New developments in paediatric cardiac functional ultrasound imaging

\u3cp\u3eUltrasound imaging can be used to estimate the morphology as well as the motion and deformation of tissues. If the interrogated tissue is actively deforming, this deformation is directly related to its function and quantification of this deformation is normally referred as 'strain imaging'. Tissue can also be deformed by applying an internal or external force and the resulting, induced deformation is a function of the mechanical tissue characteristics. In combination with the load applied, these strain maps can be used to estimate or reconstruct the mechanical properties of tissue. This technique was named 'elastography' by Ophir et al. in 1991. Elastography can be used for atherosclerotic plaque characterisation, while the contractility of the heart or skeletal muscles can be assessed with strain imaging. Rather than using the conventional video format (DICOM) image information, radio frequency (RF)-based ultrasound methods enable estimation of the deformation at higher resolution and with higher precision than commercial methods using Doppler (tissue Doppler imaging) or video image data (2D speckle tracking methods). However, the improvement in accuracy is mainly achieved when measuring strain along the ultrasound beam direction, so it has to be considered a 1D technique. Recently, this method has been extended to multiple directions and precision further improved by using spatial compounding of data acquired at multiple beam steered angles. Using similar techniques, the blood velocity and flow can be determined. RF-based techniques are also beneficial for automated segmentation of the ventricular cavities. In this paper, new developments in different techniques of quantifying cardiac function by strain imaging, automated segmentation, and methods of performing blood flow imaging are reviewed and their application in paediatric cardiology is discussed.\u3c/p\u3

Cardiac motion estimation using ultrafast ultrasound imaging tested in a finite element model of cardiac mechanics

Recent developments in ultrafast ultrasound imaging allow accurate assessment of 3D cardiac deformation in cardiac phases with high deformation rates. This paper investigates the performance of a multiple spherical wave (SW) ultrasound transmission scheme in combination with a motion estimation algorithm for cardiac deformation assessment at high frame rates. Ultrasound element data of a realistically deforming 3D cardiac finite element model were simulated for a phased array transducer, transmitting five SWs (PRF 2500 Hz). After delay-and-sum beamforming, coherent compounding of multiple SW transmissions was performed to generate radiofrequency data (frame rate 500 Hz). Axial and lateral displacements were determined using a normalized cross-correlation-based technique. Good agreement was obtained between estimated and ground truth displacements derived from the model over the cardiac cycle. This study indicates that high frame rate displacement estimation using multiple SWs is feasible and serves as an important step towards high frame rate 3D cardiac deformation imaging