Diffusion Measurements Research Articles

Isotropic sampling of tensor-encoded diffusion MRI.

The purpose of this study is to develop a method for selecting uniform wave vectors for double diffusion encoding (DDE) to improve the accuracy and reliability of diffusion measurements. The method relies on identifying orthogonal wave vectors with rotations, and representing these rotations as points on a three-dimensional sphere in four dimensions using quaternions. This enables an electrostatic repulsion algorithm to achieve a uniform distribution of these points. The optimal points are then converted back into orthogonal wave vectors (or rotations). The method was validated by comparing the distribution of directions to those generated by uniform sampling and by evaluating the error in the powder-averaged signal for various models. Our results demonstrate that the electrostatic repulsion approach effectively achieves a uniform distribution of wave vectors. The proposed method provides a systematic way to generate uniform diffusion directions suitable, for example, for DDE, enhancing the precision of diffusion measurements and reducing potential bias in experimental results. The method is also capable of generating uniform sets of B-tensors, and is thus applicable for general free waveform encoding.

Temporally resolved concentration profiling via computationally limited, distributed sensor nodes

AbstractAccurate mapping of chemical concentrations in reactor networks remains an obstacle to establish complete systems‐level insight and control. This issue extends beyond traditional reactor design to biological and other inaccessible systems of interest. Recent developments in novel materials with non‐volatile memory allow autonomous sensor nodes to record information with minimal external supervision. Integrating these materials in solution suspended particles demonstrates the unique potential for diffuse measurements of chemical data at the microscale. In this study, we establish a generalized workflow for the simulated deployment of time aware particle sensors (TAPS) in ideal reactor systems to measure analyte profiles, using Gillespie kinetic Monte Carlo algorithms (KMC). Our results show that computationally‐limited, chemically sensitive tracer particles capable of timestamping an analyte detection event can provide accurate analyte profiles throughout multistage reactors in an ensemble fashion.

Structural Characterization and Hydration Dynamics of Cross-Linked Collagen and Hyaluronic Acid Scaffolds by Nuclear Magnetic Resonance.

Understanding a biomaterial's structural and hydration dynamics is essential for its development and applications in tissue regeneration. In this study, collagen-hyaluronic acid (HA) scaffolds were analyzed utilizing Nuclear Magnetic Resonance (NMR) techniques to elucidate how different cross-linking conditions influence the internal architecture and interaction with solvents in these scaffolds. The scaffolds were fabricated using 3D printing and cross-linked with 1,4-butanediol diglycidyl ether (BDDGE), a process known to impact their mechanical properties. We gained insights into the microstructural organization and hydration behavior within the scaffolds when exposed to water and ethanol by employing proton relaxation and diffusion measurements. To better understand the system's performance, static and dynamic experiments were performed. Our results indicate that the degree of cross-linking affects the scaffold's ability to retain water, with higher cross-linking leading to more rigid structures. This also altered the hydration dynamics mainly due to a difference in the diffusion of water within the scaffold. In addition, the anisotropy of the collagen fibers also decreases with the cross-linking. Ethanol, a less polar solvent, provided a contrasting environment that further revealed the structural dependencies on the cross-linking density. The study's findings contribute to a deeper understanding of how the structure and morphology affect the functionality of collagen-HA scaffolds, offering critical information for optimizing their design for specific biomedical applications, such as soft tissue regeneration. Our experiments show how NMR is a valuable tool to provide information on dynamic processes not only in collagen-HA scaffolds but also in many biocompatible polymeric samples. The outcomes of this research provide a foundation for future work aimed at tailoring scaffold properties to enhance their performance in clinical settings, ultimately advancing the field of tissue engineering.

High Pressure Melting Curve of Fe-Si: Implication for the Thermal Properties in Mercury's Core.

The motion of liquid iron (Fe) alloy materials in the outer core drives the dynamo, which generates Mercury's magnetic field. The assessment of core models requires laboratory measurements of the melting temperature of Fe alloys at high pressure. Here, we experimentally determined the melting curve of Fe9wt%Si and Fe17wt%Si up to 17GPa using in situ and ex situ measurements of intermetallic fast diffusion that serves as the melting criterion in a large-volume press. Our determined melting slopes are comparable with previous studies up to about 17GPa. However, when extrapolated, our melting slopes significantly deviate from previous studies at higher pressures. For Mercury's core with a model composition of Fe9wt%Si, the melting temperature-depth profile determined in our study is lower by ∼150-250K when compared with theoretical calculations. Using the new melting curve of Fe9wt%Si and the electrical resistivity values from a previous study of Fe8.5wt%Si, we estimate that the electronic thermal conductivity of liquid Fe9wt%Si is 30 Wm-1K-1 at the Mercury's CMB pressure of 5GPa and 37Wm-1K-1 at an assumed ICB of 21GPa, corresponding to heat flux values of 23mWm-2 and 32mWm-2, respectively. These values provide new constraints on the core models.

White matter integrity and cognitive performance in the subacute phase after ischemic stroke in young adults

IntroductionReduced white matter integrity outside the stroke lesion may be a potential contributor of post-stroke cognitive impairment. We aimed to investigate how a stroke lesion affects the integrity of surrounding white matter, and whether the integrity of the non-lesioned part of white matter tracts is associated with cognitive performance after ischemic stroke in young adults. MethodsPatients from the ODYSSEY study, aged 18–49 years, with a first-ever ischemic stroke, underwent 3T MRI and cognitive assessment within six months after the index event. Using TractSeg and free water imaging, we analyzed free water corrected fractional anisotropy (FAT), free water corrected mean diffusivity (MDT), and free water (FW) of all white matter tracts outside the stroke lesion. We calculated FAT and FW in the lesioned white matter tracts at 2 mm incremental distances from the lesion, extending up to 10 mm, represented as Z-scores using the diffusion measures of controls. We categorized patients as no/mild or major vascular cognitive disorder (VCD) and compared with a stroke-free control group (n = 23). Group differences in diffusion measures were examined. We investigated associations between FAT, FW and cognitive performance across seven domains. ResultsAmong 66 patients (median age 40.3 years (IQR 31.3–46.2); 54.5 % women), 22 had major VCD. In the different lesion expansions, we found differences in FAT (p = 0.009) and FW (p = 0.049). Patients with major VCD had lower FAT [range of Cohen’s d (0.65; 1.65)] and higher FW [Cohen’s d (−1.40; −0.64)] values compared to controls, both in the hemisphere affected by the lesion and the unaffected hemisphere. Performance in processing speed correlated with FAT across eight tracts in the affected hemisphere [range of R2adj (0.30; 0.37)], and with FW in four tracts in the affected and three in the unaffected hemisphere [R2adj (0.28; 0.38)]. DiscussionIn the first months after a stroke, we observed a trend of microstructural changes remote from the lesion that diminish as the distance from the lesion increases. Tissue changes in the white matter outside the lesion are present in both hemispheres, but are more pronounced in the hemisphere affected by the stroke, and may contribute to worse cognitive performance.

Influence of moisture on the diffusion of ultrasound in concrete

This study aimed to investigate the effects of internal moisture migration and subsequent drying-shrinkage-induced micro-cracking in concrete on diffuse ultrasound, through a series of experiments that comprised multiple drying and rewetting cycles carried out over the long-term. Cyclic drying and wetting phenomena in concrete were physically established following a predefined protocol and were traced measuring the mass change of specimens. Diffuse-wave tests were conducted using a pair of PZT patches bonded to cylindrical specimens, which acted as the ultrasonic transmitter and receiver in the range of 250–550 kHz. The results present that measured diffuse-wave parameters, diffusivity and dissipation, showed distinct varying and cyclic behaviors to drying and wetting processes, but they did not recover their original values in the saturated condition, revealing possible micro-cracking damage caused by the drying process, which should be understood to improve the reliability of diffuse ultrasound measurements in concrete subjected to environmental changes.

Deep medullary veins integrity and relationships with small vessel disease and interstitial diffusivity measures in patients with a recent small subcortical infarct.

The role of the venous compartment in cerebral small vessel disease has yet to be fully understood. As such, we evaluated how deep medullary veins integrity relates to MRI-based small vessel disease severity markers and glymphatic function assessed by DTI measures in patients with a recent small subcortical infarct. We gathered demographic, clinical, and 3 Tesla-MRI imaging data from 50 patients with a recent small subcortical infarct. We evaluate the venular integrity using two visual scales based on their appearance on SWI. We assessed the number of lacunes and microbleeds, white matter hyperintensities volume, perivascular spaces volume in basal ganglia and white matter, summary-small vessel disease score, and brain volume. Diffusivity measures in normal-appearing white matter included free water fraction, mean diffusivity and fractional anisotropy with and without free water correction, and DTI along the perivascular spaces. After categorizing the cohort in quartiles according to both venular scores, we assessed their correlations with small vessel disease markers and diffusivity measures using multivariable ordinal regression analyses adjusting for age, sex, smoking, and summary small vessel disease score. In univariate analysis most of the imaging variables, except for microbleeds, perivascular spaces in white matter and DTI-along the perivascular spaces, were associated with one or both venular scores. In multivariate analysis (OR, 95% CI), free water (1.33, 1.03-1.73), mean diffusivity (4.56, 1.32-15.81), fractional anisotropy (0.77, 0.63-0.93), free water-corrected mean diffusivity and fractional anisotropy (2.39, 1.06-5.39;0.78, 0.65-0.94, respectively), associated with vein appearance, while only brain volume (0.48, 0.25-0.94), fractional anisotropy with and without free water correction (0.82,0.86-0.99; 0.83, 0.7-0.99, respectively) remained significant for vein count. In patients with a recent small subcortical infarct, disruption of the deep medullary veins, increased extracellular water, and white matter injury appear to be associated. SVD=small vessel disease; DMV=deep medullary veins; WMH=white matter hyperintensities; PVS=perivascular spaces; DTI-ALPS=diffusion tensor image analysis along the perivascular spaces; FW=free water; MD=mean diffusivity; FA= fractional anisotropy; BG=basal ganglia.

Diffusion kurtosis imaging, MAP-MRI and NODDI selectively track gray matter myelin density in the primate cerebral cortex

Abstract Diffusion magnetic resonance imaging (dMRI) has been widely used to model the trajectory of myelinated fiber bundles in the white matter. Increasingly, it is also used to evaluate the microstructure of the cerebral cortex gray matter. For example, in diffusion tensor imaging (DTI) of the cortex, fractional anisotropy (FA) correlates strongly with the anisotropy of cellular anatomy, while radial diffusivity (RD) tracks the anisotropy of myelinated fibers. However, no DTI parameter shows specificity to gray matter myelin density. Here, we show that three higher-order diffusion parameters—the mean diffusion kurtosis (MK), the Neurite Density Index (NDI) from neurite orientation dispersion and density imaging (NODDI), and the Non-Gaussian (NG) parameter from mean apparent propagator (MAP)-MRI—each track the laminar and regional myelin density of the primate cerebral cortex in fine detail. We carried out ultra-high-resolution, multi-shelled dMRI in ex-vivo marmoset monkey brains. We compared the spatial mapping of the MK, NDI, and ND diffusion parameters to the cortical myelin distribution of these brains, with the latter obtained in two ways: First, using histological sections finely co-registered to the MRI, and second using magnetization transfer ratio MRI scans (MTR), an established non-diffusion method for imaging myelin density. We found that, in contrast to DTI parameters, each of these higher-order diffusion measures captured the spatial variation of myelin density in the cortex. The demonstration that diffusion parameters exhibit both sensitivity and specificity for gray matter myelin density will allow dMRI to more effectively track human disease, in which myelinated and non-myelinated tissue compartments are affected differentially.

High-pressure characterization of Ag3AuTe2: Implications for strain-induced band tuning

Recent band structure calculations have suggested the potential for band tuning in the chiral semiconductor Ag3AuTe2 to zero upon application of negative strain. In this study, we report on the synthesis of polycrystalline Ag3AuTe2 and investigate its transport and optical properties and mechanical compressibility. Transport measurements reveal the semiconducting behavior of Ag3AuTe2 with high resistivity and an activation energy Ea of 0.2 eV. The optical bandgap determined by diffuse reflectance measurements is about three times wider than the experimental Ea. Despite the difference, both experimental gaps fall within the range of predicted bandgaps by our first-principles density functional theory (DFT) calculations employing the Perdew–Burke–Ernzerhof and modified Becke–Johnson methods. Furthermore, our DFT simulations predict a progressive narrowing of the bandgap under compressive strain, with a full closure expected at a strain of −4% relative to the lattice parameter. To evaluate the feasibility of gap tunability at such substantial strain, the high-pressure behavior of Ag3AuTe2 was investigated by in situ high-pressure x-ray diffraction up to 47 GPa. Mechanical compression beyond 4% resulted in a pressure-induced structural transformation, indicating the possibility of substantial gap modulation under extreme compression conditions.

Influence of Rapid Heat Treatment on the Photocatalytic Activity and Stability of Barium Titanates Against a Broad Range of Pollutants.

Barium titanate photocatalysts were synthesized via a sol-gel method involving a unique, cost-effective calcination technique that includes rapid heating and short exposure. The samples were characterized by X-ray diffractometry, scanning electron microscopy, diffuse reflectance spectroscopy, photoluminescence spectroscopy, infrared spectroscopy, and nitrogen adsorption-desorption measurements. The photooxidation activity and stability of the samples were evaluated by the degradation of phenol, oxalic acid, and chlorophenol. Their photoreduction activity was also investigated by the photocatalytic conversion of CO2 to CO. In both cases, UV irradiation was applied to activate the catalysts. As references, commercially available cubic and tetragonal barium titanates were used, with the addition of benchmark P25 TiO2 in some cases. Increasing the calcination temperature resulted in increased primary crystallite sizes, decreased specific surface areas, and slightly redshifted band gaps. On the one hand, the overall photooxidation activity of the samples for pollutant degradation was rather low, possibly due to their unfavorable valence band maximum position. On the other hand, our samples displayed significantly superior photoreduction activity, surpassing that of all the references, including P25 TiO2. The high photoactivity was mainly attributed to the specific surface areas that changed per the efficiency of the samples. Last, the cost comparison calculations showed that applying our calcination technique is 29.5% more cost-efficient than conventional calcination, and the same amount of energy is sufficient for preparing even a 1.4 times higher amount of barium titanite.

Application of Hybrid Absorptive-Diffusive Panels with Variable Acoustic Characteristics Based on Wooden Overlays Designed Using Third-Degree-of-Freedom Bezier Curves.

This manuscript describes the application of novel hybrid acoustic panels with variable acoustic properties that could be used in the design process. Despite the significant growth in the modern acoustic absorbing and diffusing panel sector in recent years, there is still a need for sustainable and original designs that will fit standard interior design trends. The most significant requirement is satisfying the design needs of variable acoustic venues. The availability of acoustic panels with variable properties is minimal, as most designs are based on textiles in the form of rolling banners; therefore, there is no market diversity. The current paper presents an original solution for a novel perforated wooden panel based on third-degree-of-freedom curves. Due to the possibility of exchanging the front panel, the acoustic surface can be varied and adjusted to the room considering different requirements for the acoustic climate, for example, by modifying the attenuation range from low to mid-high frequencies. The novel panels have unique esthetic properties with functional acoustic features regarding sound diffusion and absorption. In this paper, sound absorption and diffusion measurements will be presented for the different variants of the panels, presenting the option to modify the parameters to adjust the panel's features to the room's needs. In situ acoustic measurements in a laboratory were conducted to test the variable acoustic panels' influence on the room's acoustic parameters, such as T30 and C80. In summary, the advantages of this kind of design will be discussed, alongside the possible impact on modern construction materials' utilization in architecture.

Exploring cognitive functions and brain structure in Hereditary Transthyretin amyloidosis using brain MRI and neuropsychological assessment.

Central nervous system symptoms, such as cognitive dysfunction, have been reported in Hereditary Transthyretin Amyloidosis (ATTRv). However, there is a lack of neuroimaging studies investigating structural alterations in the brain related to cognition in ATTRv amyloidosis. This study aimed to investigate cognition and cortical morphology in a cohort of ATTRv patients. 29 ATTRv patients and 26 healthy controls completed neuropsychological assessment. 21 of these patients underwent 3T brain MRI, and 23 healthy subjects constituted the control group for MRI. Cortical measures of volume, thickness, fractional anisotropy (FA), and mean diffusivity (MD) were obtained for both groups. Correlation analyses between brain and cognitive measurements were performed. Patients displayed worse performance than controls in executive functions, verbal and visual memory, visuospatial domains, and language tests. Our study indicated cortical thinning in ATTRv patients in the temporal, occipital, frontal, and parietal areas. The inferior temporal gyrus correlated with verbal memory. Insula and, pars opercularis correlated with both verbal memory and executive function. Cortical thickness in the inferior temporal gyrus, pars opercularis, and insula were linked to memory and executive function. We observed no correlations between cortical volume measures and cognition. Further investigations are imperative to confirm these findings across different populations.

Comparative analysis of hydrazinyl coumarin derivative incorporation in resin-modified and conventional glass ionomer cement

ObjectiveThe study aimed to conduct a comparative analysis of the effects of incorporating hydrazinyl coumarin derivative (HCD) in resin-modified (RMGIC) and conventional glass ionomer cement (cGIC) on their release profiles and antibacterial properties. MethodResin-modified GIC, Fuji II LC (F2) and high-fluoride cGIC, Fuji VII (F7) were used as controls. HCD was synthesized in-house, incorporated into both RMGIC and cGICs at 1 % and 2 % weight percentages (w/w), and chemically analyzed using Fourier transform infrared (FTIR) spectroscopy. Then, the F2 containing HCD (GIC-HCD F2) and F7 containing HCD (GIC-HCD F7) were evaluated for HCD and fluoride release profiles using UV Visible spectrophotometer and pH/ISE benchtop fluoridemeter, respectively. The antibacterial properties were assessed against Streptococcus sanguinis using the agar well diffusion method and measurement of bacterial growth turbidity, followed by the observation of the bacterial morphology using scanning electron microscope. The data were statistically analyzed using one-way ANOVA and Bonferroni post hoc tests. ResultsThe FTIR spectra confirmed the presence of HCD in the GIC-HCD matrices. HCD was successfully released from both GIC-HCD F2 and GIC-HCD F7 matrices at both weight percentages. Higher fluoride release and inhibitory zones were observed compared to the control groups, with GIC-HCD F2 having a more significant effect than GIC-HCD F7. Additionally, the incorporation of HCD slowed down the growth of Streptococcus sanguinis and showed remarkable changes in bacterial shape specifically on GIC-HCD F2. ConclusionThe incorporation of HCD into both RMGIC and cGIC improved fluoride release and enhanced the antibacterial activities, with a more significant effect observed in RMGIC compared to cGIC.

Segmental abnormalities of white matter microstructure in multiple sclerosis and neuromyelitis optica spectrum disorder identified by automated fiber quantification

BackgroundMultiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD) are different in pathogenesis, but both could lead to white matter (WM) microstructural damage. The aim of this study was to explore the differences in the patterns of WM fiber tract damage in relapsing-remitting MS (RRMS) and NMOSD by automated fiber quantification (AFQ). Materials and MethodsForty-one RRMS patients, 30 NMOSD patients and 30 healthy controls (HC) underwent MRI examination. AFQ was applied to identify and quantify 100 equally spaced nodes of specific WM fiber tracts for each participant. Measurements of fractional anisotropy (FA), mean diffusion (MD), axial diffusivity (AD) and radial diffusivity (RD) for each segment of a specific fiber tract were compared between RRMS, NMOSD and HC. ResultsThe decrease in FA was found in 7 fiber tracts in entire tract comparison and 9 fiber tracts in pointwise comparison in RRMS patients. However, the FA in left thalamic radiation (TR) and right uncinate fasciculus showed significant differences between RRMS and HC only in the pointwise comparison, but not in the entire tract comparison. The MD, AD and RD of WM fiber tracts in RRMS patients were extensively increased both in the entire level and in the pointwise level. NMOSD patients showed significant FA decrease in left TR and callosum forceps minor (CF_minor), and significant RD increase in CF_minor in the pointwise level. In the pointwise comparison between RRMS and NMOSD, significant FA decrease was found in right inferior fronto-occipital fasciculus and bilateral inferior longitudinal fasciculus in RRMS patients, focal or widespread MD, AD and RD increase was found in multiple fiber tracts. ConclusionThe AFQ approach is a more sensitive way to reflect WM microstructural abnormalities, revealing extensive WM microstructural damage in RRMS and limited WM fiber tract damage in NMOSD.

Thermal diffusivity measurement of polymer microfibers while eliminating the effect of heat radiation

The thermal transport properties of polymer fibers are important for heat dissipation in apparel, matrix of wearable devices, and so on. However, it is difficult to precisely determine the thermal properties of a single polymer fiber because of non-negligible thermal radiation due to its relatively low thermal conductivity and high surface-area-to-volume ratio. Here, we developed a system in which the apparent thermal diffusivity and size of microfibers can be measured to estimate their intrinsic thermal diffusivity. We determined the thermal diffusivities of three fibrous materials: silk, spider silk, and cellulose microfibers to be 4.2 (±0.8)×10−7, 1.8 (±0.7)×10−7, and 4.7 (±0.5)×10−7, respectively. For all fibers, the apparent thermal diffusivity strongly depended on the fiber size, indicating that eliminating the radiation effect is indispensable for determining the thermal transport properties of polymer microfibers.

Covalent Bonds versus van der Waals Forces: A Picture in Thermal Conduction of Organic Materials.

We present a direct comparison of the heat transport properties between the state in which the constituent molecules are assembled by intermolecular forces and the one in which they are covalently bonded, in a molecular system with identical constituent elements and masses, as well as a nearly identical structure and density. This comparison leading to an essential understanding of thermal conduction in organic materials is made possible by the unique compound found by Wudl et al., which exhibits a single-crystal-to-single-crystal topochemical polymerization with a yield of >99%, in combination with microtemperature wave analysis (μTWA), which allows accurate measurements of the thermal diffusivity of small single crystals. At room temperature, the thermal conductivity of monomer and polymer single crystals is not significantly different. For both crystals, the thermal conductivity increases monotonically with decreasing temperature. However, below the Debye temperature, the thermal conductivity of the polymer single crystal increases exponentially, giving much larger values than those of the monomer single crystal. Based on physical quantities related to the behavior of phonons, derived from the specific heat analysis, we discuss the differences in heat transport properties in the two states and provide guidelines for achieving high thermal conductivity in organic materials.

Stimulated echo acquisition mode (STEAM) diffusion tensor imaging with different diffusion encoding times in the supraspinatus muscle: Test-retest reliability and comparison to spin echo diffusion tensor imaging.

Diffusion tensor imaging (DTI) provides insight into the skeletal muscle microstructure and can be acquired using a stimulated echo acquisition mode (STEAM)-based approach to quantify time-dependent tissue diffusion. This study examined diffusion metrics and signal-to-noise ratio (SNR) in the supraspinatus muscle obtained with a STEAM-DTI sequence with different diffusion encoding times (Δ) and compared them to measures from a spin echo (SE) sequence. Ten healthy subjects (mean age 31.5 ± 4.7years; five females) underwent 3-Tesla STEAM and SE-DTI of the shoulder in three sessions. STEAM was acquired with Δ of 100/200/400/600 ms. The diffusion encoding time in SE scans was 19ms (b = 500s/mm2). Region of interest-based measurement of fractional anisotropy (FA), mean diffusivity (MD), and SNR was performed. Intraclass correlation coefficients (ICCs) were computed to assess test-retest reliability. ANOVA with post-hoc pairwise tests was used to compare measures between different Δ of STEAM as well as STEAM and SE, respectively. FA was significantly higher (FASTEAM: 0.38-0.46 vs. FASE: 0.26) and MD significantly lower (MDSTEAM: 1.20-1.33 vs. MDSE: 1.62×10-3mm2/s) in STEAM compared to SE (p < 0.001, respectively). SNR was significantly higher for SE (72.3 ± 8.7) than for STEAM (p < 0.001). ICCs were excellent for FA in STEAM (≥0.911) and SE (0.960). For MD, ICCs were good for STEAM100ms-600ms (≥0.759) and SE (0.752). STEAM and SE exhibited excellent reliability for FA and good reliability for MD in the supraspinatus muscle. SNR was significantly higher in SE compared to STEAM.

In-plane thermal anisotropy of natural cork and its variability

This study investigates the natural cork thermal anisotropy and its variability using plane slice samples of 1.4 mm thickness, cut along the principal radial, longitudinal, and tangential directions, from bark previously treated for cork stoppers production. Heating was pointwise applied to the rear face using a copper needle coupled to a Peltier element, while an in-plane thermographic technique monitored temperature evolution on the front surfaces using a Flir SC5650 infrared camera. Thermal diffusivity measurements yielded values of 0.172 ± 0.038 mm2/s (radial), 0.161 ± 0.022 mm2/s (longitudinal), and 0.160 ± 0.027 mm2/s (tangential). Additionally, a volumetric heat capacity of 0.25 MJ/(m3·K) was determined using the Hot Disk technique. This information enabled the calculation of thermal conductivity, ranging from 0.033 to 0.048 W/(m·K). Findings align with existing literature, which reports thermal diffusivity between 0.08 and 0.24 mm2/s and thermal conductivity between 0.035 and 0.045 W/(m·K). This study contributes valuable insights into the thermal properties of natural cork and their orientation-dependent variability.

Hippocampal microscopic fractional anisotropy is reduced in temporal lobe epilepsy

Abstract Surgical resection is the method of choice for treating drug-resistant focal temporal lobe epilepsy (TLE). Postsurgical outcomes are better when magnetic resonance imaging (MRI) findings can localize the seizure focus for resection. However, many patients are MR-negative, meaning the focus cannot be differentiated from normal tissue in relaxation-weighted MRI. Diffusion MRI shows promise as a preoperative marker of neuronal abnormalities due to its sensitivity to cellular changes such as axon damage, indexed by fractional anisotropy. Microscopic fractional anisotropy is a recently introduced diffusion MRI metric that is sensitive to axon integrity regardless of axon orientation in both grey and white matter. In contrast, regular fractional anisotropy is only sensitive to axon integrity in coherently oriented bundles of fibers. This work investigated whether microscopic fractional anisotropy is sensitive to hippocampal abnormalities in drug-resistant TLE. Diffusion MRI was performed on a 3T scanner in 19 patients (age = 31±10 years) with drug-resistant TLE (of which 10 were MR-negative) and 18 healthy volunteers (age = 38±15). A deep-learning method was employed to segment the hippocampus into smaller subregions corresponding to the subiculum, cornu ammonis (CA) 1, CA2/3, and CA4 plus dentate gyrus (DG). Mean measurements of subregion volume, diffusivity, fractional anisotropy, and microscopic fractional anisotropy were compared between cohorts. In a subset of the TLE cohort suspected to have unilateral pathology (n=15, age = 32±10 years), the percentage differences between measurements ipsilateral and contralateral to the epileptogenic zone were evaluated to assess asymmetry. Microscopic fractional anisotropy was reduced in the hippocampus of drug-resistant TLE patients relative to healthy volunteers. In subregion-specific analysis, microscopic fractional anisotropy was significantly reduced in only the CA4/DG region in patients compared to healthy volunteers, after corrections for multiple comparisons. In the 15 patients with suspected unilateral pathology, microscopic fractional anisotropy was reliably and statistically lower in the ipsilateral CA4/DG region compared to the contralateral side. Significant differences were not observed between TLE patients and healthy volunteers, or between hemispheres for patients with suspected unilateral pathology, for the fractional anisotropy or volume metrics. Diffusion MRI may complement standard imaging procedures by detecting abnormalities in MRI-negative patients. Due to its ability to detect abnormality regardless of axon orientation, microscopic fractional anisotropy may improve seizure focus localization in surgical candidates.

Investigating the association between the GAP-43 concentration with diffusion tensor imaging indices in Alzheimer’s dementia continuum

BackgroundSynaptic degeneration, axonal injury, and white matter disintegration are among the pathological events in Alzheimer’s disease (AD), for which growth-associated protein 43 (GAP-43) and diffusion tensor imaging (DTI) could be an indicator. In this study, the cerebrospinal fluid (CSF) GAP-43 clinical trajectories and their association with progression and AD hallmarks with white matter microstructural changes were evaluated.MethodsA total number of 133 participants were enrolled in GAP-43 and DTI values were compared between groups, both cross-sectionally and longitudinally with two and four-year follow-ups. Subsequently, the correlation between GAP-43 levels in the CSF and DTI values was investigated using Spearman’s correlation.ResultsThe CSF level of GAP-43 is negatively correlated with the mean diffusivity measures in Fornix (Cres)/Stria terminals in early and late MCI (rs=-0.478 p = 0.021 and rs=-0.425 p = 0.038). Additionally, the CSF level of GAP-43 is negatively correlated with fractional anisotropy in the cingulum in late MCI (rs=-0.437 p = 0.033). Moreover, the axial diffusivity in superior corona radiate (rs=-0.562 p = 0.005 and rs=-0.484 p = 0.036) and radial diffusivity in superior fronto-occipital fasciculus was negatively correlated with GAP-43 level in the early and mid-MCI participants (rs=-0.520 p = 0.011 and rs=-0.498 p = 0.030).ConclusionsPresynaptic marker GAP-43 in combination with DTI can be used as a novel biomarker to identify microstructural synaptic degeneration in the early MCI. In addition, it can be used as a biomarker for tracking the progression of AD and monitoring treatment efficacy.