Quantitative Confounder Analysis of Electrocardiogram Signals in Cardiac Magnetic Resonance at 1.5, 3 and 7 T—Assessing Standardized Electrode Positions and Sequence Types—Towards Quality Assurance

Background The electrocardiogram (ECG) used for gating in cardiac MRI may be compromised by multiple confounders inside the scanner bore. Purpose To quantify the influence of magnetic field strengths (1.5 T/3 T/7 T), standardized electrode positions, and imaging sequences on ECG signals used for gating. Study Type Prospective. Population Sixteen healthy volunteers (eight male; mean age 26.25 ± 7.67 years). Field Strength/Sequence Balanced steady‐state free precession cine (1.5 T/3 T), fast low‐angle shot cine (7 T), and 4D flow (1.5 T/3 T/7 T) sequences. Assessment ECG‐signals were recorded during breath‐hold and non‐breath‐hold short axis cine (sax‐bh and sax‐nbh, respectively) and 4D flow scans at 1.5 T/3 T/7 T. All scans were repeated with 4 standardized electrode positionings (pos1–4) at each field strength. Pos1/2 were vendor‐recommended positionings for 1.5 T/3 T/7 T scans, respectively, whereas pos3/4 were alternative positionings recommended in previous studies. Similarity between confounded ECG‐signals and unconfounded baseline ECG‐signals was assessed by QRS‐feature correlation. Cine image quality (IQ) was assessed by 3 readers (with 6, 10, and 22 years experience) on a four‐point Likert scale. Statistical Tests Linear mixed models with type III tests of fixed effects (overall) and t tests with adjusted degrees of freedom (pairwise subgroup‐comparisons) at significance level p < 0.05. Results Increasing field strength resulted in significantly decreasing similarity to baseline measurements, with r values (provided with 95% confidence interval) of 1.5 T: 97% (92.6–101.3); 3 T: 91.4% (87.1–95.8); 7 T: 50.4% (46–54.9) and lower IQ: 1.5 T: 2.33 (2.12–2.55); 3 T: 1.96 (1.75–2.17); 7 T: 0.91 (0.7–1.12). Vendor‐specified electrode positions pos1: 91.8% (87.2–96.5), pos2: 88.3% (83.7–92.9) showed significantly higher correlation with baseline measurements than alternative positions pos3: 67.5% (62.9–72.1) and pos4: 70.8% (66.2–75.4). The evaluated standardized sequences showed similar amounts of electrocardiogram distortion, with r values of: sax‐bh: 77.3% (73–81.7); 4D: 79.3% (75–83.7), p = 0.54; sax‐nbh: 82.1% (77.8–86.5), p = 0.31, but the difference between sax‐bh and sax‐nbh: 4.8% (2.88–6.72) was significant. Data Conclusion Increasing field strength leads to significant ECG signal distortions. Vendor‐specified positions 1/2 resulted in less distorted ECG signals than alternative positions 3/4 recommended in previous publications. Level of Evidence 2. Technical Efficacy Stage 5.