Discover the EACVI Textbook of Echocardiography 2nd edition
SECTION 1 Basic instrumentation and modalities 1 General principles of echocardiography 3 Madalina Garbi, Jan D’hooge, and Evgeny Shkolnik 2 Transthoracic echocardiography/two-dimensional and M-mode echocardiography 15 Miguel Ángel García Fernández and José Juan Gómez de Diego 3 Doppler echocardiography 27 Jaroslaw D. Kasprzak, Anita Sadeghpour, and Ruxandra Jurcut 4 Deformation echocardiography 35 Matteo Cameli, Partho Sengupta, and Thor Edvardsen 5 Storage and report 42 Steven Droogmans, Alessandro Salustri, and Bernard Cosyns 6 Transoesophageal echocardiography 46 Frank A. Flachskampf, Mauro Pepi, and Silvia Gianstefani 7 Three-dimensional echocardiography 59 Luigi P. Badano, Roberto M. Lang, and Alexandra Goncalves 8 Contrast echocardiography 70 Asrar Ahmed, Leda Galiuto, Mark Monaghan, and Roxy Senior 9 Hand-held echocardiography 79 Denis Pellerin, Nuno Cardim, and Christian Prinz 10 Intracardiac and intravascular echocardiography 85 Gilbert Habib, Carlo di Mario, and Guy Van Camp 11 Stress echocardiography: introduction and pathophysiology 90 Rosa Sicari and Raluca Dulgheru 12 Stress echocardiography: methodology 92 Maria João Andrade and Albert Varga 13 Stress echocardiography: image acquisition and modalities 96 Rosa Sicari, Edyta Płońska-Gościniak, and Jorge Lowenstein 14 Stress echocardiography: diagnostic criteria and interpretation 99 Paolo Colonna, Monica Alcantara, and Katsu Tanaka 15 Stress echocardiography: diagnostic and prognostic values and specific clinical subsets 104 Luc A. Pierard and Lauro Cortigiani 16 Lung ultrasound 111 Luna Gargani and Marcelo-Haertel Miglioranza 17 Digital echocardiography laboratory 115 Reidar Bjørnerheim, Genevieve Derumeaux, and Andrzej Gackowski
Chapter 1 General principles of echocardiography Madalina Garbi, Jan D’hooge, and Evgeny Shkolnik Contents Principles of ultrasound 3 Physics of ultrasound 3 Reflection and transmission of ultrasound at interfaces 4 Transducers 5 Transducer construction and characteristics 5 Transducer types 5 Transducer selection 7 Ultrasound imaging principles 7 Imaging modes (advantages and limitations) 7 Signal processing 8 Harmonic imaging 8 Image storage 9 Image quality optimization 9 Artefacts and pitfalls of imaging 10 Biological effects of ultrasound and safety 11 Quality assurance and ultrasound instruments 14 Further reading 14 Principles of ultrasound Physics of ultrasound Ultrasound waves are sound waves with a higher than audible frequency. The audible frequency range is 20 hertz (Hz) to 20,000 Hz (20 kilohertz (kHz)). Cardiac imaging applications use an ultrasound frequency range of 1–45 megahertz (MHz) (% Table 1.1). The sound wave is a longitudinal compression wave, consisting of cyclic pressure variation which travels, inducing displacement of encountered media particles in the direction of wave propagation. The wavelength determines imaging resolution. In echocardiography, adequate resolution is obtained with wavelengths less than 1 mm. The characteristics of the ultrasound wave are illustrated in % Fig. 1.1. A shorter wavelength corresponds to a higher frequency, and vice versa. The wavelength (cycle length) multiplied by frequency (cycles per second) gives the ultrasound wave propagation speed, which is constant in a certain medium: Propagation speed (m/s) = wavelength (m) × frequency (HZ). The average propagation speed in soft tissues is 1540 m/s, higher in less compressible media (e.g. bone) and lower in more compressible media (e.g. air in the lungs). The average propagation speed is used by the ultrasound machine to calculate the distance of a structure and confine it to an appropriate location in the image formed. Ultrasound is a form of energy, travelling in a beam. The energy transferred in the unit of time defines the power, measured in milliwatts (mW). The power per unit of beam cross-sectional area represents the average intensity (mW/cm 2 ). Power and intensity are proportional with the square of the wave amplitude. The intensity increases with power increase or cross-sectional area decrease by focusing the ultrasound beam. The intensity varies across the beam, being highest in the centre and lower towards the edges. An estimate of peak intensity is given by the mechanical index (MI) calculated from the peak negative pressure (MPa) divided by the square root of transmitted frequency (MHz). Current echocardiography uses intermittent repetitive generation of ultrasound pulses consisting of a few cycles each. Continuous transmission is used only for continuous wave Doppler. Consequently, the ultrasound beam intensity varies with time, being zero in between pulses. The intensity varies also within each pulse, decreasing throughout the pulse length, as a result of damping.