Calibration of myocardial T2 and T1 against iron concentration.

BACKGROUND: The assessment of myocardial iron using T2* cardiovascular magnetic resonance (CMR) has been validated and calibrated, and is in clinical use. However, there is very limited data assessing the relaxation parameters T1 and T2 for measurement of human myocardial iron. METHODS: Twelve hearts were examined from transfusion-dependent patients: 11 with end-stage heart failure, either following death (n=7) or cardiac transplantation (n=4), and 1 heart from a patient who died from a stroke with no cardiac iron loading. Ex-vivo R1 and R2 measurements (R1=1/T1 and R2=1/T2) at 1.5 Tesla were compared with myocardial iron concentration measured using inductively coupled plasma atomic emission spectroscopy. RESULTS: From a single myocardial slice in formalin which was repeatedly examined, a modest decrease in T2 was observed with time, from mean (± SD) 23.7 ± 0.93 ms at baseline (13 days after death and formalin fixation) to 18.5 ± 1.41 ms at day 566 (p<0.001). Raw T2 values were therefore adjusted to correct for this fall over time. Myocardial R2 was correlated with iron concentration [Fe] (R2 0.566, p<0.001), but the correlation was stronger between LnR2 and Ln[Fe] (R2 0.790, p<0.001). The relation was [Fe] = 5081•(T2)-2.22 between T2 (ms) and myocardial iron (mg/g dry weight). Analysis of T1 proved challenging with a dichotomous distribution of T1, with very short T1 (mean 72.3 ± 25.8 ms) that was independent of iron concentration in all hearts stored in formalin for greater than 12 months. In the remaining hearts stored for <10 weeks prior to scanning, LnR1 and iron concentration were correlated but with marked scatter (R2 0.517, p<0.001). A linear relationship was present between T1 and T2 in the hearts stored for a short period (R2 0.657, p<0.001). CONCLUSION: Myocardial T2 correlates well with myocardial iron concentration, which raises the possibility that T2 may provide additive information to T2* for patients with myocardial siderosis. However, ex-vivo T1 measurements are less reliable due to the severe chemical effects of formalin on T1 shortening, and therefore T1 calibration may only be practical from in-vivo human studies

Optimization of scantiming in abdominal breathhold contrast-enhanced MRA: an empirical guideline

The objective of this study to determine a suitable scan timing scheme in contrast enhanced MRA for the depiction of the arterial. the portal and the systemic venous system in the abdomen with maximum signal intensity in healthy subjects and in patients with cirrhosis. The signal intensity in the aorta, hepatic artery. portal vein, left renal vein and the supra- and infrarenal IVC were measured in 40 consecutive orthotopic liver transplantation candidates with cirrhosis and 20 healthy renal donors in a bolus triggered arterial scan and after 30, 60, 90 and 150 s respectively. The aorta and hepatic artery showed the highest signal intensity on the arterial scan. The portal and left renal vein showed the highest signal intensity after 30 s, the suprarenal IVC after 60 s and the infrarenal IVC after 90 s. No significant differences were found between healthy subjects and patients with cirrhosis. The arterial, portal and systemic venous system in the abdomen can be visualized selectively with maximum signal intensity by proper timing of the scans, hereby reducing redundant scans. Scanning at just the right time to achieve optimal vessel opacification can he promoted by using data from this study. The proposed scan scheme is suitable for subjects with and without cirrhosis. (C) 2001 Elsevier Science Inc. All rights reserved