Education / Common Ultrasound Terms
Acoustic: Containing, producing, arising from, actuated by, related to or associated with sound.
Acoustic shadow: Refers to a reduced echo from regions lying beyond an attenuating object. This artifact can occur from such things as a foreign body or from thicker or calloused skin. It is important to distinguish between a shadow and a true area of low reflectivity.
Anechoic: Appearing echo-free. Pure fluid will be anechoic.
Anisotropic: Refers to phenomenon where an area or structure will have varying acoustic properties according to the direction in which they are imaged. Tendon will appear hypoechoic when the ultrasound beam is not at right angles to the tendon fibers.
Artifact: An echo pattern that does not reflect the true acoustic properties of an area. Shadowing is an example of an artifact.
Attenuation: The decrease in amplitude or intensity as sound travels through a material. This is due to absorption, scattering or beam divergence.
B-Mode: The ultrasound system where an image is displayed by the modulation of the brightness of the return echoes. The EPISCAN is a B-Mode scanner.
Bandwidth:The range of frequencies a device is capable of sending or receiving.
Broadband Signal: Signal containing a wide range of frequencies.
Center Frequency: The average frequency over the bandwidth of a signal.
Color Palette: A display that has assigned colors to the various brightness of a gray scale image. The advantage is to give the human eye the ability to distinguish subtle variations of a gray scale image. The EPISCAN has various color palettes.
Coupling Agent: A medium used to enhance transmission of sound from the transducer to the body.
Depth: The distance from the point of entry into the patient to the area of interest.
Digital: A signal whose value exists as discrete numerical values stored in digital circuits or memory rather than being composed of variable voltage, acoustic field or electro-magnetic field.
Echo: Sound wave that has been reflected and arrives with a magnitude and time interval that is distinguishable as a repetition of it.
Echogenic: A structure or medium that is capable of producing echoes.
Frequency: The number of cycles of a periodic process per unit of time. This is expressed in hertz (Hz) or multiples as megahertz (MHz). 1Hz = 1 cycle per second. The EPISCAN utilizes a 20 MHz transducer.
Gain: The variable gain control provides overall amplification of the received signal shown in the status bar as a percentage of the system's maximum gain. You can control the variable gain by pressing the left and right cursor keys on the keyboard - the left cursor decreases the gain, and the right cursor increases it. The gain can also be changed using the Gain RF slider on the scan control bar. You will find that the amount of gain you need to get a good image will vary depending on the feature you are examining and its depth in the tissue - generally, the amount of gain you need will increase with depth. Try to avoid over-amplification, as this will cause black areas and white areas in the image that obscure the features you are trying to scan. Similarly, you should try to avoid under-amplification as the image will not use the full range of colors available and so will be poorly defined. A good gain setting for the start of an investigation is 50%, and in most circumstances you should not have to use a gain outside the range 10%-70%. If you find that you are consistently using higher gain settings, you should contact your distributor as this may be indicative of a problem. The variable gain setting only affects the amplification of the received signal, and does not change the ultrasound energy emission.
Gray Scale: A display in which the echo information is displayed in variations of brightness or shades of gray.
Hyperehoic: High reflective pattern. An area where the echoes are brighter than normal or brighter than surrounding tissue.
Hypoechoic: Low reflective pattern. An area where the echoes are not as bright as normal or less bright than surrounding tissue. Fluid or edema will appear hypoechoic.
Linear Array: A transducer that has elements arranged in a straight line. The elements are configured to control characteristics of an acoustic beam along the array length.
Noise: Unwanted and usually random signals
Position: he scan position sets the distance of the top of the scan image from the transducer in millimeters. To change the scan position, use the - (minus) key on the numeric keypad to decrease it, and the + (plus) to increase it. The position can also be changed using the Skin Pos slider on the scan control bar. You should be sure to keep the scan position higher than 14 mm, otherwise your scan image will be of the water in the cone. You should also aim to keep the scan position below about 25 mm as otherwise the image may be affected by the next signal to be transmitted by the transducer. Since the distance between the transducer and the membrane is 16 mm, this is the ideal position to use in normal circumstances. You should also note that variations in the thickness of the coupling gel will affect the starting position of the scan image.
Reflection: The change of amplitude and direction of a wave when it encounters a large interface with another medium of a different acoustic property.
Resolution: The ability to display distinguishable images of two closely positioned objects. It is expressed as the minimal distance between two objects that can be distinguished. The EPISCANS resolution is to 65 microns.
Scan: The movement of an acoustic beam to produce an image.
Scanner: A device that moves an acoustic beam to produce an image. It applies to the whole ultrasound system.
Scatter: The generation of secondary waves in response to the insonification by a primary wave, by regions in the target that have heterogeneities in density and/or compressibility.
Shadowing: Reduction in echoes beyond a strongly reflecting or absorbing structure.
Sonogram: The pictorial record of an ultrasound examination.
Sonography: A imaging method utilizing sound waves producing an image or usable data.
Transducer: A device capable of converting energy from one form to another. In ultrasound it refers to the ability to convert electrical energy to sound waves in the ultrasound spectrum and conversely converting sound waves back to electrical energy.
TGC Ramp: As the ultrasound signal travels through soft tissue it becomes attenuated, so those signals that have traveled furthest (i.e. reflected from deeper tissue) are weaker than those that are reflected from surface tissue. The TGC amplifier allows you to compensate for this by applying a ramped gain to the received signal, starting at 0 dB for the earliest signals and going up to a maximum of +30 dB for later reflected signals.(i.e. depth of reflection) ideal signal after TGC Figure 23: combined effect of variable gain and TGC You can adjust the TGC from the keyboard by holding down the control key on the computer's keyboard (marked Ctrl) and pressing the left or right cursor keys. The left cursor key reduces the TGC and the right cursor key increases it. The TGC level is shown in the status bar as a percentage of the system's maximum available gain. The TGC can also be changed using the TGC Ramp slider on the scan control bar.
TGC Start: This corresponds to the distance of the transducer from the membrane, and is factory set to 0% (which represents 16 mm). Under normal circumstances it should not be necessary for you to change this setting.
Ultrasound: Acoustic oscillation whose frequency is above audible sound