Cross-correlation Phase Correction Method on
Ultrasonic Synthetic Focused Signal Distortion
Cai-qun YE, Lin LUO *, Xiao-rong GAO, Li-rong JIANG, Hai-lin YUE
1
Photoelectric Engineering Institute, Southwest Jiaotong University, Chengdu 610031, China
2
Southwest Jiaotong University NDT Research Center & Olympus NDT Joint Laboratory of Nondestructive Testing, Chengdu 610031, China
Abstract: Synthetic aperture ultrasonic imaging is currently widely used in railway, aviation, automobile
manufacturing and petrochemical, major in non-destructive testing the defects of key components and materials,
and showing them in form of image. Due to inhomogeneity of testing materials and errors of detection systems,
detected signals have phase errors, and distortion exists on synthesis images. This paper presents an effective
phase correction method on ultrasonic synthetic focused signal distortion. A parameter, the relative signal-to-
noise ratio, is introduced to be the indicator for later analysis. Via experimental results and the relative signal-
to-noise ratios of the synthetic focusing images before and after phase correlation, the feasibility of the program
is proved. Thus, the phase correction method here is worth putting the use into various ultrasonic application
fields.
Key words: ultrasonic synthetic aperture; ultrasound imaging; phase correction; inhomogeneity
1 Introduction
Ultrasonic synthetic aperture focusing imaging is very
important and commonly used for testing work-pieces,
materials, and machines to prevent accidents in railway or
other industries. Synthetic aperture focusing technology
(SAFT) is an ultrasound imaging method derived from
synthetic aperture radar (SAR) [1, 2]. 3-D SAF methods,
investigated and applied to a single-element trans-rectal
ultrasound transducer, perform almost identically for
simulated scatterers and give a significant improvement in
azimuth resolution and a constant resolution in elevation
[3]. An adaptive synthetic-aperture focusing technique
(ASAFT) was proposed and demonstrated to be able to
provide images of blood vessels with better lateral
resolution both at different depths and along various
directions compared with one-dimensional and 2D SAFT
[4]. A new algorithm for SAFT was presented and applied
to interior imaging of cylindrical structures. Compared
with existing methods, it yields lower side lobes and better
resolution for wide-beam transducers [5]. Synthetic
aperture sequential beam-forming (SASB) is a novel
technique which allows to implement synthetic aperture
beam-forming on a system with a restricted complexity,
and without storing RF-data. The objective is to improve
lateral resolution and obtain a more depth independent
resolution compared to conventional ultrasound imaging
[6]. A phantom and an in vivo evaluation of the SA method
with bidirectional pixel-based focusing (Bi-PBF) was
presented in comparison with the conventional beam-
forming [7].
However, considering the delay error derived from the
inhomogeneity of materials, the revolution and SNR of
ultrasound images will be reduced, so the ultrasonic
imaging algorithm should be modified to improve the
resolution and SNR. Phase response of the transducer
elements in the derivation of the PC-MUSIC algorithm
makes use of phase information from multiple frequencies
to reduce noise effects and preserve the super resolution
[8]. The proposed ω-k algorithm provides an exact solution
to the inverse problem for the assumed forward wave
propagation model [9-11]. Correlation processing using
fully common spatial frequencies of overlapping sub-
apertures is explored to adapt beam-forming for motion
and phase aberrations [12].Phase-correction algorithms
improve image quality by compensating for tissue-induced
errors in beam-forming. Using the illustrative example of
transcranial ultrasound, the authors have evaluated their
ability to perform adaptive imaging with a real-time, 3-D
scanner [13].A novel cross algorithm is proposed to
implement the NFSR algorithm on two-dimensional arrays.
This algorithm is tested with a simulated data set acquired
with a two-dimensional array, and the result shows that the
cross algorithm performs better than the all-row-plus-two-
column NFSR algorithm [14].
Cross-correlation phase correction method will be
described in section 2. And then relative signal-to-noise
ratio, SNR, will be introduced in section 3 as the
experimental index. Section 4 will show the experiment
and the results in detail. The conclusion of this paper that
cross-correlation phase correction algorithm can improve
the quality of the ultrasound images is stated in section 5.
2 Cross-correlation Phase Correction
principle
2.1 Synthetic aperture ultrasonic imaging
In recent years, single-element synthetic aperture
techniques have been developed into a serious of improved
____________________________________
978-1-47-- /1/$31.00 ©201 IEEE