3T cardiac imaging with on-line 12-lead ECG monitoring

Abstract

Background: We previously demonstrated rapid detection of acute ischemia inside MRI using a prototype MRI-conditional 12-lead ECG system [1] equipped with hardware to remove artifacts produced by the MRI gradients. We also synchronized [2] high-field (1.5-7T) scanners using triggers from 12-lead traces following Magneto-Hydro-Dynamic voltage removal. A commercial 12-lead ECG system might allow performing MR imaging studies with a greater risk of ischemic events, as well as the execution of high-risk MRI-guided interventions, such as ventricular tachycardia ablation. Our objective is to validate the performance of an alpha-site version of a commercial MRI-compatible 12-lead ECG system during cardiac imaging at 3T. Methods: A pre-release commercial MRI-conditional 12-lead ECG system (MIRTLE, E-TROLZ, Andover, MA) was used in the study of 4 volunteers (32, 35, 42, 57 yrs. old) in a Siemens 3T Skyra during the execution of routine SSFP and GRE cine, as well as Black-Blood TSE cardiac (CMR) imaging. This system removes the largest (>50 milliVolt) ECG gradientartifacts overlaid on the true 12-lead traces [Figure 1A, B] using hardware switches, together with sample-and-hold (memory) circuits that reduce switching artifacts. The resulting “cleaned” intra-MRI ECG traces are, thereafter, processed by 12-lead vector-cardiogram (VCG) software, which uses (“training”) traces acquired outside the MRI to detect the QRS complex in each R-R cycle, despite the presence of Magneto-Hydro- Dynamic voltages on traces inside the MRI. The 12-lead system was used to (a) continuously monitor subjects' ECG inside the bore, including during imaging, and (b) output triggers at each detected QRS complex, which were fed into the scanner's wireless gating system, allowing for acquisition of retrospective and prospective CMR sequences. We evaluated the fraction of QRS complexes detected (scan efficiency), and the image quality (IQ) obtained using the system [Figure 1B], relative to the scanner's 4-lead gating. We also evaluated the quality of the ECG traces obtained during imaging, relative to ECG traces obtained during imaging pauses [Figure 1C]. Results: The noise on MRI images was identical (+0.5dB) with the system OFF and ON. Scan efficiency was equivalent (TSE) or ∼20% superior (SSFP, GRE) to 4-lead gating. TSE and Cine SSFP IQ was equivalent (Figure 1D, E) to 4-lead-gated. Conclusions: The MIRTLE pre-release 12-lead ECG system performed well in imaging and ECG quality tests. The system will now be evaluated in patients at 1.5T and 3T clinical sites. (Figure presented).