Biomedical subjects

Zhaohua Ding

Publications and source records attributed to Zhaohua Ding.

10 recordsLinked to original sources

PubMed2006

Unified framework for anisotropic interpolation and smoothing of diffusion tensor images.

To enhance the performance of diffusion tensor imaging (DTI)-based fiber tractography, this study proposes a unified framework for anisotropic interpolation and smoothing of DTI data. The critical component of this framework is an anisotropic sigmoid interpolation kernel which is adaptively modulated by the local image intensity gradient profile. The adaptive modulation of the sigmoid kernel permits image smoothing in homogeneous regions and meanwhile guarantees preservation of structural boundaries. The unified scheme thus allows piece-wise smooth, continuous and boundary preservation interpolation of DTI data, so that smooth fiber tracts can be tracked in a continuous manner and confined within the boundaries of the targeted structure. The new interpolation method is compared with conventional interpolation methods on the basis of fiber tracking from synthetic and in vivo DTI data, which demonstrates the effectiveness of this unified framework.

Algorithms↗

PubMed2006

Improved fiber tractography with Bayesian tensor regularization.

Diffusion tensor tractography suffers from the effects of noise and partial volume averaging (PVA). For reliable reconstruction of fiber pathways, tracking algorithms that are robust to these artifacts are called for. To meet this need, the present study establishes a novel Bayesian regularization framework for fiber tracking that takes into account the effects of noise and PVA, thereby improving tracking accuracy and precision. With this framework, the propagation of a fiber path follows an optimal vector determined by Bayes decision rule; the probability functions involved are modeled on the basis of multivariate normal distributions of diffusion tensor elements, which allows the optimal solution with maximum a posteriori probability to be derived analytically. Parameters for the probability functions are estimated from the uncertainty of tensor elements and the variance among tensors within an oriented sampling volume weighted by fractional anisotropy. Experiments with Monte Carlo simulations, synthetic, and in vivo human diffusion tensor data demonstrate that this specialized scheme enhances the immunity of fiber tracking to noise and PVA, and hence enables fibers to be more faithfully reconstructed.

Adult↗

PubMed2005

Reduction of noise in diffusion tensor images using anisotropic smoothing.

To improve the accuracy of tissue structural and architectural characterization with diffusion tensor imaging, a novel smoothing technique is developed for reducing noise in diffusion tensor images. The technique extends the traditional anisotropic diffusion filtering method by allowing isotropic smoothing within homogeneous regions and anisotropic smoothing along structure boundaries. This is particularly useful for smoothing diffusion tensor images in which direction information contained in the tensor needs to be restored following noise corruption and preserved around tissue boundaries. The effectiveness of this technique is quantitatively studied with experiments on simulated and human in vivo diffusion tensor data. Illustrative results demonstrate that the anisotropic smoothing technique developed can significantly reduce the impact of noise on the direction as well as anisotropy measures of the diffusion tensor images.

Algorithms↗

PubMed2005

Quantification of multiple sclerosis lesion load and brain tissue volumetry using multiparameter MRI: methodology and reproducibility.

Quantitative characterization of multiple sclerosis (MS) lesion load is of considerable interest to clinical follow-up studies. Based on fuzzy clustering of multiparameter magnetic resonance images, we have developed a computer-assisted system for volumetric quantification of brain tissue. Tests on patient data show that the system is very efficient, and volumetric measurements characterized are highly reproducible. The high reproducibility and efficiency offer the potential of routine laboratory and clinical use for quantification of MS lesion load.

Algorithms↗

PubMed2004

Influence of curvature dynamics on pulsatile coronary artery flow in a realistic bifurcation model.

The coronary arteries undergo large dynamic variations during each cardiac cycle due to their position on the beating heart. The local artery curvature varies significantly. In this study the influence of dynamic curvature on coronary artery hemodynamics is analyzed numerically. A realistic model of the bifurcation of the left anterior descending coronary artery and its first diagonal branch is curved by attaching it to the surface of a sphere with time-varying radius based on experimental dynamic curvature data. The description of the blood flow uses the time-dependent, three-dimensional, incompressible Navier-Stokes equations for Newtonian fluids, where the influence of the time-dependent flow domain is taken into account employing the Arbitrary Lagrangian-Eulerian technique. The inlet velocity profiles used in the computer simulation are physiologically realistic. The results show that the skewing of the axial velocity profiles near the branching site is mainly determined by the vessel branch; the bifurcating flow generally dominates the effect of curvature. The influence of curvature increases downstream of the branch. During systole, when curvature is greatest and high curvature variations appear, their effect on the flow patterns and the wall shear stress is dominated by the flow wave. Due to the smaller curvature changes during diastole, only minor effects of curvature variation on the high and relatively constant diastolic flow occur. The results demonstrate the importance of including physiologically realistic flow in the correct phase relationship with vessel motion when simulating coronary artery hemodynamics.

Biomechanical Phenomena↗

PubMed2003

Cluster analysis of muscle functional MRI data.

Muscle functional magnetic resonance imaging (mfMRI) is frequently used to determine spatial patterns of muscle involvement in exercising humans. A frequent finding in mfMRI is that, even within synergistic muscle groups, signal intensity (SI) data from individual voxels can be quite heterogeneous. The purpose of this study was to develop a novel method for organizing heterogeneous mfMRI data into clusters whose members behave similarly to each other but distinctly from members of other clusters and apply it in studies of functional compartmentalization in the anterior compartment of the leg. An algorithm was developed that compared the SI time courses of adjacent voxels and grouped together voxels that were sufficiently similar. The algorithm's performance was verified by using simulated data sets with known regional differences in SI time courses that were then applied to experimental mfMRI data acquired from six male subjects (age 22.6 +/- 0.9 yr, mean +/- SE) who sustained isometric contractions of the dorsiflexors at 40% of maximum voluntary contraction. The experimental data were also characterized by using a traditional analysis (user-specified regions of interest from a single image), in which the relative change in SI and the contrast-to-noise ratio [CNR; 100%x(SI(RESTING) - SI(ACTIVE)/(noise standard deviation)] were measured. In general, clusters were found in areas in which the CNR exceeded 5. Cluster analysis made functional distinctions between regions of muscle that were not seen with traditional analysis. In conclusion, cluster analysis's use of the full SI time course provides more sensitivity to muscle functional compartmentation than traditional analysis.

Adult↗

PubMed2003

Classification and quantification of neuronal fiber pathways using diffusion tensor MRI.

Quantitative characterization of neuronal fiber pathways in vivo is of significant neurological and clinical interest. Using the capability of MR diffusion tensor imaging to determine the local orientations of neuronal fibers, novel algorithms were developed to bundle neuronal fiber pathways reconstructed in vivo with diffusion tensor images and to quantify various physical and geometric properties of fiber bundles. The reliability of the algorithms was examined with reproducibility tests. Illustrative results show that consistent physical and geometric measurements of novel properties of neuronal tissue can be obtained, which offer considerable potential for the quantitative study of fiber pathways in vivo.

Algorithms↗

PubMed2003

Effects of cardiac motion on right coronary artery hemodynamics.

The purpose of this work was to investigate the effects of physiologically realistic cardiac-induced motion on hemodynamics in human right coronary arteries. The blood flow patterns were numerically simulated in a modeled right coronary artery (RCA) having a uniform circular cross section of 2.48 mm diam. Arterial motion was specified based on biplane cineangiograms, and incorporated physiologically realistic bending and torsion. Simulations were carried out with steady and pulsatile inflow conditions (mean ReD=233, alpha=1.82) in both fixed and moving RCA models, to evaluate the relative importance of RCA motion, flow pulsation, and the interaction between motion and flow pulsation. RCA motion with a steady inlet flow rate caused variations in wall shear stress (WSS) magnitude up to 150% of the inlet Poiseuille value. There was significant spatial variability in the magnitude of this motion-induced WSS variation. However, the time-averaged WSS distribution was similar to that predicted in a static model representing the time-averaged geometry. Furthermore, the effects of flow pulsatility dominated RCA motion-induced effects; specifically, there were only modest differences in the WSS history between simulations conducted in fixed and moving RCA models with pulsatile inflow. RCA motion has little effect on time-averaged WSS patterns. It has a larger effect on the temporal variation of WSS, but even this effect is overshadowed by the variations in WSS due to flow pulsation. The hemodynamic effects of RCA motion can, therefore, be ignored as a first approximation in modeling studies.

Arteries↗

PubMed2002

Validation of diffusion tensor MRI-based muscle fiber tracking.

Diffusion-tensor (DT) MRI fiber tracking may potentially be used for in vivo structural analysis. The purpose of this study was to assess quantitatively the ability of a DT-MRI fiber-tracking algorithm to measure the fiber orientation (pennation) in skeletal muscle in vivo. In five adult Sprague-Dawley rats, the pennation angle (theta) was measured in the rat lateral gastrocnemius with DT-MRI (theta(DT-MRI)) and by direct anatomical inspection (DAI) (theta(DAI)). The mean theta(DT-MRI) was not significantly different from the mean theta(DAI). In addition, the two methods were highly correlated (r = 0.89) and the regression of theta(DT-MRI) on theta(DAI) resulted in a slope not significantly different from 1 and an intercept not significantly different from zero. These data indicate that DT-MRI-based fiber tracking as implemented here is a valid tool for in vivo structural analysis of small-animal skeletal muscle.

Animals↗

PubMed2002

Coronary artery dynamics in vivo.

There is considerable evidence that the localization and evolution of vascular disease are mediated, at least in part, by mechanical factors. The mechanical environment of the coronary arteries, which are tethered to the beating heart, is influenced by cardiac motion; the motion of the vessels must be described quantitatively to characterize fully the mechanical forces acting on and in the vessel wall. Several techniques that have been used to characterize coronary artery dynamics from biplane cineangiograms are described and illustrated. There is considerable variability in dynamic geometric parameters from site to site along a vessel, between the right and left anterior descending arteries, and among individuals, consistent with the hypotheses that variations in stresses mediated by geometry and dynamics affect the localization of atherosclerosis and individual risk of coronary heart disease. The few frankly atherosclerotic vessels that have been examined exhibit high torsions in the neighborhood of lesions, an observation which may have etiologic or diagnostic implications.

Algorithms↗