Spatially Resolved MR-Compatible Doppler Ultrasound: Proof of Concept for Triggering of Diagnostic Quality Cardiovascular MRI for Function and Flow Quantification at 3T

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Abstract
Objectives: We demonstrate the use of a Magnetic-Resonance (MR)-compatible ultrasound (US) imaging probe using spatially-resolved Doppler for diagnostic quality cardiovascular MR imaging as an initial step towards hybrid US/MR fetal imaging. Methods: A newly developed technology for a dedicated MR-compatible phased array ultrasound-imaging probe acquired pulsed color Doppler carotid images, which were converted in near-real time to a trigger signal for cardiac cine and flow quantification MRI. Ultrasound and MR data acquired simultaneously were interference free. Conventional ECG and the proposed spatially-resolved Doppler triggering were compared in 10 healthy volunteers. A synthetic éfalse-triggeredé image was retrospectively processed using Metric Optimized Gating (MOG). Images were scored by expert readers and sharpness, cardiac function and aortic flow were quantified. 4D flow (two volunteers) showed feasibility of Doppler triggering over a long acquisition time. Results. Imaging modalities were compatible. US probe positioning was stable and comfortable. Image quality scores and quantified sharpness were statistically equal for Doppler- and ECG-triggering (p=1.00). ECG-, Doppler-triggered and MOG ejection fractions were equivalent (p=1.00), with false-triggered values significantly lower (p0.05). 4D Flow quantification gave consistent results between ECG and Doppler triggering. Conclusion. We report interference-free pulsed color Doppler ultrasound during MR data acquisition. Cardiovascular MRI of diagnostic quality was successfully obtained with pulsed color Doppler triggering. Significance. The hardware platform could further enable advanced free-breathing cardiac imaging. Doppler ultrasound triggering is applicable where ECG is compromised due to pathology or interference at higher magnetic fields, and where direct ECG is impossible i.e. fetal imaging.
Funding Information
  • Centre for Biomedical Imaging (CIBM) of EPFL
  • University of Geneva
  • University Hospitals of Geneva and Lausanne via the Swiss National Foundation under R'Equip (326030_150816)

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