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created 6 years ago by Annabelle
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1

1 1/2 Dimensional Array

a linear, curvilinear, or phased array in which some elevational focus and beam forming is done electronically. In conventional arrays the elevational focusing is done only with a lens. By providing a limited degree of electronic focusing elevationally, the slice thickness can be made smaller over an extended range. The term 1 1/2 D refers to the fact that whereas an array usually has over 128 elements laterally, it may have only 5 or so elements in the elevational plane.

2

3-dB rule

a way to remember that when the output of a scanner increases (decreases) by 3 decibels, the power and the intensity doubles (halves). If the power is 20 mW and the sonographer reduces it by 9 dB (three 3-dB increments) repeated application of the 3-dB rule tells you the the reduced power is
20 mW x 1/2 x 1/2 x 1/2 = 2.5 mW

3

absorption

conversion of acoustical energy into heat. Absorption is on mechanism leading to ultrasound beam attenuation in tissue

4

acoustical impedance

the speed of sound in a medium multiplied by its density. Part of the energy of an ultrasound beam is reflected at interfaces between materials that have unequal acoustical impedances

5

acoustical power

quantity describing the rate at which acoustical energy is emitted by the ultrasound transducer of an ultrasound instrument.

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acoustical pressure amplitude

the maximum cycle-to-cycle increase (or decrease) in the pressure due to a sound wave, relative to the background pressure

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acoustical wave

sound wave

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active aperture

the area of an array transducer that is actively transmitting or receiving; the active aperture is determined by whichever elements are transmitting of receiving

9

address

a unique number associated with each memory location in a computer of other digital device

10

aliasing

the production of artifactual, lower frequency components in a Doppler signal spectrum when the pulse repetition frequency of the Doppler instument is less than two times the maximum frequency of the Doppler sugnal.

11

A-mode display

amplitude mode display
method of displaying pulse-echo ultrasound signals in which a trace presents the instantaneous echo signal amplitude versus time after transmission of an acoustic pulse. SInce the time is proportional to reflecto distance, this trace also is a record of echo signal amplitude versus reflector distance

12

amplitude

maximum cyclical change in a quantity, such as the pressure in an ultrasound wave

13

amplitude reflection coeffient

the ratio of the reflected pressure amplitude (Pr) to the incident pressure amplitude (Pi) at an interface

14

analog-to-digital (A/D) converter

component or device that accepts analog signals, such as from a transducer of an amplifier, and converts these to a digital format for processing

15

annular array

a transducer array consisting of a number of ring-shaped piezoelectric elements arranged concentrically, along with a central disk. AN annular array can provide multiple transmit focal zones, dynamic receive focusing, and dynamic aperture. However, scanning must be done by mechanically sweeping the beam.

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aperture

another name for the active radiating or receiving surface of a transducer

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apodization

decreasing the relative excitation near the edges of the radiating surface of a transducer during transmission, or decreasing the relative sensitivity near the edge of the receiving surface of the transducer, in order to reduce side lobes.
Apodization is used in most array transducer assemblies.

18

artifact

in an ultrasound image or record any echo signal whose displayed position does not correspond to the actual position of the reflector in the body of whose displayed amplitude is not indicative of the reflecting or scattering properties of the region from which the echo originated

19

attenuation

reduction in the amplitude and intensity of a sound wave as it propagates through a medium. Attenuation of ultrasound waves in tissue is caused by absorption and by scattering and reflection

20

attenuation coeffient

the amount of attenuation per unit distance traveled by a wave; typical units are dB/cm

21

auto scanner

another name for a B-mode scanning instrument in which the sweep of the ultrasound beam is done, either mechanically or electronically, by the scan head. Real-time scanners are a type of auto scanner

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axial resolution

minimum reflector spacing along the axis of an ultrasound beam that results in separate, distinguishable echoes on the display. The shorter the pulse duration, the better the axial resolution, that is, the closer the reflectors can be and be distinguished

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base plus fog

a slight opacity of photographic of x-ray film, found upon developing without exposure

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beam

the directed ultrasound field produced by an ultrasound transducer

25

beam former

part of an imaging instrument that provides the pulse-delay sequences for transmit focusing and for dynamic receive focusing. The beam former also controls the beam direction for electronically scanned array.

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binary number

a number consisting of a series of 0s and 1s to represent a quantity. Binary numbers are used in digital computers. They have 2 as a base, in contrast to the decimal number system which has 1 as its base.

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biplane imaging

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