A Framework for the Generation of Realistic Synthetic Cardiac Ultrasound and Magnetic Resonance Imaging Sequences From the Same Virtual Patients.

The use of synthetic sequences is one of the most promising tools for advanced in silico evaluation of the quantification of cardiac deformation and strain through 3-D ultrasound (US) and magnetic resonance (MR) imaging. In this paper, we propose the first simulation framework which allows the generation of realistic 3-D synthetic cardiac US and MR (both cine and tagging) image sequences from the same virtual patient. A state-of-the-art electromechanical (E/M) model was exploited for simulating groundtruth cardiac motion fields ranging from healthy to various pathological cases, including both ventricular dyssynchrony and myocardial ischemia. The E/M groundtruth along with template MR/US images and physical simulators were combined in a unified framework for generating synthetic data. We efficiently merged several warping strategies to keep the full control of myocardial deformations while preserving realistic image texture. In total, we generated 18 virtual patients, each with synthetic 3-D US, cine MR, and tagged MR sequences. The simulated images were evaluated both qualitatively by showing realistic textures and quantitatively by observing myocardial intensity distributions similar to real data. In particular, the US simulation showed a smoother myocardium/background interface than the state-of-the-art. We also assessed the mechanical properties. The pathological subjects were discriminated from the healthy ones by both global indexes (ejection fraction and the global circumferential strain) and regional strain curves. The synthetic database is comprehensive in terms of both pathology and modality, and has a level of realism sufficient for validation purposes. All the 90 sequences are made publicly available to the research community via an open-access database.

In-vivo validation of a new clinical tool to quantify three-dimensional myocardial strain using ultrasound.

Three-dimensional (3D) strain analysis based on real-time 3-D echocardiography (RT3DE) has emerged as a novel technique to quantify regional myocardial function. The goal of this study was to evaluate accuracy of a novel model-based 3D tracking tool (eSie Volume Mechanics, Siemens Ultrasound, Mountain View, CA, USA) using sonomicrometry as an independent measure of cardiac deformation. Thirteen sheep were instrumented with microcrystals sutured to the epi- and endocardium of the inferolateral left ventricular wall to trace myocardial deformation along its three directional axes of motion. Paired acquisitions of RT3DE and sonomicrometry were made at baseline, during inotropic modulation and during myocardial ischemia. Accuracy of 3D strain measurements was quantified and expressed as level of agreement with sonomicrometry using linear regression and Bland-Altman analysis. Correlations between 3D strain analysis and sonomicrometry were good for longitudinal and circumferential strain components (r = 0.78 and r = 0.71) but poor for radial strain (r = 0.30). Accordingly, agreement (bias ± 2SD) was -5 ± 6 % for longitudinal, -5 ± 7 % for circumferential, and 15 ± 19 % for radial strain. Intra-observer variability was low for all components (intra-class correlation coefficients (ICC) of respectively 0.89, 0.88 and 0.95) while inter-observer variability was higher, in particular for radial strain (ICC = 0.41). The present study shows that 3D strain analysis provided good estimates of circumferential and longitudinal strain, while estimates of radial strain were less accurate between observers.

A spectroscopic study of the chromatic properties of GafChromicEBT3 films.

PURPOSE: This work provides an interpretation of the chromatic properties of GafChromicEBT3 films based on the chemical nature of the polydiacetylene (PDA) molecules formed upon interaction with ionizing radiation. The EBT3 films become optically less transparent with increasing radiation dose as a result of the radiation-induced polymerization of diacetylene monomers. In contrast to empirical quantification of the chromatic properties, less attention has been given to the underlying molecular mechanism that induces the strong decrease in transparency. METHODS: Unlaminated GafChromicEBT3 films were irradiated with a 6 MV photon beam to dose levels up to 20 Gy. The optical absorption properties of the films were investigated using visible (vis) spectroscopy. The presence of PDA molecules in the active layer of the EBT3 films was investigated using Raman spectroscopy, which probes the vibrational modes of the molecules in the layer. The vibrational modes assigned to PDA's were used in a theoretical vis-absorption model to fit our experimental vis-absorption spectra. From the fit parameters, one can assess the relative contribution of different PDA conformations and the length distribution of PDA's in the film. RESULTS: Vis-spectroscopy shows that the optical density increases with dose in the full region of the visible spectrum. The Raman spectrum is dominated by two vibrational modes, most notably by the ν(C≡C) and the ν(C=C) stretching modes of the PDA backbone. By fitting the vis-absorption model to experimental spectra, it is found that the active layer contains two distinct PDA conformations with different absorption properties and reaction kinetics. Furthermore, the mean PDA conjugation length is found to be 2-3 orders of magnitude smaller than the crystals PDA's are embedded in. CONCLUSIONS: Vis- and Raman spectroscopy provided more insight into the molecular nature of the radiochromic properties of EBT3 films through the identification of the excited states of PDA and the presence of two PDA conformations. The improved knowledge on the molecular composition of EBT3's active layer provides a framework for future fundamental modeling of the dose-response.

Semi-automatic outlining of levator hiatus.

OBJECTIVE: To create a semi-automated outlining tool for the levator hiatus, to reduce interobserver variability and and speed up analysis. METHODS: The proposed automated hiatus segmentation (AHS) algorithm takes a C-plane image, in the plane of minimal hiatal dimensions, and manually defined vertical hiatal limits as input. The AHS then creates an initial outline by fitting predefined templates on an intensity-invariant edge map, which is further refined using the B-spline explicit active surfaces framework. The AHS was tested using 91 representative C-plane images. Reference hiatal outlines were obtained manually and compared with the AHS outlines by three independent observers. The mean absolute distance (MAD), Hausdorff distance and Dice and Jaccard coefficients were used to quantify segmentation accuracy. Each of these metrics was calculated both for computer-observer differences (COD) and for interobserver differences. The Williams index was used to test the null hypothesis that the automated method would agree with the operators at least as well as the operators agreed with each other. Agreement between the two methods was assessed using the intraclass correlation coefficient (ICC) and Bland-Altman plots. RESULTS: The AHS contours matched well with the manual ones (median COD, 2.10 (interquartile range (IQR), 1.54) mm for MAD). The Williams index was greater than or close to 1 for all quality metrics, indicating that the algorithm performed at least as well as did the manual references in terms of interrater variability. The interobserver differences using each of the metrics were significantly lower, and a higher ICC was achieved (0.93), when obtaining outlines using the AHS compared with manually. The Bland-Altman plots showed negligible bias between the two methods. Using the AHS took a median time of 7.07 (IQR, 3.49) s, while manual outlining took 21.31 (IQR, 5.43) s, thus being almost three-fold faster. Using the AHS, in general, the hiatus could be outlined completely using only three points, two for initialization and one for manual adjustment. CONCLUSIONS: We present a method for tracing the levator hiatal outline with minimal user input. The AHS is fast, robust and reliable and improves interrater agreement. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Integration of Multi-Plane Tissue Doppler and B-Mode Echocardiographic Images for Left Ventricular Motion Estimation.

Although modern ultrasound acquisition systems allow recording of 3D echocardiographic images, tracking anatomical structures from them is still challenging. In addition, since these images are typically created from information obtained across several cardiac cycles, it is not yet possible to acquire high-quality 3D images from patients presenting varying heart rhythms. In this paper, we propose a method to estimate the motion field from multi-plane echocardiographic images of the left ventricle, which are acquired simultaneously during a single cardiac cycle. The method integrates tri-plane B-mode and tissue Doppler images acquired at different rotation angles around the long axis of the left ventricle. It uses a diffeomorphic continuous spatio-temporal transformation model with a spherical data representation for a better interpolation in the circumferential direction. This framework allows exploiting the spatial relation among the acquired planes. In addition, higher temporal resolution of the transformation in the beam direction is achieved by uncoupling the estimation of the different components of the velocity field. The method was validated using a realistic synthetic dataset including healthy and ischemic cases, obtaining errors of 0.14 ± 0.09 mm for displacements, 0.96 ± 1.03% for longitudinal strain and 3.94 ± 4.38% for radial strain estimation. In addition, the method was also demonstrated on a healthy volunteer and two patients with ischemia.

A Pipeline for the Generation of Realistic 3D Synthetic Echocardiographic Sequences: Methodology and Open-Access Database.

Quantification of cardiac deformation and strain with 3D ultrasound takes considerable research efforts. Nevertheless, a widespread use of these techniques in clinical practice is still held back due to the lack of a solid verification process to quantify and compare performance. In this context, the use of fully synthetic sequences has become an established tool for initial in silico evaluation. Nevertheless, the realism of existing simulation techniques is still too limited to represent reliable benchmarking data. Moreover, the fact that different centers typically make use of in-house developed simulation pipelines makes a fair comparison difficult. In this context, this paper introduces a novel pipeline for the generation of synthetic 3D cardiac ultrasound image sequences. State-of-the art solutions in the fields of electromechanical modeling and ultrasound simulation are combined within an original framework that exploits a real ultrasound recording to learn and simulate realistic speckle textures. The simulated images show typical artifacts that make motion tracking in ultrasound challenging. The ground-truth displacement field is available voxelwise and is fully controlled by the electromechanical model. By progressively modifying mechanical and ultrasound parameters, the sensitivity of 3D strain algorithms to pathology and image properties can be evaluated. The proposed pipeline is used to generate an initial library of 8 sequences including healthy and pathological cases, which is made freely accessible to the research community via our project web-page.

Improved myocardial motion estimation combining tissue Doppler and B-mode echocardiographic images.

We propose a technique for myocardial motion estimation based on image registration using both B-mode echocardiographic images and tissue Doppler sequences acquired interleaved. The velocity field is modeled continuously using B-splines and the spatiotemporal transform is constrained to be diffeomorphic. Images before scan conversion are used to improve the accuracy of the estimation. The similarity measure includes a model of the speckle pattern distribution of B-mode images. It also penalizes the disagreement between tissue Doppler velocities and the estimated velocity field. Registration accuracy is evaluated and compared to other alternatives using a realistic synthetic dataset, obtaining mean displacement errors of about 1 mm. Finally, the method is demonstrated on data acquired from six volunteers, both at rest and during exercise. Robustness is tested against low image quality and fast heart rates during exercise. Results show that our method provides a robust motion estimate in these situations.

Whole myocardium tracking in 2D-echocardiography in multiple orientations using a motion constrained level-set.

The segmentation and tracking of the myocardium in echocardiographic sequences is an important task for the diagnosis of heart disease. This task is difficult due to the inherent problems of echographic images (i.e. low contrast, speckle noise, signal dropout, presence of shadows). In this article, we extend a level-set method recently proposed in Dietenbeck et al. (2012) in order to track the whole myocardium in echocardiographic sequences. To this end, we enforce temporal coherence by adding a new motion prior energy to the existing framework. This motion prior term is expressed as new constraint that enforces the conservation of the levels of the implicit function along the image sequence. Moreover, the robustness of the proposed method is improved by adjusting the associated hyperparameters in a spatially adaptive way, using the available strong a priori about the echocardiographic regions to be segmented. The accuracy and robustness of the proposed method is evaluated by comparing the obtained segmentation with experts references and to another state-of-the-art method on a dataset of 15 sequences (≃ 900 images) acquired in three echocardiographic views. We show that the algorithm provides results that are consistent with the inter-observer variability and outperforms the state-of-the-art method. We also carry out a complete study on the influence of the parameters settings. The obtained results demonstrate the stability of our method according to those values.

3D strain assessment in ultrasound (Straus): a synthetic comparison of five tracking methodologies.

This paper evaluates five 3D ultrasound tracking algorithms regarding their ability to quantify abnormal deformation in timing or amplitude. A synthetic database of B-mode image sequences modeling healthy, ischemic and dyssynchrony cases was generated for that purpose. This database is made publicly available to the community. It combines recent advances in electromechanical and ultrasound modeling. For modeling heart mechanics, the Bestel-Clement-Sorine electromechanical model was applied to a realistic geometry. For ultrasound modeling, we applied a fast simulation technique to produce realistic images on a set of scatterers moving according to the electromechanical simulation result. Tracking and strain accuracies were computed and compared for all evaluated algorithms. For tracking, all methods were estimating myocardial displacements with an error below 1 mm on the ischemic sequences. The introduction of a dilated geometry was found to have a significant impact on accuracy. Regarding strain, all methods were able to recover timing differences between segments, as well as low strain values. On all cases, radial strain was found to have a low accuracy in comparison to longitudinal and circumferential components.

Assessment of strain and strain rate by two-dimensional speckle tracking in mice: comparison with tissue Doppler echocardiography and conductance catheter measurements.

AIMS: This study was designed in order to compare the strain and strain rate deformation parameters assessed by speckle tracking imaging (STI) with those of tissue Doppler imaging (TDI) and conductance catheter measurements in chronic murine models of left ventricular (LV) dysfunction. METHODS AND RESULTS: Twenty-four male C57BL/6J mice were assigned to wild-type (n = 8), myocardial infarction (n = 8) and transaortic constriction (n = 8) groups. Echocardiographic and conductance measurements were simultaneously performed at rest and during dobutamine infusion (5 µg/kg/min) in all animals 10 weeks post-surgery. The LV circumferential strain (Scirc) and the strain rate (SRcirc) were derived from grey scale and tissue Doppler data at frame rates of 224 and 375 Hz, respectively. Scirc and SRcirc by TDI/STI correlated well with the preload recruitable stroke work (PRSW) (r = -0.64 and -0.71 for TDI; r = -0.46 and -0.50 for STI, P < 0.05). Both modalities showed a good agreement with respect to Scirc and SRcirc (r = 0.60 and r = 0.63, P < 0.05). During stress, however, TDI-estimated Scirc and SRcirc values were predominantly higher than those measured by STI (P < 0.05). The similarity of Scirc and SRcirc measurements with respect to the STI/TDI data was examined by the Bland-Altman analysis. CONCLUSION: In mice, the STI- and TDI-derived strain and strain rate deformation parameters relate closely to intrinsic myocardial function. At low heart rate-to-frame rate ratios (HR/FR), both STI and TDI are equally acceptable for assessing the LV function non-invasively in these animals. At HR/FR (e.g. dobutamine challenge), however, these methods cannot be used interchangeably as STI underestimates S and SR at high values.

Automatic segmentation of in-vivo intra-coronary optical coherence tomography images to assess stent strut apposition and coverage.

The implantation of intracoronary stents is currently the standard approach for the treatment of coronary atherosclerotic disease. The widespread adoption of this technology has boosted an intensive research activity in this domain, with continuous improvements in the design of these devices, aiming at reducing problems of restenosis (re-narrowing of the stented segment) and thrombosis (sudden occlusion due to thrombus formation). Recently, a new, light-based intracoronary imaging modality, optical coherence tomography (OCT), was developed and introduced into clinical practice. Due to its very high axial resolution (10-15 µm), it allows for in vivo evaluation of both stent strut apposition and neointima coverage (a marker of healing of the treated segment). As such, it provides valuable information on proper stent deployment, on the behaviour of different stent types in-vivo and on the effect of new types of stents (e.g. drug-eluting stents) on vessel wall healing. However, the major drawback of the current OCT methodology is that analysis of these images requires a tremendous amount of-currently manual-post-processing. In this manuscript, an algorithm is presented that allows for fully automated analysis of stent strut apposition and coverage in coronary arteries. The vessel lumen and stent struts are automatically detected and segmented through analysis of the intensity profiles of the A-lines. From these data, apposition and coverage can then be measured automatically. The algorithm was validated using manual assessments by two experienced operators as a reference. High Pearson's correlation coefficients were found (R = 0.96-0.97) between the automated and manual measurements while Bland-Altman analysis showed no significant bias with good limits of agreement. As such, it was shown that the presented algorithm provides a robust and fast tool to automatically estimate apposition and coverage of stent struts in in-vivo OCT pullbacks. This will be important for the integration of this technology in clinical routine and for the analysis of datasets of larger clinical trials.

Detection of the whole myocardium in 2D-echocardiography for multiple orientations using a geometrically constrained level-set.

The segmentation of the myocardium in echocardiographic images is an important task for the diagnosis of heart disease. This task is difficult due to the inherent problems of echographic images (i.e. low contrast, speckle noise, signal dropout, presence of shadows). In this article, we propose a method to segment the whole myocardium (endocardial and epicardial contours) in 2D echographic images. This is achieved using a level-set model constrained by a new shape formulation that allows to model both contours. The novelty of this work also lays in the fact that our framework allows to segment the whole myocardium for the four main views used in clinical routine. The method is validated on a dataset of clinical images and compared with expert segmentation.

The relative value of strain and strain rate for defining intrinsic myocardial function.

It is well accepted that strain and strain rate deformation parameters are not only a measure of intrinsic myocardial contractility but are also influenced by changes in cardiac load and structure. To date, no information is available on the relative importance of these confounders. This study was designed to investigate how strain and strain rate, measured by Doppler echocardiography, relate to the individual factors that determine cardiac performance. Echocardiographic and conductance measurements were simultaneously performed in mice in which individual determinants of cardiac performance were mechanically and/or pharmacologically modulated. A multivariable analysis was performed with radial and circumferential strains and peak systolic radial and circumferential strain rates as dependent parameters and preload recruitable stroke work (PRSW), arterial elastance (E(a)), end-diastolic pressure, and left ventricular myocardial volume (LVMV) as independent factors representing myocardial contractility, afterload, preload, and myocardial volume, respectively. Radial strain was most influenced by E(a) (ß = -0.58, R(2) = 0.34), whereas circumferential strain was strongly associated with E(a) and moderately with LVMV (ß = 0.79 and -0.52, respectively, R(2) = 0.54). Radial strain rate was related to both PRSW and LVMV (ß = 0.79 and -0.62, respectively, R(2) = 0.50), whereas circumferential strain rate showed a prominent correlation only with PRSW (ß = -0.61, R(2) = 0.51). In conclusion, strain (both radial and circumferential) is not a good surrogate measure of intrinsic myocardial contractility unless the strong confounding influence of afterload is considered. Strain rate is a more robust measure of contractility that is less influenced by changes in cardiac load and structure. Thus, peak systolic strain rate is the more relevant parameter to assess myocardial contractile function noninvasively.

A dual-chamber, thick-walled cardiac phantom for use in cardiac motion and deformation imaging by ultrasound.

Determination of the mechanical properties of the myocardium is crucial for cardiac diagnosis. Cardiac strain and strain rate imaging may enable such quantification. To further develop these methodologies, an experimental setup allowing the recording of ultrasonic deformation data in a reproducible manner is necessary. Such setup with biventricular polyvinyl alcohol heart phantoms has been built. To test this setup, segmental longitudinal, radial and circumferential displacement, velocity, strain and strain rate in the phantoms were measured using a clinical ultrasound scanner and commercially available deformation imaging algorithms (based on both tissue velocity imaging and speckle tracking). The model deformation was close to that observed in the human left ventricular wall and was highly reproducible (e.g., the average peak longitudinal strain for the mid- and apical phantom segments equals -15.32 +/- 0.53% and -19 +/- 6% for the ventricle wall). The experimental setup is a valuable source of data for the development of algorithms for deformation estimation.

Influence of left-ventricular shape on passive filling properties and end-diastolic fiber stress and strain.

Passive filling is a major determinant for the pump performance of the left ventricle and is determined by the filling pressure and the ventricular compliance. In the quantification of the passive mechanical behaviour of the left ventricle and its compliance, focus has been mainly on fiber orientation and constitutive parameters. Although it has been shown that the left-ventricular shape plays an important role in cardiac (patho-)physiology, the dependency on left-ventricular shape has never been studied in detail. Therefore, we have quantified the influence of left-ventricular shape on the overall compliance and the intramyocardial distribution of passive fiber stress and strain during the passive filling period. Hereto, fiber stress and strain were calculated in a finite element analysis of passive inflation of left ventricles with different shapes, ranging from an elongated ellipsoid to a sphere, but keeping the initial cavity volume constant. For each shape, the wall volume was varied to obtain ventricles with different wall thickness. The passive myocardium was described by an incompressible hyperelastic material law with transverse isotropic symmetry along the muscle fiber directions. A realistic transmural distribution in fiber orientation was assumed. We found that compliance was not altered substantially, but the transmural distribution of both passive fiber stress and strain was highly dependent on regional wall curvature and thickness. A low curvature wall was characterized by a maximum in the transmural fiber stress and strain in the mid-wall region, while a steep subendocardial transmural gradient was present in a high curvature wall. The transmural fiber stress and strain gradients in a low and high curvature wall were, respectively, flattened and steepened by an increase in wall thickness.

Deformation imaging describes right ventricular function better than longitudinal displacement of the tricuspid ring.

AIMS: To quantify right ventricular (RV) function in patients with chronic thromboembolic pulmonary hypertension (CTEPH) before and after pulmonary endarterectomy (PEA). METHODS: Out of 33 patients, 16 were evaluated clinically and with echocardiography (conventional and myocardial deformation parameters) before PEA (preop) and at 1 week, 1 month, 3 months and 6 months after PEA. RV fractional area change (RVFAC), tricuspid annular plane systolic excursion (TAPSE) as well as mid-apical and basal peak ejection strain (S) and strain rate (SR) of the RV free wall were measured. Left ventricular (LV) apical lateral wall motion was regarded as indicating changes in overall heart rocking motion (RM). Heart catheterisation was performed before, within 1 week and at 6 months after PEA. RESULTS: Clinical and haemodynamic parameters improved significantly after PEA. This correlated with the improvement in RVFAC, S and SR. TAPSE, on the other hand, showed a biphasic response (14.5 (4) mm preop, 8.5 (2.7) mm at 1 week and 11 (1.5) mm at 6 months). Changes in LV apical motion explain this finding. At baseline, TAPSE was enhanced by rocking motion of the heart as a result of the failing RV. Unloading the RV by PEA normalised the rocking motion and TAPSE decreased. CONCLUSIONS: RV function of CTEPH patients improves steadily after PEA. Unlike S, SR and RVFAC, this is not reflected by TAPSE because of postoperative changes in overall heart motion. Motion independent deformation parameters (S, SR) appear superior in the accurate description of regional RV function.

Echocardiographic assessment of left ventricular untwist rate: comparison of tissue Doppler and speckle tracking methodologies.

AIMS: The study was designed to test the influence of the temporal resolution, at which tissue Doppler imaging (TDI) and speckle tracking imaging (STI) operate, on the accurate assessment of left ventricular (LV) untwist rate (UR). METHODS AND RESULTS: Echo imaging and invasive LV pressure measurements were performed during right atrial (RA) pacing and dobutamine challenge in eight pigs. LV torsion and torsional rate profiles were analysed from grey scale and tissue Doppler data (apical and basal short axis) at frame rates of 82 +/- 17 and 183 +/- 14 Hz, respectively. Temporal subsampling of TDI data sets was performed at 82 +/- 6 Hz in order to mimic the mean temporal resolution of STI and the LV torsional curves were again extracted. At rest, LV UR values were comparable for both imaging techniques. However, during dobutamine stimulation, TDI estimated peak UR was predominantly higher than UR measured by STI (-112.1 +/- 64.5 degrees /s vs. -75.5 +/- 31.4 degrees /s, P < 0.05). The similarity of LV UR measurements with respect to the STI/TDI data was examined by a Bland-Altman analysis. CONCLUSION: Although both methods regarding LV UR correlated well, these methods cannot be interchanged. STI showed a bias to underestimate UR at high values.

Influence of heart rate reduction on Doppler myocardial imaging parameters in a small animal model.

In small animals studies, sick animals often have a significant reduction in heart rate while under anesthesia. The influence of heart rate reduction on Doppler myocardial imaging (DMI) parameters is not known. The aim of the present study was to assess the effect of heart rate reduction on DMI parameters in a small animal model. Twenty-four rats underwent transthoracic echocardiography at baseline and during the administration of ivabradine IV. In all rats, left ventricular (LV) systolic velocity, strain and strain rate were measured in the anteroseptal and inferolateral wall segments from short axis views. In 12 rats (group A), M-mode analysis was also performed for assessment of global LV function. In the other 12 rats (groups B), contractility was quantified invasively using the end-systolic pressure-volume relation (ESPVR) and the preload recruitable stroke work (PRSW). During ivabradine, administration heart rate decreased by 18% in group A (p < 0.001) and 36% in group B (p < 0.001). There was a slight increase in LVEDD and LVESD, with no change in cardiac output or LV ejection fraction. During ivabradine administration, DMI parameters did not change significantly in any group. No significant correlation between DMI parameters and heart rate (r(2) = 0.05) or ejection time (r(2) = 0.14) could be found. The absence of changes in contractility was confirmed by the absence of change in PRSW and end-systolic elastance (Ees). In conclusion, moderate heart rate reduction did not influence DMI measurements in this specific rat model. Therefore, in the interpretation of DMI data when performing small animal studies, moderate heart rate reduction does not need to be taken into account.

Quantitative dobutamine stress echocardiography for the early detection of cardiac allograft vasculopathy in heart transplant recipients.

BACKGROUND: A non-invasive method to detect the presence of cardiac allograft vasculopathy (CAV) remains an important goal in clinical cardiology. OBJECTIVE: To assess the value of quantitative dobutamine stress echocardiography (DSE) for the early detection of CAV. METHODS: 42 heart transplant recipients underwent DSE with acquisition of both conventional two-dimensional and colour tissue Doppler data. All studies were analysed conventionally and quantitatively using regional deformation parameters-that is, peak systolic longitudinal strain (in(peak sys)), strain rate (SR(peak sys)) and post-systolic strain index. Myocardial segments were classified as normal, mildly abnormal or severely abnormal based on correlative angiographic findings. RESULTS: At baseline, in(peak sys) was significantly lower in severely abnormal segments than in normal ones. However, at peak stress, in(peak sys) was able to separate three groups of segments. Receiver operating characteristic analysis showed an SR(peak sys) response of <0.5/s to identify patients with CAV with a sensitivity of 88%, specificity of 85% and a negative predictive value of 92%. CONCLUSION: Regional myocardial function is impaired in heart transplant recipients with CAV even when the disease is considered to be non-significant on conventional angiography. Systolic deformation parameters tended to detect the existence of CAV more accurately than conventional visual DSE assessment. Strain rate imaging during stress can therefore safely be used as a non-invasive screening test for detecting CAV in heart transplant recipients.

Radial strain assessment of the interventricular septum wall by a new technique in healthy subjects.

The aim of this study was to design a new approach for the acquisition of regional radial strain from the middle portion of the interventricular septum. We designed and wrote a program in Matlab (computer-assisted method) for use on a personal computer so that the septum thickness throughout the cardiac cycle could be measured instantaneously. Computer-assisted and conventional manual methods were used on the same 2D echocardiography image frames. Then, real-time 2D color Doppler myocardial imaging and conventional 2D imaging of the septum walls of 12 healthy participants at rest using apical four-chamber view were acquired. Wall thickness was measured using both the computerized program and velocity data used for tracking the segment and intensity line profile modification automatically. Then, the radial strain was estimated. Bland-Altman statistical analysis shows good agreement between the computer-assisted method and conventional manual method. The average of the peak and mean radial strains from the mid-septum of 12 healthy participants were 63.5 +/- 10.7 and 31.7 +/- 7.5%, respectively. We introduced a simple approach that is capable of radial strain estimation of the septum wall, which cannot be measured by current Doppler based methods in echocardiography systems.