Quatech Audio/Video Capture USB 2.0 Specifikace stáhnout pdf (Strana 372)

15-6 z.one ultra and z.one ultra sp OPERATOR MANUAL

Enhancement is an increased relative amplitude of echoes caused by an

intervening structure of low attenuation.

Focal enhancement, also known as focal banding, is the increased intensity in

the focal region that appears as a brightening of the echoes on the display.

Mirror imaging artifact is most commonly seen around the diaphragm; this

artifact results from sound reflecting off another reflector and back.

Mirroring is the appearance of artifacts on a spectral display when there is

improper separation of forward and reverse signal processing channels.

Consequently, strong signals from one channel mirror into the other.

Multi-path positioning and refraction artifacts describe the situation in which

the paths to and from a reflector are different. The longer the sound takes

traveling to or from a reflector, the greater the axial error in reflector positioning

(increased range). Refraction and multi-path positioning errors are normally

relatively small and contribute to general degradation of the image rather than to

gross errors in object location.

Propagation speed errors occur when the assumed value for propagation speed

by the ultrasound system is incorrect. If the actual speed is greater than that

assumed, the calculated distance to a reflector is too small, and the reflector will

be displayed too far from the transducer. Speed error can cause a structure to be

displayed with incorrect size and shape.

Range ambiguity can occur when reflections are received after the next pulse is

transmitted. In ultrasound imaging, it is assumed that for each pulse produced, all

reflections are received before the next pulse is sent out. The ultrasound system

calculates the distance to a reflector from the echo arrival time assuming that all

echoes were generated by the last emitted pulse. The maximum depth to be

imaged unambiguously by the system determines its maximum pulse repetition

frequency.

Reverberation is the continuing reception of a particular signal because of

reverberation rather than reflection from a particular acoustic interface. This

phenomenon is analogous to the effect created by mirrors positioned on opposite

walls when an object, a head for instance, is placed between the mirrors. The

image of the head is reflected back and forth infinitely between the two mirrors,

creating the optical illusion of multiple heads. Reverberations are easily

identifiable, because they are equally spaced on the display screen.

Scattering is the diffuse, low-amplitude sound waves that occur when acoustic

energy reflects off tissue interfaces smaller than a wavelength. In diagnostic

ultrasound, Doppler signals come primarily from acoustic energy back-scattered

from red blood cells.

Shadowing is the reduction in echo amplitude from reflectors that lie behind a

strongly reflecting or attenuating structure. This phenomenon occurs when

scanning a lesion or structure with an attenuation rate higher than that of the

surrounding tissue. The lesion causes a decrease in beam intensity, which results

in decreased echo signals from the structures beyond the lesion. Consequently, a

dark cloud behind the lesion image forms on the screen. This cloud, or shadow, is

useful as a diagnostic clue.

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Quatech Audio/Video Capture USB 2.0 Specifikace Strana 372

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