Rofo 2008; 180 - A14
DOI: 10.1055/s-2008-1052575

Magnetic Field Strength Independent Cardiac Gating at 1.5 T, 3.0 T and 7.0 T

T Frauenrath 1, U Heinrichs 1, S Kozerke 2, P Bösiger 2, T Niendorf 1
  • 1Division of Experimental MRI, Department of Diagnostic Radiology, University of Aachen, Germany
  • 2Institute of Biomedical Engineering and Medical Informatics, University of Zurich, Switzerland

Purpose: In clinical MRI cardiac motion is commonly dealt with using ECG based synchronization. ECG is prone to interference with electromagnetic fields and to magneto-hydrodynamic effects, in particular at (ultra)high magnetic field strengths (1). For all these reasons, a non- invasive, fully MR compatible cardiac monitoring and gating approach which presents suitability for all magnetic field strengths is conceptually appealing. For this purpose a cardiac monitoring and gating device that employs acoustic signals was developed. The applicability and robustness of the proposed triggering device is explored in cardiac gated, 3D phase contrast MR angiography (3D PCMRA) studies at 1.5 T, 3.0 T and 7.0 T.

Material and Methods: An acoustic sensor and a wave guide were employed for signal acquisition and transmission of the heart tone. Signal processing was conducted using dedicated electronic circuits (2). The resulting waveform was delivered to the internal physiological signal controller circuitry of a clinical scanner. Volunteer studies were performed on 1.5 T, 3.0 T and 7.0 T MR systems (Achieva, Philips, Best, The Netherlands). 3D PCMRA (TE=6.8ms, TR=12.6ms, matrix=384×384, FOV=(240×168) cm2, trigger delay=shortest) was applied to evaluate acoustic triggering in a prospective gating regime. For comparison, the same imaging protocol was conducted using conventional ECG-triggering.

Results: The acoustic MR-stethoscope provided cardiograms at 1.5 T, 3.0 T and 7.0 T free of interference from electromagnetic fields or magneto-hydrodynamic effects and proved to be suitable for robust synchronization. In comparison, ECG waveforms were susceptible to T-wave elevation, which was pronounced at 3.0 T and 7.0 T. Acoustically triggered 3D PCMRA acquisitions produced images free of motion artefacts even at (ultra)high magnetic field strengths. Conversely, R-wave mis-registration occurred in ECG-triggered acquisitions at 3.0 T and 7.0 T, which made 3D PCMRA prone to motion artefacts.

Conclusion: The proposed acoustic approach proved to be B0-independent while fully meeting the demands of cardiac triggered MRI.