Purpose: To measure the transverse relaxation rate (1/T2) and magnetic susceptibility of the heart in conditions of iron overload by using magnetic resonance (MR) imaging and to correlate these with the tissue iron concentration in a gerbil model.
Materials and methods: With prior approval by the institutional animal care and use committee, iron overload was induced with one to 15 weekly subcutaneous injections of iron dextran. Nine gerbils had one to five injections, 10 had six to 10, and eight had 13-15. T2 of the whole heart was measured ex vivo (n=27), and the magnetic susceptibility of the tissue was estimated through measurement of the tissue lysate (n=25). The iron level was measured (in milligrams of iron per gram of wet tissue) with chemical analysis after MR imaging. While 1/T2 and magnetic susceptibility are not equivalent measures of the chemically determined tissue iron level, correlations were expected and were identified by using linear regression models.
Results: Iron concentration range was 0.28-1.95 mg/g wet tissue. Iron concentration was strongly correlated with 1/T2 (r=0.92, P <.001, and the root of the mean squares error of the linear prediction, epsilonRMS, was 0.17 mg Fe/g wet tissue with a repetition time of 700 msec). Iron concentration also was strongly correlated with magnetic susceptibility (r=0.90, P <.001, epsilonRMS=0.19 mg Fe/g wet tissue). Multiple regression analysis with combined 1/T2 (with repetition time of 700 msec) and magnetic susceptibility data led to a slight increase in r and decrease in epsilon(RMS) (r=0.93, P <.001, epsilonRMS=0.16 mg Fe/g wet tissue).
Conclusion: The results of this animal model study demonstrate that 1/T2 and magnetic susceptibility values can be used for estimation of the iron level in the heart.