The ellipsoidal area ratio: an alternative anisotropy index for diffusion tensor imaging

The Effect of Design and Size of the Fluid-Bed Equipment on the Particle Size-Dependent Trend of Particle Coating Thickness and Drug Prolonged-Release Profile

The focus of the current work is to study and demonstrate the impact of the design, the scale, and settings of fluid-bed coating equipment on the differences in pellet coating thickness, which in case of prolonged-release pellets dictates the drug release. In the first set of coating experiments, the pellet cores were coated with the Tartrazine dye with the aim of estimating the coating equipment performance in terms of coating thickness distribution, assessed through color hue. In the second set, drug-layered pellets were film-coated with prolonged-release coating and dissolution profile tests were performed to estimate the thickness and uniformity of the coating thickness among differently sized pellets. In both study parts, film coating was performed at the laboratory and the pilot scale and essentially two types of distribution plate and different height adjustments of the draft tube were compared. The dye coating study proved to be extremely useful, as the results enable process correction and the optimal use of the process equipment in combination with the appropriate process parameters. Preferential film coating of larger drug-containing pellets was confirmed on the laboratory scale, while on the pilot scale, it was possible to achieve preferential coating of smaller pellets using rational alternatives of settings, which is desirable in terms of particle size-independent drug release profile of such prolonged-release dosage forms.

Abundance of coral-associated fauna in relation to depth and eutrophication along the leeward side of Curaçao, southern Caribbean

Coral-associated invertebrates contribute much to the biodiversity of Caribbean coral reefs. Although the nature of their symbiotic relation is usually not fully understood, they can cause damage to their hosts, especially when they occur in high densities. The abundance of seven groups of coral-associated invertebrates was investigated on reefs along the leeward side of Curaçao, southern Caribbean. In particular, coral barnacles (Pyrgomatidae), boring mussels (Mytilidae: Leiosolenus spp.), gall crabs (Cryptochiridae), and Christmas tree worms (Serpulidae: Spirobranchus spp.) were recorded together with their host corals by means of a photo survey at four depths (5, 10, 15, 20 m) and across seven sites with high and five sites with low eutrophication values (based on δ15N isotope data). Feather duster worms (Sabellidae: Anamobaea), coral blennies (Chaenopsidae: Acanthemblemaria), and worm snails (Vermetidae: Petaloconchus) were insufficiently abundant for thorough quantitative analyses. The results show a decrease in the number of barnacles and Christmas tree worms per host over depth, which could be related to the availability of their host corals. Sites with high δ15N values show a higher abundance of barnacles and Christmas tree worms per host than sites with low values. This indicates that eutrophication could be favourable for these filter feeding organisms but when their densities become too high, they tend to overgrow their hosts and may become a threat to them.

Investigating the structure-function relationship of the corticomotor system early after stroke using machine learning

BACKGROUND

Motor outcomes after stroke can be predicted using structural and functional biomarkers of the descending corticomotor pathway, typically measured using magnetic resonance imaging and transcranial magnetic stimulation, respectively. However, the precise structural determinants of intact corticomotor function are unknown. Identifying structure-function links in the corticomotor pathway could provide valuable insight into the mechanisms of post-stroke motor impairment. This study used supervised machine learning to classify upper limb motor evoked potential status using MRI metrics obtained early after stroke.

METHODS

Retrospective data from 91 patients (49 women, age 35-97 years) with moderate to severe upper limb weakness within a week after stroke were included in this study. Support vector machine classifiers were trained using metrics from T1- and diffusion-weighted MRI to classify motor evoked potential status, empirically measured using transcranial magnetic stimulation.

RESULTS

Support vector machine classification of motor evoked potential status was 81% accurate, with false positives more common than false negatives. Important structural MRI metrics included diffusion anisotropy asymmetry in the supplementary and pre-supplementary motor tracts, maximum cross-sectional lesion overlap in the sensorimotor tract and ventral premotor tract, and mean diffusivity asymmetry in the posterior limbs of the internal capsule.

INTERPRETATIONS

MRI measures of corticomotor structure are good but imperfect predictors of corticomotor function. Residual corticomotor function after stroke depends on both the extent of cross-sectional macrostructural tract damage and preservation of white-matter microstructural integrity. Analysing the corticomotor pathway using a multivariable MRI approach across multiple tracts may yield more information than univariate biomarker analyses.

Valproic acid-induced changes of 4D nuclear morphology in astrocyte cells

Histone deacetylase inhibitors, such as valproic acid (VPA), have important clinical therapeutic and cellular reprogramming applications. They induce chromatin reorganization that is associated with altered cellular morphology. However, there is a lack of comprehensive characterization of VPA-induced changes of nuclear size and shape. Here, we quantify 3D nuclear morphology of primary human astrocyte cells treated with VPA over time (hence, 4D). We compared volumetric and surface-based representations and identified seven features that jointly discriminate between normal and treated cells with 85% accuracy on day 7. From day 3, treated nuclei were more elongated and flattened and then continued to morphologically diverge from controls over time, becoming larger and more irregular. On day 7, most of the size and shape descriptors demonstrated significant differences between treated and untreated cells, including a 24% increase in volume and 6% reduction in extent (shape regularity) for treated nuclei. Overall, we show that 4D morphometry can capture how chromatin reorganization modulates the size and shape of the nucleus over time. These nuclear structural alterations may serve as a biomarker for histone (de-)acetylation events and provide insights into mechanisms of astrocytes-to-neurons reprogramming.

Claudin-18 Loss Alters Transcellular Chloride Flux but not Tight Junction Ion Selectivity in Gastric Epithelial Cells

BACKGROUND & AIMS

Tight junctions form a barrier to the paracellular passage of luminal antigens. Although most tight junction proteins reside within the apical tight junction complex, claudin-18 localizes mainly to the basolateral membrane where its contribution to paracellular ion transport is undefined. Claudin-18 loss in mice results in gastric neoplasia development and tumorigenesis that may or may not be due to tight junction dysfunction. The aim here was to investigate paracellular permeability defects in stomach mucosa from claudin-18 knockout (Cldn18-KO) mice.

METHODS

Stomach tissue from wild-type, heterozygous, or Cldn18-KO mice were stripped of the external muscle layer and mounted in Ussing chambers. Transepithelial resistance, dextran 4 kDa flux, and potential difference (PD) were calculated from the chambered tissues after identifying differences in tissue histopathology that were used to normalize these measurements. Marker expression for claudins and ion transporters were investigated by transcriptomic and immunostaining analysis.

RESULTS

No paracellular permeability defects were evident in stomach mucosa from Cldn18-KO mice. RNAseq identified changes in 4 claudins from Cldn18-KO mice, particularly the up-regulation of claudin-2. Although claudin-2 localized to tight junctions in cells at the base of gastric glands, its presence did not contribute overall to mucosal permeability. Stomach tissue from Cldn18-KO mice also had no PD versus a lumen-negative PD in tissues from wild-type mice. This difference resulted from changes in transcellular Cl- permeability with the down-regulation of Cl- loading and Cl- secreting anion transporters.

CONCLUSIONS

Our findings suggest that Cldn18-KO has no effect on tight junction permeability in the stomach from adult mice but rather affects anion permeability. The phenotype in these mice may thus be secondary to transcellular anion transporter expression/function in the absence of claudin-18.

A panel of criteria for comprehensive assessment of severity of ultraviolet B radiation-induced non-melanoma skin cancers in SKH-1 mice

The study of causes and cures for ultraviolet B radiation (UVB)-induced non-melanoma skin cancers (NMSC) has been greatly facilitated by use of the albino SKH-1 hairless mice. These mice develop multiple tumors of different sizes and the severity of cancer is often measured by one or more of the four criteria, namely the prevalence, multiplicity, area and volume of tumors. However, there are inherent limitations of each criterion: the prevalence and number do not account for size differences among tumors, area measurement ignores the tumor height, and volume measurement overcompensates for the height at the cost of planar dimensions. Here, using our dataset from an ongoing NMSC study, we discuss the limitations of these four criteria, and suggest refinements in measuring prevalence. We recommend the use of three more criteria, namely the Knud Thomsen tridimensional surface that apportions optimal weightage to three tumor dimensions, weekly occurrence of new tumors and tumor growth-rate to reveal initiation and growth of tumors in early and late phase of NMSC development, respectively. Together, use of this comprehensive panel of seven criteria can provide an accurate assessment of severity of NMSC and lead to a testable hypothesis whether the experimental manipulation of mice has affected the early initiation or growth phase of NMSC tumors.

A diffusion tensor imaging study of brain microstructural changes related to religion and spirituality in families at high risk for depression

INTRODUCTION

Previously in a three-generation study of families at high risk for depression, we found that belief in the importance of religion/spirituality (R/S) was associated with thicker cortex in bilateral parietal and occipital regions. In the same sample using functional magnetic resonance imaging and electroencephalograph (EEG), we found that offspring at high familial risk had thinner cortices, increased default mode network connectivity, and reduced EEG power. These group differences were significantly diminished in offspring at high risk who reported high importance of R/S beliefs, suggesting a protective effect.

METHODS

This study extends previous work examining brain microstructural differences associated with risk for major depressive disorder (MDD) and tests whether these are normalized in at-risk offspring who report high importance of R/S beliefs. Diffusion tensor imaging (DTI) data were selected from 99 2nd and 3rd generation offspring of 1st generation depressed (high-risk, HR) or nondepressed (low-risk, LR) parents. Whole-brain and region-of-interest analyses were performed, using ellipsoidal area ratio (EAR, an alternative diffusion anisotropy index comparable to fractional anisotropy). We examined microstructural differences associated with familial risk for depression within the groups of high and low importance of R/S beliefs (HI, LI).

RESULTS

In the LI group, HR individuals showed significantly decreased EAR in white matter regions neighboring the precuneus, superior parietal lobe, superior and middle frontal gyrus, and bilateral insula, supplementary motor area, and postcentral gyrus. In the HI group, HR individuals showed reduced EAR in white matter surrounding the left superior, and middle frontal gyrus, left superior parietal lobule, and right supplementary motor area. Microstructural differences associated with familial risk for depression in precuneus, frontal lobe, and temporal lobe were nonsignificant or less significant in the HI group.

CONCLUSION

R/S beliefs may affect microstructure in brain regions associated with R/S, potentially conferring resilience to depression among HR individuals.

Analytical performance bounds for multi-tensor diffusion-MRI

PURPOSE

To examine the effects of MR acquisition parameters on brain white matter fiber orientation estimation and parameter of clinical interest in crossing fiber areas based on the Multi-Tensor Model (MTM).

MATERIAL AND METHODS

We compute the Cramér-Rao Bound (CRB) for the MTM and the parameter of clinical interest such as the Fractional Anisotropy (FA) and the dominant fiber orientations, assuming that the diffusion MRI data are recorded by a multi-coil, multi-shell acquisition system. Considering the sum-of-squares method for the reconstructed magnitude image, we introduce an approximate closed-form formula for Fisher Information Matrix that has the simplicity and easy interpretation advantages. In addition, we propose to generalize the FA and the mean diffusivity to the multi-tensor model.

RESULTS

We show the application of the CRB to reduce the scan time while preserving a good estimation precision. We provide results showing how the increase of the number of acquisition coils compensates the decrease of the number of diffusion gradient directions. We analyze the impact of the b-value and the Signal-to-Noise Ratio (SNR). The analysis shows that the estimation error variance decreases with a quadratic rate with the SNR, and that the optimum b-values are not unique but depend on the target parameter, the context, and eventually the target cost function.

CONCLUSION

In this study we highlight the importance of choosing the appropriate acquisition parameters especially when dealing with crossing fiber areas. We also provide a methodology for the optimal tuning of these parameters using the CRB.

Depth-Independent Reproduction in the Reef Coral Porites astreoides from Shallow to Mesophotic Zones

Mesophotic coral ecosystems between 30–150 m may be important refugia habitat for coral reefs and associated benthic communities from climate change and coastal development. However, reduced light at mesophotic depths may present an energetic challenge to the successful reproduction of light-dependent coral organisms, and limit this refugia potential. Here, the relationship of depth and fecundity was investigated in a brooding depth-generalist scleractinian coral, Porites astreoides from 5–37 m in the U.S. Virgin Islands (USVI) using paraffin tissue histology. Despite a trend of increasing planulae production with depth, no significant differences were found in mean peak planulae density between shallow, mid-depth and mesophotic sites. Differential planulae production over depth is thus controlled by P. astreoides coral cover, which peaks at 10 m and ~35 m in the USVI. These results suggest that mesophotic ecosystems are reproductive refuge for P. astreoides in the USVI, and may behave as refugia for P. astreoides metapopulations providing that vertical larval exchanges are viable.

Cell shape dynamics during the staphylococcal cell cycle

Staphylococcus aureus is an aggressive pathogen and a model organism to study cell division in sequential orthogonal planes in spherical bacteria. However, the small size of staphylococcal cells has impaired analysis of changes in morphology during the cell cycle. Here we use super-resolution microscopy and determine that S. aureus cells are not spherical throughout the cell cycle, but elongate during specific time windows, through peptidoglycan synthesis and remodelling. Both peptidoglycan hydrolysis and turgor pressure are required during division for reshaping the flat division septum into a curved surface. In this process, the septum generates less than one hemisphere of each daughter cell, a trait we show is common to other cocci. Therefore, cell surface scars of previous divisions do not divide the cells in quadrants, generating asymmetry in the daughter cells. Our results introduce a need to reassess the models for division plane selection in cocci.

Staphylococci are spherical bacteria that divide in sequential orthogonal planes. Here, the authors use super-resolution microscopy to show that staphylococcal cells elongate before dividing, and that the division septum generates less than one hemisphere of each daughter cell, generating asymmetry.

Silicone Implants with Smooth Surfaces Induce Thinner but Denser Fibrotic Capsules Compared to Those with Textured Surfaces in a Rodent Model

Purpose

Capsular contracture is the most frequent long-term complication after implant-based breast reconstruction or augmentation. The aim of this study was to evaluate the impact of implant surface properties on fibrotic capsule formation in an animal model.

Materials and Methods

Twenty-four rats received 1 scaled down silicone implant each; 12 of the rats received implants with textured surfaces, and the other 12 received implants with smooth surfaces. After 60 and 120 days, rats in each group underwent 7-Tesla Magnetic Resonance Imaging (MRI) and high-resolution ultrasound (HR-US), and specimens of the capsules were acquired and used to measure capsule thickness through histology, collagen density through picro sirius red staining, and analyses of expression of pro-fibrotic and inflammatory genes (Collagen1-4, TGFb1, TGFb3, Smad3, IL4, IL10, IL13, CD68) through qRT-PCR. Furthermore, MRI data were processed to obtain capsule volume and implant surface area.

Results

On day 60, histology and HR-US showed that fibrotic capsules were significantly thicker in the textured implant group with respect to the smooth implant group (p<0.05). However, this difference did not persist on day 120 (p=0.56). Capsule thickness decreased significantly over the study period in both smooth and textured implant groups (p<0.05). Thickness measurements were substantiated by MRI analysis and volumes changed accordingly. Implant surface area did not vary between study dates, but it was different between implant types. On day 60, the density of collagen in the fibrotic capsules was significantly lower in the textured implant group with respect to the smooth group (p<0.05), but again this difference did not persist on day 120 (p=0.67). Collagen 1 and CD68 were respectively over- and under expressed in the textured implant group on day 60. Significant differences in the expression of other genes were not observed.

Conclusion

Silicone implants with textured surfaces led to temporarily thicker but less dense fibrotic capsules compared with smooth surfaces. 7-Tesla MRI and HR-US are capable for non-invasive in-vivo assessment of capsular fibrosis in an animal model and can provide unique insights into the fibrotic process by 3D reconstruction and surface area measurement.

Size-specific dose estimate (SSDE) provides a simple method to calculate organ dose for pediatric CT examinations

PURPOSE

To investigate the correlation of size-specific dose estimate (SSDE) with absorbed organ dose, and to develop a simple methodology for estimating patient organ dose in a pediatric population (5-55 kg).

METHODS

Four physical anthropomorphic phantoms representing a range of pediatric body habitus were scanned with metal oxide semiconductor field effect transistor (MOSFET) dosimeters placed at 23 organ locations to determine absolute organ dose. Phantom absolute organ dose was divided by phantom SSDE to determine correlation between organ dose and SSDE. Organ dose correlation factors (CF(organ)(SSDE)) were then multiplied by patient-specific SSDE to estimate patient organ dose. The [CF(organ)(SSDE)) were used to retrospectively estimate individual organ doses from 352 chest and 241 abdominopelvic pediatric CT examinations, where mean patient weight was 22 kg ± 15 (range 5-55 kg), and mean patient age was 6 yrs ± 5 (range 4 months to 23 yrs). Patient organ dose estimates were compared to published pediatric Monte Carlo study results.

RESULTS

Phantom effective diameters were matched with patient population effective diameters to within 4 cm; thus, showing appropriate scalability of the phantoms across the entire pediatric population in this study. Individual CF(organ)(SSDE) were determined for a total of 23 organs in the chest and abdominopelvic region across nine weight subcategories. For organs fully covered by the scan volume, correlation in the chest (average 1.1; range 0.7-1.4) and abdominopelvic region (average 0.9; range 0.7-1.3) was near unity. For organ/tissue that extended beyond the scan volume (i.e., skin, bone marrow, and bone surface), correlation was determined to be poor (average 0.3; range: 0.1-0.4) for both the chest and abdominopelvic regions, respectively. A means to estimate patient organ dose was demonstrated. Calculated patient organ dose, using patient SSDE and CF(organ)(SSDE), was compared to previously published pediatric patient doses that accounted for patient size in their dose calculation, and was found to agree in the chest to better than an average of 5% (27.6/26.2) and in the abdominopelvic region to better than 2% (73.4/75.0).

CONCLUSIONS

For organs fully covered within the scan volume, the average correlation of SSDE and organ absolute dose was found to be better than ± 10%. In addition, this study provides a complete list of organ dose correlation factors (CF(organ)(SSDE)) for the chest and abdominopelvic regions, and describes a simple methodology to estimate individual pediatric patient organ dose based on patient SSDE.

Automated assessment of the quality of diffusion tensor imaging data using color cast of color-encoded fractional anisotropy images

Diffusion tensor imaging (DTI) data often suffer from artifacts caused by motion. These artifacts are especially severe in DTI data from infants, and implementing tight quality controls is therefore imperative for DTI studies of infants. Currently, routine procedures for quality assurance of DTI data involve the slice-wise visual inspection of color-encoded, fractional anisotropy (CFA) images. Such procedures often yield inconsistent results across different data sets, across different operators who are examining those data sets, and sometimes even across time when the same operator inspects the same data set on two different occasions. We propose a more consistent, reliable, and effective method to evaluate the quality of CFA images automatically using their color cast, which is calculated on the distribution statistics of the 2D histogram in the color space as defined by the International Commission on Illumination (CIE) on lightness and a and b (LAB) for the color-opponent dimensions (also known as the CIELAB color space) of the images. Experimental results using DTI data acquired from neonates verified that this proposed method is rapid and accurate. The method thus provides a new tool for real-time quality assurance for DTI data.

Osmotolerance in the Cryptophyceae: jacks-of-all-trades in the Chroomonas Clade

No detailed studies have been performed to date on osmotolerance in cryptophytes, although one species, Chroomonas africana, had previously been reported to grow in freshwater as well as seawater. This study focused on osmotolerance in Chroomonas. Growth at different osmolalities and parameters of contractile vacuole function were examined and compared across a high-resolution phylogeny. Two evolutionary lineages in the Chroomonas clade proved to be euryhaline. Ranges of osmotolerance depended not only on osmolality, but also on culture medium. All cryptophytes contained contractile vacuoles. In the euryhaline strain CCAP 978/08 contractile vacuoles could be observed even at an osmolality beyond that of seawater. In addition the cells accumulated floridoside, an osmoprotectant likely originating from the red algal carbohydrate metabolism of the complex rhodoplast. Further evidence for functional contractile vacuoles also in marine cryptophytes was provided by identification of contractile vacuole-specific genes in the genome of Guillardia theta.

Spatial Mapping of Translational Diffusion Coefficients Using Diffusion Tensor Imaging: A Mathematical Description

In this article, we discuss the theoretical background for diffusion weighted imaging and diffusion tensor imaging. Molecular diffusion is a random process involving thermal Brownian motion. In biological tissues, the underlying microstructures restrict the diffusion of water molecules, making diffusion directionally dependent. Water diffusion in tissue is mathematically characterized by the diffusion tensor, the elements of which contain information about the magnitude and direction of diffusion and is a function of the coordinate system. Thus, it is possible to generate contrast in tissue based primarily on diffusion effects. Expressing diffusion in terms of the measured diffusion coefficient (eigenvalue) in any one direction can lead to errors. Nowhere is this more evident than in white matter, due to the preferential orientation of myelin fibers. The directional dependency is removed by diagonalization of the diffusion tensor, which then yields a set of three eigenvalues and eigenvectors, representing the magnitude and direction of the three orthogonal axes of the diffusion ellipsoid, respectively. For example, the eigenvalue corresponding to the eigenvector along the long axis of the fiber corresponds qualitatively to diffusion with least restriction. Determination of the principal values of the diffusion tensor and various anisotropic indices provides structural information. We review the use of diffusion measurements using the modified Stejskal-Tanner diffusion equation. The anisotropy is analyzed by decomposing the diffusion tensor based on symmetrical properties describing the geometry of diffusion tensor. We further describe diffusion tensor properties in visualizing fiber tract organization of the human brain.

Cholesterol-mediated membrane surface area dynamics in neuroendocrine cells

How cholesterol, a key membrane constituent, affects membrane surface area dynamics in secretory cells is unclear. Using methyl-beta-cyclodextrin (MbetaCD) to deplete cholesterol, we imaged melanotrophs from male Wistar rats in real-time and monitored membrane capacitance (C(m)), fluctuations of which reflect exocytosis and endocytosis. Treatment with MbetaCD reduced cellular cholesterol and caused a dose-dependent attenuation of the Ca(2+)-evoked increase in C(m) (IC50 = 5.3 mM) vs. untreated cells. Cytosol dialysis of MbetaCD enhanced the attenuation of C(m) increase (IC50 = 3.3 mM), suggesting cholesterol depletion at intracellular membrane sites was involved in attenuating exocytosis. Acute extracellular application of MbetaCD resulted in an immediate C(m) decline, which correlated well with the cellular surface area decrease, indicating the involvement of cholesterol in the regulation of membrane surface area dynamics. This decline in C(m) was three-fold slower than MbetaCD-mediated fluorescent cholesterol decay, implying that exocytosis is the likely physiological means for plasma membrane cholesterol replenishment. MbetaCD had no effect on the specific C(m) and the blockade of endocytosis by Dyngo 4a, confirmed by inhibition of dextran uptake, also had no effect on the time-course of MbetaCD-induced C(m) decline. Thus acute exposure to MbetaCD evokes a C(m) decline linked to the removal of membrane cholesterol, which cannot be compensated for by exocytosis. We propose that the primary contribution of cholesterol to surface area dynamics is via its role in regulated exocytosis.

Local diffusion homogeneity (LDH): an inter-voxel diffusion MRI metric for assessing inter-subject white matter variability

Many diffusion parameters and indices (e.g., fractional anisotropy [FA] and mean diffusivity [MD]) have been derived from diffusion magnetic resonance imaging (MRI) data. These parameters have been extensively applied as imaging markers for localizing white matter (WM) changes under various conditions (e.g., development, degeneration and disease). However, the vast majority of the existing parameters is derived from intra-voxel analyses and represents the diffusion properties solely within the voxel unit. Other types of parameters that characterize inter-voxel relationships have been largely overlooked. In the present study, we propose a novel inter-voxel metric referred to as the local diffusion homogeneity (LDH). This metric quantifies the local coherence of water molecule diffusion in a model-free manner. It can serve as an additional marker for evaluating the WM microstructural properties of the brain. To assess the distinguishing features between LDH and FA/MD, the metrics were systematically compared across space and subjects. As an example, both the LDH and FA/MD metrics were applied to measure age-related WM changes. The results indicate that LDH reveals unique inter-subject variability in specific WM regions (e.g., cerebral peduncle, internal capsule and splenium). Furthermore, there are regions in which measurements of age-related WM alterations with the LDH and FA/MD metrics yield discrepant results. These findings suggest that LDH and FA/MD have different sensitivities to specific WM microstructural properties. Taken together, the present study shows that LDH is complementary to the conventional diffusion-MRI markers and may provide additional insights into inter-subject WM variability. Further studies, however, are needed to uncover the neuronal mechanisms underlying the LDH.

White matter damage in asymptomatic patients with sickle cell anemia: screening with diffusion tensor imaging

BACKGROUND AND PURPOSE

Ischemic injury to the brain is a common complication of SCA. To better understand the neurologic impact of SCA, TBSS were applied to DTI data to investigate white matter injuries in pediatric patients with SCA.

MATERIALS AND METHODS

TBSS comparisons of a range of anisotropy and diffusion measures were carried out between age- and background-matched population groups: patients with SCA with no visible lesions, patients with SCA with mild gliosis, and normal controls.

RESULTS

TBSS analysis revealed that both SCA populations exhibited reduced anisotropy and increased diffusivity compared with normal controls in multiple brain regions, including the corpus callosum and centrum semiovale. Furthermore, the results suggest that the severity of SCA is positively correlated with the white matter changes in the corpus callosum.

CONCLUSIONS

The study demonstrates that TBSS is a viable technique in detecting subtle white matter damage in patients with SCA whose conventional anatomic MR imaging scans show no, or minimal, abnormalities and has the potential to evaluate the neurologic impact of the treatment of SCA.

DTI BASED STRUCTURAL DAMAGE CHARACTERIZATION FOR DISORDERS OF CONSCIOUSNESS

MRI Diffusion Tensor Imaging (DTI) has been recently proposed as a highly discriminative measurement to detect structural damages in Disorders of Consciousness patients (Vegetative State/Unresponsive Wakefulness Syndrome-(VS/UWS) and Minimally Consciousness State-MCS). In the DTI analysis, certain tensor features are often used as simplified scalar indices to represent these alterations. Those characteristics are mathematically and statistically more tractable than the full tensors. Nevertheless, most of these quantities are based on a tensor diffusivity estimation, the arithmetic average among the different strengths of the tensor orthogonal directions, which is supported on a symmetric linear relationship among the three directions, an unrealistic assumption for severely damaged brains. In this paper, we propose a new family of scalar quantities based on Generalized Ordered Weighted Aggregations (GOWA) to characterize morphological damages. The main idea is to compute a tensor diffusitivity estimation that captures the deviations in the water diffusivity associated to damaged tissue. This estimation is performed by weighting and combining differently each tensor orthogonal strength. Using these new scalar quantities we construct an affine invariant DTI tensor feature using regional tissue histograms. An evaluation of these new scalar quantities on 48 patients (23 VS/UWS and 25 MCS) was conducted. Our experiments demonstrate that this new representation outperforms state-of-the-art tensor based scalar representations for characterization and classification problems.

Improving the correction of eddy current-induced distortion in diffusion-weighted images by excluding signals from the cerebral spinal fluid

Iterative cross-correlation (ICC) is the most popularly used schema for correcting eddy current (EC)-induced distortion in diffusion-weighted imaging data, however, it cannot process data acquired at high b-values. We analyzed the error sources and affecting factors in parameter estimation, and propose an efficient algorithm by expanding the ICC framework with a number of techniques: (1) pattern recognition for excluding brain ventricles; (2) ICC with the extracted ventricle for parameter initialization; (3) gradient-based entropy correlation coefficient (GECC) for optimal and finer registration. Experiments demonstrated that our method is robust with high accuracy and error tolerance, and outperforms other ICC-family algorithms and popular approaches currently in use.

Tract based spatial statistical analysis and voxel based morphometry of diffusion indices in temporal lobe epilepsy

White matter (WM) microstructure can be evaluated by diffusion tensor imaging (DTI). Tract-based spatial statistical (TBSS) analysis provides a means of assessing alterations in WM tracts. In this paper, both voxel-based morphometry (VBM) and TBSS are examined using DTI data of temporal lobe epilepsy (TLE) patients and nonepileptic subjects. In addition to fractional anisotropy (FA), ellipsoidal area ratio (EAR) is used in this study. Significant reductions of FA and EAR are identified by TBSS in the parahippocampal white matter. Because of methodological differences, TBSS detects more localized abnormalities than VBM, while the EAR is more sensitive to WM alteration than FA.

Automated artifact detection and removal for improved tensor estimation in motion-corrupted DTI data sets using the combination of local binary patterns and 2D partial least squares

Signal variation in diffusion-weighted images (DWIs) is influenced both by thermal noise and by spatially and temporally varying artifacts, such as rigid-body motion and cardiac pulsation. Motion artifacts are particularly prevalent when scanning difficult patient populations, such as human infants. Although some motion during data acquisition can be corrected using image coregistration procedures, frequently individual DWIs are corrupted beyond repair by sudden, large amplitude motion either within or outside of the imaging plane. We propose a novel approach to identify and reject outlier images automatically using local binary patterns (LBP) and 2D partial least square (2D-PLS) to estimate diffusion tensors robustly. This method uses an enhanced LBP algorithm to extract texture features from a local texture feature of the image matrix from the DWI data. Because the images have been transformed to local texture matrices, we are able to extract discriminating information that identifies outliers in the data set by extending a traditional one-dimensional PLS algorithm to a two-dimension operator. The class-membership matrix in this 2D-PLS algorithm is adapted to process samples that are image matrix, and the membership matrix thus represents varying degrees of importance of local information within the images. We also derive the analytic form of the generalized inverse of the class-membership matrix. We show that this method can effectively extract local features from brain images obtained from a large sample of human infants to identify images that are outliers in their textural features, permitting their exclusion from further processing when estimating tensors using the DWIs. This technique is shown to be superior in performance when compared with visual inspection and other common methods to address motion-related artifacts in DWI data. This technique is applicable to correct motion artifact in other magnetic resonance imaging (MRI) techniques (e.g., the bootstrapping estimation) that use univariate or multivariate regression methods to fit MRI data to a pre-specified model.

A model of giant vacuole dynamics in human Schlemm's canal endothelial cells

Aqueous humour transport across the inner wall endothelium of Schlemm's canal likely involves flow through giant vacuoles and pores, but the mechanics of how these structures form and how they influence the regulation of intraocular pressure (IOP) are not well understood. In this study, we developed an in vitro model of giant vacuole formation in human Schlemm's canal endothelial cells (HSCECs) perfused in the basal-to-apical direction (i.e., the direction that flow crosses the inner wall in vivo) under controlled pressure drops (2 or 6 mmHg). The system was mounted on a confocal microscope for time-lapse en face imaging, and cells were stained with calcein, a fluorescent vital dye. At the onset of perfusion, elliptical void regions appeared within an otherwise uniformly stained cytoplasm, and 3-dimensional reconstructions revealed that these voids were dome-like outpouchings of the cell to form giant vacuole-like structures or GVLs that reproduced the classic "signet ring" appearance of true giant vacuoles. Increasing pressure drop from 2 to 6 mmHg increased GVL height (14 ± 4 vs. 21 ± 7 μm, p < 0.0001) and endothelial hydraulic conductivity (1.15 ± 0.04 vs. 2.11 ± 0.49 μl min⁻¹ mmHg⁻¹ cm⁻²; p < 0.001), but there was significant variability in the GVL response to pressure between cell lines isolated from different donors. During perfusion, GVLs were observed "migrating" and agglomerating about the cell layer and often collapsed despite maintaining the same pressure drop. GVL formation was also observed in human umbilical vein and porcine aortic endothelial cells, suggesting that giant vacuole formation is not a unique property of Schlemm's canal cells. However, in these other cell types, GVLs were rarely observed "migrating" or contracting during perfusion, suggesting that Schlemm's canal endothelial cells may be better adapted to withstand basal-to-apical directed pressure gradients. In conclusion, we have established an in vitro model system to study giant vacuole dynamics, and we have demonstrated that this system reproduces key aspects of giant vacuole morphology and behaviour. This model offers promising opportunities to investigate the role of endothelial cell biomechanics in the regulation of intraocular pressure in normal and glaucomatous eyes.

Opportunities and pitfalls in the quantification of fiber integrity: what can we gain from Q-ball imaging?

The quantification of fiber integrity is central to the clinical application of diffusion imaging. Compared to diffusion tensor imaging (DTI), Q-ball imaging (QBI) allows for the depiction of multiple fiber directions within a voxel. However, this advantage has not yet been shown to translate directly to superior quantification of fiber integrity. Furthermore, recent developments in QBI reconstruction with solid angle consideration have led to sharper and intrinsically normalized orientation distribution functions. The implications of this technique on quantification are also unknown. To investigate this, the generalized fractional anisotropy (GFA) from the original and the more recent QBI reconstruction scheme and the DTI derived fractional anisotropy (FA) were evaluated comparatively using Monte Carlo simulations and real MRI measurements of crossing fiber phantoms. Contrast-to-noise ratio, accuracy, independence of the acquisition setup and the relation of single fiber anisotropies to measured anisotropy in crossings were assessed. In homogeneous single-fiber regions at b-values around 1000 s/mm2, the FA performed best. While the original QBI reconstruction does not show a clear advantage even at higher b-values and in crossing regions, the new reconstruction scheme yields superior properties and is recommended for quantification at higher b-values and especially in regions of heterogeneous fiber configuration.