Yeji Han

Projection reconstruction MR imaging using FOCUSS

The focal underdetermined system solver (FOCUSS) was originally designed to obtain sparse solutions by successively solving quadratic optimization problems. This article adapts FOCUSS for a projection reconstruction MR imaging problem to obtain high resolution reconstructions from angular under‐sampled radial k‐space data. We show that FOCUSS is effective for projection reconstruction MRI, since medical images are usually sparse in some sense and the center region of the undersampled radial k‐space samples still provides a low resolution, yet meaningful, image essential for the convergence of FOCUSS. The new algorithm is successfully applied for synthetic data as well as in vivo brain imaging obtained by under‐sampled radial spin echo sequence. Magn Reson Med 57:764–775, 2007.

Brain activation related to affective dimension during thermal stimulation in humans: a functional magnetic resonance imaging study.

The aim of this study was to identify the activated brain region that is involved with the affective dimension of thermal stimulation (not pain, but innocuous warming) using functional MR imaging. Twelve healthy, right-handed male subjects participated in the study. Thermal stimulation with two different temperatures of 41°C and 34°C was applied to the subjects using a fomentation pack, wrapped around the right lower leg of each subject. On the basis of the subjects’ responses after the scanning sessions, the authors were able to observe that the subjects felt “warm” and “slightly pleasant and comfortable” under the 41°C condition. The experimental results indicated that warm stimulation produced a significant increase of activation compared to thermal neutral stimulation in various regions such as contralateral insular, ipsilateral cerebellum, ipsilateral putamen, contralateral middle frontal gyrus, ipsilateral inferior frontal gyrus, contralateral postcentral gyrus, and contralateral paracentral lobule. The activated regions are known to be related to thermal sensory, affective/emotional awareness, cognitive functions, sensory-discrimination, and emotion/affective processing, and so on. These results suggest that an appropriate thermal stimulation can produce a positive emotion and activate emotion/affect related regions of the brain.

Hierarchical fuzzy segmentation of brain MR images

In brain magnetic resonance (MR) images, image segmentation and 3D visualization are very useful tools for the diagnosis of abnormalities. Segmentation of white matter (WM), gray matter (GM), and cerebrospinal fluid (CSF) is the basic process for 3D visualization of brain MR images. Of the many algorithms, the fuzzy c‐means (FCM) technique has been widely used for segmentation of brain MR images. However, the FCM technique does not yield sufficient results under radio frequency (RF) nonuniformity. We propose a hierarchical FCM (HFCM), which provides good segmentation results under RF nonuniformity and does not require any parameter setting. We also generate Talairach templates of the brain that are deformed to 3D brain MR images. Using the deformed templates, only the cerebrum region is extracted from the 3D brain MR images. Then, the proposed HFCM partitions the cerebrum region into WM, GM, and CSF.

Skull-stripping method for brain MRI using a 3D level set with a speedup operator.

To extract the brain region from brain magnetic resonance (MR) images using a fast 3D level set method and a refinement process.

An automatic cerebellum extraction method in T1-weighted brain MR images using an active contour model with a shape prior☆

PURPOSE The objective of this paper was to automatically segment the cerebellum from T1-weighted human brain magnetic resonance (MR) images. MATERIALS AND METHODS The proposed method constructs a cerebellum template using five sets of 3-T MR imaging (MRI) data, which are used to determine the initial position and the shape prior of the cerebellum for the active contour model. Our formulation includes the active contour model with shape prior, which thereby maintains the shape of the template. The proposed active contour model is sequentially applied to sagittal-, coronal- and transverse-view images. To evaluate the proposed method, it is applied to BrainWeb data and a 3-T MRI data set and compared with FreeSurfer with respect to performance assessment metrics. RESULTS The segmented cerebellum was compared with the results from FreeSurfer. Using the manually segmented cerebellum as reference, we measured the average Jaccard coefficients of the proposed method, which were 0.882 and 0.885 for the BrainWeb data and 3-T MRI data set, respectively. CONCLUSION We presented the active contour model with shape prior for extracting the cerebellum from T1-weighted brain MR images. The proposed method yielded a robust and accurate segmentation result.

Projection-based estimation and nonuniformity correction of sensitivity profiles in phased-array surface coils.

To develop a novel approach for calculating the accurate sensitivity profiles of phased‐array coils, resulting in correction of nonuniform intensity in parallel MRI.

A pulse artifact removal method considering artifact variations in the simultaneous recording of EEG and fMRI.

A simultaneous recording of electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) can provide high spatiotemporal information of brain activity. However, a proper analysis of the EEG signals is often hindered by various artifacts. In particular, pulse artifact (PA) induced from the heartbeat of a subject interferes with reliable measurements of the EEG signal. A new PA removal method that takes into account the delay variation between the heartbeat and PA and the window size variation in PA is presented in order to improve the detection and suppression of PA in EEG signals. A PA is classified into either a normal PA or a deformed PA. Only normal PAs are averaged to generate a PA template that is used to remove PAs from the measured EEG signals. The performance of the proposed method was evaluated by simulated data and real EEG measurements from epilepsy patients. The results are compared with those from conventional methods.

High-resolution fMRI with higher-order generalized series imaging and parallel imaging techniques (HGS-parallel)

To develop a novel approach for high‐resolution functional MRI (fMRI) using the conventional gradient‐echo sequence.

Segmentation of Brain Parenchyma using Bilateral Filtering and Region Growing

When the non-diffusion weighted images (non-DWIs) and the diffusion weighted images (DWIs) are acquired by a fast imaging sequence, they suffer from several artifacts such as N/2 ghost, subject motion, eddy current, etc. These artifacts act as a noise in the background area of the human brain. To extract the brain region from the noisy background, brain parenchyma segmentation has been used. Several segmentation methods presented so far cannot address this problem well. In this study, we propose a novel segmentation method of brain contour in non-DWIs using bilateral filtering, which can reduce the background noise while edge-preserving, and region growing. We compare the segmentation results from various methods, and the proposed method shows better segmentation results than those from other schemes.

Neural Activations of Guided Imagery and Music in Negative Emotional Processing: A Functional MRI Study

BACKGROUND The Bonny Method of Guided Imagery and Music uses music and imagery to access and explore personal emotions associated with episodic memories. Understanding the neural mechanism of guided imagery and music (GIM) as combined stimuli for emotional processing informs clinical application. OBJECTIVE We performed functional magnetic resonance imaging (fMRI) to demonstrate neural mechanisms of GIM for negative emotional processing when personal episodic memory is recalled and re-experienced through GIM processes. METHODS Twenty-four healthy volunteers participated in the study, which used classical music and verbal instruction stimuli to evoke negative emotions. To analyze the neural mechanism, activated regions associated with negative emotional and episodic memory processing were extracted by conducting volume analyses for the contrast between GIM and guided imagery (GI) or music (M). RESULTS The GIM stimuli showed increased activation over the M-only stimuli in five neural regions associated with negative emotional and episodic memory processing, including the left amygdala, left anterior cingulate gyrus, left insula, bilateral culmen, and left angular gyrus (AG). Compared with GI alone, GIM showed increased activation in three regions associated with episodic memory processing in the emotional context, including the right posterior cingulate gyrus, bilateral parahippocampal gyrus, and AG. No neural regions related to negative emotional and episodic memory processing showed more activation for M and GI than for GIM. CONCLUSIONS As a combined multimodal stimulus, GIM may increase neural activations related to negative emotions and episodic memory processing. Findings suggest a neural basis for GIM with personal episodic memories affecting cortical and subcortical structures and functions.