Nonlinear propagation applied to the improvement of resolution in diagnostic medical ultrasound
作者:
B. Ward,
A. C. Baker,
V. F. Humphrey,
期刊:
The Journal of the Acoustical Society of America
(AIP Available online 1997)
卷期:
Volume 101,
issue 1
页码: 143-154
ISSN:0001-4966
年代: 1997
DOI:10.1121/1.417977
出版商: Acoustical Society of America
数据来源: AIP
摘要:
Medical B-mode scanners operating under conditions typically encountered during clinical work produce ultrasonic wave fields that undergo nonlinear distortion. In general, the resulting harmonic beams are narrower and have lower sidelobe levels than the fundamental beam, making them ideal for imaging purposes. This work demonstrates the feasibility of nonlinear harmonic imaging in medical scanners using a simple broadband imaging arrangement in water. The ultrasonic system comprises a 2.25-MHz circular transducer with a diameter of 38 mm, a membrane hydrophone, also with a diameter of 38 mm, and a polymer lens with a focal length of 262 mm. These components are arranged coaxially giving an imaging geometry similar to that used in many commercial B-scanners, but with a receiver bandwidth sufficient to record the first four harmonics. A series of continuous wave and pulse-echo measurements are performed on a wire phantom to give 1-D transverse pressure profiles and 2-D B-mode images, respectively. The reflected beamwidthswndecrease aswn/w1=1/n0.78, wherenis the harmonic number, and the reflected sidelobe levels fall off quickly with increasingn. In imaging terms, these effects correspond to a large improvement in lateral resolution and signal-to-clutter ratio for the higher harmonics.
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