Ultrasonic Assessment of Myocardial Microstructure

Summary

Echocardiography is commonly used to noninvasively characterize and quantify changes in cardiac structure and function. We describe an ultrasound-based imaging algorithm that offers an enhanced surrogate measure of myocardial microstructure and can be performed using open-access image analysis software.

Abstract

Echocardiography is a widely accessible imaging modality that is commonly used to noninvasively characterize and quantify changes in cardiac structure and function. Ultrasonic assessments of cardiac tissue can include analyses of backscatter signal intensity within a given region of interest. Previously established techniques have relied predominantly on the integrated or mean value of backscatter signal intensities, which may be susceptible to variability from aliased data from low frame rates and time delays for algorithms based on cyclic variation. Herein, we describe an ultrasound-based imaging algorithm that extends from previous methods, can be applied to a single image frame and accounts for the full distribution of signal intensity values derived from a given myocardial sample. When applied to representative mouse and human imaging data, the algorithm distinguishes between subjects with and without exposure to chronic afterload resistance. The algorithm offers an enhanced surrogate measure of myocardial microstructure and can be performed using open-access image analysis software.

Introduction

Echocardiography is a widely accessible imaging modality that is commonly used to noninvasively characterize and quantify changes in cardiac structure and function. Ultrasonic assessments of cardiac tissue can include analyses of backscatter signal intensity within a given region of interest at a single point in time, as well as over the course of the cardiac cycle. Prior studies have suggested that measures of sonographic signal intensity can identify the underlying presence of myocardial fiber disarray, viable versus nonviable myocardial tissue, and interstitial fibrosis^1-3. We refer to myocardial ‘microstructure’ as the tissue architecture th....

Protocol

1. Preparation of Images for Analyses

1. Obtain murine or human echocardiographic B-mode images in the parasternal long-axis view. Adjust time-gain compensation settings and placement of the transmit focus to optimize visualization of the LV and other cardiac structures in the parasternal view, per usual practice. Ensure all images are saved in DICOM file format. Standardized image views place the inferolateral left ventricular wall at the base of the frame. Frames must display the entirety of the left ventricular myocardium and pericardium. Resolution must be high enough to demarcate the pericardial border, myocardial wall, and endocardial border of the left....

Results

Signal intensity analysis is performed in 4 main steps (Figure 1), including: 1) image selection and formatting, 2) sampling ROI and reference areas, 3) algorithm application, and 4) processing final values to yield myocardial-to-pericardial intensity ratios. Selection and size of the ROI is standardized to limit interuser as well as intrauser variability (Figure 2). The positioning of each ROI is also standardized with respect to each subject's anatomical structures to limit intersubjec.......

Discussion

We describe the protocol for an image analysis algorithm that quantifies sonographic signal intensity distribution and, in turn, offers a surrogate measure of myocardial microstructure. Standardized features of the protocol, including selection, sizing, and positioning of the ROI and reference region, serve to minimize user- and subject-based variability. We demonstrate that when applied to end-diastolic single-frame echocardiographic images, the algorithm can appropriately distinguish between normal myocardium versus my.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
ImageJ v 1.46	NIH (Bethesda, MD)		open access software
Power ShowCase	Trillium Technology (Ann Arbor, MI)		commercial software