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Journal of Medical Ultrasonics

, Volume 44, Issue 2, pp 155–165 | Cite as

Apodized adaptive beamformer

  • Hideyuki HasegawaEmail author
Original Article

Abstract

Purpose

A number of studies aimed at improvement of ultrasound image quality, such as spatial resolution and contrast, have been conducted. Apodization is known as an important factor that determines image quality. However, in the case of amplitude and phase estimation (APES) beamforming, a kind of adaptive beamformer that has been employed in medical ultrasound recently, only rectangular apodization has been used in the previous studies. In this study, apodization was employed in adaptive beamforming, and its effects on image quality were examined in phantom experiments.

Methods

We recently proposed a modified APES beamformer that reduces the computational complexity significantly using sub-aperture beamforming. In this study, the total receiving aperture was divided into four sub-apertures, and the APES beamforming was applied to the output from the four sub-apertures. Before the delay-and-sum (DAS) beamforming in each sub-aperture, echoes received by individual transducer elements were apodized with rectangular, Gaussian, and two Hanning functions, where the apodization with two Hanning functions realized lateral modulation of the ultrasonic field. The lateral spatial resolution was evaluated by the full width at half maximum of an echo from a string phantom, and the image contrast was evaluated using a cyst phantom.

Results

The modified APES beamformer realized a significantly better spatial resolution of 0.38 mm than that of the conventional delay-and-sum beamformer (0.67 mm), even with rectangular apodization. Using Gaussian apodization, the spatial resolution was further improved to 0.34 mm, and contrast was also improved from 4.3 to 5.1 dB. Furthermore, an image obtained by the modified APES beamformer with apodization consisting of two Hanning functions was better “tagged” as compared with the conventional DAS beamformer with the same apodization.

Conclusion

Apodization was shown to be effective in adaptive beamforming, and an image obtained by the adaptive beamformer with lateral modulation seemed to have potential for improvement of the accuracy in measurement of tissue lateral motion.

Keywords

Adaptive beamformer Covariance matrix Apodization Image quality 

Notes

Acknowledgements

The author thanks Mr. Takeshi Sato at Toshiba Medical Systems Cooperation for valuable discussion on sub-array averaging. This study was partly supported by JSPS KAKENHI Grants, Nos. 26289123 and 15K13995.

Compliance with ethical standards

Ethical considerations

No animal and human subjects were used in this study.

Conflict of interest

None.

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Copyright information

© The Japan Society of Ultrasonics in Medicine 2017

Authors and Affiliations

  1. 1.Graduate School of Science and EngineeringUniversity of ToyamaToyamaJapan

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