See half-value layer.
The distance an ultrasound pulse must travel in one direction in a medium to reduce its power to one half of its original value. The half-value layer is a means for quantifying tissue attenuation
An ultrasound system that can be held in the hand. Some include the display. Those that do not include pocket ultrasound.
Related terms: pocket ultrasound, POCUS, POCKUS.
A permanent visual record stored on materials such as paper, radiographic film, or photographic film, as opposed to an image displayed on a video screen, stored on magnetic tape, or retained in a digital format such as in memory or on a disk.
See clipping.
A whole number multiple of the fundamental frequency of a periodic quantity. For example, the second harmonic of a l-MHz piezoelectric element is at 2 MHz. (Subharmonics also are possible, eg, at ½, ⅓, etc, of the fundamental frequency.)
Method of imaging in which ultrasound is transmitted at a fundamental frequency and is detected at harmonic frequencies. Harmonics are generated by the propagation medium or by nonlinear reflectors such as contrast microbubbles. The resulting harmonic is displayed as an image to improve the resolution for a given penetration.
Related term: nonlinear mode
An enclosure consisting of a relatively large volume and a straight tube having a small orifice. It will have a resonance frequency determined by the volume of the enclosure, length of the tube, area of the orifice, and speed of sound.
The standard unit of frequency, equal to 1 cycle/s. The abbreviation is Hz.
Refers to a property of a medium whose value is substantially different in different locations within the medium. Contrast with homogeneous and inhomogeneous.
An intense, highly focused ultrasonic beam designed to deliver large amounts of thermal energy to cause irreversible tissue changes. Typically used for knifeless ultrasonic surgery applications.
A lesion showing very rapid echo enhancement in the arterial phase.
A mathematical process used to calculate the quadrature component of a signal.
Related terms: analytic signal, envelope
Ultrasound-induced tissue disintegration through cavitation. A process by which repetitive high-pressure ultrasound pulses result in mechanical effects that completely disintegrate and liquefy tissues.
A 2-stage process of imaging. The object to be visualized is uniformly irradiated with ultrasound (or light), and the reflected or transmitted waves are sampled over a large area. The resulting image or hologram is generated by recording the sum of the reflected or transmitted waves and a reference wave or signal. This resulting image is an interference pattern where the contours are lines of constant phase. Although holograms contain 3-dimensional data, they are usually reconstructed in acoustics so that only 2 dimensions are displayed.
Refers to a property of a medium whose value is the same throughout the medium.
Related terms: Contrast with inhomogeneous, heterogeneous
Inhomogeneous enhancement with gross enhancing septa and with small or large unenhanced areas that are more than one half of the size of the lesion area (on 2-dimensional images). Found in liver abscesses. A particular type of inhomogeneous enhancement.
A law stating stress is proportional to strain, providing the strain is not too large. Hooke’s law may also be stated as the elongation of a body in tension is directly proportional to the stretching force, and the shortening of a body in compression is directly proportional to the compressing force.
Related term: force constant
Tube of varying cross section, larger at one end than the other, intended to achieve an acoustic impedance match and, possibly, to produce a directional effect.
The principle that states that any wave phenomenon can be synthesized by the addition of the contributory wavelets from the distribution of point sources properly selected in phase and amplitude to represent the physical situation.
A receiving transducer designed for underwater measurement of acoustic fields. The diameter of a hydrophone is usually smaller than the wavelength of ultrasound to be measured, and its bandwidth is large.
An adjective describing a region for which echoes are noticeably of a higher amplitude (brighter) than their usual ultrasonic appearance or of a higher amplitude than those from surrounding structures.
Lesion with relatively stronger echogenicity (enhancement) than the surrounding normal parenchyma.
A condition in which the body temperature rises above normal. In humans, the normal body temperature is approximately 37ºC. Often refers to the artificial heating of all or part of the body for therapeutic purposes (as to treat cancer).
An adjective describing a region for which echoes are noticeably of a lower amplitude (darker) than their usual ultrasonic appearance or of a lower amplitude than those from surrounding structures.
Lesion with relatively weaker echogenicity (enhancement) than the surrounding normal parenchyma.
An ultrasound examination, usually performed endovaginally, to evaluate the female pelvis during and after the instillation of fluid into the endometrial cavity.
Related term: sonohysterography (SHG)
Abbreviation for hertz, the unit of frequency. One hertz is 1 cycle/s.