Stress Imaging Method Research Articles

In Vivo Intravascular Optical Coherence Tomography (IVOCT) Structural and Blood Flow Imaging Based Mechanical Simulation Analysis of a Blood Vessel.

Computer modelling of blood vessels based on biomedical imaging provides important hemodynamic and biomechanical information for vascular disease studies and diagnosis. However due to lacking well-defined physiological blood flow profiles, the accuracy of the simulation results is often not guaranteed. Flow velocity profiles of a specific cross section of a blood vessel were obtained by in vivo Doppler intravascular optical coherence tomography (IVOCT) lately. However due to the influence of the catheter, the velocity profile imaged by IVOCT can't be applied to simulation directly. A simulation-experiment combined method to determine the inlet flow boundary based on in vivo porcine carotid Doppler IVOCT imaging is proposed. A single conduit carotid model was created from the 3D IVOCT structural images using an image processing-computer aided design combined method. With both high- resolution arterial model and near physiological blood flow profile, stress analysis by fluid-structure interaction and computational fluid dynamics were performed. The influence of the catheter to the wall shear stress, the hemodynamics and the stresses of the carotid wall under the measured inlet flow and various outlet pressure boundary conditions, are analyzed. This study provides a solution to the difficulty of getting inlet flow boundary for numerical simulation of arteries. It paves the way for developing IVOCT based vascular stress analysis and imaging methods for the studies and diagnosis of vascular diseases.

Imaging crystal stress in diamond using ensembles of nitrogen-vacancy centers

We present a micrometer-resolution millimeter-field-of-view stress imaging method for diamonds containing a thin surface layer of nitrogen vacancy (NV) centers. In this method, we reconstruct stress tensor elements over a two-dimensional field of view from NV optically-detected magnetic resonance (ODMR) spectra. We use this technique to study how stress inhomogeneity affects NV magnetometry performance, and show how NV stress imaging is a useful and direct way to assess these effects. This new tool for mapping stress in diamond will aid optimization of NV-diamond sensing, with wide-ranging applications in the physical and life sciences.

2-D poroelastic wave modelling with a topographic free surface by the curvilinear grid finite-difference method

The curvilinear grid finite-difference method, which is suitable for accurate modelling of seismic waves in the presence of topographic free surfaces, is applied in this study to model poroelastic waves. Poroelastic wave equations of Biot’s theory are expressed in curvilinear coordinates and solved on a collocated grid by utilizing the fourth-order Runge–Kutta time integral scheme with alternative applications of forward and backward MacCormack finite differences. Discretization of the irregular free surface with the curvilinear coordinate grid enables a good fit of the topographic surface, and this good fit results in higher numerical accuracy in comparison with stair-case approximation. The formulas of the free-surface boundary conditions for poroelastic media are also derived for the curvilinear coordinates and subsequently implemented with the traction-imaging method, which is a generalization of the stress-imaging method and can maintain high accuracy in curvilinear coordinates. To verify the performance of the proposed algorithm and determine its accuracy, we conduct numerical simulations on several different models, and compare our numerical solutions with other solutions that are calculated by analytical expressions, generalized reflection/tranmission method and spectral-element method. Besides, the fluid–solid dynamic compatibility of porous media is demonstrated using a three-layered half-space model, and effects of the irregular free-surface on poroelastic waves are investigated for a four-layered model with strong irregular free-surface topography. The good performance of the proposed algorithm suggests that the curvilinear grid finite-differece method is a useful tool for the study of poroelastic wave propagation.

A Novel Force Sensing Method Based on Stress Imaging Analysis

This paper presents a new approach to the design of multi-axial force sensing elements. We show that it is possible to measure multiple forces by detecting stress components—namely, normal stress, shear stress, and torque—with a single sensing element. Multi-axis force-torque sensors have become popular in the field of robotics, because they provide valuable information to robots during physical interaction; but these sensors have posed a challenge to researchers during fabrication, as they typically require multiple uni-axial sensing elements scattered over the mechanical structure of the force–torque sensor. We solve this problem by accomplishing the same functionality with just one sensing element. Our sensing element is composed of layers of elastomer, with conductive electrodes integrated within the two sensitive layers. When a force is applied, some (or all) of the electrodes within each layer are compressed, changing the capacitance and providing stress images. A stress-imaging analysis, thus, allows us to reliably infer the applied force. In this paper, we describe the design, fabrication, and characterization of our triaxial sensing element. After constructing the prototype, we validate its performance using a series of experiments. The results demonstrate that our stress-imaging analysis method does indeed allow the measurement of multiple force components with a single sensing element.

Vasodilator Stress Perfusion CMR Imaging Is Feasible and Prognostic in Obese Patients

This study sought to determine feasibility and prognostic performance ofstress cardiac magnetic resonance (CMR) in obese patients (body mass index [BMI] ≥30 kg/m(2)). Current stress imaging methods remain limited in obese patients. Given the impact of the obesity epidemic on cardiovascular disease, alternative methods to effectively risk stratify obese patients are needed. Consecutive patients with a BMI ≥30 kg/m(2) referred for vasodilating stress CMR were followed for major adverse cardiovascular events (MACE), defined as cardiac death or nonfatal myocardial infarction. Univariable and multivariable Cox regressions for MACE were performed to determine the prognostic association of inducible ischemia or late gadolinium enhancement (LGE) by CMR beyond traditional clinical risk indexes. Of 285 obese patients, 272 (95%) completed the CMR protocol, and among these, 255(94%) achieved diagnostic imaging quality. Mean BMI was 35.4 ± 4.8 kg/m(2), with a maximum weight of 200 kg. Reasons for failure to complete CMR included claustrophobia (n= 4), intolerance to stress agent (n= 4), poor gating (n= 4), and declining participation (n= 1). Sedation was required in 19 patients(7%; 2 patients with intravenous sedation). Sixteen patients required scanning by a 70-cm-bore system (6%). Patients without inducible ischemia or LGE experienced a substantially lowerannual rate of MACE (0.3% vs. 6.3% for those with ischemia and 6.7% for those with ischemia and LGE). Median follow-up of the cohort was 2.1 years. In a multivariable stepwise Cox regression including clinical characteristics and CMR indexes, inducible ischemia (hazard ratio 7.5; 95% confidence interval: 2.0 to 28.0; p=0.002) remained independently associated with MACE. When patients with early coronary revascularization (within 90 days of CMR) were censored on the day of revascularization, both presence of inducible ischemia and ischemia extent per segment maintained a strong association with MACE. Stress CMR is feasible and effective in prognosticating obese patients, with a verylow negative event rate in patients without ischemia or infarction.

Can quantitative synthetic aperture vascular elastography predict the stress distribution within the fibrous cap non-invasively

An imaging system that can detect and predict the propensity of an atherosclerotic plaque to rupture would reduce stroke. Radial and circumferential strain elastograms can reveal vulnerable regions within the fibrous cap. Circumferential stress imaging could predict the propensity of rupture. However, circumferential stress imaging demands either accurate knowledge of the geometric location of the fibrous cap or high quality strain information. We corroborated this hypothesis by performing studies on simulated vessel phantoms. More precisely, we computed stress elastograms with (1) precise knowledge of the fibrous cap, (2) no knowledge of the fibrous cap, (3) imprecise knowledge of the fibrous cap. We computed stress elastograms with accuracy of 8%, 15%, and 23% from high precision axial and lateral strain elastograms (i.e., 25 dB SNR) when precise, imprecise, and no geometric information was included the stress recovery method. The stress recovery method produced erroneous elastograms at lower noise level (i.e., 15 dB SNR), when no geometric information was included. Similarly, it produced elastograms with accuracy of 13% and 30% when precise and imprecise geometric information was included. The stress imaging method described in this paper performs well enough to warrant further studies with phantoms and ex-vivo samples.

基于斯托克斯参量的光弹性应力分布及成像方法研究

基于斯托克斯参量的光弹性应力分布及成像方法研究

Nichtinvasive Diagnostik der chronisch stabilen koronaren Herzkrankheit: evidenzbasierte und nicht evidenzbasierte diagnostische Algorithmen

In Germany, every second left heart catheterization has no immediate interventional or surgical consequence. One main reason for this limited quality of indication of many left heart catheterizations is presumably the inaccuracy of preinvasive testing that is mainly based on clinical evaluation and exercise ECG in Germany. However, exercise electrocardiography has several limitations. The central issues are the inability to exercise in many, especially elderly patients, and the missing interpretability of the stress ECG in cases with already pathological rest ECG. In 2006, the "Nationale Versorgungsleitlinie Chronische KHK (NVL KHK)" was published in Germany, adopting for the first time the evidence-based algorithms of the American College of Cardiology/American Heart Association (ACC/AHA) guidelines for non-invasive stress testing and complementary stress imaging. Stress imaging methods considered comparable and interchangeable are the following: stress echocardiography combined with physical or pharmacological stress testing, myocardial perfusion imaging with physical or pharmacological stress testing, dobutamine stress magnetic resonance imaging (DSMR), or myocardial perfusion magnetic resonance imaging (MRI). Basically, no stress imaging method is definitely superior to the others, each method has its own advantages and disadvantages that should be considered and adjusted to the individual patient. Of pivotal importance of all stress imaging methods is the high negative predictive value of 99% of a normal study predicting a very low (< 1%) cumulative likelihood of cardiac death or myocardial infarction for at least the next 12 months. Hence, in most clinical circumstances, coronary angiography is not necessary during the 12 months subsequent to a normal stress imaging study. In contrast to these established and evidence-based recommendations of the "Nationale Versorgungsleitlinie Chronische KHK" mainly focusing on ischemia stress imaging, many diagnostic centers have developed their own non-evidence based algorithms. In these non-evidence based algorithms the morphology-oriented non-invasive CT coronary angiography has taken over the diagnostic part of evidence-based ischemia stress imaging. However, beyond the scientifically established prognostic value of calcium scoring, there is so far no scientific evidence showing that morphology-oriented CT coronary angiography protocols are superior to functional stress imaging. A new innovative approach of staged non-invasive diagnostics for patients with intermediate likelihood (10-90%) of coronary artery disease are the 2010 recommendations of the National Institute for Health and Clinical Excellence (NICE) guiding the National Health Service (NHS) in the United Kingdom. Following this guidance, in patients with an estimated likelihood of CAD of 10-29% CT calcium scoring should be offered as first-line method, in patients with an estimated likelihood of CAD of 30-60% non-invasive functional imaging should be offered primarily, and in patients with an estimated likelihood of CAD of 61-90%, as in patients with an estimated likelihood of CAD of more than 90%, invasive coronary angiography should be preferred.

Zum Ischämienachweis reicht das Belastungs-EKG: Wann sollten andere Verfahren eingesetzt werden?

The stress-ECG is the most often adopted and most cost effective initial diagnostic test for the assessment of myocardial ischemia in patients with suspected coronary artery disease (CAD). Prerequisites for the diagnostic usefullness of stress-ECG are a clearly interpretable ST-segment, ability to reach the predicted work load, an intermediate pretest probability for CAD ranging between 10% and 90% and the absence of any contraindications for dynamic exercise. Because of the limited diagnostic sensitivity of about 70%, and a high percentage of patients, who are unable to exercise, a negative stress ECG can definitely not exclude hemodynamically significant CAD. Therefore, stress imaging techniques like myocardial scintigraphy, stress-echocardiography and stress magnetic resonance imaging play a major role in the stepwise diagnostic work-up of patients with suspected CAD. These stress imaging techniques are basically interchangeable since no method is definitely superior to one of the others. However, each method has its specific pros and cons and inherent contraindications. Therefore the choice of the stress imaging method and the form of stress applied should be based on the individual patients characteristics to gain optimal image quality and diagnostic accuracy. Moreover, the decision for one method should take the local availability and institutional expertise of diagnostic centers into account. Although partly substituted by stress imaging techniques the stress-ECG still remains the workhorse for a stepwise diagnostic work-up of patients with suspected CAD.

Medicina basata sulle evidenze: ruolo della TC multidetettore nel follow-up dei pazienti sottoposti a bypass aortocoronarici

The aim of this study was to define the role of multidetector computed tomography (MDCT) in the follow-up assessment of patients undergoing coronary artery bypass grafting (CABG) using an evidence-based medicine (EBM) approach. We performed a literature search of the most reputable studies published in the period 1990-2005 on the clinical follow-up of patients after myocardial revascularisation by CABG. Relevant studies were ranked according to levels of evidence using EBM criteria. A similar search was also conducted on the Internet to identify and review the guidelines posted by the major international scientific societies. A total of 29 papers meeting the basic reliability requirements of EBM were identified. The reported sensitivity and specificity for electrocardiogram (ECG) testing, stress echocardiography and radionuclide myocardial perfusion imaging were 45% and 82%, 86% and 90%, and 68% and 84%, respectively. All 16 CT studies (one retrospective, the remaining prospective) were validation studies comparing MDCT with conventional coronary angiography. The total number of patients and graft segments studied were 705 and 1,974, respectively. The total number of assessable graft segments were 62%-100%, with a sensitivity and specificity of 75%-100% and 76.9%-100%, respectively. The applications of MDCT in the follow-up assessment of patients after CABG are derived from indirect evidence only. The efficacy of the method should be evaluated in randomised clinical trials comparing MDCT not only with conventional coronary angiography but also with other noninvasive stress imaging methods. On the basis of the clinical evidence reported in the literature, the indications for the use of MDCT are still limited. In our view, the completion of such randomised trials combined with the development of new-generation scanners is required to correctly define the role of MDCT in the follow-up assessment of patients who have undergone CABG.

Photoelastic characterization of residual stress in GaAs-wafers

Residual stress in GaAs-wafers was investigated on different length scales by rapid full wafer imaging and by microscopic imaging of dislocation cells, using photoelastic homodyne techniques. These non-contact and non-destructive defect and stress imaging methods will be described in detail. In connection with in situ calibration of the photoelastic SIRD™ measurement system absolute shear stress values can be extracted. Local stress fields imaged in μm-scale by the photoelastic instrument SIREX™ show the defect arrangement in cell patterns and allow to characterize the local stress enhancement. The advantages and limits of the vertically integrated photoelasticity measurement employed in both systems will be discussed.

Observation of the Stress Distribution in Textile Fabrics Using Thermographic Stress Imaging Method

The thermographic stress imaging method was applied to the textile fabrics. The distribution of the stress in textile fabrics could be observed visually and numerically by this system. The analysis indicates an inhomogeneous stress distribution for the fabrics having defects or sewed parts. The analysis also showed the feature of the clamp methods in the tensile test.

Stress imaging: Current clinical options for the diagnosis, localization, and evaluation of coronary artery disease

As technology advances, new methods evolve. In this article, the methods of stress testing and related imaging in coronary disease are addressed, and dynamic and pharmacologic stress, direct and indirect methods, are defined and evaluated. The stress imaging methods related to the modalities of scintigraphy and ultrasound are reviewed and their advantages and disadvantages assessed in view of scientific and economic factors.

A consideration of current clinical options for stress imaging in the diagnosis and evaluation of coronary artery disease.

The evolution of technology and our health care system, tinctured by advocacy groups for specific imaging modalities, has produced controversy, relating to the optimal stress imaging method for coronary disease evaluation. Stress perfusion scintigraphy and stress echocardiography advocates seem to make claims that each nullify the other. This extensive, in-depth review of the subject presents facts as well as opinion and experience in an effort to assess the full portrait of the issue for consideration by advocates as well as those many yet undecided. The issue is an evolving one, affected strongly by the reader's own experience. The presentation is not meant to be the final word. Rather, it seeks to present a basis for understanding and progress in both fields.

赤外線応力画像法による下顎骨の力学的対応に関する基礎的研究 第１報 ストレインゲージ法との比較による赤外線応力画像法の有効性

In this paper in order to analyze the stress distribution on human dry skull through a thermoelastic stress imaging method the observation patterns was compared with those of strain gage method and discussed. As a result, the following conclusions have been reached:1. The thermoelastic stress imaging method allowed the measurement of the mandibular stress distribution upon positioning the bone similar to the in vivo mechanism.2. It was found that stess distribution pattern through the thermoelastic stress imaging method was similar to those through the strain gage method.3. It was considered that the thermoelastic stress imaging method was useless for measuring transverse stress or shearing stress.4. It was possible to make up for defects of each of these by using both the thermoelastic stress imaging method and the strain gage method in combination.These results showed that the thermoelastic stress imaging method may have an analyzing ability under the condition that is closer to the actual natural state than conventional methods.