Quantitative susceptibility mapping in the abdomen as an imaging biomarker of hepatic iron overload

Abstract

Purpose The purpose of this work was to develop and demonstrate feasibility and initial clinical validation of quantitative susceptibility mapping (QSM) in the abdomen as an imaging biomarker of hepatic iron overload. Theory In general, QSM is faced with the challenges of background field removal and dipole inversion. Respiratory motion, the presence of fat, and severe iron overload further complicate QSM in the abdomen. We propose a technique for QSM in the abdomen that addresses these challenges. Methods Data were acquired from 10 subjects without hepatic iron overload and 33 subjects with known or suspected iron overload. The proposed technique was used to estimate the susceptibility map in the abdomen, from which hepatic iron overload was measured. As a reference, spin-echo data were acquired for R2-based LIC estimation. Liver R2* was measured for correlation with liver susceptibility estimates. Results Correlation between susceptibility and R2-based LIC estimation was R2 = 0.76 at 1.5T and R2 = 0.83 at 3T. Further, high correlation between liver susceptibility and liver R2* (R2 = 0.94 at 1.5T; R2 = 0.93 at 3T) was observed. Conclusion We have developed and demonstrated initial validation of QSM in the abdomen as an imaging biomarker of hepatic iron overload.

Phase-corrected bipolar gradients in multi-echo gradient-echo sequences for quantitative susceptibility mapping

“…Phase corrections with higher-order errors may further improve the accuracy of the field map estimation, which has been demonstrated to be important to fat quantification using multiecho sequences with bipolar gradients [36,38,47]. The application of the presented technique may be extended from brain tissue to include venous blood by including flow compensation gradients and additional phase modeling [19],, and may be further extended to imaging organs outside the brain by including the fat component in the signal model[48,49]. …”

Assessment of MR‐based and quantitative susceptibility mapping for the quantification of liver iron concentration in a mouse model at 7T

“…MRI, being widely available and significantly more cost‐effective, can also be used to quantify magnetic susceptibility through a procedure known as quantitative susceptibility mapping (QSM), which can be performed on the same 3D gradient echo data sets acquired to quantify . Recently, linear relationships between magnetic susceptibility obtained using QSM and LIC measurements have been reported, and a good linear correlation between susceptibility measurements obtained using QSM and a superconducting quantum interference device has been observed . However, studies comparing LIC measurements and liver susceptibility measurements obtained using QSM have mostly been performed at low field strengths (e.g., 1.5 Tesla [T] and 3T), and the reproducibility of QSM liver susceptibility quantification has not been studied.…”

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

“…As a fundamental property of tissues, magnetic susceptibility is more directly related to iron concentration than R2* (20). Particularly, while both R2 and R2* are dependent on main field strength, magnetic susceptibility is not dependent on imaging parameters and this may provide better reproducibility in LIC quantification (4,9,10).…”

“…It has great potential in improving both the accuracy and precision in the quantification of in vivo iron content, as demonstrated in various studies focused on the brain (14)(15)(16)(17)(18). However, there are a few technical challenges in applying the conventional QSM algorithms to the abdomen, including the difficulties in removing the background field in the presence of multiple air-tissue interfaces and solving the ill-posed inverse problem of QSM (19,20). Several methods have been proposed to overcome these obstacles, mainly by using a simplified model of the relationship between the susceptibility distribution and magnetic field variation (19,21,22).…”

“…Several methods have been proposed to overcome these obstacles, mainly by using a simplified model of the relationship between the susceptibility distribution and magnetic field variation (19,21,22). In a recent study, the conventional 3D dipole kernel based QSM algorithm was adapted for quantifying LIC, using the abdominal fat as the reference for estimating the susceptibility of liver tissue (20). Both phase unwrapping and background field removal was performed in the whole abdominal region and the robustness could be compromised by the noisy regions outside the liver.…”