Lecture 1 Notes

For example if one desires to improve the lateral

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Unformatted text preview: tations / Bandwidth Axial resolution –  Allow electronic steering of the beam Fig. 3. The compromises for the sensitivity, tissue penetration, and spatial resolution that are needed to design an efficient ultrasoundto optimize the lateral resolution   focussing. f-number = f/2a FWHM = 1.41Af-number Fig. 1. The general components and beam properties of focused piezoelectric circular transducers. L device. For example, if one desires to improve the lateral resolution an Ultrasound Transducer by means of a low f-number aperture (i.e., f-number < 4), the From: Hunt et al, IEEE Trans BME, of field is reduced, considerably degrading the resolution depth 1983 ObJectives_ in regions away from the focal plane. Thus, a means of moving - Region or organ - Penetr ntion the focal zone over the imaging depth is required. A descrip- Desired resolution tion of the depth-of-field problem and a detailed analysis of - Speed of dhta collection various transducers used to overcome this effect are presented in Section IV. Other imoging devices Different approoches Another difficult decision is the selection of pulse frequency Genesis of Pulse-echo device te-cSingle element -Multiple element -Trsnsmission -Scattering _ Compromises ~~~~~~~~Sensitivity - Sptial rtiesolution - Dynomic ro nge ^ Transducer materiol Ceramic-PZT for sensitivity ~~~~PVDF for wide bond- pass and flexibility Others ? __ Transducer fabrication Bocking -1/4 X layers Computer modelling -Electro-mechonical characteristics D2/λ Load (Target)   ZT Matching Layer   Flat (Piston) Plate Transducer ZL To provide acoustic coupling between the crystal and patient skin and to protect surface of the crystal Z of PZT...
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