Parallel multi-focusing using plane wave decomposition

Misaridis, T; Munk, P; Jensen, JA

dc.contributor.author	Misaridis, T	en
dc.contributor.author	Munk, P	en
dc.contributor.author	Jensen, JA	en
dc.date.accessioned	2014-03-01T02:42:19Z
dc.date.available	2014-03-01T02:42:19Z
dc.date.issued	2003	en
dc.identifier.issn	10510117	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/30934
dc.subject	3d imaging	en
dc.subject	Back Propagation	en
dc.subject	Evanescent Wave	en
dc.subject	Frequency Modulated	en
dc.subject	Numerical Solution	en
dc.subject	Phased Array	en
dc.subject	Plane Waves	en
dc.subject	Spectrum	en
dc.subject	Real Time	en
dc.subject	Single Carrier	en
dc.subject	Time Varying	en
dc.subject.other	Acoustic emissions	en
dc.subject.other	Acoustic wave propagation	en
dc.subject.other	Algorithms	en
dc.subject.other	Antenna phased arrays	en
dc.subject.other	Degrees of freedom (mechanics)	en
dc.subject.other	Focusing	en
dc.subject.other	Fourier transforms	en
dc.subject.other	Signal interference	en
dc.subject.other	Signal to noise ratio	en
dc.subject.other	Synthetic apertures	en
dc.subject.other	Optimal transmission schemes	en
dc.subject.other	Plane wave decomposition	en
dc.subject.other	Sensitivity functions	en
dc.subject.other	Single-carrier pulses	en
dc.subject.other	Ultrasonic imaging	en
dc.title	Parallel multi-focusing using plane wave decomposition	en
heal.type	conferenceItem	en
heal.identifier.primary	10.1109/ULTSYM.2003.1293206	en
heal.identifier.secondary	http://dx.doi.org/10.1109/ULTSYM.2003.1293206	en
heal.publicationDate	2003	en
heal.abstract	In conventional phased-array imaging, identical short single-carrier pulses are emitted from the entire aperture, and focusing is done in one direction at a time by applying simple geometric delays. This is a sequential and not optimal transmission scheme, which limits the frame rate and makes 3-D imaging in real-time impossible. By using a transmit matrix with frequency and apodization variations across the aperture, it is possible to focus in several directions simultaneously (5 or more), significantly increasing the frame rate to 170 frames/s or more. The algorithm used for the determination of the transmitted pulses is based on the directivity spectrum method, a generalization of the angular spectrum method, containing no evanescent waves. The underlying theory is based on the Fourier slice theorem, and field reconstruction from projections. First a set of desired 2-D sensitivity functions is specified, for multi-focusing in a number of directions. The field along these directions is decomposed to a sufficiently large (for accurate specification) number of plane waves, which are then back-propagated to all transducer elements. The contributions of all plane waves result in one time function per element. The numerical solution is presented and discussed. It contains pulses with a variation in central frequency, and time-varying apodization across the aperture (dynamic apodization). The RMS difference between the transmitted field using the calculated pulse excitation and a designed multi-focused field in 3 focal directions at a depth corresponding to an F-number of 1.5 is 4%, and it increases with depth. These results demonstrate the close agreement between specified and actual acoustic fields. It is, then, shown how specification of long frequency-modulated desired field functions can yield more strongly focused fields or higher number of multi-focused beams, with the additional advantage of higher SNR.	en
heal.journalName	Proceedings of the IEEE Ultrasonics Symposium	en
dc.identifier.doi	10.1109/ULTSYM.2003.1293206	en
dc.identifier.volume	2	en
dc.identifier.spage	1565	en
dc.identifier.epage	1568	en