Chapter 3 Doppler echocardiography Jaroslaw D. Kasprzak, Anita Sadeghpour, and Ruxandra Jurcut Contents Principles of Doppler echocardiography 27 Spectral Doppler assessment of the heart 29 Assessing volumetric flow 29 Assessing stenotic lesions 30 Assessing regurgitant valves 31 Other abnormal flow patterns 32 Tissue Doppler echocardiography 32 Clinical applications of tissue Doppler 33 Doppler artefacts 34 Conclusion 34 References 34 Principles of Doppler echocardiography In 1842, Christian Doppler discovered the phenomenon of decrease or increase in sound wave frequency when it is reflected by a moving object. This ‘Doppler effect’ has become the cornerstone of in vivo measurements of flow or tissue motion velocities. Doppler frequency shift is associated with the velocity of the moving target (v), transmitted frequency (f 0 ), speed of sound in blood (c = 1540 m/s), and angle between the interrogated beam and the blood flow (cos θ). As θ increases, maximum velocity is progressively underestimated; and beyond 20°, the underestimation becomes significant. The blood flow velocity is calculated based on the following equation: v= Δ f × c 2f × cos 0 θ Spectral analysis is used to determine the Doppler shift. Through a fast Fourier transform analysis, the spectral Doppler displays the entire range of velocities against time. Thus, spectral Doppler trace yields information regarding: ◆ flow velocity in time as a graph with moving time base ◆ direction of the flow (by convention a Doppler trace above the baseline means that the blood flow moves towards the transducer and under the baseline means that the blood flow goes away from the transducer) ◆ intensity of the flow signal—intensity of spectrum is related to the number of reflectors (red cells engaged in flow), which corresponds with flow volume ◆ laminar or turbulent properties—laminar flow is characterized by ‘empty’ flow velocities contour (% Fig. 3.1). There are different forms of Doppler echocardiography used for assessing cardiac flow in practical use, including the following: 1. continuous wave Doppler (CWD) 2. pulsed wave Doppler (PWD) 3. multigate pulsed wave Doppler—high pulse repetition frequency (HPRF) mode 4. colour Doppler flow mapping (colour Doppler, CFM). 5. colour Doppler M-mode 6. three-dimensional (3D) colour Doppler flow mapping.
Chapter 4 Deformation echocardiography Matteo Cameli, Partho Sengupta, and Thor Edvardsen Contents Principles of deformation imaging 35 Modalities 36 Windows and views 37 Conclusion 40 References 41 Principles of deformation imaging Echocardiographic strain imaging, also known as myocardial deformation imaging, is a technological advancement that has been developed as a means to objectively quantify regional myocardial function [1–3]. It was first introduced as a post-processing feature of Doppler myocardial imaging (DMI) with velocity data converted to strain and strain rate. A more recent feasible and reproducible method is speckle tracking echocardiography (STE) , which is based on tracking of characteristic speckle patterns created by interference of ultrasound beams in the myocardium [5,6]. The concept of strain is complex. For a one-dimensional (1D) object the only possible deformation is lengthening or shortening and the linear strain (amount of deformation) can be defined by the formula ε = (L − L0)/L0, where ε is strain, L0 = baseline length, and L = instantaneous length at the time of measurement. The instantaneous deformation is thus expressed relative to the initial length (Lagrangian strain). The amount of deformation (positive or negative strain) is dimensionless and expressed in per cent. Negative strain values describe shortening and positive values describe thickening of a given myocardial segment related to the original length. Strain rate is the first derivative of strain, or the speed at which deformation occurs. The unit of strain rate is s −1 and the local rate of deformation or strain per time unit equals velocity difference per unit length. Current echocardiographic equipment allows 1D measurements based on tissue Doppler imaging (TDI) and two-dimensional (2D) strain measurements based on STE. Myocardial regional mechanics assessed by echocardiography have been described by four principal types of strain or deformation: longitudinal, radial, circumferential, and circumferential–longitudinal shear occurring along the long axis of the left ventricle (LV) which results in rotational deformation (% Fig. 4.1). Strain and strain rate are emerging applications of echocardiography and have initially been used in the assessment of systolic and diastolic function of the LV [7,8] and more recently they have been applied to assess right ventricular [9,10], left atrial [11–14], and right atrial [15,16] function.