Apodized adaptive beamformer
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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.
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.
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.
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.
KeywordsAdaptive beamformer Covariance matrix Apodization Image quality
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
No animal and human subjects were used in this study.
Conflict of interest
- 4.Honjo Y, Hasegawa H, Kanai H. Two-dimensional tracking of heart wall for detailed analysis of heart function at high temporal and spatial resolutions. Jpn J Appl Phys. 2010; 49:07HF14-1–9.Google Scholar
- 6.Shahmirzadi D, Li RX, Konofagou EE. Pulse-wave propagation in straight-geometry vessels for stiffness estimation: Theory, simulations, phantoms and in vitro findings. J Biomech Eng. 2012; 134:114502-1–6.Google Scholar
- 10.Takahashi H, Hasegawa H, Kanai H. Echo speckle imaging of blood particles with high-frame-rate echocardiography. Jpn J Appl Phys. 2014; 53:07KF08-1–7.Google Scholar
- 11.Jespersen SK, Wilhjelm JE, Sillesen H. Multi-angle compound imaging. Ultrason. Imaging. 1998;20:81–102.Google Scholar
- 22.Blomberg AEA, Holfort IK, Austeng A, Synnevåg JF, Holm S, Jensen JA. APES beamforming applied to medical ultrasound imaging. In: 2009 IEEE Intern’l Ultrason. Symp. Proc. pp. 2347–50.Google Scholar
- 24.Hasegawa H. Improvement of penetration of modified amplitude and phase estimation beamformer. J Med Ultrason. 2016 (in press).Google Scholar