Improved R2* measurements in myocardial iron overload.
OBJECTIVE
To optimize R2*(1/T2*) measurements for cardiac iron detection in sickle cell and thalassemia patients.


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.


CONCLUSIONS
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.
Ghugre
Nilesh R
NR
Division of Cardiology, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California 90027, USA.
Enriquez
Cathleen M
CM
Coates
Thomas D
TD
Nelson
Marvin D
MD
Wood
John C
JC
D000755:Anemia, Sickle Cell / Q000378:metabolism*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D019190:Iron Overload / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D013789:Thalassemia / Q000378:metabolism*