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Journal of Medical Ultrasonics

, Volume 43, Issue 3, pp 317–325 | Cite as

Impact of element pitch on synthetic aperture ultrasound imaging

  • Hideyuki HasegawaEmail author
  • Chris L. de Korte
Original Article

Abstract

Purpose

Synthetic aperture imaging was introduced in medical ultrasound to obtain high-quality images. In synthetic aperture ultrasound imaging, spherical transmit waves illuminate a target region from different positions, resulting in low-resolution images for each transmission. By coherent compounding of the resulting low-resolution images, a high-resolution image is obtained. Multiple steered receiving beams need to be created to obtain each low-resolution image and, thus, grating lobes should influence the image quality. In the present study, an array ultrasonic probe with a small element pitch was introduced to reduce the influences of grating lobes, and the effect of element pitch on image quality was examined in detail.

Method

A linear array ultrasonic probe at a nominal center frequency of 7.5 MHz with an element pitch of 0.1 mm has been introduced. This probe does not produce grating lobes within the imaging region in theory because the element pitch of this probe is half of the ultrasonic wavelength. The contrast of an ultrasonic image was evaluated using a cyst phantom.

Results

The contrasts obtained by synthetic aperture imaging with element pitches of 0.1 and 0.2 mm were 4.88 and 4.69 dB, respectively, which were similar to the 4.67 dB obtained by conventional beamforming with focused transmit beams, when the number of transmissions was 121. The contrast obtained with an element pitch of 0.1 mm was similar (4.34 dB) even when the number of transmissions was decreased to 61. However, the contrast obtained with an element pitch of 0.2 mm showed a larger degradation (3.77 dB) at 31 transmissions.

Discussion and conclusion

Even with larger element pitches, good image contrast could be obtained when the number of transmissions was large. This is because echoes from grating lobes are incoherent among transmissions, and they are suppressed by compounding low-resolution images obtained by individual transmissions. On the other hand, an array probe with smaller element pitches achieves good image contrast even with a smaller number of transmissions and, thus, it would be preferable to realize a higher frame rate.

Keywords

Synthetic aperture imaging Diverging beam Element pitch Image quality 

Notes

Acknowledgments

This study was supported by JSPS KAKENHI Grant Numbers 26289123 and 15K13995.

Compliance with ethical standards

Conflict of interest

None.

Ethical considerations

Animal and human subjects were not used in this study.

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Copyright information

© The Japan Society of Ultrasonics in Medicine 2016

Authors and Affiliations

  1. 1.Graduate School of Science and Engineering for ResearchUniversity of ToyamaToyamaJapan
  2. 2.Radboud University Nijmegen Medical CentreNijmegenThe Netherlands

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