Iron and fat quantification
Hepatic iron concentration (HIC or LIC) can be estimated by both methods: T2* calculation or the signal intensity ratio (SIR) between the liver and the paravertebral muscles. Both methods have advantages:
- T2* is certainly the best methods as soon phase oscillation due to steatosis is managed and as soon the shortest TE used allows a correct T2* estimation in case of high overload.
- SIR method is easier to perform with no need of a multiecho gradient echo sequence since the measurement is "calibrated" by the muscle used as a reference. The precision is probably not as good as that obtained by the T2* assessment. The MR acquisition protocol must use the body coil. SIR method can better estimate high overload by reducing the TE below the value initially proposed. This reduction du TE introduce a phase contrast and can only be used when the signal is falled-down on the in-phase TEs.
The evaluation of the fat fraction (FF) can be done via phase imaging by comparing the signal of the liver on the images in phase and in phase opposition. A joint estimate is necessary because each overload can influence the quantification of the other overload.