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Improved R2* measurements in myocardial iron overload
Nilesh R Ghugre1, Cathleen M Enriquez, Thomas D Coates
1Division of Cardiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California 90027, USA.
Purpose:
To optimize R2*(1/T2*) measurements for cardiac iron detection in sickle cell and thalassemia patients.
Materials And Methods:
We studied 31 patients with transfusion-dependent sickle cell disease and 48 patients with thalassemia major; myocardial R2* was assessed in a single midpapillary slice using a gated gradient-echo pulse sequence. Pixel-wise maps were coregistered among the patients to determine systematic spatial fluctuations in R2*. The contributions of minimum TE, echo spacing, signal-decay model, and region-of-interest (ROI) choice were compared in synthetic and acquired images.
Results:
Cardiac relaxivity demonstrated characteristic circumferential variations regardless of the degree of iron overload. Within the interventricular septum, a gradient in R2* from right to left ventricle was noted at high values. Pixel-wise and ROI techniques yielded nearly identical values. Signal decay was exponential but a constant offset or second exponential term was necessary to avoid underestimation at high iron concentration. Systematic underestimation of R2* was observed for higher minimum TE, limiting the range of iron concentrations that can be profiled. Fat-water oscillations, although detectable, represented only 1% of the total signal.
Conclusion:
Clinical cardiac R2* measurements should be restricted to the interventricular septum and should have a minimum TE < or = 2 msec. ROI analysis techniques are accurate; however, offset-correction is essential.
