MR liver iron quantification

MR liver iron quantification is a non-invasive means of measuring liver iron concentration, a key indicator in the management of patients with haemochromatosis (primary or secondary).

Apart from being non-invasive, sampling occurs in a large cross section of the liver, as opposed to biopsy which typically represents 1/50,000 of the whole liver. 

The acquisition for both methods described below is typically short and usually takes up 10 minutes of magnet time only.

Physics

There are two principle methods of liver iron quantification by MRI

T2 relaxometry

Iron within liver has paramagnetic properties and results in a decrease in T2 relaxation times. The accelerated relaxation is proportional to iron content. Decay models are attributed to the average signal intensity at  different echo times. These values may also be expressed as relaxation rates R2 (1/T2) or R2* (1/T2*). To To obtain reliable measurements of T2 times at different levels of iron overload, acquisition sequences with several different echo times are needed. The signal Signal intensity is then plotted as a function of echo time andcan be used to obtain a T2 parametric map.¹

Signal intensity Ratio (SIR)

The ratio between the signal intensity of the liver and the signal intensity of paraspinal muscle that does not accumulate iron can be used to determine liver iron concentration Using the same slice, signal intensity measurements are performed using ROIs, avoiding large vessels in the liver. The sequences used are gradient recalled echoes as these are more sensitive to the paramagnetic effect of iron. One of the most recognised SIR method was developed at the University of Rennes, France.² This method of quantification is automatically obtainedpresented here, including an online calculator.