Protocol for testing suitability of compact US imaging systems for use inside MRI suites, and application to one commercial US system

Abstract

This note presents a testing protocol developed to assess the suitability of a compact ultrasound (US) system for potential use inside a 1.5 T interventional magnetic resonance imaging (MRI) suite. Test results for specific commercial US and MRI systems in a particular clinical use case are also presented. The protocol consisted of safety testing and evaluations of image quality of both MRI and US systems at the proposed clinical use configuration. Safety tests included magnetic field measurements inside MRI suite, handheld magnet assessments of magnetic properties of the US system, and magnetic displacement force measurements. The safety tests were followed by direct assessments of US system components inside MRI suite. Each US system component was demonstrated to have no risk of displacement at the proposed locations with a large safety margin. No clinically relevant difference in US image quality was observed compared to images acquired outside MRI suite. While MR image quality met the American College of Radiology standards for clinical scanning, increases in noise levels and radiofrequency (RF) interference associated with the presence of US scanner in MRI suite were observed. The ‘sleep mode’ operating condition of the US system resulting in consistent absence of RF interference and minimal noise increase was identified and proposed for use during MRI scanning. Our results demonstrate the utility of our testing methods, and the suitability of this particular compact US system for safe use in our site-specific configuration inside the 1.5 T MRI suite. These results would be dependent on the specific test systems.