Fang Pu

A numerical study on the flow of blood and the transport of LDL in the human aorta: the physiological significance of the helical flow in the aortic arch

It has been proposed that a mass transfer phenomenon called concentration polarization of low-density lipoproteins (LDLs) may occur in the arterial system and is likely involved in the localization of atherogenesis. To test the hypothesis that concentration polarization of LDL may be suppressed by the helical flow pattern in the human aorta, hence sparing the ascending aorta from atherosclerosis, the effects of aortic torsion, branching, curvature, and taper on blood flow and LDL transport in the lumen were simulated numerically under steady-state flow conditions using four aorta models constructed based on in vivo MRI slices. The results showed that it was the aortic torsion that induced the helical flow in the aortic arch, stabilizing the flow of blood in the aorta, and compensated the adverse effects of the aortic curvature on blood flow and LDL transport. The helical flow reduced the luminal surface LDL concentration in the aortic arch and probably played a role in suppressing severe polarization of LDL at the entrances of the three branches on the arch, hence, protecting them from atherogenesis. The taper of the aorta was another important feature of the aorta that further stabilized the flow of blood and delayed the attenuation of the helical flow, making it move beyond the arch and into the beginning part of the descending aorta. The results therefore may account for why the ascending aorta and the arch are relatively free of atherosclerosis.

Why Do Woodpeckers Resist Head Impact Injury: A Biomechanical Investigation

Head injury is a leading cause of morbidity and death in both industrialized and developing countries. It is estimated that brain injuries account for 15% of the burden of fatalities and disabilities, and represent the leading cause of death in young adults. Brain injury may be caused by an impact or a sudden change in the linear and/or angular velocity of the head. However, the woodpecker does not experience any head injury at the high speed of 6–7 m/s with a deceleration of 1000 g when it drums a tree trunk. It is still not known how woodpeckers protect their brain from impact injury. In order to investigate this, two synchronous high-speed video systems were used to observe the pecking process, and the force sensor was used to measure the peck force. The mechanical properties and macro/micro morphological structure in woodpeckers head were investigated using a mechanical testing system and micro-CT scanning. Finite element (FE) models of the woodpeckers head were established to study the dynamic intracranial responses. The result showed that macro/micro morphology of cranial bone and beak can be recognized as a major contributor to non-impact-injuries. This biomechanical analysis makes it possible to visualize events during woodpecker pecking and may inspire new approaches to prevention and treatment of human head injury.

Hippocampal Shape Analysis of Alzheimer Disease Based on Machine Learning Methods

BACKGROUND AND PURPOSE: Alzheimer disease (AD) is a neurodegenerative disease characterized by progressive dementia. The hippocampus is particularly vulnerable to damage at the very earliest stages of AD. This article seeks to evaluate critical AD-associated regional changes in the hippocampus using machine learning methods. MATERIALS AND METHODS: High-resolution MR images were acquired from 19 patients with AD and 20 age- and sex-matched healthy control subjects. Regional changes of bilateral hippocampi were characterized using computational anatomic mapping methods. A feature selection method for support vector machine and leave-1-out cross-validation was introduced to determine regional shape differences that minimized the error rate in the datasets. RESULTS: Patients with AD showed significant deformations in the CA1 region of bilateral hippocampi, as well as the subiculum of the left hippocampus. There were also some changes in the CA2–4 subregions of the left hippocampus among patients with AD. Moreover, the left hippocampal surface showed greater variations than the right compared with those in healthy control subjects. The accuracies of leave-1-out cross-validation and 3-fold cross-validation experiments for assessing the reliability of these subregions were more than 80% in bilateral hippocampi. CONCLUSION: Subtle and spatially complex deformation patterns of hippocampus between patients with AD and healthy control subjects can be detected by machine learning methods.

Flow patterns and wall shear stress distribution in human internal carotid arteries: The geometric effect on the risk for stenoses

It has been widely observed that atherosclerotic stenosis occurs at sites with complex hemodynamics, such as arteries with high curvature or bifurcations. These regions usually have very low or highly oscillatory wall shear stress (WSS). In the present study, 3D sinusoidally pulsatile blood flow through the models of internal carotid artery (ICA) with different geometries was investigated with computational simulation. Three preferred sites of stenoses were found along the carotid siphon with low and highly oscillatory WSS. The risk for stenoses at these sites was scaled with the values of time-averaged WSS and oscillating shear index (OSI). The local risk for stenoses at every preferred site of stenoses was found different between 3 types of ICA, indicating that the geometry of the blood vessel plays significant roles in the atherogenesis. Specifically, the large curvature and planarity of the vessel were found to increase the risk for stenoses, because they tend to lower WSS and elevate OSI. Therefore, the geometric study makes it possible to estimate the stenosis location in the ICA siphon as long as the shape of ICA was measured.

Regional white matter decreases in Alzheimer's disease using optimized voxel-based morphometry

Background: Most studies that attempt to clarify structural abnormalities related to functional disconnection in patients with Alzheimers disease (AD) have focused on exploring pathological changes in cortical gray matter. However, white matter fibers connecting these cerebral areas may also be abnormal. Purpose: To investigate the regional changes of white matter volume in patients with AD compared to healthy subjects. Material and Methods: White matter volume changes in whole-brain magnetic resonance images acquired from 19 patients with AD and 20 healthy subjects (control group) were observed using the optimized voxel-based morphometry (VBM) method. In addition, the corpus callosum (CC) of AD patients and the control group was investigated further by outlining manually the boundary of the CC on a midsagittal slice. Each area of the CC was then corrected by dividing each subjects intracranial area in the midsagittal plane. Results: Compared with the control group, AD patients showed significantly reduced white matter volumes in the posterior part of the CC and the temporal lobe in the left and right hemispheres. Moreover, the voxel showing peak statistical difference in the posterior of the CC was left sided. The five subdivisions of the CC were also significantly smaller among the AD patients relative to the control group. Conclusion: Our findings suggest that these abnormalities in white matter regions may contribute to the functional disconnections in AD.

Reliability and Validity of Kinect RGB-D Sensor for Assessing Standing Balance

Microsoft Kinect uses a built-in RGB-D sensor and the skeleton tracking algorithm to capture 3-D movements of the human body. It also has the potential for assessing postural stability, which is fundamental for most motor activities. The aim of this paper was to investigate whether standing balance can be evaluated reliably and validly by this low-cost device. Nine healthy subjects were required to maintain balance during three standing positions (double limb stance with feet apart, double limb stance with feet together and single limb stance). The center of mass (COM) was calculated from the bodys kinematic data acquired by the Kinect system and Optotrak Certus motion capture system. The position variability and average velocity of the COM in the horizontal plane were calculated and used to evaluate the subjects balance. These COM parameters from the two systems showed excellent and comparable test-retest reliability (intraclass correlation coefficient ). In addition, although the average velocity of the COM calculated from Kinect was significantly lower, each COM parameter showed excellent concurrent validity and a significant linear relationship existed between the two systems, which meant that biases may be corrected using linear calibration equations. Therefore, Kinect may be a valid, reliable, and convenient device for assessing standing balance when its measured COM parameters are properly calibrated.

Age-related changes in brain structural covariance networks

Previous neuroimaging studies have suggested that cerebral changes over normal aging are not simply characterized by regional alterations, but rather by the reorganization of cortical connectivity patterns. The investigation of structural covariance networks (SCNs) using voxel-based morphometry is an advanced approach to examining the pattern of covariance in gray matter (GM) volumes among different regions of the human cortex. To date, how the organization of critical SCNs change during normal aging remains largely unknown. In this study, we used an SCN mapping approach to investigate eight large-scale networks in 240 healthy participants aged 18–89 years. These participants were subdivided into young (18–23 years), middle aged (30–58 years), and older (61–89 years) subjects. Eight seed regions were chosen from widely reported functional intrinsic connectivity networks. The voxels showing significant positive associations with these seed regions were used to describe the topological organization of an SCN. All of these networks exhibited non-linear patterns in their spatial extent that were associated with normal aging. These networks, except the primary motor network, had a distributed topology in young participants, a sharply localized topology in middle aged participants, and were relatively stable in older participants. The structural covariance derived using the primary motor cortex was limited to the ipsilateral motor regions in the young and older participants, but included contralateral homologous regions in the middle aged participants. In addition, there were significant between-group differences in the structural networks associated with language-related speech and semantics processing, executive control, and the default-mode network (DMN). Taken together, the results of this study demonstrate age-related changes in the topological organization of SCNs, and provide insights into normal aging of the human brain.

Effect of different labor forces on fetal skull molding

Fetal head molding is important for adapting the fetal head to the birth canal during vaginal delivery; however, excessive deformation of fetal head may lead to severe complications. Although labor force is one of the major factors which cause deformation of the fetal head, its effect on fetal head molding has not been quantitatively investigated yet. We examined this effect by using a finite element modeling approach. Firstly, a geometric model was created by scanning a polyethylene replica of fetal skull model with a white light three-dimensional scanner. Secondly, a nonlinear finite element model was proposed based on the geometric model. Next, the simulation results of the proposed model were verified against the experimental data reported in other literatures and they showed good agreement with the experimental observations. After this validation, the proposed model was used to simulate the fetal skull deformations under different labor forces. Simulation results illustrated that the fetal skull diameters and modified molding index (MMI) increased when the labor force was increased. Parietal bone around bregma and frontal bone around coronal suture undertook more stress, and parietal and frontal bones around coronal suture undertook more spatial and rotational displacement under larger labor force. The suboccipito-bregmatic diameter (SOBD) was more sensitive to the changes of labor force than other fetal skull diameters. The simulation results revealed the quantitative relationship between the labor force and fetal skull molding during delivery. In the future, if the degree of fetal skull molding is directly related to that of the head injury, the relationship investigated in this study may be used to predict the head injury by measuring the labor force during delivery.

Abnormal Changes of Multidimensional Surface Features Using Multivariate Pattern Classification in Amnestic Mild Cognitive Impairment Patients

Previous studies have suggested that amnestic mild cognitive impairment (aMCI) is associated with changes in cortical morphological features, such as cortical thickness, sulcal depth, surface area, gray matter volume, metric distortion, and mean curvature. These features have been proven to have specific neuropathological and genetic underpinnings. However, most studies primarily focused on mass-univariate methods, and cortical features were generally explored in isolation. Here, we used a multivariate method to characterize the complex and subtle structural changing pattern of cortical anatomy in 24 aMCI human participants and 26 normal human controls. Six cortical features were extracted for each participant, and the spatial patterns of brain abnormities in aMCI were identified by high classification weights using a support vector machine method. The classification accuracy in discriminating the two groups was 76% in the left hemisphere and 80% in the right hemisphere when all six cortical features were used. Regions showing high weights were subtle, spatially complex, and predominately located in the left medial temporal lobe and the supramarginal and right inferior parietal lobes. In addition, we also found that the six morphological features had different contributions in discriminating the two groups even for the same region. Our results indicated that the neuroanatomical patterns that discriminated individuals with aMCI from controls were truly multidimensional and had different effects on the morphological features. Furthermore, the regions identified by our method could potentially be useful for clinical diagnosis.

Age-related changes in the surface morphology of the central sulcus

We utilized a sulcus-based computational approach to investigate the relationship between the three-dimensional (3D) morphology of the central sulcus (CS) and age. The anterior and posterior walls of the CS were manually outlined using high-resolution magnetic resonance images of 295 right-handed healthy participants (age range: 18~94years). Surface reconstruction and parameterization methods were employed to create anatomical correspondence of surface locations across participants. Four surface metrics, including average sulcal length (SL), surface area, fractal dimension (FD) and sulcal span, were used to represent the 3D morphology of the CS. We found significant age-related decreases in the surface area for all walls of the CS, the SL for posterior walls of the CS and the FD for posterior wall of right CS. Age-related increases were found in the sulcal spans between the anterior and posterior walls. These surface metrics (except FD) exhibited leftward asymmetries. Specifically, age-related changes in surface morphology progressed more rapidly in the posterior than in the anterior walls. Finally, sex differences were found only in the FD of the right anterior wall of the CS. Taken together, our results show age-related changes in the surface morphology of the CS and therefore provide insights into the normal aging process.