Biomedical subjects

Jiun-Jie Wang

Publications and source records attributed to Jiun-Jie Wang.

4 recordsLinked to original sources

PubMed2006

The effects of single-trial averaging on the temporal resolution of functional MRI.

Computer simulations and event-related functional MRI (ER-fMRI) experiments were performed to investigate the effects of single-trial averaging and the corresponding contrast-to-noise ratio (CNR) on the minimal resolvable hemodynamic timing difference between brain areas. Three ER-fMRI sessions with temporally delayed (250, 500 and 1,000 ms) visual stimulations between two hemifields, each with 70 repeated single trials, were examined on two subjects. From the computer simulation, the temporal resolution improved as the CNR increased, which reached 500 and 100 ms for CNRs of 1.55 and 6.44, respectively. In the ER-fMRI experiments, the measured CNR increased as more single trials were averaged. The detectability of temporal differences was positively correlated (P<.05) with the CNR in all sessions for one subject but only in the 1,000-ms session for the other subject. Temporal resolution of 1,000 ms was achieved when more than 10 trials were averaged. The 500- and 250-ms delays might be differentiable when more than 20 trials were averaged, but the results were subject-dependent. This study demonstrated that the CNR could be significantly improved by single-trial averaging, which led to an improved temporal resolution of ER-fMRI. Temporal resolution in the range of hundreds of milliseconds was subject-dependent, which might be attributed to the intrinsic spatial variations in the timing of the blood oxygenation level-dependent (BOLD) response.

Adult↗

PubMed2006

Novel diffusion anisotropy indices: an evaluation.

PURPOSE: To systematically evaluate diffusion anisotropy (DA) using newly defined indices based on the diffusion deviation and mean diffusivity approach. MATERIALS AND METHODS: Measures of amplitude, area, and volume of the DA index (DAI) were measured and compared with regard to their sensitivity to changes in DA, susceptibility to noise in the original diffusion-weighted (DW) images, and contrast-to-noise ratio (CNR) in homogenous regions. Simulations were performed under different levels of noise and DA. Human DTI data were acquired from eight normal volunteers. RESULTS: Indices of area and volume measures provided improved resolution for characterizing the DA compared to the eigenvalue ratio. The amplitude measure showed consistent performances with good CNR and less susceptibility to noise in the original data. CONCLUSION: These indices are rotationally invariant without the requirement of eigenvalue sorting. At low anisotropy, all indices have a similar CNR. For larger DA, the first index (the deviation tensor divided by the DT) shows improved sensitivity, contrast-to-noise ratio (CNR), and noise immunity compared to the other indices.

Adult↗

PubMed2005

Selective averaging for the diffusion tensor measurement.

The multishot echo planar imaging sequence was often used in the high-resolution diffusion measurements. However, it is susceptible to motion artifacts because of the requirements of combining the raw data from different acquisitions into one complete k-space data set. Conventional solutions used cardiac gating but greatly extended the total acquisition time. Here we propose a selective averaging algorithm based on the information in the navigator echoes. The data were sampled continuously without cardiac gating. Contributions contaminated by motion were detected by a thresholding algorithm and were discarded during postprocessing. The data were then averaged in the modulus or complex format. Diffusion tensor imaging (DTI) data with isotropic spatial resolution were acquired in phantom as well as from two normal volunteers. The information in the navigator echoes proved to be a good indicator for the extent of motion contamination. Differences were noticed between modulus and complex averaging in DTI quantification, but both showed reduced artifact and improved signal-to-noise ratio.

Adult↗

PubMed2004

3D DT-MRI using a reduced-FOV approach and saturation pulses.

Diffusion tensor imaging (DTI) can provide vital insights into brain connectivity, and may become an important tool for the diagnosis and treatment of neurological disease. However, DTI's intrinsic low signal-to-noise ratio (SNR) and vulnerability to ghosting artifacts can result in poor image quality with low spatial resolution, which limits its clinical applications. In this study, a new double-shot EPI sequence (half-FOV EPI) with high spatial resolution was developed. This method enables DT measurements to be obtained with high isotropic spatial resolution and whole-brain coverage. To avoid ghosting artifacts, the data are combined in image space rather than in k-space.

Adult↗