echo

1. A reverberating sound sometimes heard during auscultation of the chest. 2. In ultrasonography, the acoustic signal received from scattering or reflecting structures or the corresponding pattern of light on a CRT or ultrasonogram. 3. In magnetic resonance imaging, the signal detected following an inverting pulse. [G.]

- atrial e. electrical reactivation of the atrium by a retrograde impulse returning from the A-V node while the antegrade impulse continues to the ventricle; characterized electrocardiographically, by a pair of P waves enclosing a QRS complex, the second P wave being opposite in polarity (usually inverted in lead II), indicating that it is the reverse (the retrograde pathway) of the pathway of the first P wave (the antegrade pathway).

- navigator e. a method of respiratory gating q.v., used in magnetic resonance imaging to limit respiratory motion artifact; a signal is derived from the top of the diaphragm, and image data are collected only when it is in a selected range.

- nodus sinuatrialis e., NS e. a postectopic sinus beat occurring earlier than would be expected from the preceding sinus node discharge interval; i.e., the interval following a premature beat of supraventricular origin is less than the ordinary cycle length between sinus beats, whereas ordinarily the interval would be expected to exceed cycle length.

- e. planar a method of magnetic resonance imaging that allows rapid image acquisition during free induction decay, using technically demanding rapidly oscillating radiofrequency gradients.

- spin e. a commonly used technique to recover T1 and T2 relaxation signals in magnetic resonance imaging, by using a 180° inverting pulse in the pulse sequence to compensate for loss of transverse magnetization caused by magnetic field inhomogeneities.

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echocardiography; enteric cytopathic human orphan [virus]; Etoposide, cyclophosphamide, Adriamycin, and vincristine

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echo abbr echocardiogram; echocardiography

echo 'ek-(.)ō n, pl ech·oes also echos

1) the repetition of a sound that is caused by reflection of sound waves

2) the sound that is due to reflection of sound waves

echo vb, ech·oed; echo·ing 'ek-(.)ō-iŋ, 'ek-ə-wiŋ

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(ekґo) [Gr. ēchō a returned sound] 1. repetition of a sound as a result of reverberation of sound waves. 2. the reflection of ultrasonic, radio, or radar waves. sometimes used in reference to any kind of repetition.