Echocardiographic-Based Assessment of Myocardial Fiber Structure in Individual, Excised Hearts

Abstract

The objective of this study was to assess the feasibility of using echocardiographic imaging as an approach for determining the myocardial fiber structure of intact, individual hearts. Seven formalin-fixed, ex vivo sheep hearts were imaged using a commercially available echocardiographic imaging system, and the intrinsic fiber structure for the reconstructed short-axis cross section was determined for a specific distance from the apex of each heart. Diffusion tensor magnetic resonance (DT-MR) images of each heart were acquired and fiber maps were created for comparison with the fiber structure obtained from the corresponding reconstructed echocardiographic images. These two methods of obtaining the fiber structure showed relatively good agreement, suggesting that measurements of fiber orientation for individual hearts can be derived from echocardiographic images. Further development of this method may provide a clinically useful approach for mapping the fiber orientation in individual patients over the heart cycle.

Toward 3-D Echocardiographic Determination of Regional Myofiber Structure

“…(Milne et al 2012) That study, limited to 2D short-axis reconstructions, found that echocardiographic-based measurements of fiber structure in a specific transverse plane qualitatively agreed with the corresponding estimates obtained using diffusion tensor magnetic resonance imaging (MRI) methods. The objective of the current study is to extend the previous work on single planes of the heart by demonstrating the feasibility of creating quantitative myofiber multiplane structure maps over the entire volume of intact hearts based on 3D echocardiographic information.…”

“…(Milne et al 2012) In brief, after fixation preparation was completed, each heart was placed base-down in a cylindrical water-filled tank in preparation for collecting backscatter data. A series of apical echocardiographic images, in 5-degree rotational increments about the apex of each heart, were obtained using a General Electric Vivid 7 clinical imaging system (GE Healthcare, Wauwatosa, WI, USA) at a nominal center frequency of 5.0 MHz in fundamental imaging mode (Figure 1a).…”

“…This determination was carried out by making use of previously acquired backscatter data relating the magnitude of the scattered signal to the orientation of the acoustic beam relative to the fiber direction. (Milne et al 2012) In this previous study, cylindrical myocardial cores from an additional set of fixed sheep hearts were insonified from different angles using the same clinical echocardiographic imaging system configured in the same fashion as described above. The resulting grayscale images and the relative core/ultrasonic probe orientation data were analyzed to relate signal strength to fiber direction relative to the interrogating acoustic beam (Figure 1c).…”

Imaging technologies for cardiac fiber and heart failure: a review

“…Three-dimensional imaging techniques have the capability to improve heart disease diagnosis and outcomes. Among the cardiac imaging systems are also ultrasound [56–58], chest X-ray [59, 60], cardiac catheterization [61, 62], magnetic resonance imaging (MRI) [52, 63, 64], computerized tomography (CT) [65, 66], cardiac positron emission tomography (PET) [67–69], cardiac single-photon emission computed tomography (SPECT) [70], and intravascular ultrasound [71, 72]. Ultrasound allows for non-invasive visualization of blood flow through the heart using Doppler [73].…”

“…Some animal models that have been used with these imaging protocols for HF studies are rat [76, 77], canine [2, 10, 50, 78, 79], rabbit [12, 80], pig [81], sheep [56, 80, 82], and mice [14, 83]. Figure 3 shows representative DT-MRI images of hearts from a mouse, a rabbit, and a sheep.…”