High frame rate imaging with a small number of array elements

摘要

Recently, a high frame rate imaging method has been developed tonconstruct either 2-D or 3-D images (about 3750 frames or volumes/s at andepth of about 200 mm in biological soft tissues because only onentransmission is needed). The signal-to-noise ratio (SNR) is high usingnthis method because all array elements are used in transmission and thentransmit beams do not diverge. In addition, imaging hardware with thennew method can be greatly simplified. Theoretically, the element spacingn(distance between the centers of two neighboring elements) of an arraynshould be Λ/2, where Λ is the wavelength, to avoid gratingnlobes in imaging. This requires an array of a large number of elements,nespecially, for 3-D imaging in which a 2-D array is needed. In thisnpaper, we study quantitatively the relationship between the quality ofnimages constructed with the new method and the element spacing of arrayntransducers. In the study, two linear arrays were used. One has annaperture of 18.288 mm, elevation dimension of 12.192 mm, a centernfrequency of 2.25 MHz, and 48 elements (element spacing is 0.381 mm orn0.591 Λ). The other has a dimension of 38.4 mm×10 mm, ancenter frequency of 2.5 MHz, and 64 elements (0.6 mm or 1.034 Λnelement spacing). Effective larger element spacings were obtained byncombining signals from adjacent elements. Experiments were performednwith both the new and the conventional delay-and-sum methods. Resultsnshow that resolution of constructed images is not affected by thenreduction of a number of elements, but the contrast of images isndecreased dramatically when the element spacing is larger than aboutn2.365 Λ for objects that are not too close to the transducers.nThis suggests that an array of about 2.365 Λ spacing can be usednwith the new method. This may reduce the total number of elements of anfully sampled 128×128 array (0.5 Λ spacing) from 16384 tonabout 732 considering that the two perpendicular directions of a 2-Dnarray are independent (ignoring the larger element spacing in diagonalndirections of 2-D arrays)