Improved transverse relaxation rate measurement techniques for the assessment of hepatic and myocardial iron content

Abstract

To develop and validate an optimized respiratory-gated, gradient-echo sampling of free induction decay and echo (GESFIDE) pulse sequence for the simultaneous measurement of R2, R2*, and R2' in the liver or heart. Fifteen subjects (12 thalassemia patients and three normal volunteers) were scanned using an optimized navigator-gated GESFIDE pulse sequence for the measurement of R2, R2*, and R2' in the liver and heart. For imaging the myocardium, dark-blood preparation was used to suppress the blood signal to improve accuracy. The results were compared with those obtained from breath-held GESFIDE and multi-gradient-echo (GRE) scans. Good agreement between breath-held and navigator-gated scans was found for R2, R2*, and R2' values in the liver (slopes = 0.97-0.99, r = 0.997-0.998, P < 0.0001) and for R2* in the heart (slope = 1.02, r = 0.85, P < 0.0001). Both R2* and R2' were closely correlated to R2 in the liver, with correlation factors of 0.998 and 0.994, respectively, but weaker correlations were observed in the heart (r = 0.72 for R2* vs. R2 and r = 0.51 for R2' vs. R2). The improved sequence enables free-breathing measurements of transverse relaxation rates of the myocardium and liver. The method precludes the need for multiple breath-held scans and possible misregistration issues, and may prove most beneficial for imaging young children and patients who may have difficulty with prolonged or repeated breath-holds.