T2* MRI in Thalassemia Major: ECG Gating versus Peripheral Pulse Gating for Myocardial Iron Assessment

Background: T2* MRI is the current non-invasive gold standard for myocardial iron quantification. Major societal guidelines (including SCMR) recommend ECG-gated acquisitions as standard practice. However, ECG gating requires additional setup time for attaching electrodes, which can be particularly challenging in smaller or uncooperative children. Adopting PP gating may help streamline workflow by reducing scan preparation time, minimizing electrode use, and supporting more sustainable MRI practices - an important consideration in resource-limited settings with a high burden of Thalassemia. This study aimed to compare the accuracy of ECG-gated versus peripheral pulse (PP) gated T2* MRI in myocardial iron assessment in patients with Thalassemia Major.

Methods: A total of 96 patients with Thalassemia Major referred for myocardial iron quantification underwent prospective T2* MRI of the heart and liver on a Siemens 1.5Tesla Aera scanner, using both ECG and PP gating. MRI protocol included localisers, cine short axis stack, T2* of heart by both ECG and PP gating and T2* of liver. Myocardial T2* was calculated by placing a single septal ROI, analyzed by two independent observers using cvi42 software (version 5.13, Circle Cardiovascular Imaging Inc, Calgary, Canada), using truncation method. The average value was taken for analysis. A 4-point Likert scale was used to grade image quality (IQ) in both methods.

Results: The mean age of the cohort was 22.41 years (range: 2.6 - 47 years) with 63 males. Average duration of the scan was 12 min (range 10-23 min). The median myocardial T2* with ECG gating was 32.29 ms (IQR: 14.59), while with PP gating it was 30.55 ms (IQR: 12.51). There was excellent intra-class correlation between ECG and PP gated values (ICC = 0.95, p< 0.001). Agreement in T2* classification ( >20 ms = normal, 10–20 ms = mild–moderate, < 10 ms = severe iron overload) was excellent (weighted kappa = 0.97, 95% CI: 0.89-1). Only 1 patient with normal ECG gated T2* was reclassified as mild-moderate category on PP gating (Net Reclassification index= -0.009). Bland–Altman analysis showed that differences in the values obtained by the two methods were greater at higher T2* values ( >30 ms), though without clinical impact as all remained in the normal range. The image quality of ECG as well as PP derived images were diagnostic with no significant difference in number of artefacts (p=0.54).

Conclusion: ECG- and PP-gated T2* MRI demonstrate excellent agreement for myocardial iron quantification and classification in Thalassemia Major patients. PP gating can serve as a reliable alternative, particularly in scenarios where ECG gating is impractical or challenging.

Category wise distribution of patients in ECG versus PP gated T2*

Iron overload categories	ECG gated T2 *	PP gated T2*
Normal ( >20 ms)	79 (82.29%)	78 (81.25%)
Mild to moderate(10-20ms)	6 (6.25%)	7 (7.29%)
Severe ( < 10ms)	11 (11.46%)	11 (11.46%)

Comparison of ECG vs PP gated T2* in a 8-year-old male with thalassemia major
Bland Altman plot showing difference in T2* values of the heart using ECG and PP gating methods