Name: quantification of mouse heart left ventricular function, myocardial strain, and hemodynamic forces by cardiovascular magnetic resonance imaging
Uploaded: 2021-05-24T15:00:00.000+00:00
Duration: 11 min 13 s
Description: Watch this Scientific Journal Video about Quantification of Mouse Heart Left Ventricular Function, Myocardial Strain, and Hemodynamic Forces by Cardiovascular Magnetic Resonance Imaging at JoVE.com

The authors thank Dorita Dekkers and Fatimah Al Darwish for assistance with the mouse measurements and data analysis.

<ol>
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Cardiovascular Imaging. 12 (2), 377-379 (2019).</li><li>T&#246;ger, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intracardiac+hemodynamic+forces+using+4D+flow:+a+new+reproducible+method+applied+to+healthy+controls,+elite+athletes+and+heart+failure+patients.">Intracardiac hemodynamic forces using 4D flow: a new reproducible method applied to healthy controls, elite athletes and heart failure patients.</a> Journal of Cardiovascular Magnetic Resonance. 18, 61 (2016).</li><li>Eriksson, J., Bolger, A. F., Ebbers, T., Carlh&#228;ll, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+left+ventricular+hemodynamic+forces+in+healthy+subjects+and+patients+with+dilated+cardiomyopathy+using+4D+flow+MRI.">Assessment of left ventricular hemodynamic forces in healthy subjects and patients with dilated cardiomyopathy using 4D flow MRI.</a> Physiological Reports. 4 (3), 12685 (2016).</li><li>Coolen, B. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+T1+mapping+of+the+mouse+heart+using+variable+flip+angle+steady-state+MR+imaging.">Three-dimensional T1 mapping of the mouse heart using variable flip angle steady-state MR imaging.</a> NMR in Biomedicine. 24 (2), 154-162 (2011).</li><li>Nijm, G. M., Swiryn, S., Larson, A. C., Sahakian, A. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+the+magnetohydrodynamic+effect+as+a+signal+from+the+surface+electrocardiogram+during+cardiac+magnetic+resonance+imaging.">Characterization of the magnetohydrodynamic effect as a signal from the surface electrocardiogram during cardiac magnetic resonance imaging.</a> Computers in Cardiology. 33, 269-272 (2006).</li><li>Domenichini, F., Pedrizzetti, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemodynamic+forces+in+a+model+left+ventricle.">Hemodynamic forces in a model left ventricle.</a> Physical Review Fluids. 1, 083201 (2016).</li><li>Voigt, J. U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Definitions+for+a+common+standard+for+2D+speckle+tracking+echocardiography:+consensus+document+of+the+EACVI/ASE/Industry+Task+Force+to+standardize+deformation+imaging.">Definitions for a common standard for 2D speckle tracking echocardiography: consensus document of the EACVI/ASE/Industry Task Force to standardize deformation imaging.</a> European Heart Journal - Cardiovascular Imaging. 16 (1), 1-11 (2015).</li><li>Pedrizzetti, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+computation+of+hemodynamic+forces+in+the+heart+chambers.">On the computation of hemodynamic forces in the heart chambers.</a> Journal of Biomechanics. 95, 109323 (2019).</li><li>Hoffman, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myocardial+strain+and+cardiac+output+are+preferable+measurements+for+cardiac+dysfunction+and+can+predict+mortality+in+septic+mice.">Myocardial strain and cardiac output are preferable measurements for cardiac dysfunction and can predict mortality in septic mice.</a> Journal of American Heart Association. 8 (10), 012260 (2019).</li></ol>

Ruslan Garipov is an employee of MR Solutions Ltd., Guildford, United Kingdom. David Hautemann is an employee of Medis medical imaging systems B.V., Leiden, The Netherlands.

The presented protocol describes the use of CMR imaging for longitudinal, non-invasive, in vivo experiments to analyze heart function in mice. These results are examples of healthy animals to demonstrate the feasibility of using CINE images to quantify the cardiac parameters. However, the methods described can be used for various animal models. Although specific disease models might require small alterations to the protocol, its basic structure to assess the different cardiac functional parameters will be very similar. One particular case worth mentioning is a myocardial infarction model where part of the heart has significant loss in contractility. This can cause low quality of the cardiac navigator signal within this slice. In this case, an alternative option would be acquiring the navigator from a separate slice, as described in a previous study by Coolen et al.16. CINE images in different views are reconstructed from retrospectively gated data using CS algorithms and are analyzed using image analysis software to calculate the strain and HDF values.
The quality of the acquired images naturally depends on all preparation steps, which need to be carefully performed before starting the cardiac MRI protocol. For instance, if no clear ECG and respiratory signals are seen when placing the animal inside the MRI scanner, this will likely result in suboptimal acquisitions and even increased scan times due to the added effect of magnetohydrodynamic distortions17. It is important to realize that due to the sequential planning of the slice orientations, the animals cannot just be repositioned in between scans. It is therefore not possible to re-adjust the ECG leads in between scans, as this will alter the position of the mouse in the scanner. During scanning, temperature control is crucial for maintaining a constant cardiac and respiratory interval, which especially benefits the quality of the retrospectively gated scans that are acquired over a longer period of time. During this high-duty-cycle scan, the temperature of the animal might steadily increase, causing the heart rate and respiratory rate to increase. Adjusting the temperature of the heating system and the anesthesia could greatly contribute to stabilizing the respiratory rate prior to or during scanning.
A critical step during the analysis is the consistency in contour drawing. While automatic segmentation works well for clinical data, it does not perform robustly in the case of mouse cardiac data (not tested for rats). The high heart rate and high blood flow during specific cardiac phases, especially at the start of LV filling, may cause intravoxel dephasing and signal voids, compromising myocardial wall delineation. It is therefore not advised to analyze each frame independently, but visually inspect the motion of the myocardial wall between frames and take this into account when drawing the contours across all frames. It is advised to copy and adjust the endocardial contour between two consecutive frames to maintain a more natural contractile motion in the analysis. In this protocol, papillary muscles are excluded from the ventricular lumen volume in the SA images for systolic and diastolic function assessment, while they are included in the 2CH, 3CH, and 4CH views for strain and HDF analysis because the latter relies on knowledge of the precise motion of the myocardial wall, rather than the precise volume of the ventricular lumen.
Whereas systolic and diastolic function parameters are based on measuring LV volumes throughout the cardiac cycle, strain and HDF parameters depend on motion patterns within the myocardial wall as well. For this, feature-tracking techniques are used where the displacement of the myocardial segment can be assessed by recognizing distinct anatomical features and signal intensities between subsequent CINE phases. The strong contrast between blood pool and myocardium in CMR images facilitates the use of feature-tracking for subsequent strain and HDF analysis8. Prior to CMR feature-tracking, the myocardial strain was determined with speckle tracking echography and CMR tissue-tagging. CMR feature-tracking does not require additional scanning time compared to CMR tissue-tagging. However, despite the use of retrospective triggering, CMR still has a limited temporal resolution, which could make it difficult to correctly evaluate fast deformations within the cardiac cycle.
Assessment of HDF throughout the cardiac cycle requires measurements of the diameters of the mitral and aortic valves to calculate the HDF in apex-base and inferolateral-anteroseptal directions using previously described equations18. This method has shown consistent estimates of the HDF compared to the reference standard 4D-flow MRI, which has a limited availability in clinical use due to its complexity6. It is important to know that robust estimation of the valve diameters is difficult, and therefore, the valve diameters should be kept constant for a group of animals and across repeated measurements in a longitudinal study, as variations in this parameter by incorrect estimations could easily overshadow subtle changes in HDF parameters. The specific software used to calculate GLS and HDF parameters might not be available to all users. Therefore, one can refer to Voigt et al.19&#160;(GLS) as well as Pedrizzetti et al.6,20 (HDF), which contain all mathematical descriptions that form the basis of the respective calculations as performed by the analysis software.
For the purpose of this study, the protocol was evaluated in healthy animals (N = 6). A representative set of time curves for LV volume, dV/dt, endoGLS, and HDF are shown in Figure 5A-C. Mean values of multiple cardiac functional parameters (EF, E&#39;/A&#39;-ratio, peak GLS, and HDF) are shown in Figure 5D. These agree well with comparable protocols used in the literature21. Literature on GLS and HDF data in mice is scarce. A mean GLS value of -22.8% was measured, which is in the same range as clinical data8, indicating that GLS measurements obtained with the described method are feasible in mice. HDF curves obtained in mice also show the same distinct phases as seen in human data, showing the successful translation of this technique to preclinical research. While HDF parameters are hypothesized to serve as early biomarkers of cardiac dysfunction, more studies are warranted to investigate the diagnostic and predictive value of this new parameter. The results in this protocol do show that HDF and GLS outcomes are expected to be more variable across animals, which needs to be taken into account when subtle differences in animal models or treatment effects are expected.

Cardiovascular magnetic resonance (CMR) in small animals provides an accurate in vivo measurement of myocardial function, making CMR an optimal tool for preclinical research in cardiovascular disease. Due to the high spatial resolution and high contrast between blood and myocardium in CMR images, it is possible to delineate the endo- and epicardial contours and calculate myocardial mass and ventricular volumes1,2. Despite the high heart rates of up to 600 beats/min, the use of electrocardiogram (ECG) and respiratory triggering allows high-quality measurements of different cardiac phases (also called CINE images) without respiratory motion artifacts. In this way, multiple slices can be used to cover the heart from apex to base to extract systolic function parameters such as ejection fraction (EF), end-systolic volume (ESV), end-diastolic volume (EDV), and cardiac output (CO)3. Aside from basic systolic function assessment, additional CMR techniques have been recently developed to assess diastolic dysfunction4, myocardial strain5, and hemodynamic forces (HDF)6.
ECG gating allows synchronization to the cardiac cycle by starting MR signal acquisition after detection of the R-peak and recording a defined number of cardiac phases during the R-R interval. However, the number of cardiac phases (frame rate) that can be acquired this way depends on the lowest possible repetition time (TR) the system can reach while maintaining an acceptable signal-to-noise ratio (SNR) and spatial resolution4. Furthermore, because the use of high magnetic field gradients can temporarily distort the ECG signal, the acquisition is usually stopped before the end-diastolic phase. Both factors limit the use of such scans to systolic function assessments, as the calculation of other cardiac functional parameters requires a better definition of the left ventricular (LV) volume-time curve.
High-frame-rate CINE images can be acquired by retrospective gating, whereby MR signal is continuously acquired during scanning, and an incorporated navigator echo after radiofrequency (RF) excitation detects cardiac and respiratory motion. Because the CMR acquisition is performed asynchronously with the cardiac motion, the acquired MR signals can then be assigned to a retrospectively chosen number of cardiac frames. In this way, if sufficient data is collected, high-frame-rate CINE images can be reconstructed4,7. This then allows for diastolic function assessment, represented by the ratio between the peak early filling rate (E&#39;) and peak late filling rate from atrial contraction (A&#39;).
In clinical research, CINE images can be analyzed with CMR feature-tracking to assess the myocardial strain and HDF6,8. Myocardial strain is a cardiac deformation parameter that measures the difference in percentages between the initial length (usually in end-diastolic length) and maximum length (usually in end-systole) of a myocardial segment9. Myocardial strain measurements can be of incremental value for assessing the LV function as strain values quantify myocardial wall shortening and thickening. A reduction in shortening function might be an indication of subendocardial fiber damage10. Alterations in myocardial strain can occur independent of EF and could be a precursor for underlying complications.
Specifically, the global longitudinal strain (GLS) and global circumferential strain (GCS) have been shown to be of added value in characterizing heart disease10,11,12. Similarly, HDF has been suggested to be a potential novel parameter to indicate altered cardiac function6,13. These HDF or interventricular pressure gradients (IVPG) drive the blood motion during ejection and filling of the heart and are affected by the momentum exchange between blood and myocardium, including the aortic and mitral valve14,15.
In this study, a comprehensive protocol is described for performing robust small animal CMR measurements to quantify LV function, myocardial strain, and HDF of mouse hearts. It contains the necessary steps for animal preparation, data acquisition using both prospectively and retrospectively gated CINE images of the heart, as well as analysis with dedicated software capable of calculating the volumetric measurements, E&#39;/A&#39; ratio, myocardial strain, and HDF of the heart. This protocol can be used for the extensive assessment of LV function in various mouse models of cardiovascular disease.

<table><tbody><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>AccuSens single and multi-channel signal conditioner</td><td>Opsens solutions inc., Canada</td><td>&amp;nbsp;ACS-P4-N-62SC</td><td>Used with fiber optic temperature sensor to monitor body temperature</td></tr><tr><td>Duratears eye ointment</td><td>Alcon Nederland B.V., Netherlands</td><td></td><td></td></tr><tr><td>Mouse cell</td><td>&amp;Eacute;quipment V&amp;eacute;t&amp;eacute;rinaire Minerve, France</td><td></td><td>referred to as mouse cradle</td></tr><tr><td>MR-compatible Monitoring &amp;amp; Gating System for Small animals</td><td>SA Intuments, Inc., United States</td><td>Model 1030</td><td>ERT Module (ECG/respiratory interface module) , ERT Control/Gating Module, battery pack and subdermal ECG Electrode Set</td></tr><tr><td>MRI scanner</td><td>MR Solutions Ltd., United Kingdom</td><td>Model: MRS-7024&amp;nbsp;&amp;nbsp;</td><td>Preclinical MRI System 7.0T/24 cm</td></tr><tr><td>Multistation temperature control unit and High Flow PCA</td><td>&amp;Eacute;quipment V&amp;eacute;t&amp;eacute;rinaire Minerve, France</td><td>Model: URT Multipostes</td><td>animal heating system</td></tr><tr><td>Respiration Sensor</td><td>Graseby Medical Limited, United Kingdom</td><td>Ref 2005100</td><td></td></tr><tr><td>RF coil</td><td>MR Solutions Ltd., United Kingdom</td><td>MRS-MVC</td><td>38mm mouse volume RF coil for mouse body studies</td></tr><tr><td>SF flowmeter</td><td>flow-meter, Italy</td><td>SF 3</td><td></td></tr><tr><td>Vaporizer sigma delta Intermed</td><td>Penlon Ltd., United Kingdom</td><td></td><td></td></tr><tr><td>&lt;strong&gt;Materials&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Isoflurane</td><td>AST farma, Netherlands</td><td></td><td></td></tr><tr><td>Vaseline petroleum jelly</td><td>Unilever, United Kingdom</td><td></td><td></td></tr><tr><td>&lt;strong&gt;Software&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>BART toolbox</td><td></td><td></td><td>https://mrirecon.github.io/bart/</td></tr><tr><td>Mathematica 12.0</td><td>Wolfram Research, Inc., United States</td><td></td><td></td></tr><tr><td>MATLAB 2019a</td><td>The MathWorks,Inc., United States</td><td></td><td></td></tr><tr><td>MEDIS Suite MR</td><td>Medis Medical Imaging Systems B.V. ,Netherlands</td><td></td><td>Image analysis software</td></tr><tr><td>PC-SAM</td><td>SA Intuments, Inc., United States</td><td></td><td></td></tr><tr><td>Preclinical Scan</td><td>MR Solutions Ltd., United Kingdom</td><td></td><td>Scanning software</td></tr><tr><td>Retrospective version 7.0</td><td>Amsterdam UMC, the Netherlands</td><td></td><td>Reconstuction software: https://github.com/Moby1971?tab=repositories</td></tr></tbody></table>

quantification of mouse heart left ventricular function, myocardial strain, and hemodynamic forces by cardiovascular magnetic resonance imaging

Mouse models have contributed significantly to understanding genetic and physiological factors involved in healthy cardiac function, how perturbations result in pathology, and how myocardial diseases may be treated. Cardiovascular magnetic resonance imaging (CMR) has become an indispensable tool for a comprehensive in vivo assessment of cardiac anatomy and function. This protocol shows detailed measurements of mouse heart left ventricular function, myocardial strain, and hemodynamic forces using 7-Tesla CMR. First, animal preparation and positioning in the scanner are demonstrated. Survey scans are performed for planning imaging slices in various short- and long-axis views. A series of prospective ECG-triggered short-axis (SA) movies (or CINE images) are acquired covering the heart from apex to base, capturing end-systolic and end-diastolic phases. Subsequently, single-slice, retrospectively gated CINE images are acquired in a midventricular SA view, and in 2-, 3-, and 4-chamber views, to be reconstructed into high-temporal resolution CINE images using custom-built and open-source software. CINE images are subsequently analyzed using dedicated CMR image analysis software.
Delineating endomyocardial and epicardial borders in SA end-systolic and end-diastolic CINE images allows for the calculation of end-systolic and end-diastolic volumes, ejection fraction, and cardiac output. The midventricular SA CINE images are delineated for all cardiac time frames to extract a detailed volume-time curve. Its time derivative allows for the calculation of the diastolic function as the ratio of the early filling and atrial contraction waves. Finally, left ventricular endocardial walls in the 2-, 3-, and 4-chamber views are delineated using feature-tracking, from which longitudinal myocardial strain parameters and left ventricular hemodynamic forces are calculated. In conclusion, this protocol provides detailed in vivo quantification of the mouse cardiac parameters, which can be used to study temporal alterations in cardiac function in various mouse models of heart disease.

Using the previously described protocol, a group of healthy C57BL/6 wildtype mice (n = 6, age 14 weeks) was scanned using a 7-Tesla MRI scanner using a 38-mm-diameter birdcage coil. During each scan session, the multi-slice CINE SA images were acquired using prospectively gated GRE sequences, while the single-slice midventricular SA, 2CH, 3CH, and 4CH views CINE images were acquired using retrospective gating. Representative high-frame rate reconstructions of retrospectively gated scans using a custom-built, post-processing software can be seen in Supplemental Video 1. From the resulting images, volume-time curves during the cardiac cycle (Figure 5A) were determined as well as the corresponding first-derivative curves (dV/dt) for calculation of systolic (EF = 72.4 &#177; 2.8%) and diastolic function parameters (E&#39;/A&#39; ratio = 1.5 &#177; 0.3) respectively.
The 2CH, 3CH, and 4CH view CINE images were analyzed using image analysis software to determine endocardial GLS (endoGLS) changes across the cardiac cycle (Figure 5B) and corresponding peak GLS values (-22.8 &#177; 2.4%) as a measure for myocardial strain. Additionally, the software calculates the root mean square (RMS) HDF in longitudinal (apex-base) (135.2 &#177; 31.7%) and transversal (inferolateral-anteroseptal) (12.9 &#177; 5.0%) directions. For each animal, it is also possible to produce an HDF time profile, which follows a consistent pattern of positive and negative peaks that represent the magnitude and direction of the HDF during the cardiac cycle (Figure 5C). Descriptive results of all outcome parameters are summarized in Figure 5D.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/62595/62595fig05.jpg" /> 
Figure 5: Quantification of LV functional parameters based on the mouse heart. (A)&#160;Representative volume-time curve and corresponding dV/dt curve. The latter depicts the flow velocity with distinct early filling peak (E&#39;) and atrial contraction (A&#39;) peak. (B) Representative GLS curve indicating strain deformation in the longitudinal direction throughout the cardiac cycle. (C) Representative HDF curve with distinct force peaks in the apex-base direction, starting with the systolic ejection force and followed by a downward force at the transition between systole and diastole, E-wave deceleration force, A-wave acceleration, and deceleration force. (D) Descriptive results of all animals for values of EF, E&#39;/A&#39; ratio, peak GLS, and root mean square of the HDF in apex-base and inferolateral-anteroseptal directions. Values are expressed as mean &#177; SD. Abbreviations: LV = left ventricle; V = volume; t = time; GLS = global longitudinal strain; HDF = hemodynamic forces; EF = ejection fraction. <a href="https://www.jove.com/files/ftp_upload/62595/62595fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplemental Video 1:&#160;Representative reconstruction of retrospectively gated CINE images in SA, 2CH, 3CH, and 4CH views. Abbreviations: SA = short axis; CH = chamber. <a href="https://www.jove.com/files/ftp_upload/62595/Supplemental_Material_movie.mp4" target="_blank">Please click here to download this Video.</a>
Supplemental Material:&#160;<a href="https://www.jove.com/files/ftp_upload/62595/Supplemental_Material_script.nb" target="_blank">Please click here to download this File.</a>

Watch this Scientific Journal Video about Quantification of Mouse Heart Left Ventricular Function, Myocardial Strain, and Hemodynamic Forces by Cardiovascular Magnetic Resonance Imaging at JoVE.com

Quantification of Mouse Heart Left Ventricular Function, Myocardial Strain, and Hemodynamic Forces by Cardiovascular Magnetic Resonance Imaging

This study describes a comprehensive cardiovascular magnetic resonance imaging (CMR) protocol to quantify the left ventricular functional parameters of the mouse heart. The protocol describes the acquisition, post-processing, and analysis of the CMR images as well as assessment of different cardiac functional parameters.

Mouse models have contributed significantly to understanding genetic and physiological factors involved in healthy cardiac function, how perturbations ...

quantification-mouse-heart-left-ventricular-function-myocardial

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Bioengineering

6.1K Views.  University of Amsterdam. Dit CMRI-protocol vergemakkelijkt niet-invasieve in vivo kwantificering van cardiale functionele parameters van muizen, waaronder ejectiefractie, E over A-verhouding, globale longitudinale stam en hemodynamische krachten. Alle functionele cardiale parameters kunnen worden verkregen uit een enkel cardiaal MRI-onderzoek en er zijn geen complexe tagging of dichte scans nodig om sterktes of hemodynamische krachten te kwantificeren. Er zijn aanwijzingen dat wereldwijde longitudinale spanning en he...

Video: Quantification of Mouse Heart Left Ventricular Function, Myocardial Strain, and Hemodynamic Forces by Cardiovascular Magnetic Resonance Imaging

High-frequency High-resolution Echocardiography: First Evidence on Non-invasive Repeated Measure of Myocardial Strain, Contractility, and Mitral Regurgitation in the Ischemia-reperfused Murine Heart

Ischemia-reperfusion (IR) was surgically performed in murine hearts which were then subjected to repeated imaging to monitor temporal changes in functional parameters of key clinical significance. Two-dimensional movies were acquired at high frame rate (8 kHz) and were utilized to estimate high-quality myocardial strain. Two-dimensional elastograms (strain images), as well as strain profiles, were visualized. Results were powerful in quantitatively assessing IR-induced changes in cardiac events including left-ventricular (LV) contraction, LV relaxation and isovolumetric phases of both pre-IR and post-IR beating hearts in intact mice. In addition, compromised sector-wise wall motion and anatomical deformation in the infarcted myocardium were visualized.  The elastograms were uniquely able to provide information on the following parameters in addition to standard physiological indices that are known to be affected by myocardial infarction in the mouse: internal diameters of mitral valve orifice and aorta, effective regurgitant orifice, myocardial strain (circumferential as well as radial), turbulence in blood flow pattern as revealed by the color Doppler movies and velocity profiles, asynchrony in LV sector, and changes in the length and direction of vectors demonstrating slower and asymmetrical wall movement. This work emphasizes on the visual demonstration of how such analyses are performed. 

High-frequency High-resolution Echocardiography: First Evidence on Non-invasive Repeated Measure of Myocardial Strain, Contractility, and Mitral Regurgitation in the Ischemia-reperfused Murine Heart 

High frequency Doppler ultrasound is a novel technology for assessing regional myocardial function. This work presents first evidence demonstrating applicability of this versatile imaging platform for the repeated measure of myocardial strain, dp/dt, and mitral regurgitation in the ischemia-reperfused (IR) murine heart.

Ischemia-reperfusion (IR) was surgically performed in murine hearts which were then subjected to repeated imaging to monitor temporal changes in ...

Medicine

Magnetic Resonance Derived Myocardial Strain Assessment Using Feature Tracking 

Purpose: An accurate and practical method to measure parameters like strain in myocardial tissue is of great clinical value, since it has been shown, that strain is a more sensitive and earlier marker for contractile dysfunction than the frequently used parameter EF. Current technologies for CMR are time consuming and difficult to implement in clinical practice. Feature tracking is a technology that can lead to more automization and robustness of quantitative analysis of medical images with less time consumption than comparable methods.
Methods: An automatic or manual input in a single phase serves as an initialization from which the system starts to track the displacement of individual patterns representing anatomical structures over time. The specialty of this method is that the images do not need to be manipulated in any way beforehand like e.g. tagging of CMR images.
Results: The method is very well suited for tracking muscular tissue and with this allowing quantitative elaboration of myocardium and also blood flow.
Conclusions: This new method offers a robust and time saving procedure to quantify myocardial tissue and blood with displacement, velocity and deformation parameters on regular sequences of CMR imaging. It therefore can be implemented in clinical practice.

Magnetic Resonance Derived Myocardial Strain Assessment Using Feature Tracking

An accurate and practical method to measure parameters like strain in myocardial tissue is of great clinical value, since it has been shown, that strain is a more sensitive and earlier marker for contractile dysfunction than the frequently used parameter EF.

Purpose: An accurate and practical method to measure parameters like strain in myocardial tissue is of great clinical value, since it has been shown, that ...

Assessment of Right Ventricular Structure and Function in Mouse Model of Pulmonary Artery Constriction by Transthoracic Echocardiography

Emerging clinical data support the notion that RV dysfunction is critical to the pathogenesis of cardiovascular disease and heart failure1-3. Moreover, the RV is significantly affected in pulmonary diseases such as pulmonary artery hypertension (PAH). In addition, the RV is remarkably sensitive to cardiac pathologies, including left ventricular (LV) dysfunction, valvular disease or RV infarction4. To understand the role of RV in the pathogenesis of cardiac diseases, a reliable and noninvasive method to access the RV structurally and functionally is essential.
A noninvasive trans-thoracic echocardiography (TTE) based methodology was established and validated for monitoring dynamic changes in RV structure and function in adult mice. To impose RV stress, we employed a surgical model of pulmonary artery constriction (PAC) and measured the RV response over a 7-day period using a high-frequency ultrasound microimaging system. Sham operated mice were used as controls. Images were acquired in lightly anesthetized mice at baseline (before surgery), day 0 (immediately post-surgery), day 3, and day 7 (post-surgery). Data was analyzed offline using software.
Several acoustic windows (B, M, and Color Doppler modes), which can be consistently obtained in mice, allowed for reliable and reproducible measurement of RV structure (including RV wall thickness, end-diastolic&#160;and end-systolic dimensions), and function (fractional area change, fractional shortening, PA peak velocity, and peak pressure gradient) in normal mice and following PAC.
Using this method, the pressure-gradient resulting from PAC was accurately measured in real-time using Color Doppler mode and was comparable to direct pressure measurements performed with a Millar high-fidelity microtip catheter. Taken together, these data demonstrate that RV measurements obtained from various complimentary views using echocardiography are reliable, reproducible and can provide insights regarding RV structure and function. This method will enable a better understanding of the role of RV cardiac dysfunction.

Right ventricle (RV) dysfunction is critical to the pathogenesis of cardiovascular disease, yet limited methodologies are available for its evaluation. Recent advances in ultrasound imaging provide a noninvasive and accurate option for longitudinal RV study. Herein, we detail a step-by-step echocardiographic method using a murine model of RV pressure overload.

Emerging clinical data support the notion that RV dysfunction is critical to the pathogenesis of cardiovascular disease and heart failure1-3. Moreover, ...

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

The use of Micro-Computed Tomography (MicroCT) for in vivo studies of small animals as models of human disease has risen tremendously due to the fact that MicroCT provides quantitative high-resolution three-dimensional (3D) anatomical data non-destructively and longitudinally. Most importantly, with the development of a novel preclinical iodinated contrast agent called eXIA160, functional and metabolic assessment of the heart became possible. However, prior to the advent of commercial MicroCT scanners equipped with X-ray flat-panel detector technology and easy-to-use cardio-respiratory gating, preclinical studies of cardiovascular disease (CVD) in small animals required a MicroCT technologist with advanced skills, and thus were impractical for widespread implementation. The goal of this work is to provide a practical guide to the use of the high-speed Quantum FX MicroCT system for comprehensive determination of myocardial global and regional function along with assessment of myocardial perfusion, metabolism and viability in healthy mice and in a cardiac ischemia mouse model induced by permanent occlusion of the left anterior descending coronary artery (LAD).

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

This method outlines the use of Quantum Micro-Computed Tomography (MicroCT) to assess cardiac morphology, function, perfusion, metabolism and viability with iodinated contrast agent in mice with experimentally-induced myocardial ischemia. The technique can be applied for non-destructive high-throughput longitudinal in vivo imaging of various animal models of human heart disease.

The use of Micro-Computed Tomography (MicroCT) for in vivo studies of small animals as models of human disease has risen tremendously due to the fact that ...

Noninvasive Assessment of Cardiac Abnormalities in Experimental Autoimmune Myocarditis by Magnetic Resonance Microscopy Imaging in the Mouse

Myocarditis is an inflammation of the myocardium, but only ~10% of those affected show clinical manifestations of the disease. To study the immune events of myocardial injuries, various mouse models of myocarditis have been widely used. This study involved experimental autoimmune myocarditis (EAM) induced with cardiac myosin heavy chain (Myhc)-&#945; 334-352 in A/J mice; the affected animals develop lymphocytic myocarditis but with no apparent clinical signs. In this model, the utility of magnetic resonance microscopy (MRM) as a non-invasive modality to determine the cardiac structural and functional changes in animals immunized with Myhc-&#945; 334-352 is shown. EAM and healthy mice were imaged using a 9.4 T (400 MHz) 89 mm vertical core bore scanner equipped with a 4 cm millipede radio-frequency imaging probe and 100 G/cm triple axis gradients. Cardiac images were acquired from anesthetized animals using a gradient-echo-based cine pulse sequence, and the animals were monitored by respiration and pulse oximetry. The analysis revealed an increase in the thickness of the ventricular wall in EAM mice, with a corresponding decrease in the interior diameter of ventricles, when compared with healthy mice. The data suggest that morphological and functional changes in the inflamed hearts can be non-invasively monitored by MRM in live animals. In conclusion, MRM offers an advantage of assessing the progression and regression of myocardial injuries in diseases caused by infectious agents, as well as response to therapies.

This study demonstrates the successful establishment of magnetic resonance microscopy imaging as a non-invasive tool to assess the cardiac abnormalities in mice affected with autoimmune myocarditis. The data indicate that the technique can be used to monitor the disease-progression in live animals.

Myocarditis is an inflammation of the myocardium, but only ~10% of those affected show clinical manifestations of the disease. To study the immune events ...

Assessment of Cardiac Morphological and Functional Changes in Mouse Model of Transverse Aortic Constriction by Echocardiographic Imaging

Transverse aortic constriction (TAC) in mice has been used as a valuable model to study mechanisms of cardiac hypertrophy and heart failure1. A reliable noninvasive method is essential to assess real-time cardiac morphological and functional changes in animal models of heart disease. Transthoracic echocardiography represents an important tool for noninvasive assessment of cardiac structure and function2. Here we used a high-resolution ultrasound imaging system to monitor myocardial remodeling and heart failure progression over time in a mouse model of TAC. B-mode, M-mode, and Doppler imaging were used to precisely assess cardiac hypertrophy, ventricular dilatation, and functional deterioration in mice following TAC. Color and pulse wave (PW) Doppler imaging was used to noninvasively measure pressure gradient across the aortic constriction created by TAC and to assess transmitral blood flow in mice. Thus transthoracic echocardiographic imaging provides comprehensive noninvasive measurements of cardiac dimensions and function in mouse models of heart disease.

The goal of this protocol is to noninvasively assess cardiac structural and functional changes in a mouse model of heart disease created by transverse aortic constriction, using B- and M-mode echocardiography and color/pulse wave Doppler imaging.

Transverse aortic constriction (TAC) in mice has been used as a valuable model to study mechanisms of cardiac hypertrophy and heart failure1. A reliable ...

Echocardiographic Approaches and Protocols for Comprehensive Phenotypic Characterization of Valvular Heart Disease in Mice

The aim of this manuscript and accompanying video is to provide an overview of the methods and approaches used for imaging heart valve function in rodents, with detailed descriptions of the appropriate methods for anesthesia, the echocardiographic windows used, the imaging planes and probe orientations for image acquisition, the methods for data analysis, and the limitations of emerging technologies for the evaluation of cardiac and valvular function. Importantly, we also highlight several future areas of research in cardiac and heart valve imaging that may be leveraged to gain insights into the pathogenesis of valve disease in preclinical animal models. We propose that using a systematic approach to evaluating cardiac and heart valve function in mice can result in more robust and reproducible data, as well as facilitate the discovery of previously underappreciated phenotypes in genetically-altered and/or physiologically-stressed mice.

This protocol provides a detailed description of the echocardiographic approach for comprehensive phenotyping of heart and heart valve function in mice.

The aim of this manuscript and accompanying video is to provide an overview of the methods and approaches used for imaging heart valve function in ...

Quantification of Biventricular Function and Morphology by Cardiac Magnetic Resonance Imaging in Mice with Pulmonary Artery Banding

Right ventricular (RV) function and failure are major determinants of outcome in acquired and congenital heart diseases, including pulmonary hypertension. Assessment of RV function and morphology is complex, partly due to the complex shape of the RV. Currently, cardiac magnetic resonance (CMR) imaging is the golden standard for noninvasive assessment of RV function and morphology. The current protocol describes CMR imaging in a mouse model of RV pressure load induced by pulmonary artery banding (PAB). PAB is performed by placing a 6-0 suture around the pulmonary artery over a 23 G needle. The PAB gradient is determined using echocardiography at 2 and 6 weeks. At 6 weeks, the right and left ventricular morphology and function is assessed by measuring both end-systolic and end-diastolic volumes and mass by ten to eleven cine slices 1 mm thick using a 9.4 T magnetic resonance imaging scanner equipped with a 1,500 mT/m gradient. Representative results show that PAB induces a significant increase in RV pressure load, with significant effects on biventricular morphology and RV function. It is also shown that at 6 weeks of RV pressure load, cardiac output is maintained. Presented here is a reproducible protocol for the quantification of biventricular morphology and function in a mouse model of RV pressure load and may serve as a method for experiments exploring determinants of RV remodeling and dysfunction.

To understand the pathophysiology of right ventricular (RV) adaptation to abnormal loading, experimental models are crucial. However, assessment of RV dimensions and function is complex and challenging. This protocol provides a method to perform cardiac magnetic resonance imaging (CMR) as a noninvasive benchmark procedure in mice subjected to RV pressure load.

Right ventricular (RV) function and failure are major determinants of outcome in acquired and congenital heart diseases, including pulmonary hypertension. ...

Biventricular Assessment of Cardiac Function and Pressure-Volume Loops by Closed-Chest Catheterization in Mice

Assessment of cardiac function is essential to conduct cardiovascular and pulmonary-vascular preclinical research. Pressure-volume loops (PV loops) generated by recording both pressure and volume during cardiac catheterization are vital when assessing both systolic and diastolic cardiac function. Left and right heart function are closely related, reflected in ventricular interdependence. Thus, recording biventricular function in the same animal is important to get a complete assessment of cardiac function. In this protocol, a closed chest approach to cardiac catheterization consistent with the way catheterization is performed in patients is adopted in mice. While challenging, the closed chest strategy is a more physiological approach, because opening the chest results in major changes in preload and afterload that create artifacts, most notably a fall in systemic blood pressure. While high-resolution echocardiography is used to assess rodents, cardiac catheterization is invaluable, particularly when assessing diastolic pressures in both ventricles.
Described here is a procedure to perform invasive, closed chest, sequential left and right ventricular pressure-volume (PV) loops in the same animal. PV loops are acquired using&#160;admittance technology with a mouse pressure-volume catheter and pressure-volume system acquisition. The procedure is described, beginning with the neck dissection, which is required to access the right jugular vein and the right carotid artery, to the insertion and positioning of the catheter, and finally the data acquisition. Then, the criteria required to ensure the acquisition of high-quality PV loops are discussed. Finally, the analysis of the left and right ventricular PV loops and the different hemodynamic parameters available to quantify systolic and diastolic ventricular function are briefly described.

Presented here is a protocol to assess biventricular heart function in mice by generating pressure-volume (PV) loops from the right and left ventricle in the same animal using closed chest catheterization. The focus is on the technical aspect of surgery and data acquisition.

Assessment of cardiac function is essential to conduct cardiovascular and pulmonary-vascular preclinical research. Pressure-volume loops (PV loops) ...

Estimating Bilateral Atrial Function by Cardiovascular Magnetic Resonance Feature Tracking in Patients with Paroxysmal Atrial Fibrillation

Atrial fibrillation (AF) is the most common form of arrhythmia. Atrial remodeling is considered the most critical mechanism for the presence and development of atrial fibrillation. Also, atrial remodeling can lead to the enlargement and dysfunction of the left atrium (LA), resulting in thrombosis and heart failure. Functional changes in left atrial strain and strain rate occur before structural alterations and are closely associated with structural remodeling and left atrial fibrosis. These parameters are sensitive biomarkers for atrial function. Cardiac magnetic resonance feature tracking (CMR-FT) is a novel, non-invasive, post-processing technique that can evaluate left atrial strain and strain rate. The CMR-FT was utilized in this investigation to assess the bilateral atrium strain rate in individuals with paroxysmal AF. Modifications in each segmental strain were evaluated using segmental analysis. The CMR-FT is recommended for non-invasive evaluations in the clinical assessment of atrial strain among existing strain imaging techniques. Further, it is a flexible parameter measurement with good reproducibility, high soft-tissue resolution, and post-processing based on standard cine balanced steady-state free precision (bSSFP) long-axis images without requiring a new sequence acquisition.

The atrial function is associated with the strain and strain rate. The cardiac magnetic resonance feature tracking (CMR-FT) technique was used in this study to quantify left and right atrial global and segmental longitudinal strain and strain rate in individuals with paroxysmal atrial fibrillation.

Quantification of Mouse Heart Left Ventricular Function, Myocardial Strain, and Hemodynamic Forces by Cardiovascular Magnetic Resonance Imaging

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