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Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

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III ¢ __ Red;e'vane';ons-~ThicknessvariationsFIGURE 16-19. A: A single-element transducer produces the mainultrasound beam in "thickness mode" vibration; however, radialexpansion and contraction also occurs. B: Side-lobe energy is createdfrom the radial transducer vibration, which is directed away from themain beam. Echoes received from the side lobe energy are mappedinto the main beam, creating unwanted artifacts.duces a spectrum of acoustic wavelengths that reduces the emission of side lobeenergy. For multielement arrays, side lobe emission occurs in a <strong>for</strong>ward directionalong the main beam (Fig. 16-20). By keeping the individual transducer elementwidths small (less than half the wavelength) the side lobe emissions are reduced.Another method to minimize side lobes with array transducers is to reduce the~~~~LobesSideFIGURE 16-20. Side and grating lobes are off-axisenergy emissions produced by linear and phased arraytransducers. Side lobes are <strong>for</strong>ward directed; gratinglobes are emitted from the array surface at very largeangles.

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