A new validated T2* analysis method with certainty estimates for cardiac and liver iron load determination
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: P52 (2015)
Accurate quantification of iron load is of importance in tailoring the therapy for patients with iron load disease. Magnetic resonance (MR) imaging is commonly used to assess iron load in different organs by calculating the T2* value. Estimation of precision and uncertainty of the obtained T2* value may be useful for determining changes in iron load between follow-up scans and for titration of treatment. Therefore, the purpose of this study was to develop and validate a new T2* analysis method, providing certainty estimates for quantification of iron load in heart and liver.
The proposed method is a region of interest (ROI)-based algorithm which changes curve-fitting procedure based on the results from an initial T2* estimate using a 3-parameter, noise-corrected model. The certainty estimate, presented as the T2* value confidence interval, is derived from multiple sub-regions within the selected ROI. Except for ROI delineation, the proposed method does not require any user interaction.
Phantom imaging was performed on a 1.5T system, with two clinically available multi-echo gradient-recalled echo sequences for cardiac and liver imaging. Phantoms were constructed to cover the clinically important range of T2*. A T2* single-echo gradient-echo sequence with TR set to 6 × T1 and a 50° flip angle was used as reference standard. Computer simulations were performed to assess accuracy and precision from 2 000 repetitions at SNR=15. Inter- and intra-observer variability was obtained in patients (n=22) by one experienced and one inexperienced observer.
The phantom study showed bias and variability of 0.21 ± 2.19 ms (bias ± SD) and -0.16 ± 0.90 ms, for cardiac and liver sequences respectively (Figure 1). Simulation results are shown in Figure 2. The proposed method demonstrated high accuracy and precision, with certainty estimates close to confidence intervals derived from 2 000 repetitions. In patients, intra-observer and inter-observer variability was -0.03 ± 0.76 ms (bias ± SD) and 0.27 ± 1.89 ms, respectively.
The proposed method accurately quantifies T2*, also providing T2* certainty estimates. The algorithm is freely available for research purposes.
The Swedish Heart-Lung Foundation; the Medical Faculty of Lund University, Sweden; Skane University Hospital Lund, Sweden; the Swedish Societies of Medicine, Radiology and Cardiology, Sweden; Region Scania, Sweden; the Swedish Research Council; Wellcome Trust, UK; British Heart Foundation, UK.
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Bidhult, S.L., Xanthis, C.G., Liljekvist, L.L. et al. A new validated T2* analysis method with certainty estimates for cardiac and liver iron load determination. J Cardiovasc Magn Reson 17 (Suppl 1), P52 (2015). https://doi.org/10.1186/1532-429X-17-S1-P52