Study on application of complementary Golay code into high frame rate ultrasonic imaging system

doi:10.1016/j.ultras.2006.06.030

Ultrasonics

Volume 44, Supplement, 22 December 2006, Pages e93-e96

https://doi.org/10.1016/j.ultras.2006.06.030 Get rights and content

Abstract

The high frame rate (HFR) ultrasonic imaging system, which is developed with limited diffraction beams, constructs images at a high frame rate. However the rectangular imaging area, to some extent, restricts the far field imaging information. At the same time, by virtue of one transmission event for constructing image, the system suffers from low SNR. In this paper we present a computationally efficient method to construct sector mode image and to increase the SNR in HFR system. The method uses orthogonal complementary Golay coded excitation to realize two transmit and receive events. Each emission simultaneously transmits two plane waves with different transmission angle. Then according to Golay code orthogonality, the received echo signals related to different angles are isolated and used to construct two images of different imaging area by HFR method. Finally the two images are synthesized to one frame of sector mode image.

Introduction

A kind of high frame rate (HFR) ultrasonic imaging system was developed by Lu in [1], [2] and has been extensively studied. In this system, a plane wave pulse is transmitted to illuminate objects, and the echoes returned from the objects are received with the same transducer but weighted to produce a limited diffraction array beam response with different parameters. The weighted signals are used to construct 2D or 3D ultrasonic images by simple Fourier transformation. Because only one transmission is required to construct 2D or 3D images, this method can achieve a maximum frame rate of about 3750 frames/s for imaging of biological soft tissues at a depth of 200 mm in theory.

Two features of the said system are discussed respectively. The first one is that this HFR system uses plane waves as transmit field, so the imaging area is rectangular but not conventional sector, which restricts the far field imaging information. The second is that only one transmission is required to construct a frame of image, the SNR of the received signal is low, hence the imaging quality is sensitive to noise influence in practice.

In this paper, a new method has been developed with orthogonal complementary Golay sequence. In this method, orthogonal complementary Golay sequences [3] are used as excited signal to realize two transmit and receive events. Each emission simultaneously transmits two plane waves with different transmission angle. The received echo signals related to different angle are isolated by orthogonality property of the excited signal and used to construct two images of different area by HFR method. Finally the two images are synthesized to one frame of sector mode image. The SNR is effectively improved.

Section snippets

Theory

The existing HFR imaging systems only discuss the condition of the transmit direction perpendicular to the linear transducer, and therefore in order to get sector format imaging, plane waves with different directions are wanted. In this paper HFR imaging model with arbitrary angles is first discussed, then orthogonal complementary Golay code is introduced.

Application of Golay complementary sequences to HFR system

Simulations are carried out in the 2D space. Provided that the transducer is a 1D linear array. The desired simulation result is a sector format image.

The one of differences between a HFR imaging system and a conventional sector B-mode imaging is that the imaging area of the former is rectangular but the latter’s is sector. In order to widen the view of the imaging area, two or more transmit waves with different angles are needed to illuminate the object to be imaged. As shown in Fig. 2 a plane

Conclusion

Based on one transmission the HFR imaging system suffers from weak echo signals and so is sensitive to noise interference. Scheme advanced in this paper makes full use of the property of the orthogonal complementary Golay code, which not only realizes sector mode imaging in HFR system but also increases SNR soundly. This promotes further the HFR system applied to practical uses. Ofcourse, the scheme has some shortages in practical application. For instance, if the imaging object moves too fast,

Acknowledgements

This Project-sponsored partly by NSF of China (60471057) and by SRF for ROCS.

References (3)

Jian-yu Lu
IEEE Transactions on UFFC
(1997)

There are more references available in the full text version of this article.

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