Eric T. Han

Bio: Eric T. Han is an academic researcher from GE Healthcare. The author has contributed to research in topics: Diffusion MRI & Imaging phantom. The author has an hindex of 27, co-authored 41 publications receiving 3563 citations. Previous affiliations of Eric T. Han include General Electric & University of California, San Diego.

Musculoskeletal MRI at 3.0 T: relaxation times and image contrast.

Abstract: OBJECTIVE The purpose of our study was to measure relaxation times in musculoskeletal tissues at 15 and 30 T to optimize musculoskeletal MRI methods at 30 TMATERIALS AND METHODS In the knees of five healthy volunteers, we measured the T1 and T2 relaxation times of cartilage, synovial fluid, muscle, marrow, and fat at 15 and 30 T The T1 relaxation times were measured using a spiral Look-Locker sequence with eight samples along the T1 recovery curve The T2 relaxation times were measured using a spiral T2 preparation sequence with six echoes Accuracy and repeatability of the T1 and T2 measurement sequences were verified in phantomsRESULTS T1 relaxation times in cartilage, muscle, synovial fluid, marrow, and subcutaneous fat at 30 T were consistently higher than those measured at 15 T Measured T2 relaxation times were reduced at 30 T compared with 15 T Relaxation time measurements in vivo were verified using calculated and measured signal-to-noise results Relaxation times were used to deve

Q-ball reconstruction of multimodal fiber orientations using the spherical harmonic basis.

Abstract: Diffusion tensor imaging (DTI) accurately delineates white matter pathways when the Gaussian model of diffusion is valid. However, DTI yields erroneous results when diffusion takes on a more complex distribution, as is the case in the brain when fiber tracts cross. High angular resolution diffusion imaging (HARDI) overcomes this limitation of DTI by more fully characterizing the angular dependence of intravoxel diffusion. Among the various HARDI methods that have been proposed, QBI offers advantages such as linearity, model independence, and relatively easy implementation. In this work, reconstruction of the q-ball orientation distribution function (ODF) is reformulated in terms of spherical harmonic basis functions, yielding an analytic solution with useful properties of a frequency domain representation. The harmonic basis is parsimonious for typical b-values, which enables the ODF to be synthesized from a relatively small number of noisy measurements and thus brings the technique closer to clinical feasibility from the standpoint of total imaging time. The proposed method is assessed using Monte Carlo computer simulations and compared with conventional q-ball reconstruction using spherical RBFs. In vivo results from 3T whole-brain HARDI of adult volunteers are also provided to verify the underlying mathematical theory.

PROMO: Real-time prospective motion correction in MRI using image-based tracking.

Abstract: Artifacts caused by patient motion during scanning remain a serious problem in most MRI applications The prospective motion correction technique attempts to address this problem at its source by keeping the measurement coordinate system fixed with respect to the patient throughout the entire scan process In this study, a new image-based approach for prospective motion correction is described, which utilizes three orthogonal two-dimensional spiral navigator acquisitions, along with a flexible image-based tracking method based on the extended Kalman filter algorithm for online motion measurement The spiral navigator/extended Kalman filter framework offers the advantages of image-domain tracking within patient-specific regions-of-interest and reduced sensitivity to off-resonance-induced corruption of rigid-body motion estimates The performance of the method was tested using offline computer simulations and online in vivo head motion experiments In vivo validation results covering a broad range of staged head motions indicate a steady-state error of less than 10% of the motion magnitude, even for large compound motions that included rotations over 15 deg A preliminary in vivo application in three-dimensional inversion recovery spoiled gradient echo (IR-SPGR) and three-dimensional fast spin echo (FSE) sequences demonstrates the effectiveness of the spiral navigator/extended Kalman filter framework for correcting three-dimensional rigid-body head motion artifacts prospectively in high-resolution three-dimensional MRI scans

DWI of the spinal cord with reduced FOV single-shot EPI

Abstract: Single-shot echo-planar imaging (ss-EPI) has not been used widely for diffusion-weighted imaging (DWI) of the spinal cord, because of the magnetic field inhomogeneities around the spine, the small cross-sectional size of the spinal cord, and the increased motion in that area due to breathing, swallowing, and cerebrospinal fluid (CSF) pulsation. These result in artifacts with the usually long readout duration of the ss-EPI method. Reduced field-of-view (FOV) methods decrease the required readout duration for ss-EPI, thereby enabling its practical application to imaging of the spine. In this work, a reduced FOV single-shot diffusion-weighted echo-planar imaging (ss-DWEPI) method is proposed, in which a 2D spatially selective echo-planar RF excitation pulse and a 180 degrees refocusing pulse reduce the FOV in the phase-encode (PE) direction, while suppressing the signal from fat simultaneously. With this method, multi slice images with higher in-plane resolutions (0.94 x 0.94 mm(2) for sagittal and 0.62 x 0.62 mm(2) for axial images) are achieved at 1.5 T, without the need for a longer readout.

Isotropic MRI of the Knee with 3D Fast Spin-Echo Extended Echo-Train Acquisition (XETA): Initial Experience

Abstract: OBJECTIVE The purpose of our study was to prospectively compare a recently developed method of isotropic 3D fast spin-echo (FSE) with extended echo-train acquisition (XETA) with 2D FSE and 2D fast recovery FSE (FRFSE) for MRI of the kneeSUBJECTS AND METHODS Institutional review board approval, Health Insurance Portability and Accounting Act (HIPAA) compliance, and informed consent were obtained We studied 10 healthy volunteers and one volunteer with knee pain using 3D FSE XETA, 2D FSE, and 2D FRFSE Images were obtained both with and without fat suppression Cartilage and muscle signal-to-noise ratio (SNR) and cartilage-fluid contrast-to-noise ratio (CNR) were compared using a Student's t test We also compared reformations of 3D FSE XETA with 2D FSE images directly acquired in the axial planeRESULTS Cartilage SNR was higher with 3D FSE XETA (568 ± 9 [SD]) compared with the 2D FSE (458 ± 8, p < 001) and 2D FRFSE (325 ± 53, p < 001) Muscle SNR was significantly higher with 3D FSE XETA (521 ±

T1, T2 relaxation and magnetization transfer in tissue at 3T

Abstract: T1, T2, and magnetization transfer (MT) measurements were performed in vitro at 3 T and 37 degrees C on a variety of tissues: mouse liver, muscle, and heart; rat spinal cord and kidney; bovine optic nerve, cartilage, and white and gray matter; and human blood. The MR parameters were compared to those at 1.5 T. As expected, the T2 relaxation time constants and quantitative MT parameters (MT exchange rate, R, macromolecular pool fraction, M0B, and macromolecular T2 relaxation time, T2B) at 3 T were similar to those at 1.5 T. The T1 relaxation time values, however, for all measured tissues increased significantly with field strength. Consequently, the phenomenological MT parameter, magnetization transfer ratio, MTR, was lower by approximately 2 to 10%. Collectively, these results provide a useful reference for optimization of pulse sequence parameters for MRI at 3 T.