Sound Velocity Estimation and Beamform Correction by Simultaneous Multimodality Imaging with Ultrasound and Magnetic Resonance

Ken Inagaki,Shimpei Arai,Iwaki Akiyama,Kengo Namekawa

doi:10.3390/app8112133

Abstract

Since the sound velocity for medical ultrasound imaging is usually set at 1540 m/s, the ultrasound imaging of a patient with a thick layer of subcutaneous fat is degraded due to variations in the sound velocity. This study proposes a method of compensating for image degradation to correct beamforming. This method uses the sound velocity distribution measured in simultaneous ultrasound (US) and magnetic resonance (MR) imaging. Experiments involving simultaneous imaging of an abdominal phantom and a human neck were conducted to evaluate the feasibility of the proposed method using ultrasound imaging equipment and a 1.5 T MRI scanner. MR-visible fiducial markers were attached to an ultrasound probe that was developed for use in an MRI gantry. The sound velocity distribution was calculated based on the MRI cross section, which was estimated as a corresponding cross section of US imaging using the location of fiducial markers in MRI coordinates. The results of the abdominal phantom and neck imaging indicated that the estimated values of sound velocity distribution allowed beamform correction that yielded compensated images. The feasibility of the proposed method was then evaluated in terms of quantitative improvements in the spatial resolution and signal-to-noise ratio.

Highlights

Ultrasound diagnostic equipment, which has widely been used in clinical diagnosis, assumes that sound velocity has a uniform distribution, since it is based on pulse-echo imaging
The transducer array was located along the central line between two rows formed by magnetic resonance (MR)-visible fiducial markers
The cross section of an magnetic resonance imaging (MRI) image corresponding to a cross section of an fiducial markers

Summary

Introduction

Ultrasound diagnostic equipment, which has widely been used in clinical diagnosis, assumes that sound velocity has a uniform distribution, since it is based on pulse-echo imaging. The sound velocity in mammalian fat tissues ranges from 1400 m/s to 1490 m/s [1]. Various methods for the in vivo measurement of the sound velocity distribution have been proposed [2,3,4,5]. Aoki et al [6] and Nitta et al [7] proposed methods for the measurement of the sound velocity in cartilage using magnetic resonance imaging (MRI) and US imaging. Sound velocity is estimated based on the length of cartilage, as measured with MRI, divided by the time-of-flight, as measured with the ultrasonic pulse-echo technique. Since the estimated sound velocity is obtained at different times and

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Conclusion