Serial assessment of left ventricular morphology and function in a rodent model of ischemic cardiomyopathy.

Left ventricular remodelling (LVr) occurs post myocardial infarction (MI), predisposing people to heart failure (HF). LV mechanics and morphology are important in this process. We hence sort to characterize LV mechanics and geometry in a post-MI rodent model. Thirty-two male Sprague-Dawley rats (150-200 g) sustained MI (n = 24) or sham (Sham; n = 8) surgery. In another six sham rats invasive blood pressure measurements were performed. Ultrasound imaging was done at baseline, and 1, 3, 7, 14, 30 and 60 days following surgery, and LV mechanics and morphology assessed. LV volumes increased with time (p < 0.01), at a greater rate in the MI group than the Sham group (p < 0.01). Strain was impaired in MI rats at day 1 (13.50 ± 6.64 vs. 25.71 ± 4.94%, p < 0.01) and remained impaired at day 60 (14.07 ± 5.37 vs. 22.98 ± 5.87%, p < 0.01). Strain rate was lower at day 1 (4.11 ± 1.29 vs. 8.10 ± 2.18%/s, p < 0.01), remained lower throughout follow-up (p < 0.01), and decreased at a greater rate in MI rats (p < 0.01). Mean systolic (204 ± 43 vs. 322 ± 75 1/m, p < 0.01) and diastolic (167 ± 21 vs. 192 ± 11 1/m, p < 0.01) curvature was lower in the MI rats at day 1 post surgery and throughout follow-up (p < 0.01). Maximum principal curvature decreased throughout time (p < 0.01), while minimum principal curvature did not (p = 0.86). Wall stress increased significantly after infarction in MI rats (p < 0.01). ST-elevation myocardial infarction (STEMI) changed LV shape and contractile function. The assessment of these indices may prove useful in understanding LVr and the development of HF.

Cardiovascular magnetic resonance myocardial feature tracking using a non-rigid, elastic image registration algorithm: assessment of variability in a real-life clinical setting.

BACKGROUND: Cardiovascular magnetic resonance myocardial feature tracking (CMR-FT) is a promising technique for quantification of myocardial strain from steady-state free precession (SSFP) cine images. We sought to determine the variability of CMR-FT using a non-rigid elastic registration algorithm recently available in a commercial software package (Segment, Medviso) in a real-life clinical setting. METHODS: Firstly, we studied the variability in a healthy volunteer who underwent 10 CMR studies over five consecutive days. Secondly, 10 patients were selected from our CMR database yielding normal findings (normal group). Finally, we prospectively studied 10 patients with known or suspected myocardial pathology referred for further investigation to CMR (patient group). In the patient group a second study was performed respecting an interval of 30 min between studies. All studies were manually segmented at the end-diastolic phase by three observers. In all subjects left ventricular (LV) circumferential and radial strain were calculated in the short-axis direction (EccSAX and ErrSAX, respectively) and longitudinal strain in the long-axis direction (EllLAX). The level of CMR experience of the observers was 2 weeks, 6 months and >20 years. RESULTS: Mean contouring time was 7 ± 1 min, mean FT calculation time 13 ± 2 min. Intra- and inter-observer variability was good to excellent with an coefficient of reproducibility (CR) ranging 1.6% to 11.5%, and 1.7% to 16.0%, respectively and an intraclass correlation coefficient (ICC) ranging 0.89 to 1.00 and 0.74 to 0.99, respectively. Variability considerably increased in the test-retest setting with a CR ranging 4.2% to 29.1% and an ICC ranging 0.66 to 0.95 in the patient group. Variability was not influenced by level of expertise of the observers. Neither did the presence of myocardial pathology at CMR negatively impact variability. However, compared to global myocardial strain, segmental myocardial strain variability increased with a factor 2-3, in particular for the basal and apical short-axis slices. CONCLUSIONS: CMR-FT using non-rigid, elastic registration is a reproducible approach for strain analysis in patients routinely scheduled for CMR, and is not influenced by the level of training. However, further improvement is needed to reliably depict small variations in segmental myocardial strain.

Strain assessment in the carotid artery wall using ultrasound speckle tracking: validation in a sheep model.

The aim of this study was to validate carotid artery strain assessment in-vivo using ultrasound speckle tracking. The left carotid artery of five sheep was exposed and sonomicrometry crystals were sutured onto the artery wall to obtain reference strain. Ultrasound imaging was performed at baseline and stress, followed by strain estimation using an in-house speckle tracking algorithm tuned for vascular applications. The correlation between estimated and reference strain was r = 0.95 (p < 0.001) and r = 0.87 (p < 0.01) for longitudinal and circumferential strain, respectively. Moreover, acceptable limits of agreement were found in Bland-Altman analysis (longitudinally: -0.15 to 0.42%, circumferentially: -0.54 to 0.50%), which demonstrates the feasibility of estimating carotid artery strain using ultrasound speckle tracking. However, further studies are needed to test the algorithm on human in-vivo data and to investigate its potential to detect subclinical cardiovascular disease and characterize atherosclerotic plaques.

2-D strain assessment in the mouse through spatial compounding of myocardial velocity data: in vivo feasibility.

Ultrasound assessment of myocardial strain can provide valuable information on regional cardiac function. However, Doppler-based methods often used in practice for strain estimation suffer from angle dependency. In this study, a partial solution to that fundamental limitation is presented. We have previously reported using simulated data sets that spatial compounding of axial velocities obtained at three steering angles can theoretically outperform 2-D speckle tracking for 2-D strain estimation in the mouse heart. In this study, the feasibility of the method was analyzed in vivo using spatial compounding of Doppler velocities on six mice with myocardial infarction and five controls, and results were compared with those of tagged microscopic magnetic resonance imaging (µMRI). Circumferential estimates quantified by means of both ultrasound and µMRI could detect regional dysfunction. Between echocardiography and µMRI, a good regression coefficient was obtained for circumferential strain estimates (r = 0.69), whereas radial strain estimates correlated only moderately (r = 0.37). A second echocardiography was performed after µMRI to test the reproducibility of the compounding method. This yielded a higher correlation coefficient for the circumferential component than for the radial component (r = 0.74 circumferentially, r = 0.49 radially).

Comparison of a new methodology for the assessment of 3D myocardial strain from volumetric ultrasound with 2D speckle tracking.

An alternative approach to extract 3D myocardial strain based on elastic registration of the ultrasound images (3DSE) was developed by our lab. The aim of the present study was to test its clinical performance by comparing strain values obtained by 3DSE with the ones obtained with 2D speckle tracking (2DST). Standard 2D B-mode and volumetric datasets were acquired in 12 patients with coronary heart disease (CHD) and in 12 control subjects. Longitudinal (ε(LL)), circumferential (ε(CC)) and radial (ε(RR)) strain values were obtained from 2D datasets using commercially available 2DST software and from volumetric datasets using the 3DSE approach. 3DSE provided lower strain values than 2DST. With both approaches global ε(LL) and ε(CC) were significantly lower in patients with CHD than in controls. Global ε(LL) and ε(CC) correlated well between both methods (R = 0.83, R = 0.86, respectively), while segmental correlations were moderate [R = 0.63 (ε(LL)), R = 0.41 (ε(CC))]. The highest differences in ε(LL) values obtained by the two methods and the highest number of erroneous ε(LL) with 3DSE were observed in the basal LV segments. This study shows that in real-life datasets our 3DSE method provides global and regional ε(LL) and ε(CC) values that are comparable with the ones obtained from 2DST, even though they are not interchangeable with each other. As only a single acquisition is required, 3D methods may offer advantages over the current 2D techniques. However, the accuracy of the 3DSE can still be improved by solving the problems that appear with deformation estimation in the basal segments.