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BME 240

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The Trigger of IVUS

(1)  Acoustic Dead zone

    The acoustic dead zone is caused by the transient effect of amplifier saturation at the time of short burst of acoustic energy.  This short period of time no reflected acoustic waves (echoes) can be detected.  The sizes of the dead zones are different from designs.  The following figure is a schematic of dead zones for three different types of intravascular echo catheters.  The dead zone of arrayed piezoelectric transducer is the largest and is bigger than catheter.  The dead zones of mechanical systems are equal and smaller than catheter, which is superior than arrayed piezoelectric transducer.

(2)  Resolution

    The resolution of IVUS is determined by the size of the acoustic beam, which is determined by the wavelength of the acoustic wave.  Because the nature of attenuation of acoustic wave, the frequency range of acoustic wave is limited up to 40 MHz. This determined the wavelength of the acoustic wave and also the pulse length.  The pulse length determined the axial resolution along the radial line perpendicular to the catheter.  As frequency increases the wavelength of acoustic wave decreased, and thus the pulse length decrease and the axial resolution is increased.

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(3)  Quantification

    Underestimation and overestimation of diseases located at tortuous vessels are possible due to the inability to maintain a constant catheter.  The calcify and fibrous lesions could cause echo drop outs because of the acoustic beam cannot penetrate through calcium layers.

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