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



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.


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.


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.


Synthetic aperture imaging Diverging beam Element pitch Image quality 



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

Compliance with ethical standards

Conflict of interest


Ethical considerations

Animal and human subjects were not used in this study.


  1. 1.
    Ara SR, Alam F, Rahman H, et al. Bimodal multiparameter-based approach for benign–malignant classification of breast tumors. Ultrasound Med Biol. 2015;41:2022–38.CrossRefPubMedGoogle Scholar
  2. 2.
    Wojcinski S, Farrokh A, Hille U, et al. Optimizing breast cancer follow-up: diagnostic value and costs of additional routine breast ultrasound. Ultrasound Med Biol. 2011;37:198–206.CrossRefPubMedGoogle Scholar
  3. 3.
    Shankar PM, Forsberg F, Lown L. Statistical modeling of atherosclerotic plaque in carotid B mode images—a feasibility study. Ultrasound Med Biol. 2003;29:1305–9.CrossRefPubMedGoogle Scholar
  4. 4.
    Akkus Z, Carvalho DDB, van den Oord SCH, et al. Fully automated carotid plaque segmentation in combined contrast-enhanced and B-mode ultrasound. Ultrasound Med Biol. 2015;41:517–31.CrossRefPubMedGoogle Scholar
  5. 5.
    Soumekh M. Synthetic aperture radar. Signal processing with MATLAB algorithms. New York: Wiley; 1999.Google Scholar
  6. 6.
    O’Donnell M, Thomas LJ. Efficient synthetic aperture imaging from a circular aperture with possible application to catheter-based imaging. IEEE Trans Ultrason Ferroelectr Freq Contr. 1992;39:366–80.CrossRefGoogle Scholar
  7. 7.
    Jensen JA, Nikolov SI, Gammelmark KL, et al. Synthetic aperture ultrasound imaging. Ultrasonics. 2006;44:e5–15.CrossRefPubMedGoogle Scholar
  8. 8.
    Gran F, Jensen JA. Directional velocity estimation using a spatio-temporal encoding technique based on frequency division for synthetic transmit aperture ultrasound. IEEE Trans Ultrason Ferroelectr Freq Contr. 2006;53:1289–99.CrossRefGoogle Scholar
  9. 9.
    Karaman M, Li P-C, O’Donnell M. Synthetic aperture imaging for small scale systems. IEEE Trans Ultrason Ferroelectr Freq Contr. 1995;42:429–42.CrossRefGoogle Scholar
  10. 10.
    Karaman M, O’Donnell M. Subaperture processing for ultrasonic imaging. IEEE Trans Ultrason Ferroelectr Freq Contr. 1998;45:126–35.CrossRefGoogle Scholar
  11. 11.
    Lockwood GR, Foster FS. Design of sparse array imaging systems. Proc IEEE Ultrason Symp. 1995;2:1237–43.Google Scholar
  12. 12.
    Lockwood GR, Talman JR, Brunke SS. Real-time 3-D ultrasound imaging using sparse synthetic aperture beamforming. IEEE Trans Ultrason Ferroelectr Freq Contr. 1998;45:980–8.CrossRefGoogle Scholar
  13. 13.
    Nikolov SI, Gammelmark K, Jensen JA. Recursive ultrasound imaging. Proc IEEE Ultrason Symp. 1999;2:1621–5.Google Scholar
  14. 14.
    Ponnle A, Hasegawa H, Kanai H. Multi element diverging beam from a linear array transducer for transverse cross sectional imaging of carotid artery: simulations and phantom vessel validation. Jpn J Appl Phys. 2011;50:07HF05-1-10.CrossRefGoogle Scholar
  15. 15.
    van Wijk MC, Thijssen JM. Performance testing of medical ultrasound equipment: fundamental vs. harmonic mode. Ultrasonics. 2002;40:585–91.CrossRefPubMedGoogle Scholar
  16. 16.
    Thijssen JM, Weijers G, de Korte CL. Objective performance testing and quality assurance of medical ultrasound equipment. Ultrasound Med Biol. 2007;33:460–71.CrossRefPubMedGoogle Scholar
  17. 17.
    Montaldo G, Tanter M, Bercoff J, et al. Coherent plane-wave compounding for very high frame rate ultrasonography and transient elastography. IEEE Trans Ultrason Ferroelectr Freq Contr. 2009;56:489–506.CrossRefGoogle Scholar
  18. 18.
    Hasegawa H, Kanai H. Simultaneous imaging of artery-wall strain and blood flow by high frame rate acquisition of RF signals. IEEE Trans Ultrason Ferroelectr Freq Contr. 2008;55:2626–39.CrossRefGoogle Scholar
  19. 19.
    Bercoff J, Montaldo G, Loupas T, et al. Ultrafast compound Doppler imaging: providing full blood flow characterization. IEEE Trans Ultrason Ferroelectr Freq Contr. 2011;58:134–47.CrossRefGoogle Scholar
  20. 20.
    Hansen HHG, Lopata RPG, Idzenga T, et al. Full 2D displacement vector and strain tensor estimation for superficial tissue using beam steered ultrasound imaging. Phys Med Biol. 2010;5:3201–18.CrossRefGoogle Scholar

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

Personalised recommendations