Myocardial iron quantification using T2* and native T1mapping - a 250 patient study
© Abdel-Gadir et al; licensee BioMed Central Ltd. 2015
Published: 3 February 2015
The management of iron overload has been transformed by the use of T2* as a surrogate marker of cardiac iron loading. The presence of iron however not only changes T2*, but also T2 and T1. Recent advances make T1 mapping a possible complementary technique to T2*. Preliminary data are encouraging, but the relative advantages and disadvantages and optimal mathematical model for the relationship between T1 and T2* remain unknown.
This was a single centre prospective study of 250 patients (age 37 ± 13 years) referred with potential iron overload for T2* assessment, with 50 healthy volunteers (age 44 ± 11 years) as a reference comparison group. Each participant underwent short axis septal T2* (standard Siemens sequence using 8 different TE) at 1.5T and in addition myocardial T1 mapping (ShMOLLI sequence).
27% of patients required more than one T2* acquisition to obtain optimal images for analysis compared with 12% for T1 mapping. ShMOLLI images were uninterpretable in 2 patients due to the presence of an MRI conditional pacemaker, and the positioning of a PORT-A-CATH implantable venous access system. It is known that some patients were unable to complete T2* sequences (21 heart beat scan), but these were not captured by the inclusion criteria of the study.
The derived equivalent T1 cutpoints for published T2* cutoffs for mild, moderate and severe iron were 20ms (846ms); 14ms (705ms) and 10ms (636ms). If T1 is accurate for iron, then using the lower limit of normal for T1 (895ms) would suggest that the normal limit for T2* would be 29ms. However, of the 50 healthy volunteers, 8 (16%) had T2*s lower than this, possibly due to relatively lower precision of T2* measurements.
In potential cardiac iron overload, not all patients manage good image quality on the first breath-hold with either technique. Measured myocardial T1 and T2* are best modelled using an exponential curve fit but only correlate below a T2* of 20ms. T1 data suggests that the lower limit of normal T2* should be 29ms and thus far more patients have myocardial iron than is currently recognised - but such a high cutpoint for T2* would generate a poor specificity.
AAG is supported by a research grant from the Rosetrees Trust.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.