Quantification of liver iron concentration using the apparent susceptibility of hepatic vessels

Abstract

Background: The quantification of liver iron concentration (LIC) is important for the monitoring of the body iron level in patients with iron overload. Conventionally, LIC is quantified through R2 or R2* mapping using MRI. In this paper, we demonstrate an alternative approach for LIC quantification through measuring the apparent susceptibility of hepatic vessels using quantitative susceptibility mapping (QSM).Methods: QSM was performed in the liver region with the iterative susceptibility weighted imaging and mapping (iSWIM) algorithm, using the geometry of the vessels extracted from magnitude images as constraints. The susceptibilities of liver tissue were estimated from the apparent susceptibility of the hepatic veins and then converted to LIC. The accuracy of the proposed method was first validated using simulations, and then confirmed using in vivo data collected on 8 healthy controls and 11 patients at 3T. The effects of data acquisition parameters were studied using simulations, and the LICs estimated using QSM were compared with those estimated using R2* mapping. Results:Simulation results showed that the use of a 3D data acquisition protocol with higher image resolution led to improved accuracy in LIC quantification using QSM. Both simulations and in vivo data results demonstrated that the LICs estimated using the proposed QSM method agreed well with those estimated using R2* mapping. With the shortest echo time being 2.5ms in the multi-echo gradient echo sequence, simulations results showed that LIC up to 12.45 mg iron/g dry tissue can be quantified using the proposed QSM method. For the in vivo data, the highest LIC measured was 11.32 mg iron/g dry tissue.Conclusions: The proposed method offers a reliable and flexible way to quantify LIC and has the potential to extend the range of LIC that can be accurately measured using R2* and QSM.

Analysis of different phase unwrapping methods to optimize quantitative susceptibility mapping in the abdomen

“…The resulting synthetic susceptibility map was then used to calculate phase maps for 3T magnetic field strength at 6 different echo times (TE = 4.92, 9.84, 14.76, 19.68, 24.60, and 29.52 ms) using a forward model as described in a previous work . Corresponding magnitude images were simulated by applying the following R2* values to the different anatomical regions: liver (52.27 s –1 ), kidney (20.16 s –1 ), fat (27.50 s –1 ), and remaining soft tissue (36.23 s –1 ) . Magnitude values at TE = 0 ms were the same for all regions, apart from bones and air, which were set to 0.…”

“…Several recent studies have proposed application outside the brain, including the breast, prostate, and articular cartilage . In 2 studies the feasibility of the determination of iron uptake in the liver in patients with iron overload was shown . Other abdominal organs, such as the kidney, have recently been studied in mice .…”

“…6 In 2 studies the feasibility of the determination of iron uptake in the liver in patients with iron overload was shown. [7][8][9][10][11] Other abdominal organs, such as the kidney, have recently been studied in mice. [12][13][14] It was demonstrated that inflammation and fibrosis led to a decrease of susceptibility in the kidneys.…”

Iron deposition quantification: Applications in the brain and liver

“…Using the known mathematical relationship to the susceptibility distribution, early studies calculated the B 0 field to reflect the underlying susceptibility. These works compared the B 0 field difference between liver parenchyma and portal venous blood, and between liver parenchyma and adjacent tissues (fat, muscle). Work by Taylor et al demonstrated that the field inhomogeneity was correlated to ( R 2 = 0.85), from which the corresponding derived LIC also correlated well ( R 2 = 0.94).…”

Quantitative Susceptibility Mapping for Characterization of Intraplaque Hemorrhage and Calcification in Carotid Atherosclerotic Disease

“…Quantitative susceptibility mapping (QSM) is a novel technique used to quantify tissue magnetic susceptibility properties [9][10][11] . Recently, QSM has been proposed to differentiate diamagnetic calcifications and paramagnetic hemorrhages in the brain [12] and a phase based method has been used for vessel wall imaging in the major peripheral arteries [13] .…”