Recommended Ultrasound Terminology
G
gain
The increase in signal power or signal amplitude produced by a system. For an amplifier, it is the ratio of the output voltage to the input voltage, usually expressed in decibels (dB).
gamma (display monitor)
Term that quantifies the relationship between the monitor luminance (brightness) and applied voltage. The relationship is of the form luminance = C x voltagegamma, where C is a constant.
gamma (photographic)
The slope of the straight part of the film density versus the exposure characteristic curve. The higher the gamma, the higher the contrast.
gantry
A mechanical support device for mounting an object, such as a transducer probe, and providing a means for motion of the object.
gas body
A stabilized collection of gas within a liquid or solid. A bubble is a gas body that is completely (or nearly completely) surrounded by liquid.
gas body activation
A form of acoustic cavitation nucleated by stable gas bodies of a size large enough to be visible with an optical microscope.
gas bubble
A volume of gas completely surrounded by a liquid. Bubbles tend to be spherical in shape.
gas vesicle
A class of genetically encodable air-filled protein nanostructures that provide micrometer-scale caveating bubbles as an imaging contrast.
gate
A device that can be switched electronically to control the passage of a signal. A gate may select a part of the signal based on the time interval during which the signal was received. For example, a range gate may be designed to accept signals only from a specific range, or an electrocardiographically triggered gate may pass signals from a specified portion of the cardiac cycle.
geometric area of an ultrasonic transducer
The area defined by the ultrasonic transducer dimensions or ultrasonic transducer element group dimensions. The unit is square meter (m2).
geometric beam boundary
The surface containing straight lines passing through the geometric focus and all points around the periphery of the transducer aperture (see Figure 5).
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geometric cylindrical focus
A geometric cylindrical focus is an axis centered on equidistant radial acoustic delay paths from a cylindrical (or its quadratic approximation) transducer or reflector radiating surface.
geometric focal length
The distance along the beam axis from the center of the face of the transducer or lens to the geometric focal point. In the case of an array, there may be a separate focal length for a mechanical lens and another for electronic focusing (see Figures 3 and 5).
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geometric focal point
The point of intersection of the greatest number of rays from the active transmitting element(s) of the transducer. Each ray is perpendicular to a small element of a given surface area and may be refracted by lenses and/or reflected by mirrors in the sound path.
geometric line focus
An axis of symmetry for acoustic delay paths from a transducer or reflector radiating surface with cylindrical symmetry (see Figure 8).
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geometric radius of a hydrophone active element
The radius derived from the equivalent circular area determined by the dimensions of the active element of a hydrophone. The unit is meter (m).
geometric spherical focus
The focal point that has equidistant total delay paths (acoustic and/or electronic) from a spherical transducer, lens, or reflector radiating surface. Sometimes called point focus (see Figure 8).
GHz
Abbreviation for gigahertz, equal to 1 billion hertz; 1 GHz = 109 Hz.
globular enhancement
A discontinuous ring of contrast-enhanced peripheral globules (puddles or nodules) predominantly in the arterial or portal phase. These globules usually enlarge over time, with centripetal enhancement of the lesion. This is a common feature of liver hemangioma.
Golay code
An error-correcting code in which words of up to 12 bits are encoded into 23 or 24 bits according to specific rules.
graphical user interface
An interface that employs graphical elements (such as dialog boxes, icons, menus, and scroll bars) in addition to text characters to let users interact with the device (ultrasound system or computer).
grating lobes
Beams of sound radiating in directions different from the primary beam resulting from the multielement structure of transducer arrays. The grating lobes may be responsible for introducing artifactual echoes into an ultrasound image. A grating lobe is an approximate replica of the main lobe at another angle, and its direction is determined by the interelement spacing and the wavelength (see Figure 10).
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Related term: Contrast with side lobes
gray scale
A display technique in which echo amplitude or intensity information is recorded as variations in brightness (shades of gray).
grayscale compression
A form of image processing that compresses the dynamic range of selected gray levels in the image.
Related term: Contrast with grayscale stretching
grayscale map
A table or relationship between the echo signal amplitude and the displayed brightness (shade of gray) on a sonogram. The grayscale map is used in postprocessing to relate values of the echo signal, Doppler shift, or other ultrasound data residing in memory to signals that control grayscale or color values in the display.
grayscale stretching
A form of image processing that extends the dynamic range of selected gray levels in the image. It is effective when an original image does not use the entire range of gray levels.
Related term: Contrast with grayscale compression
group velocity
Velocity of the envelope of a group of waves traveling in the same direction having different frequencies and phase velocities. Group velocity is ordinarily the velocity of propagation of the energy associated with an ultrasonic pulse.
Related term: Contrast with phase velocity
