Development of a hybrid magnetic resonance and ultrasound imaging system.

Victoria Sherwood,David J Collins,John Civale,Ian Rivens,Gail R Ter Haar,Martin O Leach

doi:10.1155/2014/914347

Abstract

A system which allows magnetic resonance (MR) and ultrasound (US) image data to be acquired simultaneously has been developed. B-mode and Doppler US were performed inside the bore of a clinical 1.5 T MRI scanner using a clinical 1–4 MHz US transducer with an 8-metre cable. Susceptibility artefacts and RF noise were introduced into MR images by the US imaging system. RF noise was minimised by using aluminium foil to shield the transducer. A study of MR and B-mode US image signal-to-noise ratio (SNR) as a function of transducer-phantom separation was performed using a gel phantom. This revealed that a 4 cm separation between the phantom surface and the transducer was sufficient to minimise the effect of the susceptibility artefact in MR images. MR-US imaging was demonstrated in vivo with the aid of a 2 mm VeroWhite 3D-printed spherical target placed over the thigh muscle of a rat. The target allowed single-point registration of MR and US images in the axial plane to be performed. The system was subsequently demonstrated as a tool for the targeting and visualisation of high intensity focused ultrasound exposure in the rat thigh muscle.

Highlights

In recent years there has been a move towards multimodality imaging techniques for clinical diagnosis, most commonly including various combinations of computed tomography (CT), single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI)
signal-tonoise ratio (SNR) values for the region of interest (ROI) marked in blue are plotted in Figure 6 for the various combinations of MR and US imaging sequences/modes, with and without aluminium foil shielding of the US probe and cable
This was achieved using standard commercially available clinical imaging equipment: a 1.5 T MR scanner and an US imaging system modified with an 8 m cable to ensure conditions were MR safe

Summary

Introduction

In recent years there has been a move towards multimodality imaging techniques for clinical diagnosis, most commonly including various combinations of computed tomography (CT), single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI). The evolution and development of these hybrid systems have been reviewed in the literature [1,2,3,4,5]. In many of these systems, there is an emphasis on combining anatomical and physiological information by overlaying two image data sets. Hybrid imaging reduces the reliance on image coregistration as the patient remains in the same position while both data sets are acquired. Tracer uptake can provide good quantitative physiological information, the spatial resolution of SPECT and PET is relatively poor compared with other modalities [5]. The longer each image acquisition time, the greater the potential for patient motion

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Discussion

Conclusion