Real-time myocardial contrast echocardiography for assessing perfusion and function in healthy and infarcted wistar rats

Early and dynamic detection of doxorubicin induced cardiotoxicity by myocardial contrast echocardiography combined with two-dimensional speckle tracking echocardiography in rats

Background

Anthracycline-induced cardiotoxicity is well-known as a side effect of chemotherapy. Currently, clinical imaging techniques are not capable to detect doxorubicin (DOX)-induced cardiotoxicity before a functional decline. The purpose of this study was to evaluate whether myocardial contrast echocardiography (MCE) can dynamically monitor the cardiac changes in the early stage in the DOX-induced rat model of cardiotoxicity.

Methods

A weekly injection of 2.5 mg/kg of DOX was used to generate a rat model of cardiotoxicity. All groups underwent ultrasonic examinations including standard echocardiography, 2D speckle tracking echocardiography (2D-STE), and MCE. Then all rats were sacrificed immediately for histopathological evaluation.

Results

A total of eight control rats and 32 DOX-treated rats were included in the study and grouped according to their treatment period. Decreased quantitative parameters of myocardial blood flow (MBF) (control vs. group 1: 133.31 ± 20.23 dB/s vs. 103.35 ± 21.60 dB/s, P = 0.048) and β (control vs. group 2: 11.17 ± 1.48/s vs. 7.15 ± 1.23/s, P < 0.001) were observed after 2 and 4 weeks of treatment, respectively, while left ventricular global strain (control vs. group 3: -23.67 ± 3.92% vs. -16.01 ± 3.40%, P = 0.002) decreased after 6 weeks of treatment and left ventricular ejection fraction (LVEF) (control vs. group 4: 82.41 ± 3.20% vs. 70.89 ± 9.30%, P = 0.008) decreased after 8 weeks of treatment. The main histopathological features are increased myocardial vacuolization and interstitial fibrosis and decreased myocardial microvessel density.

Conclusion

Compared with standard echocardiography and 2D-STE, MCE can accurately and non-invasively detect changes in early myocardial perfusion, demonstrating the clinical potential of continuous and dynamic monitoring of DOX-induced cardiotoxicity.

A multi-model framework to estimate perfusion parameters using contrast-enhanced ultrasound imaging

PURPOSE

Contrast-enhanced ultrasound imaging has expanded the diagnostic potential of ultrasound by enabling real-time imaging and quantification of tissue perfusion. Several perfusion models and curve fitting methods have been developed to quantify the temporal behavior of tracer signal and standardize perfusion quantification. While the least-squares approach has traditionally been applied for curve fitting, it can be inadequate for noisy and complex data. Moreover, previous research suggests that certain perfusion models may be more relevant depending on the organ or tissue imaged. We propose a multi-model framework to select the most appropriate perfusion model and curve fitting method for each diagnostic application.

METHODS

Our multi-model approach uses a system identification method, which estimates perfusion parameters from the model with the best fit to a given time-intensity curve. We compared current perfusion quantification methods that use a single perfusion model and curve fitting method and our proposed multi-model framework on bolus 3D dynamic contrast-enhanced ultrasound (DCE-US) in vivo images obtained in mice implanted with a colon cancer, as well as on simulation data. The quality of fit in estimating perfusion parameters was evaluated using the Spearman correlation coefficient, the coefficient of determination (R² ), and the normalized root-mean-square error (NRMSE) to ensure that the multi-model framework finds the best perfusion model and curve fitting algorithm.

RESULTS

Our multi-model framework outperforms conventional single perfusion model approaches with least-squares optimization, providing more robust perfusion parameter estimation. R² and NRMSE are 0.98 and 0.18, respectively, for our proposed method. By comparison, the performance of the traditional approach is much more dependent upon the selection of the appropriate model. The R² and NRMSE are 0.91 and 0.31, respectively.

CONCLUSIONS

The proposed multi-model framework for perfusion modeling outperforms the current approach of single perfusion modeling using least-squares optimization and more robustly estimates perfusion parameters when using empiric data labeled by an expert as the gold standard. Our technique is minimally sensitive to issues affecting the accuracy of perfusion parameter estimation, including rise time, noise, region of interest size, and frame rate. This framework could be of key utility in modeling different perfusion systems in different tissues and organs.

Evaluation of tumor angiogenesis in a mouse PC-3 prostate cancer model using dynamic contrast-enhanced sonography

OBJECTIVES

The purpose of this study was to evaluate tumor angiogenesis in a mouse xenograft model injected with human PC-3 prostate cancer cells using contrast-enhanced sonography.

METHODS

Sixteen nude mice were injected with human prostate cancer cells on the back or the flank. Contrast-enhanced sonography was performed with a 5- to 12-MHz broadband linear transducer after a 500-μL bolus injection of a sonographic contrast agent composed of lipid shells and sulfur hexafluoride. Contrast-enhanced sonograms were obtained by the pulse inversion coded harmonic technique with a low mechanical index of 0.07. A region of interest was drawn to encompass the tumor, and time-intensity curves were acquired. After fitting the curve by a gamma variate function, the maximum intensity, area under the curve for up to 50 seconds, time to peak, shape parameter, and scale parameter were derived. The tumor volume, percentage of vascular endothelial growth factor expression, and CD31-positive vessel count (microvessel density) were correlated with the parameters derived from the time-intensity curve.

RESULTS

The maximum intensity was positively correlated with the microvessel density with statistical significance (r = 0.552; P = .03). The percentage of vascular endothelial growth factor expression did not have any correlation with the parameters from the curve.

CONCLUSIONS

Contrast-enhanced sonography can reflect tumor vascularity in a prostate cancer animal model. Sonography of tumor angiogenesis may permit functional assessment of the tumor vasculature and provide an imaging biomarker for tumor responses to antiangiogenic therapies.

Clinical usefulness of low-dose dobutamine stress real-time myocardial contrast echocardiography for detection of viable myocardium

OBJECTIVES

To evaluate and compare the diagnostic accuracy of semi-quantitative and quantitative real-time myocardial contrast echocardiography (RT-MCE) with low-dose dobutamine stress echocardiography (LD-DSE) in detecting viable myocardium.

METHODS

Thirty in-patients with coronary artery disease and regional wall motion abnormalities underwent RT-MCE without and with LD-DSE. Percutaneous coronary intervention was performed within 1 week after RT-MCE in all patients. Myocardial perfusion was evaluated from A, β, and A × β indices from microbubble replenishment curves. The motion of each myocardium segment was observed by routine echocardiography 1, 3, and 6 months after percutaneous coronary intervention and its improvement over time was the criterion of viable myocardium.

RESULTS

RT-MCE sensitivity and specificity for the assessment of viable myocardium were 71.7% and 69.8%, rising to 81.3% and 76.7% (p < 0.05) when combined with LD-DSE. Using quantitative RT-MCE with cutoff values of A, β, and A × β, the sensitivity and specificity were 75.6%, 78.8%, 82.1%, and 82.4%, 77.9%, 78.6%, respectively. When combined with LD-DSE, the sensitivity and specificity were 86.0%, 83.2%; 88.9% and 84.1%; 89.6%, 79.9%, respectively.

CONCLUSIONS

Quantitative RT-MCE analysis yielded higher sensitivity and specificity than semi-quantitative RT-MCE with or without LD-DSE for the detection of viable myocardium.

Indicator dilution models for the quantification of microvascular blood flow with bolus administration of ultrasound contrast agents

Indicator dilution methods have a long history in the quantification of both macro- and microvascular blood flow in many clinical applications. Various models have been employed in the past to isolate the primary pass of an indicator after an intravenous bolus injection. The use of indicator dilution techniques allows for the estimation of hemodynamic parameters of a tumor or organ and thus may lead to useful diagnostic and therapy monitoring information. In this paper, we review and discuss the properties of the lognormal function, the gamma variate function, the diffusion with drift models, and the lagged normal function, which have been used to model indicator dilution curves in different fields of medicine. We fit these models to contrast-enhanced ultrasound time-intensity curves from liver metastases and the ovine corpora lutea. We evaluate the models' performance on the image data and compare their predictions for hemodynamic-related parameters such as the area under the curve, the mean transit time, the full-width at half-maximum, the time to the peak intensity, and wash-in time. The models that best fit the experimental data are the lognormal function and the diffusion with drift.

Measurement of myocardial infarct size in preclinical studies

Ischemic heart disease is a major cause of morbidity and mortality worldwide. Myocardial ischemia followed by reperfusion results in tissue injury termed ischemia/reperfusion injury which is characterized by decreased myocardial contractile function, occurrence of arrhythmias, and development of tissue necrosis (infarction). These pathologies are all relevant as clinical consequences of myocardial ischemia/reperfusion injury and they are also important as experimental correlates and endpoints. The most critical determinant of acute and long-term mortality after myocardial infarction is the volume of the infarcted tissue. Therefore, development of cardioprotective therapies aims at reducing the size of the infarct developing due to myocardial ischemia/reperfusion injury. Different techniques are available to measure myocardial infarct size in humans and in experimental settings, however, accurate determination of the extent of infarction is necessary to evaluate interventions that may delay the onset of necrosis and/or limit the total extent of infarct size during ischemia/reperfusion. This paper highlights recent advances of the different techniques to measure infarct size.

Wideband high-frequency echocardiography to evaluate myocardial infarct size

OBJECTIVE

This study was designed to validate the feasibility of wideband high-frequency ultrasound imaging to resolve in vivo the degree, location, and morphologic changes of myocardial infarction (MI) in a rat model.

METHODS

The left anterior descending coronary artery was ligated in the test group (n = 41), and the sham control group did not have ligation (n = 7). The rats were examined with 10- to 22-MHz echocardiography to evaluate the MI size, location, and geometric formation.

RESULTS

The endocardial chamber shape was deformed, with enlargement of the anteroposterior dimension and fractional shortening, and was comparable with the degree of MI both in short- and long-axis sections of the left ventricle. Histologic analysis showed remodeling to different extents corresponding to different MI sizes (small, medium, and large).

CONCLUSIONS

The results suggest that this technique can be used in vivo to evaluate the MI location, size, and morphologic changes corresponding to the extent of the injury.

High resolution contrast ultrasound and NADH fluorescence imaging of myocardial perfusion in excised rat hearts

Simultaneous imaging of myocardial flow and hypoxia could be vital for identifying acute ischemic mechanisms that may trigger an arrhythmia. We have studied the distribution of flow and hypoxia in excised locally ischemic rat hearts using simultaneous contrast ultrasound imaging and beta-nicotinamide adenine dinucleotide (NADH) fluorescence imaging. Local ischemia was induced by controlling flow within a major coronary artery. Intra-myocardial flow was imaged using contrast high-resolution ultrasound (linear probe; 13-6 MHz). An ultrasound contrast agent (UCA) was used to highlight the ischemic border. We observed distinct borders between two perfusion beds. UCA images showed high contrast borders of flow. The progression of UCA through the tissue was clearly visible. Intramyocardial regions of flow overlap could be identified by superimposing images of UCA from two perfusion zones. Borders between hypoxic and normoxic tissue were clearly revealed by increased NADH fluorescence. Hypoxic borders were oriented along borders of flow. In summary, simultaneous ultrasound and NADH imaging of excised hearts from small animals provide high fidelity images for characterizing the distribution of flow and hypoxic tissue during acute localized ischemia.