Evaluation of a commercial multi-dimensional echocardiography technique for ventricular volumetry in small animals

Abstract

Background: The assessment of ventricular volumes using conventional echocardiography methods is limited with regards to the need of geometrical assumptions. In the present study, we aimed to evaluate a novel commercial system for three-dimensional echocardiography (3DE) in preclinical models by direct comparison with conventional 1D- and 2D-echocardiography (1DE; 2DE) and the gold-standard technique magnetic resonance imaging (MRI). Further, we provide a standard operating protocol for image acquisition and analysis with 3DE.

Methods: 3DE was carried out using a 30 MHz center frequency transducer coupled to a Vevo®3100 Imaging System. We evaluated under different experimental conditions: 1) in vitro phantom measurements served as controlled setting in which boundaries were clearly delineated; 2) a validation cohort composed of healthy C57BL/6 J mice and New Zealand Obese (NZO) mice was used in order to validate 3DE against cardiac MRI; 3) a standard mouse model of pressure overload induced-heart failure was investigated to estimate the value of 3DE.

Results: First, in vitro volumetry revealed good agreement between 3DE assessed volumes and the MRI-assessed volumes. Second, cardiac volume determination with 3DE showed smaller mean differences compared to cardiac MRI than conventional 1DE and 2DE. Third, 3DE was suitable to detect reduced ejection fractions in heart failure mice. Fourth, inter- and intra-observer variability of 3DE showed good to excellent agreement regarding absolute volumes in healthy mice, whereas agreement rates for the relative metrics ejection fraction and stroke volume demonstrated good to moderate observer variabilities.

Conclusions: 3DE provides a novel method for accurate volumetry in small animals without the need for spatial assumptions, demonstrating a technique for an improved analysis of ventricular function. Further validation work and highly standardized image analyses are required to increase reproducibility of this approach.

Keywords: 3D echocardiography; Heart failure; Preclinical imaging; Small animals; Volumetry.

Fig. 1

Concept of 3D-echocardiography in small animals. a 3D-motor installed on the transducer. b 3D-motor allows the transducer to move unidirectional realizing 3DE. c Recording different cardiac slices during the cardiac cycle. d Chronogram demonstrating the link between spatial (3D) and temporal dimension (4D). e Multi-slice reconstruction of 3DE. f 3D-volume tracking of exemplary SHAM and TAC-mice along the cardiac cycle (4DE)

Fig. 2

In vitro volumetry. a Photo of round-shaped phantom. Scale = 1 cm. b Exemplary 2DE, c 3DE, d and magnetic resonance images of phantoms with and without exemplary tracings and 3D reconstructions. e Bland-Altman analysis of 2DE and f 3DE volumes compared to gold standard magnetic resonance imaging (MRI) assessed phantom volumes. n = 6

Fig. 3

In vivo volumetry. a Exemplary 1DE, b 2DE, C 3DE and d cardiac magnetic resonance (CMR) images of left ventricles of NZO mice. Mean differences of echocardiographic-assessed e ESV, f EDV, G SV and h EF to values assessed with gold standard CMR (CMR) imaging. n = 10. *p < .05, **p < .01 vs. 3DE

Fig. 4

Echocardiographic method comparison in healthy controls and mice with pressure overload-induced heart failure. a Statistical comparison of echocardiographic imaging modalities assessing ESV, EDV, SV and EF in SHAM-control mice. b Statistical comparison of echocardiographic imaging modalities assessing ESV, EDV, SV and EF in TAC-mice. Mean + SEM. SHAM: n = 7, TAC: n = 9. *p < .05, **p < .01, ***p < .001, ****p < .0001 vs. 3DE

Fig. 5

Inter-observer variability of 3DE shown as correlations and corresponding Bland-Altman plots. a Representative cube view images of single observer tracings and combined overlay. b Representative pictures of all three spatial axes with single observer tracings and combined overlay. c Bland-Altman analysis of SHAM (n = 7) and d TAC-mice (n = 9) for ESV, EDV, EF and SV showing the inter-observer variability, expressed as absolute difference between observers