- Workshop presentation
- Open Access
Limitations of VCG based gating methods in ultra high field cardiac MRI
© Krug et al; licensee BioMed Central Ltd. 2013
- Published: 30 January 2013
- Cardiac Magnetic Resonance
- Ultra High Field
- Peak Vector
- Minimum Distance Algorithm
- Static Reference Vector
The electrocardiogram (ECG) is important for gating purposes in cardiac magnetic resonance imaging (CMR). However, the magnetohydrodynamic (MHD) effect, which is caused by the flow of blood in the static magnetic field, makes it difficult to record clean ECG signals for gating. The vectorcardiogram (VCG), which can be derived from the ECG signal, is commonly used for gating purposes and has been well established for magnetic fields strength of up to 3T. However, for higher field strengths this method is prone to errors . This work tries to explain the reasons for the VCG based methods not being suitable for cardiac gating in ultra high field MRI.
ECGs were recorded using a standard 12-lead Holter ECG (Getemed, Germany) inside a 7T MR scanner (Siemens Magnetom), a 3T MR scanner (Philips Achieva) and outside the MR scanner as references. Measurements were made on five healthy volunteers while MR imaging was switched off. The VCGs were derived from the 12-lead ECG using the inverse Dower matrix . The VCG method  was implemented and applied to the acquired data sets. This method measures the distance in the VCG space between a static reference vector defined by the R-wave (R) peak of an ECG signal recorded outside the MR scanner (at 0T) and the VCG vector recorded inside the MR scanner. Those points where a minimal distance and angle between both vectors is reached are classified as R peaks.
The angle of the R peak vector substantially changed for the 7T measurement. This can be explained by the fact that the MHD effect has an intrinsic DC component. Since this DC component was removed by the ECG recorder’s high pass filter, the amplitude of the R peaks in each axis of the VCG signal changed which yielded an alteration of the R peak's angle. Additionally, the 7T VCG space is severely corrupted by the strength and complexity of the MHD signal.
This work was founded by the Federal Ministry of Education (Germany, BMBF, 03IP710) and by the Royal Academy of Engineering (UK).
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.