Liver iron content is normally < 36 µmol per gram liver dry weight.
Field strength for the MRI was 1.5 T. GRE (gradient recalled echo) sequences ranged from T1 to T2++.
ratio liver to muscle signal intensity =
= (signal intensity in liver) / (signal intensity in muscle)
Using highly weight GRE sequences (T2++ images, Figure 1):
• Threshold for ratio was 0.88. A value < 0.88 correlated with hepatic iron stores > 60 µmol per gram liver dry weight.
• A ratio of 0.2 was reached at about 86 µmol per gram liver dry weight.
Using T1 images (Figure 2), the data was a curve.
• The red line at a ratio of 0.13 corresponded with hepatic iron stores > 355 µmol per gram liver dry weight.
The authors developed an algorithm to estimate hepatic iron concentrations from the most sensitive sequence (the one with L/M ratio greater than its own saturation threshold). The algorithm is available at www.radio.univ-rennes1.fr
Performance:
• For the T2++ images, the sensitivity was 89% and specificity 80% for the threshold of 0.88. A threshold of 1 had a sensitivity of 95% and specificity of 88%.
• MRI has several advantages over liver biopsy for determining hepatic iron content. It was more acceptable to patients. About 3% of patients failed the MRI, while 5% of liver biopsies may too small for doing iron measurement studies.
