Mean Strain Rate Research Articles

Normal Values for Longitudinal Tissue Velocity and Strain Rate Imaging in Individual Segments of the Left and Right Ventricles of Healthy Adult Hearts

To quantify the normal peak mean systolic velocities and strain rate parameters in the left ventricle (LV) and right ventricle (RV) and define their regional differences in normal adult hearts. Sixty-nine healthy volunteers (42% male; mean age ± SD, 30.03 ± 5.35 years) underwent color tissue Doppler and strain rate imaging. The first and second peak mean systolic velocities, peak strain, and strain rate in the systolic ejection phase were determined for 16 LV segments, the apex (17th segment), and 3 RV free wall segments. The first peak mean systolic velocity was measurable in less than 50% of segments in the inferior and septal (-posterior) walls and RV free wall and in greater than 70% of segments of the other LV walls. The first and second peak mean systolic velocities of all LV walls and the RV free wall decreased significantly from the basal to apical region (P < .001).The strain and strain rate in the lateral and anterior walls decreased significantly from base to apex, whereas the anteroseptal and posterior walls were homogeneous. The strain rate in the inferior wall increased remarkably from base to apex, whereas it decreased significantly from the mid level to the apex. The strain in the RV was homogeneous, whereas the strain rate decreased significantly from the mid level to the apex. The apex (17th segment) showed the lowest value for each of the study parameters. Longitudinal velocities decreased from base to apex, whereas deformation measurements did not show uniform patterns in LV walls and the RV free wall. In most cases, there are 1 peak systolic velocity in the inferior and septal (-posterior) walls and 2 peak systolic velocities in the other 4 LV walls.

Deduction of surface accumulation history from ice-core age/depth data

AbstractIce-core data are the only source of ice response on timescales of hundreds to thousands of years, which is necessary to describe polar ice-sheet flows and their interaction with changing climatic conditions. Ice properties, such as a grain growth relation, require knowledge of each ice particle’s history since first deposited at the surface, and not simply the present core state. This study is an analysis of 11 ‘present’ ice cores, using their age/depth data and present accumulation, to infer their past accumulation and mean strain rate and, in turn, the strain at each level of the core. These are the ingredients necessary to determine the particle paths and associated evolution of properties. The conventional assumptions of a purely vertical velocity distribution with a uniform compressive strain rate in the core are made, but unlike an earlier analysis which allowed independent surface accumulation and strain-rate histories, it is now assumed that the strain rate is proportional to the accumulation. Determination of the past accumulation and proportionality factor is accomplished by correlation with the present age/depth data, and while good correlations are obtained – a consistent solution – other close correlations can yield quite different accumulation histories and corresponding proportional strain-rate histories.

Comparison of magnetic resonance feature tracking for longitudinal strain calculation with spatial modulation of magnetization imaging analysis

Background Feature-tracking (FT) analysis offers a novel, fast and practicable method to calculate strain from routinely acquired steady state free precession (SSFP) images without the need to perform additional tagged sequences. There is no validation of this technique, however, against a reference standard myocardial tagging analysis for any strain parameter other than mid-left ventricular whole slice circumferential strain in children. In an adult study of patients with dilated cardiomyopathy (DCM) and healthy controls, we sought to validate the FT method (TomTec Imaging systems, Munich) against spatial modulation of magnetization (SPAMM) tissue tagging analysis (Cardiac Image Modeling Package (CIMTAG), University of Auckland) for the computation of long axis function. Methods We compared measures of peak systolic longitudinal strain from the horizontal long axis view using the 2 techniques in 30 patients (median age 42 yr, male 40%). Normal healthy adults were identified from an ongoing prospective, observational research study examining the effects of living kidney donation on cardiovascular structure and function (NCT01028703) while DCM patients underwent routine tagging during CMR studies performed for clinical requirements. A timed retrospective off-line analysis was performed on matched tagged and SSFP slices by 2 independent blinded observers (WEM and RJT). Results Mean peak systolic longitudinal strain and strain rate determined by FT were significantly reduced in DCM patients compared with healthy controls (-6.7 ± 1.7% vs. -20.4 ± 3.7%, P<0.001 and -1.21 ± 0.14 /s vs. -0.61 ± 0.09 /s, both P<0.0001). The mean peak systolic longitudinal strain of DCM patients determined by CIMTAG (-6.7 ± 1.7%) and FT (-7.0 ± 1.4%) was not significantly different (P = NS). In an analysis of all patients, mean FT systolic longitudinal strain values were highly correlated with CIMTAG values, with a Pearson correlation coefficient of 0.67 (P=0.0001, Figure 1). The individual longitudinal systolic strain values obtained for each

Multiscale modeling of incompressible turbulent flows

Developing an effective turbulence model is important for engineering applications as well as for fundamental understanding of the flow physics. We present a mathematical derivation of a closure relating the Reynolds stress to the mean strain rate for incompressible flows. A systematic multiscale analysis expresses the Reynolds stress in terms of the solutions of local periodic cell problems. We reveal an asymptotic structure of the Reynolds stress by invoking the frame invariant property of the cell problems and an iterative dynamic homogenization of large- and small-scale solutions. The recovery of the Smagorinsky model for homogeneous turbulence validates our derivation. Another example is the channel flow, where we derive a simplified turbulence model using the asymptotic structure near the wall. Numerical simulations at two Reynolds numbers (Re’s) using our model agrees well with both experiments and Direct Numerical Simulations of turbulent channel flow.

The Explicit Algebraic Reynolds Stress Models for Turbulent Flows

The explicit algebraic Reynolds stress models are obtained from second-order closure models that are valid for three-dimensional turbulent flows in non-inertial frames. The purpose of this present research is to simplify the development of the Reynolds stress anisotropy tensor. This anisotropy stress tensor has seven scalar coefficients and has seven tensor polynomial groups that are the integrity basis for the functions of both symmetric and antisymmetric tensors. This research will also explicitly determine the six independent invariants of the mean strain rate tensor and of the mean rotation rate tensor. The resulting algebraic equation for the anisotropy tensor depends on the choice of the model that is used to determine the dissipation rate and pressure-strain correlation. These equations also represent the slow pressure strain rate and an isotropic dissipation rate tensor of the Rotta model. The results of present research can be compared with the results of Gatski and Speziale that give the complete expression for a traceless symmetric second order tensor which depended on the symmetric and the antisymmetric tensor that involved ten tensor polynomial groups with five independent invariants. The present work reduces the ten tensor polynomial groups down to seven groups which drastically decreases computational time.

Large eddy simulations of turbulent Couette–Poiseuille and Couette flows inside a square duct

AbstractTurbulent Couette–Poiseuille and Couette flows at different mean strain rates (velocity ratio of Couette wall to bulk flow, $r= 0. 6$–$3. 15$), in a square duct at a bulk Reynolds number $\approx $10 000 are investigated by large eddy simulation. The numerical framework consists of a finite-volume method with a staggered-grid arrangement of dependent variables. Spatial derivatives are approximated using second-order centred differencing, and a fractional-step method is used for temporal integration. Simulations are conducted with $160\ensuremath{\times} 160\ensuremath{\times} 256$ grids. Secondary flow near the Couette wall shows a gradual change of vortex size and position as the moving wall velocity increased, where the two clockwise rotating vortices gradually merge in tandem with speed of the moving wall and form a large clockwise vortex. A linear relation is observed to exist between the angle of the two vortices and the parameter $r$, and the angle saturates beyond $r\ensuremath{\sim} 2. 06$. Also, at $0. 6\lt r\lt 1. 6$, together with a small counter-clockwise corner vortex, this vortex pattern is similar to that observed in the corner region of the duct flow with a free surface. The change of the vortex patterns also influences the dominant transport terms in the streamwise vorticity transport equation. Near the moving wall due to the reduction of the streamwise velocity fluctuation at the moving wall, turbulence structure gradually moves towards a rod-like axisymmetric turbulence, and as $r$ increases beyond $1. 2$, turbulence reverts to the disc-like structure.

On the anisotropy of a low-Reynolds-number grid turbulence

AbstractThe anisotropy of a low-Reynolds-number grid turbulence is investigated through direct numerical simulations based on the lattice Boltzmann method. The focus is on the anisotropy of the Reynolds-stress (${b}_{ij} $) and Reynolds-stress dissipation-rate (${d}_{ij} $) tensors and the approach taken is that using the invariant analysis introduced by Lumley &amp; Newman (J. Fluid Mech., vol. 82, 1977, pp. 161–178). The grid is made up of thin square floating elements in an aligned configuration.The anisotropy is initially high behind the grid and decays quickly as the downstream distance increases. The anisotropy invariant map (AIM) analysis shows that the return-to-isotropic trend of both ${b}_{ij} $ and ${d}_{ij} $ is fast and follows a perfectly axisymmetic expansion, although just behind the grid there is an initial tendency toward a one-component state. It is found that the linear relation ${d}_{ij} = A{b}_{ij} $ with $A= 0. 21$ is satisfied during the return-to-isotropy phase of the turbulence decay, although close to the grid a form ${d}_{ij} = f({b}_{ij} )$, where $f$ is a nonlinear function of ${b}_{ij} $, is more appropriate. For large downstream distances, ${d}_{ij} $ becomes almost independent of ${b}_{ij} $, suggesting that despite the absence of an inertial range, the (dissipative) small scales present a high degree of isotropy. It is argued that (i) the very small values of the mean strain rate and (ii) the weak anisotropy of the large scales are in fact responsible for this result.

Analysis of necking in high speed experiments by stereocorrelation

Tensile tests with Hopkinson bars are monitored with high speed cameras to extract 3D displacement fields and the corresponding strain fields by resorting to stereocorrelation. The aim of the experiments is to analyze the onset and development of necking for various strain rates and samples. Various challenges have to be dealt with, namely small definition of the pictures, large displacements that occur during the experiment, and the need for good spatial resolutions to capture the strain levels within the neck. In order to address all these issues, pre-correction techniques are used to allow for the required stability and accuracy of the analysis.Eight experiments on cylinders and parallelepipeds at different loading rates are analyzed. Either single or multiple neck inceptions were observed, irrespective of the mean strain rate, supporting a random nucleation picture rather than a deterministic result of the constitutive law. Local strains up to about 600% were measured. In the case of multiple necking, a selection leading to the growth of a dominant one is observed, in agreement with Mott's theory of an “unloading wave” emanating from neck inception. A propagation speed of this wave can be estimated from the analysis and is shown to agree with the theoretical prediction.

Direct numerical simulation of the turbulent flow in a baffled tank driven by a Rushton turbine

AbstractWe present a direct numerical simulation (DNS) of the turbulent flow in a baffled tank driven by by a Rushton turbine. The DNS is compared to a Large Eddy Simulation (LES), a Reynolds Averaged Navier‐Stokes (RANS) simulation, Laser Doppler Velocimetry data, and Particle Image Velocimetry data from the literature. By Reynolds averaging the DNS‐data, we validate the turbulent viscosity hypothesis by demonstrating strong alignment between the Reynolds stress and the mean strain rate. Although the turbulent viscosity νT in the DNS is larger than in the RANS simulation, the turbulent viscosity parameter Cμ = νTϵ/k2, is an order of magnitude smaller than the standard 0.09 value of the k‐ϵ model. By filtering the DNS‐data, we show that the Smagorinsky constant CS is uniformly distributed over the tank with CS ≈ 0.1. Consequently, the dynamic Smagorisnky model does not improve the accuracy of the LES. © 2012 American Institute of Chemical Engineers AIChE J, 2012

Derivation from the Field Equation of the Mean Consumption Velocity for Front Propagation in Homogeneous Turbulent Flow

Based on purely geometrical considerations of the level sets of the scalar G(x, t) satisfying the field equation ( G - equation), A. Kerstein, T. Ashurst and F. Williams [Phys. Rev. A, 37, 2728, (1988)] derived the expression for the mean flame consumption velocity in a 1D premixed turbulent flame in a homogeneous flow of uniform density in terms of the volume average of |▽ G(x, t)| for a particular choice of the initial condition G(x, t = 0). In the present study we develop further the KAW work in two directions. First, in section 2, in contrast with the KAW approach, we consider the G - equation immediately and, using ensemble averaging, obtain the expression for the mean flame consumption velocity in terms of ensemble averages equivalent to the KAW result. Then, in section 3 the developed approach is applied to the case of homogeneous turbulent flow with a uniform mean strain rate field depending only on time.

Diagnostic accuracy of global myocardial deformation indexes in coronary artery disease: a velocity vector imaging study

The aim of our study was to assess the diagnostic accuracy of a global longitudinal strain and strain rate (GLS, GLSR) and mean radial strain and strain rate (MRS, MRSR) of the left ventricle to predict multivessel disease. In 113 patients, who underwent coronary angiography, left ventricular deformation was analysed by speckle-tracking based velocity vector imaging. In three standard apical views strain and strain rate curves were generated corresponding with two opposite basal, mid, and apical segments. The negative peaks of systolic strain and strain rate from 18 curves were averaged as GLS and GLSR. Similarly, in short axis view 6 negative systolic peaks were averaged and considered as MRS and MRSR. Four subgroups were defined: (1) without significant coronary stenosis, 0-vessel disease (0VD), (2) single-vessel disease (1VD), (3) double-vessel disease (2VD), and (4) triple-vessel disease (3VD). In comparison with patients without significant coronary artery disease, all deformation indexes were significantly decreased in patients with 3VD. The left ventricular ejection fraction (LVEF) and wall motion score index (WMSI) showed lower significance level as deformation parameters. MRSR was the strongest predictor of multivessel disease. Receiver-operating characteristic curves (ROC) showed that MRSR had the highest diagnostic accuracy. Comparing ROC areas, MRSR had significantly higher diagnostic accuracy than LVEF and WMSI. The results of our study show that global deformation indexes have a good diagnostic accuracy in differentiating multivessel disease. MRSR tended to be better in identification of 3VD than traditional indexes of global and regional left ventricular function.

Recalculation of Flow Stresses from Industrial Process Data for Heavy Plate Rolling Using a 2D Finite Element Model

AbstractIn hot rolling, the quantities rolling load, torque, and power consumption are important measurable process parameters. For the determination of rolling loads in hot flat rolling processes, like heavy plate rolling, Sims's model1 is a well‐known approach represented by an analytical formula. The solution of Sims's equation leads to the multiplier Q, which is a function of the roll gap geometry. The rolling load is then computed by applying the width of the plate, the contact length, the multiplier, and an average material flow stress called kfm. This flow stress is commonly recalculated from process data as a function of temperature, pass strain, and a mean strain rate, applying the Sims model itself. One question arises from this method: Are the recalculated flow stresses physically based values or in other words, what is the (physical) meaning or interpretation of these values? The present paper tries to give an answer to this question by determining the influence of the roll gap geometry alternatively by means of a simple 2D FEM model which gives a corresponding multiplier referred to as QFE. Flow stresses are recalculated from a set of process data using both factors. The results are compared to experimental flow stress data from hot compression tests. It is shown, that the recalculated flow stresses using QFE are in better agreement with the laboratory data than the recalculated values using Sims's Q.

A Novel Viscosity-Based Model for Low Cycle Fatigue–Creep Life Prediction of High-Temperature Structures

Damage evolution during low cycle fatigue, creep, and their interaction behavior is actually a ductility exhaustion process in response to cyclic and static creep. In this article, a novel viscosity-based model for low cycle fatigue–creep life prediction is presented in an attempt to condition viscosity-based approaches for general use in isothermal and thermo-mechanical loading. In this model, it was assumed that only plastic and creep strains caused by tensile stress lead to ductility consumption under stress-controlled loading. Moreover, with its simple expression, the mechanisms of the loading waveform, temperature, and mean stress effects are taken into account within a low cycle fatigue–creep regime. Predicted fatigue lives using the proposed model were found to be in good agreement with reported experimental data from literature. Compared with the generalized strain energy damage function method, the mean strain rate, Smith–Watson–Topper and Goswami’s ductility models, the proposed model is widely applicable and more precise in the prediction of low cycle fatigue–creep life.

Compressive and extensive strain along gradient trajectories

Based on direct numerical simulations of forced turbulence, shear turbulence, decaying turbulence, a turbulent channel flow as well as a Kolmogorov flow with Taylor based Reynolds numbers Reλ between 69 and 295, the normalized probability density function of the length distribution P̃(l̃) of dissipation elements, the conditional mean scalar difference < Δk | l > at the extreme points as well as the scaling of the two-point velocity difference along gradient trajectories < Δun> are studied. Using the field of the instantanous turbulent kinetic energy k as a scalar, we find a good agreement between the model equation for P̃(l̃) as proposed by Wang and Peters (2008) and the results obtained in the different DNS cases. This confirms the independance of the model solution from both, the Reynolds number and the type of turbulent flow, so that it can be considered universally valid. In addition, we show a 2/3 scaling for the mean conditional scalar difference. In the second part of the paper, we examine the scaling of the conditional two-point velocity difference along gradient trajectories. In particular, we compare the linear s/τ scaling, where τ denotes an integral time scale and s the separation arclength along a gradient trajectory in the inertial range as derived by Wang (2009) with the s · a∞ scaling, where a∞ denotes the asymtotic value of the conditional mean strain rate of large dissipation elements.

Longitudinal Left Ventricular Function in Normotensive Prediabetics: A Tissue Doppler and Strain/Strain Rate Echocardiography Study

Although diabetes mellitus is well known to result in systolic and diastolic left ventricular (LV) dysfunction at the subclinical level, even when it is not accompanied by hypertension and coronary artery disease, this situation has not been sufficiently investigated in prediabetes, which is the precursor of diabetes. The aims of the present study were to investigate LV systolic and diastolic function in normotensive and low-risk prediabetic and diabetic subjects for coronary disease using sensitive tissue Doppler echocardiographic parameters, to investigate early possible negative effects of glucose metabolism impairment on LV longitudinal function. Two hundred subjects (92 with prediabetes, 48 with type 2 diabetes, and 60 age-matched healthy volunteers) were studied by conventional, tissue Doppler, and strain and strain rate echocardiography. All study subjects were normotensive, and coronary artery disease was excluded. Forty-eight patients had isolated fasting glucose impairment, and 44 patients had combined fasting glucose and glucose tolerance impairment. Longitudinal peak systolic strain and the peak systolic and diastolic strain rates of six walls in the apical four-chamber, long-axis, and two-chamber views were evaluated. Clinical and standard echocardiographic characteristics were comparable among all groups. Mean systolic (P= .01) and diastolic (P= .02) tissue velocities, mean strain (P= .004), and mean systolic (P=.002) and diastolic (P= .001) strain rates were significantly lower in the diabetic groups than in control subjects. There were no difference between patients with isolated fasting glucose impairment and controls for tissue Doppler parameters, but mean early diastolic tissue velocity and mean strain and strain rates were statistically lower in patients with combined fasting glucose and glucose tolerance impairment compared with controls (P < .05). LV longitudinal systolic and diastolic function was impaired in both normotensive diabetic and prediabetic patients.

Deformation and Heat Transfer Analysis for High Speed Dieless Drawing of AZ31 Magnesium Alloy Tubes

The effect of drawing speed and heating length on deformation behavior was investigated by numerical approach for AZ31 magnesium alloy tubes to realize high speed dieless drawing process. The length of deformation zone expands with increasing the feeding speed. The increase in heating length leads to expanding length of deformation zone. The mean strain rate increases with increasing the feeding speed firstly, and then rate of increase in the strain rate becomes gradual under condition of any length of heating band. Based on these results, a limiting reduction in area of 52.5% under higher speed and larger heating length conditions can be realized experimentally.

Effect of axial tibial torque direction on ACL relative strain and strain rate in an in vitro simulated pivot landing

Anterior cruciate ligament (ACL) injuries most frequently occur under the large loads associated with a unipedal jump landing involving a cutting or pivoting maneuver. We tested the hypotheses that internal tibial torque would increase the anteromedial (AM) bundle ACL relative strain and strain rate more than would the corresponding external tibial torque under the large impulsive loads associated with such landing maneuvers. Twelve cadaveric female knees [mean (SD) age: 65.0 (10.5) years] were tested. Pretensioned quadriceps, hamstring, and gastrocnemius muscle-tendon unit forces maintained an initial knee flexion angle of 15°. A compound impulsive test load (compression, flexion moment, and internal or external tibial torque) was applied to the distal tibia while recording the 3D knee loads and tibofemoral kinematics. AM-ACL relative strain was measured using a 3 mm DVRT. In this repeated measures experiment, the Wilcoxon signed-rank test was used to test the null hypotheses with p < 0.05 considered significant. The mean (±SD) peak AM-ACL relative strains were 5.4 ± 3.7% and 3.1 ± 2.8% under internal and external tibial torque, respectively. The corresponding mean (± SD) peak AM-ACL strain rates reached 254.4 ± 160.1%/s and 179.4 ± 109.9%/s, respectively. The hypotheses were supported in that the normalized mean peak AM-ACL relative strain and strain rate were 70 and 42% greater under internal than under external tibial torque, respectively (p = 0.023, p = 0.041). We conclude that internal tibial torque is a potent stressor of the ACL because it induces a considerably (70%) larger peak strain in the AM-ACL than does a corresponding external tibial torque.

Maximum Principal Strain and Strain Rate Associated with Concussion Diagnosis Correlates with Changes in Corpus Callosum White Matter Indices

On-field monitoring of head impacts, combined with finite element (FE) biomechanical simulation, allow for predictions of regional strain associated with a diagnosed concussion. However, attempts to correlate these predictions with in vivo measures of brain injury have not been published. This article reports an approach to and preliminary results from the correlation of subject-specific FE model-predicted regions of high strain associated with diagnosed concussion and diffusion tensor imaging to assess changes in white matter integrity in the corpus callosum (CC). Ten football and ice hockey players who wore instrumented helmets to record head impacts sustained during play completed high field magnetic resonance imaging preseason and within 10 days of a diagnosed concussion. The Dartmouth Subject-Specific FE Head model was used to generate regional predictions of strain and strain rate following each impact associated with concussion. Maps of change in fractional anisotropy (FA) and median diffusivity (MD) were generated for the CC of each athlete to correlate strain with change in FA and MD. Mean and maximum strain rate correlated with change in FA (Spearman ρ = 0.77, p = 0.01; 0.70, p = 0.031), and there was a similar trend for mean and maximum strain (0.56, p = 0.10; 0.6, p = 0.07), as well as for maximum strain with change in MD (-0.63, p = 0.07). Change in MD correlated with injury-to-imaging interval (ρ = -0.80, p = 0.006) but change in FA did not (ρ = 0.18, p = 0.62). These results provide preliminary confirmation that model-predicted strain and strain rate in the CC correlate with changes in indices of white matter integrity.

A Three-Equation Variant of the SST k-ω Model Sensitized to Rotation and Curvature Effects

A new variant of the SST k-ω model sensitized to system rotation and streamline curvature is presented. The new model is based on a direct simplification of the Reynolds stress model under weak equilibrium assumptions [York et al., 2009, “A Simple and Robust Linear Eddy-Viscosity Formulation for Curved and Rotating Flows,” International Journal for Numerical Methods in Heat and Fluid Flow, 19(6), pp. 745–776]. An additional transport equation for a transverse turbulent velocity scale is added to enhance stability and incorporate history effects. The added scalar transport equation introduces the physical effects of curvature and rotation on turbulence structure via a modified rotation rate vector. The modified rotation rate is based on the material rotation rate of the mean strain-rate based coordinate system proposed by Wallin and Johansson (2002, “Modeling Streamline Curvature Effects in Explicit Algebraic Reynolds Stress Turbulence Models,” International Journal of Heat and Fluid Flow, 23, pp. 721–730). The eddy viscosity is redefined based on the new turbulent velocity scale, similar to previously documented k-ɛ- υ2 model formulations (Durbin, 1991, “Near-Wall Turbulence Closure Modeling without Damping Functions,” Theoretical and Computational Fluid Dynamics, 3, pp. 1–13). The new model is calibrated based on rotating homogeneous turbulent shear flow and is assessed on a number of generic test cases involving rotation and/or curvature effects. Results are compared to both the standard SST k-ω model and a recently proposed curvature-corrected version (Smirnov and Menter, 2009, “Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart-Shur Correction Term,” ASME Journal of Turbomachinery, 131, pp. 1–8). For the test cases presented here, the new model provides reasonable engineering accuracy without compromising stability and efficiency, and with only a small increase in computational cost.

Role of Noninvasive Imaging in the Diagnosis of Cardiac Allograft Vasculopathy

Cardiac allograft vasculopathy (CAV) is common, with a prevalence of 52% at 10 years after transplantation, and represents a leading cause of death beyond the first year, responsible for approximately 15% of deaths annually.1 It is characterized by diffuse and concentric intimal proliferation, typically involving the intramural as well as epicardial coronary arteries. Its diagnosis is difficult to establish clinically because of denervation of the transplanted heart. Consequently, it presents late with silent myocardial infarction, progressive heart failure, or arrhythmic sudden death.2 Screening is therefore required for its early detection. Although coronary intravascular ultrasound (IVUS) is considered the gold-standard technique for detecting the anatomic features of CAV (Table 1), its broad clinical use in this context is limited by cost and lack of widespread expertise, and its evaluation is limited to epicardial vessels.3 Coronary angiography, performed annually or biannually, remains the most common clinical screening method.4 However, because of the diffuse nature of CAV with a lack of normal reference segments and the relatively late occurring luminal narrowing, the sensitivity of angiography is as low as 30% when compared with IVUS (Figure 1).5 As a result, complications frequently occur before disease is evident angiographically.6 Furthermore, angiography is associated with significant albeit uncommon complications (overall complication rate, 7.4/1000 procedures, including rates of 0.65/1000, 1.6/1000, and 0.72/1000 for cerebrovascular accidents, vascular complications, and death, respectively), is disliked by transplant recipients, is costly, and repeated studies are associated with an important cumulative radiation dose.7 View this table: Table 1. Stanford Classification of CAV Severity on IVUS Figure 1. Invasive assessment of cardiac allograft vasculopathy (CAV) in a patient with severe disease, highlighting the limited sensitivity of conventional coronary angiography. Although no left anterior descending (LAD) flow-limiting stenoses are seen on angiography ( A ), intravascular ultrasound ( B ) shows significant intimal thickening, measuring up to …