Echocardiography essentials: Physics and instrumentation
- Warren J Manning, MD
Warren J Manning, MD
- Section Editor — Noninvasive Cardiac Imaging and Stress Testing
- Professor of Medicine and Radiology
- Harvard Medical School
Echocardiography is the primary noninvasive imaging modality for quantitative and qualitative evaluation of cardiac anatomy, physiology, and function [1,2]. Two-dimensional (2D) echocardiography provides tomographic or "thin-slice" imaging. Comprehensive echocardiographic examination typically involves imaging the heart from multiple "viewing" orientations as well as with multiple imaging techniques (ie, 2D, Doppler). An understanding of the fundamental principles of cardiac ultrasound is necessary for the proper acquisition and interpretation of echocardiographic data.
The basic physics principles that apply to echocardiography and its instrumentation are reviewed here. The normal anatomic views and protocols for echocardiography, as well as its clinical uses, are presented separately. (See "Transthoracic echocardiography: Normal cardiac anatomy and tomographic views".)
Sound waves are mechanical vibrations that can be described in terms of frequency or Hertz (Hz), ie, the number of repetitions or cycles per second. Other characteristics include wavelength, the distance between excitations, measured in mm; and the amplitude of excitation, measured in decibels (dB). A 6-dB change results in a doubling (or halving) of the signal amplitude.
Medical ultrasound imaging typically uses sound waves at frequencies of 1,000,000 to 20,000,000 Hz (1.0 to 20 MHz). In contrast, the human auditory spectrum comprises frequencies between 20 and 20,000 Hz.
Frequency and wavelength are mathematically related to the velocity of the ultrasound beam within the tissue (approximately 1,540,000 mm/sec for human tissue) as indicated by the following equations:
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- ULTRASOUND WAVES
- INTERACTION OF ULTRASOUND WAVES WITH TISSUES
- ULTRASOUND TRANSDUCERS
- Second harmonic imaging
- IMAGING MODALITIES
- Two-dimensional (2D) imaging
- BIOEFFECTS AND SAFETY
- Thermal effects
- SUMMARY AND RECOMMENDATIONS