Feasibility of coronary artery wall thickening assessment in asymptomatic coronary artery disease using phase-sensitive dual-inversion recovery MRI at 3 T

Objectives

The purpose of this study was to (a) investigate the image quality of phase-sensitive dual-inversion recovery (PS-DIR) coronary wall imaging in healthy subjects and in subjects with known coronary artery disease (CAD) and to (b) investigate the utilization of PS-DIR at 3 T in the assessment of coronary artery thickening in subjects with asymptomatic but variable degrees of CAD.

Materials and Methods

A total of 37 subjects participated in this institutional review board-approved and HIPAA-compliant study. These included 21 subjects with known CAD as identified on multidetector computed tomography angiography (MDCT). Sixteen healthy subjects without known history of CAD were included. All subjects were scanned using free-breathing PS-DIR magnetic resonance imaging (MRI) for the assessment of coronary wall thickness at 3 T. Lumen–tissue contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR) and quantitative vessel parameters including lumen area and wall thickness were measured. Statistical analyses were performed.

Results

PS-DIR was successfully completed in 76% of patients and in 88% of the healthy subjects. Phase-sensitive signed-magnitude reconstruction, compared to modulus-magnitude images, significantly improved lumen–tissue CNR in healthy subjects (26.73 ± 11.95 vs. 14.65 ± 9.57, P < .001) and in patients (21.45 ± 7.61 vs. 16.65 ± 5.85, P < .001). There was no difference in image CNR and SNR between groups. In arterial segments free of plaques, coronary wall was thicker in patients in comparison to healthy subjects (1.74 ± 0.27 mm vs. 1.17 ± 0.14 mm, P < .001), without a change in lumen area (4.51 ± 2.42 mm² vs. 5.71 ± 3.11 mm², P = .25).

Conclusions

This is the first study to demonstrate the feasibility of successfully obtaining vessel wall images at 3 T using PS-DIR in asymptomatic patients with known variable degrees of CAD as detected by MDCT. This was achieved with a fixed subject-invariant planning of blood signal nulling. With that limitation alleviated, PS-DIR coronary wall MRI is capable of detecting arterial thickening and positive arterial remodeling at 3 T in asymptomatic CAD.     

The hemodynamic study of the cerebral artery using numerical simulations based on medical imaging data

The paper aims to investigate effects of blood vessel geometry on hemodynamics of the cerebral artery, particularly the internal carotid artery using computer graphics. The medical statistics show that generation and rupture of the cerebral aneurysms is strongly correlated with the wall shear stress and flow patterns in the blood vessel. In order to provide better understanding of phenomena, the paper presents the numerical analysis system, which consists of pre-processing, simulation and postprocessing. In the pre-processing, the medical imaging data, mainly CT (Computerized Tomographic) angiography, are used to construct the three-dimensional geometry of the artery. Various simulations are carried out varying curvature or location of bifurcation, and the results are visualized to investigate geometry effect.     

3D reconstruction of a carotid bifurcation from 2D transversal ultrasound images

Visualizing and analyzing the morphological structure of carotid bifurcations are important for understanding the etiology of carotid atherosclerosis, which is a major cause of stroke and transient ischemic attack. For delineation of vasculatures in the carotid artery, ultrasound examinations have been widely employed because of a noninvasive procedure without ionizing radiation. However, conventional 2D ultrasound imaging has technical limitations in observing the complicated 3D shapes and asymmetric vasodilation of bifurcations. This study aims to propose image-processing techniques for better 3D reconstruction of a carotid bifurcation in a rat by using 2D cross-sectional ultrasound images. A high-resolution ultrasound imaging system with a probe centered at 40 MHz was employed to obtain 2D transversal images. The lumen boundaries in each transverse ultrasound image were detected by using three different techniques; an ellipse-fitting, a correlation mapping to visualize the decorrelation of blood flow, and the ellipse-fitting on the correlation map. When the results are compared, the third technique provides relatively good boundary extraction. The incomplete boundaries of arterial lumen caused by acoustic artifacts are somewhat resolved by adopting the correlation mapping and the distortion in the boundary detection near the bifurcation apex was largely reduced by using the ellipse-fitting technique. The 3D lumen geometry of a carotid artery was obtained by volumetric rendering of several 2D slices. For the 3D vasodilatation of the carotid bifurcation, lumen geometries at the contraction and expansion states were simultaneously depicted at various view angles. The present 3D reconstruction methods would be useful for efficient extraction and construction of the 3D lumen geometries of carotid bifurcations from 2D ultrasound images.     

Simulative analysis of co-existing 2.5 G/10 G asymmetric XG-PON system using RZ and NRZ data formats

In this paper, a fiber optic communication system has been employed using co-existing 10 G/2.5 G asymmetric gigabit passive optical network (XG-PON) architecture. In this system, bidirectional optical fiber has been used for upstream and downstream data transmission. The system performance has been investigated for non-return-to-zero (NRZ) and return-to-zero (RZ) data formats operating at varying bit rates by varying the length of the fiber for analyzing the feasibility of this co-existence. The results have been compared for NRZ and RZ formats for upstream and downstream data in terms of Q value and eye opening. It is observed that RZ modulation format is superior as compared to conventional NRZ format and the faithful transmission of signal has been carried up to 90 km at 1577 nm for downstream and 140 km at 1270 nm for upstream.     

Intravascular ultrasound allows a hyperplasia diagnosis in vivo in rat as accurate as histomorphometry

Objective and motivation

Intravascular ultrasound (IVUS) allows in vivo invasive intra-luminal real-time examination of the arterial wall structure. In this study, we aimed to validate for the first time the in vivo IVUS performing as a diagnostic tool by comparison to the well-established histomorphometry approach, in the largely used rat model of carotid angioplasty model that mimics the angioplasty procedure in humans.

Methods

Atherosclerotic lesions were allowed to develop during four weeks after balloon catheter inflation of the left carotid artery, whereas the intact right carotid artery was used as control. Four weeks after injury, a Boston Scientific 40 MHz device to perform IVUS exams in vivo on both carotid arteries. Then, both carotid arteries were examined in vitro by histomorphometry and correlation between IVUS and histomorphometric parameters (plaque plus media cross-sectional areas [CSA] and eccentricity index) were researched.

Results

After ANOVA analysis, comparative statistical analysis showed significant correlations between IVUS and histomorphometry when examining the intact right carotid artery (r = 0.662 with p < 0.003 for plaque plus media CSA; r = 0.774 with p < 0.002 for eccentricity index), but also when exploring the injured left carotid artery (r = 0.805 with p < 0.0001 for plaque plus media CSA; r = 0.775 with p < 0.002 for eccentricity index).

Conclusions and outcome

We report here for the first time the ability of IVUS to study therapeutic vascular effects in vivo in alive rats. This result is of major importance since it will allow this device to be used for restenosis drug testing in rat model of carotid angioplasty.     

Constrained snake vs. conventional snake for carotid ultrasound automated IMT measurements on multi-center data sets

Accurate intima-media thickness (IMT) measurement of the carotid artery from minimal plaque ultrasound images is a relevant clinical need, since IMT increase is related to the progression of atherosclerosis.In this paper, we describe a novel dual snake-based model for the high-performance carotid IMT measurement, called Carotid Measurement Using Dual Snakes (CMUDS). Snakes (which are deformable contours) adapt to the lumen-intima (LI) and media-adventitia (MA) interfaces, thus enabling the IMT computation as distance between the LI and MA snakes. However, traditional snakes might be unable to maintain a correct distance and in some spatial location along the artery, it might even collapse between them or diverge. The technical improvement of this work is the definition of a dual snake-based constrained system, which prevents the LI and MA snakes from collapsing or bleeding, thus optimizing the IMT estimation.The CMUDS system consists of two parametric models automatically initialized using the far adventitia border which we automatically traced by using a previously developed multi-resolution approach. The dual snakes evolve simultaneously and are constrained by the distances between them, ensuring the regularization of LI/MA topology. We benchmarked our automated CMUDS with the previous conventional semi-automated snake system called Carotid Measurement Using Single Snake (CMUSS).Two independent readers manually traced the LIMA boundaries of a multi-institutional, multi-ethnic, and multi-scanner database of 665 CCA longitudinal 2D images. We evaluated our system performance by comparing it with the gold standard as traced by clinical readers.CMUDS and CMUSS correctly processed 100% of the 665 images. Comparing the performance with respect to the two readers, our automatically measured IMT was on average very close to that of the two readers (IMT measurement biases for CMUSS was equal to −0.011 ± 0.329 mm and −0.045 ± 0.317 mm, respectively, while for CMUDS, it was 0.030 ± 0.284 mm and −0.004 ± 0.273 mm, respectively). The Figure-of-Merit of the system was 98.5% and 94.4% for CMUSS, while 96.0% and 99.6% for CMUDS, respectively. Results showed that the dual-snake system CMUDS reduced the IMT measurement error accuracy (Wilcoxon, p < 0.02) and the IMT error variability (Fisher, p < 3 × 10⁻²).We propose the CMUDS technique for use in large multi-centric studies, where the need for a standard, accurate, and automated IMT measurement technique is required.     

Structural analysis of the c(4 × 2) reconstruction in Si(0 0 1) and Ge(0 0 1) surfaces by low-energy electron diffraction

The c(4 × 2) structures in (0 0 1) surfaces of Si and Ge have been studied by low-energy electron diffraction (LEED). Using a proper cleaning method for the Si surface, we were able to observe clear c(4 × 2) LEED patterns up to incident energy of ∼400 eV as well as the Ge surface. Extensive experimental intensity-voltage curves allowed us to optimize the asymmetric dimer model up to the eighth layer (including the dimer layer) in depth in the dynamical LEED calculation. Optimized structural parameters are almost the same for the Si and Ge except for the height of the buckled-up atom of the asymmetric dimer. For the Ge surface, the structural parameters are in excellent agreement with those obtained by a previous theoretical calculation. The tilt angle and bond length of the dimer are 18 ± 1 (19 ± 1)° and 2.4 ± 0.1 (2.5 ± 0.1) Å for the Si(0 0 1) (Ge(0 0 1)), respectively.     

Core-level shifts at the Pt/W(1 1 0) monolayer bimetallic interface

We have measured W and Pt 4f_7/2 core-level photoemission spectra from interfaces formed by ultrathin Pt layers on W(1 1 0), completing our core-level measurements of W(1 1 0)-based bimetallic interfaces involving the group-10 metals Ni, Pd, and Pt. With increasing Pt coverage the sequence of W spectra can be described using three interfacial core-level peaks with binding-energy (BE) shifts (compared to the bulk) of −0.220 ± 0.015, −0.060 ± 0.015, and +0.110 ± 0.010 eV. We assign these features to 1D, 2D pseudomorphic (ps), and 2D closed-packed (cp) Pt phases, respectively. For ∼1 ps ML the Pt 4f_7/2 BE is 71.40 ± 0.02 eV, a shift of +0.46 ± 0.09 eV with respect to the BE of bulk Pt metal. The W 4f_7/2 core-level shifts induced by all three adsorbates are semiquantitatively described by the Born-Haber-cycle based partial-shift model of Nilsson et al. [39]. As with Ni/W(1 1 0), the difference in W 4f_7/2 binding energies between ps and cp Pt phases has a large structural contribution. The Pt 4f lineshape is consistent with a small density of states at the Fermi level, reflective of the Pt monolayer having noble-metal-like electronic structure.     

50 km bidirectional FTTH transmission comparing different PON standards

In this paper, a bidirectional Fiber To The Home (FTTH) is proposed where WDM transmitter is used as a seeding source with wavelength of 1550 nm. The system utilizes a Travelling wave Semiconductor Optical Amplifier (TSOA) with injection current 0.15A. 50 km range FTTH architecture is demonstrated for both downstream and upstream channels. We investigated the impact of different data rates on upstream and downstream data. The BER results show that the performance of our scheme is good for 10 Gbps system for downstream transmission as it accommodates 64 ONUs. From simulation results show the BER of 9.95e-009 is reported at 15 Gbps but only in case of 32 ONUs. Similarly, in case of upstream transmission, Q-Factor of 15.04 dB is reported for 32 ONUs. So this scheme is a practical solution to meet the data rate of the optical links simultaneously in tomorrow's PON access networks.     

Ultrasonically assisted evaluation of the impact of atherosclerotic plaque on the pulse pressure wave propagation: a clinical feasibility study

The purpose of this work was to evaluate ultrasound modality as a non-invasive tool for determination of impact of the degree of the atherosclerotic plaque located in human internal carotid arteries on the values of the parameters of the pulse wave. Specifically, the applicability of the method to such arteries as brachial, common, and internal carotid was examined. The method developed is based on analysis of two characteristic parameters: the value of the mean reflection coefficient modulus |Γ|_a of the blood pressure wave and time delay Δt between the forward (travelling) and backward (reflected) blood pressure waves. The blood pressure wave was determined from ultrasound measurements of the artery’s inner (internal) diameter, using the custom made wall tracking system (WTS) operating at 6.75 MHz. Clinical data were obtained from the carotid arteries measurements of 70 human subjects. These included the control group of 30 healthy individuals along with the patients diagnosed with the stenosis of the internal carotid artery (ICA) ranging from 20% to 99% or with the ICA occlusion. The results indicate that with increasing level of stenosis of the ICA the value of the mean reflection coefficient measured in the common carotid artery, significantly increases from |Γ|_a = 0.45 for healthy individuals to |Γ|_a = 0.61 for patients with stenosis level of 90-99%, or ICA occlusion. Similarly, the time delay Δt decreases from 52 ms to 25 ms for the respective groups. The method described holds promise that it might be clinically useful as a non-invasive tool for localization of distal severe artery narrowing, which can assist in identifying early stages of atherosclerosis especially in regions, which are inaccessible for the ultrasound probe (e.g. carotid sinus or middle cerebral artery).     

Noninvasive estimation of the ocular elastic modulus for age-related macular degeneration in the human eye using sequential ultrasound imaging

Introduction

Elastic modulus estimation may be an important clinical criterion, as it seems to affect such eye parameters as intraocular pressure, ocular pulsation, blood flow, effect of topical medications, and post-refractive surgery complications. The purpose of this study was to examine the differences in elasticity in the ocular axial length, posterior wall thickness (posterior pole), and retina-choroid thickness under normal and aged-related macular degeneration (AMD) conditions in the human eye by directly estimating the elastic modulus with sequential and noninvasive ultrasound image processing.

Materials and Methods

In this study, 25 healthy subjects and 20 patients with non-neovascular AMD participated in the experiment. The deformation of the ocular axial length, posterior wall thickness and retina-choroid complex thickness was captured using high-resolution ultrasonography before and after loading. The B-mode (20 MHz) and A-mode (8 MHz) frames were obtained and processed with an echo tracking technique. The elastic modulus was estimated using changes in ocular axial length, posterior wall thickness and retina-choroid complex thickness and with applied stress measurements.

Results

There was a significant difference (p < 0.05) in the ocular axial length elastic modulus between the AMD and healthy subjects (AMD patients: 95.165 ± 26.431 kPa, vs. healthy subjects: 49.539 ± 25.867 kPa). Moreover, there was a statistically significant difference (p < 0.05) in the posterior wall thickness elastic modulus between AMD patients and healthy subjects (AMD patients: 50.519 ± 12.295 kPa, vs. healthy subjects: 20.519 ± 11.827 kPa). However, no statistically significant difference (p-value > 0.05) was found in the retina-choroid complex elastic modulus between the two groups (AMD patients: 20.134 ± 3.898 kPa, vs. healthy subjects: 15.630 ± 4.250 kPa).

Conclusion

Although the results were obtained examining a relatively low number of patients, it would appear that noninvasive ultrasound estimation of the local elastic moduli of ocular axial length and posterior wall thickness is suited to aid in detection of the non-exudative AMD thus manifesting its potential as a screening tool in symptom-free individuals.     

脂肪颗粒在颈动脉中的运动及其对血液动力学的影响

很多研究表明, 动脉粥样硬化通常发生在具有复杂血液动力学的区域, 比如分叉动脉和弯曲动脉. 这些地方常伴随有低壁面剪切力或震荡壁面剪切力, 这是动脉粥样硬化形成的一大诱因. 使用计算流体力学软件对2D颈动脉分叉血管进行了模拟, 研究了脂肪颗粒在颈动脉中的运动及其对血液动力学的影响. 研究表明: 1)血管狭窄对于脂肪颗粒的运动有重要影响, 同时也影响栓塞的形成; 2)脂肪颗粒可能会黏附在血管壁面, 但由于血流的冲击作用, 脂肪颗粒会随后在壁面略微铺展; 3)颈动脉狭窄区域后方是下一个血栓的可能生长位点; 4)当栓塞形成时, 速度和壁面剪切力分布将变得复杂多变, 这对于血管是有害的.     

Low-frequency noise and inelastic tunneling spectroscopy in Fe(1 1 0)/MgO(1 1 1)/Fe(1 1 0) epitaxial magnetic tunnel junctions

We report on tunnelling magnetoresistance (TMR), current–voltage (IV) characteristics and low-frequency noise in epitaxially grown Fe(1 1 0)/MgO(1 1 1)/Fe(1 1 0) magnetic tunnel junctions (MTJs) with dimensions from 2×2 to 20×20 μm². The evaluated MgO energy barrier (0.50±0.08 eV), the barrier width (13.1±0.5 Å) as well as the resistance times area product (7±1 MΩ μm²) show relatively small variation, confirming a high quality epitaxy and uniformity of all MTJs studied. At low temperatures (T<10 K) inelastic electron tunneling spectroscopy (IETS) shows anomalies related to phonons (symmetric structures below 100 meV) and asymmetric features above 200 meV. We explain the asymmetric features in IETS as due to generation of electron standing waves in one of the Fe electrodes. The noise power, though exhibiting a large variation, was observed to be roughly anti-correlated with the TMR. Surprisingly, for the largest junctions we observed a strong enhancement of the normalized low-frequency noise in the antiparallel magnetic configuration. This behavior could be related to the influence of magnetostriction on the characteristics of the insulating barrier through changes in local barrier defects structure.     

Lattice Boltzmann method simulating hemodynamics in the three-dimensional stenosed and recanalized human carotid bifurcations

By using the lattice Boltzmann method(LBM)pulsatile blood flows were simulated in three-dimensional moderate stenosed and recanalized carotid bifurcations to understand local hemodynamics and its relevance in arterial atherosclerosis formation and progression.The helical flow patterns,secondary flow and wall dynamical pressure spatiotemporal distributions were investigated,which leads to the disturbed shear forces in the carotid artery bifurcations.The wall shear stress distributions indicated by time-averaged wall shear stress(TAWSS),oscillatory shear index(OSI),and the relative residence time(RRT)in a cardiac cycle revealed the regions where atherosclerotic plaques are prone to form,extend or rupture.This study also illustrates the point that locally disturbed flow may be considered as an indicator for early atherosclerosis diagnosis.Additionally the present work demonstrates the robust and highly efficient advantages of the LBM for the hemodynamics study of the human blood vessel system.     

Low cost solution to high capacity 32 × 32 channel FTTH duplex link employing triple play services

In this paper, low cost solution based on RSOAs is proposed for a high capacity 32 × 32 channel, 20 km, FTTH duplex link employing triple play services. Here, downstream transmitters generate a 2.5-Gbps NRZ signal which is routed to both receivers and RSOA-based upstream transmitters. The RSOA modulates this signal with a 1.25-Gbps NRZ signal that effectively overwrites the downstream signal and then it is transmitted back over the same 20 km of bidirectional fiber, where it is routed to receivers at the CO. The proposed model completely eliminates the requirement of separate lasers for upstream communication which makes the system very cost effective. The high-pass filtering effect of the RSOA becomes predominant at higher input powers which has been used as an advantage here to effectively suppress the downstream signal. The impact of RSOA input power and extinction ratio of the downstream signal have been investigated and reported.     

In vivo characterization of the aortic wall stress-strain relationship

Arterial stiffness has been shown to be a good indicator of arterial wall disease. However, a single parameter is insufficient to describe the complex stress-strain relationship of a multi-component, non-linear tissue such as the aorta. We therefore propose a new approach to measure the stress-strain relationship locally in vivo noninvasively, and present a clinically relevant parameter describing the mechanical interaction between aortic wall constituents. The slope change of the circumferential stress-strain curve was hypothesized to be related to the contribution of elastin and collagen, and was defined as the transition strain (). A two-parallel spring model was employed and three Young’s moduli were accordingly evaluated, i.e., corresponding to the: elastic lamellae (E₁), elastin-collagen fibers (E₂) and collagen fibers (E₃). Our study was performed on normal and Angiotensin II (AngII)-treated mouse abdominal aortas using the aortic pressure after catheterization and the local aortic wall diameters change from a cross-correlation technique on the radio frequency (RF) ultrasound signal at 30 MHz and frame rate of 8 kHz. Using our technique, the transition strain and three Young’s moduli in both normal and pathological aortas were mapped in 2D. The slope change of the circumferential stress-strain curve was first observed in vivo under physiologic conditions. The transition strain was found at a lower strain level in the AngII-treated case, i.e., 0.029 ± 0.006 for the normal and 0.012 ± 0.004 for the AngII-treated aortas. E₁, E₂ and E₃ were equal to 69.7 ± 18.6, 214.5 ± 65.8 and 144.8 ± 55.2 kPa for the normal aortas, and 222.1 ± 114.8, 775.0 ± 586.4 and 552.9 ± 519.1 kPa for the AngII-treated aortas, respectively. This is because of the alteration of structures and content of the wall constituents, the degradation of elastic lamella and collagen formation due to AngII treatment. While such values illustrate the alteration of structure and content of the wall constituents related to AngII treatment, limitations regarding physical assumptions (isotropic, linear elastic) should be kept in mind. The transition strain, however, was shown to be a pressure independent parameter that can be clinically relevant and noninvasively measured using ultrasound-based motion estimation techniques. In conclusion, our novel methodology can assess the stress-strain relationship of the aortic wall locally in vivo and quantify important parameters for the detection and characterization of vascular disease.     

Design of a novel bioreactor and application in vascular tissue engineering

Endothelial cells (ECs) detachment under high shear stress at the early period of transplantation resulted in thrombosis and occlusion. To solve this problem, we developed a novel bioreactor. The bioreactor mimicked the formation of pulsatile flow in physiological conditions. Human umbilical vein ECs were seeded onto the lumen of living tissue conduits grown within dog peritoneal cavity. The shear stress generated by the bioreactor was increased step by step from 1.5 ± 0.8 dyn/cm² to 5.3 ± 2.4 dyn/cm², and was applied to ECs after static culture for 2 days. The results showed that completely confluent monolayer ECs were elongated, and were oriented parallel to the flow direction. The bioreactor could provide good environment for formation of endothelium. Stepwise increase shear stress could strengthen cell-cell and cell-extracellular matrix. The flow conditions of the bioreactor play a key role to determine the quality of the ECs lining.     

Influence of modulation formats performance of the combined modulation in WDM-PON system

Different modulation modes of DPSK and OOK are separately employed in the upstream and downstream link, after the comparison with different modulation formats in the downstream including the codes of non return-to-zero (NRZ), return-to-zero (RZ) and inverse return-to-zero (IRZ), the symmetric rate of 10 Gbps with 20 km transmission is realized without the dispersion compensation. It can be shown that in the combined modulation mode with the downstream of IRZ code, higher extinction ratio in the downstream and better performance of dispersion tolerance in the upstream could be achieved, enhancing the overall property of the transmission system.     

A full-duplex radio-over-fiber link with 12-tupling mm-wave generation and wavelength reuse for upstream signal

A full-duplex radio-over-fiber (RoF) link with a novel scheme to generate 60 GHz mm-waves from a 5 GHz RF signal source is investigated. In the RoF downlink, the required frequency of the RF oscillator is reduced greatly. Since the optical carrier is not modulated by downstream data, part of it is reused to carry upstream data and the upstream data is transmitted to the central station using optical single-sideband modulation. In this way, a single wavelength is used for both downstream and upstream transmissions. Based on this scheme, a full-duplex RoF link is built and its transmission performance is analyzed. Theoretical analysis and numerical simulation show that the downstream signal cannot only eliminate code form distortion caused by time shift of the code edges, but also reduce the influence of the fading effect as the 60 GHz DSB optical mm-wave signal is transmitted along the fiber, and the upstream signal is immune to both fading effect and time shift of the code edges.