately. We believe that our methods and results are helpful in the study of optic radiation fiber tract information.

A simple auto prescan calibration method for multislice fast spin echo MRI

The image quality of fast spin echo (FSE) is more sensitive than the typical spin echo pulse sequence caused by the eddy current effect. Microsecond‐scale misalignment of primary spin echoes produces a large spatial variation in image signal intensity. In this study, we describe an auto prescan calibration method that can improve the FSE image quality and minimize the eddy current effect on the image. We used a 0.32 T MRI system and obtained phantom and lumbar images. For FSE image correction, the optimal ranges and steps were determined to find the appropriate values, which were added to or subtracted from the gradient area values for each slice. The appropriate value of each slice could be found using the maximum signal intensity when the refocusing gradient area was changed by a number of steps in the optimal range. The determined value of each slice was applied before each slice image acquisition. The determined optimal step numbers and ranges were applied to in vivo image acquisition, and confirmed the reconstructed image quality. Based on our results, the obtained phantom and lumbar images were shown to be well corrected. The corrected images represented the image quality improvement and elimination of ghosting and blurring artifacts. In conclusion, we have proposed an FSE correction technique that automatically adjusts slice selection for the refocusing gradient balance during prescan, and confirmed that the calibration technique is very reliable even within complex in vivo images. We believe that our proposed technique will greatly benefit in MRI systems.

Sparse sampling MR image reconstruction using bregman iteration: A feasibility study at low tesla MRI system

MR images reconstruction need many samples that are sequentially sampled by phase encoding gradients in MRI system. MRI takes long scan time, therefore, many researchers have been studied to reduce scan time. Especially, the Compressed Sensing (CS) that is used sparse images and reconstruction from fewer sampling data which the k-space is not fully sampled. Recently, an iterative technique based on Bregman method is developed for denoising. The Bregman iteration method improves on the Total Variation (TV) regularization by gradually recovering the fine scale structures that are usually lost in the TV regularization. In this study, we studied sparse sampling image reconstruction using Bregman iteration at low tesla MRI system for improving the temporal resolution and validated the usefulness. The image was obtained at 0.32T MRI scanner (Magfinder II, Genpia, Korea) using 2D T1-weighed spin-echo pulse sequence with phantom and in-vivo human brain in the head coil. We applied the random k-space sampling and sampling ratios are determined by half of fully sampled k-space. The Bregman iteration was used to generate the final images based on the reduced data. The number of Bregman iterations used for the reconstruction was minimum 1 to maximum 100. We also calculated Root Mean Square Error (RMSE) values from error images that were performed according to number of bregman iterations. The results which are reconstructed images using the bregman iteration to sparse sampling image shown well reconstruction images compared with original images. Moreover, the RMSE values can be seen that sparse reconstructed phantom image and human images are converge to the original image. We confirmed the feasibility of sparse sampling image reconstruction methods using Bregman iteration at low tesla MRI system and obtained good results. Although our results used half of sampling ratio, this method will helpful to increase the temporal resolution at low tesla MRI system.

SU‐F‐I‐22: Development and Implementation of Task‐Specific Modular Phantom for MRI Quality Evaluation

PURPOSE To investigate the potential of a newly developed modular phantom with image quality test structure for MRI quality control. METHODS The modular phantom consists of individual basic mapping (BM) modules, image quality control (QC) modules, and accessories to improve combination variability for multipurpose use. BM modules were designed based on the stud-and-tube coupling system with an internal hollow and an individual enclosed structure. The QC modules include signal-to-noise ratio, image intensity uniformity, geometric accuracy, high-contrast spatial resolution, slice thickness accuracy, slice position accuracy and low-contrast object detectability evaluation test structure. The scanner performance on various coils were evaluated by using image QC module which inserted into BM module. The MR data acquisition was performed using a 1.5 T MRI scanner (MAGNETOM ESSENZA, Siemens, Germany) with two coils, head and breast. The 2D SE T1 axial images of assembled QC modules, which are analogous to the ACR accreditation phantom were acquired in the head coil. We scanned BM modules and QC modules to evaluation off-center impact on the image quality in the breast coil. Oil-filled BM modules and QC modules designed to evaluate geometric accuracy and image intensity uniformity were used. The 2D TSE T2 weighted axial images and short-tau inversion recovery (STIR) image of modules were acquired in the breast coil. RESULTS The evaluated MRI quality was acceptable according to the action criteria from the ACR. Due to non-uniformity across the breast coil, the residual fat contents were shown on the STIR image. For the uniformity of image intensity, the PIU was calculated as 89% in the STIR image. CONCLUSION The results showed the potential of the BM modules and image QC modules in a image quality control for MRI based on the ability of task-specific construction with modular manner. This study was supported by the Medical Metrology Program at the Korea Research Institutes of Standards and Science (16011069).

Signal intensity correction for multichannel MR images using radon transformation

The purpose of this study is to correct signal intensity at low‐field MRI system with multichannel receiver coils using Radon transformation and filtered backprojection (FBP) method. An open‐type 0.32 T MRI system and a body size phantom were used to acquire the MR images. We used various types of coils from 2‐channels to 4‐channels, which minimized the loss of signal. In the intensity correction process, Radon transform was used for the images of each channel and low‐pass filtering was applied to reduce noise. After that FBP was used for the space transform again from the Radon space to the image space. We also made changes to the projection ranges and their intervals, and then confirmed them to evaluate the optimal parameters. All the intensity corrected results were compared with its original sum‐of‐square (SOS) images, and the corrected images showed more uniform and homogeneous intensities than the images without correction. In addition, these results were also shown in the quantitative values through the signal intensity variations according to the cut view along the horizontal lines of the images. The feasibility of our approach and results for signal intensity correction may be useful and helpful for the researchers of low‐field system with multichannel coils.