Thoralf Niendorf

Electrocardiogram in an MRI Environment: Clinical Needs, Practical Considerations, Safety Implications, Technical Solutions and Future Directions

Magnetic Resonance Imaging (MRI) has been listed as the single most important medical innovation, on par with CT scanning (Fuchs & Sox 2001). In current clinical MRI ECG is being using for three major purposes. Firstly, heart motion, blood flow and blood pulsation are commonly dealt with using electrocardiogram (ECG) for synchronization of MR data acquisition with the cardiac cycle (Lanzer et.al. 1984) to address or compensate for cardiac activity related motion artifacts which is of paramount importance for an ever growing portfolio of cardiovascular MR (CMR) and neurovascular MR (NVMR) applications (Assomull et.al. 2007, Kelle et.al. 2008, Kramer et.al. 2008, Kwong & Korlakunta 2008, Niendorf et.al. 2006, Niendorf & Sodickson 2008, Niendorf & Sodickson 2006, Niendorf et.al. 2010, Pennell et.al. 2004, Schwitter 2008). Secondly, ECG is widely used to simultaneously register cardiac activity with MRI; for example to eliminate physiological fluctuations from brain activation maps derived from functional MRI studies (Purdon & Weisskoff 1998). Thirdly, there are an increasing number of clinical applications that require ECG monitoring prior to/after the MR examination while the patient is still in the MR environment but outside of the MR scanners bore using ECG devices as a patient emergency indicator. ECG waveform acquisitions, ECG co-registration and ECG monitoring during MRI pose technical challenges and requires safety measures that will not be familiar to users of other conventional ECG technologies. For all those reasons, the basic principles of using ECG in an MRI environment and their implications for clinical MRI and MRI research are provided in this chapter. Key concepts, technical solutions, practical considerations and safety implications for cardiac gated MRI using electrocardiograms are outlined. Unsolved technical problems and unmet clinical needs are also considered carefully, in an attempt to stimulate the community to throw further weight behind the solutions of remaining issues. Driven by the limitations and motivated by the challenges of ECG, the need for novel cardiac gating/triggering technology is discussed. Current trends, such as the trend towards wireless techniques and the move to acoustic cardiac gating techniques, and their