Determination of the R2* relaxation rate constant for estimating hepatic iron concentration: A customized approach that considers liver fat infiltration.

ABSTRACT

PURPOSE: Α customized approach to determine R2* relaxation rate for hepatic iron concentration (HIC) estimation is presented, and is evaluated in the context of concurrent liver fat infiltration. METHODS: The proposed method employs a customized acquisition protocol, featuring a 16-echo, gradient-echo sequence, and a bi-exponential least squares fitting that considers baseline noise and uses a cosine function to correct for fat-induced signal oscillation. 193 patients with wide-ranging HIC and liver fat fraction (FF) were imaged at 1.5 T. In severely iron-overload patients, a four-echo train technique was applied to enforce all 16 echoes in the 1.2-4.0 ms range. Acquired data were compared to corresponding results obtained with the IDEAL IQ method. RESULTS: Techniques employed to counter the rapid signal decay in iron-overloaded liver, such as the offset and the truncation methods, have to be combined with the appropriate calibration curve to provide reliable HIC estimation. When high grade steatosis and siderosis co-exist, fat-suppression may downgrade siderosis. A high correlation was observed between data obtained with the proposed technique and the IDEAL IQ method, except from the high R2* region. However, systematic differences were detected. In the concurrent presence of high FF and non-severe iron overload, it is postulated that the bi-exponential model may attribute patient siderosis grading more accurately than IDEAL IQ, while simultaneously providing reliable FF estimation. CONCLUSIONS: The proposed approach is widely available and seems capable of providing reliable R2* measurements regardless of liver steatosis grading, whilst it succeeds in averting significant R2* underestimation in severely iron-overloaded liver.