Quantitative susceptibility mapping of human brain reflects spatial variation in tissue composition

Abstract

Image phase from gradient echo MRI provides a unique contrast that reflects brain tissue composition variations, such as iron and myelin distribution. Phase imaging is emerging as a powerful tool for the investigation of functional brain anatomy and disease diagnosis. However, the quantitative value of phase is compromised by its nonlocal and orientation dependent properties. There is an increasing need for reliable quantification of magnetic susceptibility, the intrinsic property of tissue. In this study, we developed a novel and accurate susceptibility mapping method that is also phase-wrap insensitive. The proposed susceptibility mapping method utilized two complementary equations: (1) the Fourier relationship of phase and magnetic susceptibility; and (2) the first-order partial derivative of the first equation in the spatial frequency domain. In numerical simulation, this method reconstructed the susceptibility map almost free of streaking artifact. Further, the iterative implementation of this method allowed for high quality reconstruction of susceptibility maps of human brain in vivo. The reconstructed susceptibility map provided excellent contrast of iron-rich deep nuclei and white matter bundles from surrounding tissues. Further, it also revealed anisotropic magnetic susceptibility in brain white matter. Hence, the proposed susceptibility mapping method may provide a powerful tool for the study of brain physiology and pathophysiology. Further elucidation of anisotropic magnetic susceptibility in vivo may allow us to gain more insight into the white matter microarchitectures.

Combining phase images from array coils using a short echo time reference scan (COMPOSER)

“…To allow a qualitative assessment of phase images generated with approaches 1–5 above, phase wraps were removed from the combined images using Laplacian unwrapping 4 as implemented in STI suite (http://people.duke.edu/~cl160/) and were high‐pass filtered. In the first subject scanned, magnitude images M SS , M rSOS , M COMPOSER_S , and M COMPOSER_W were calculated according to Eqs.…”

Imaging Brain Oxygenation with MRI Using Blood Oxygenation Approaches: Methods, Validation, and Clinical Applications

“…76,77 Susceptibility mapping has many possible applications, including accurate in vivo measurement of the concentration of contrast agents as well as investigation of the relationship between iron content and the progression of neurodegenerative diseases. To date, only 1 study 78 has focused on blood oxygenation measurements by using susceptibility mapping, and it found that the major veins in the brain could be visualized.…”

MR Quantitative Susceptibility Imaging for the Evaluation of Iron Loading in the Brains of Patients with -Thalassemia Major

“…Conventionally, MR relaxometry on the basis of methods that use T2 and T2* mapping has been used to quantify iron in the brain. 4 Recently, the application of measuring brain iron by use of phase value of MR imaging with SWI 5,6 and quantitative susceptibility mapping (QSM) [7][8][9][10][11][12] has been evaluated for the quantification of iron content in patients with Parkinson disease. 13 QSM is an MR imaging technique that measures the magnetic susceptibility of tissues, such as blood or iron content, through mathematically modeling their induced effects on the phase of signal.…”

“…Although the derivation of a magnetic susceptibility image from the phase informa-tion obtained from MR imaging is an ill-posed problem, techniques have been established to overcome this by imposing smoothness or sparseness constraints on the susceptibility images. [9][10][11] QSM has been successfully applied in multiple sclerosis, Parkinson disease, and so forth. A recent study 14 has also established positive correlation between magnetic susceptibility values measured by use of QSM and iron content measured by x-ray fluorescence imaging and inductively coupled plasma mass spectrometry.…”