Nonlinear Regularization for Per Voxel Estimation of Magnetic Susceptibility Distributions From MRI Field Maps

Abstract

Magnetic susceptibility is an important physical property of tissues, and can be used as a contrast mechanism in magnetic resonance imaging. Recently, targeting contrast agents by conjugation with signaling molecules and labeling stem cells with contrast agents have become feasible. These contrast agents are strongly paramagnetic, and the ability to quantify magnetic susceptibility could allow accurate measurement of signaling and cell localization. Presented here is a technique to estimate arbitrary magnetic susceptibility distributions by solving an ill-posed inversion problem from field maps obtained in an MRI scanner. Two regularization strategies are considered, conventional Tikhonov regularization, and a sparsity promoting nonlinear regularization using the ℓ1 norm. Proof of concept is demonstrated using numerical simulations, phantoms, and in a stroke model mouse. Initial experience indicates that the nonlinear regularization better suppresses noise and streaking artifacts common in susceptibility estimation.

In VivoMRI Mapping of Brain Iron Deposition across the Adult Lifespan

“…The third caveat is that other paramagnetic metals such as copper, manganese, or aluminum could also, in theory, exert a QSM influence (Andrasi et al, 2005;Ramos et al, 2014), although this is quite unlikely in aging in view of their scarcity compared with brain iron (Krebs et al, 2014;Ramos et al, 2014). It was nonetheless reassuring that the concordance of QSM with past postmortem assays was high (Langkammer et al, 2012;Zheng et al, 2013), suggesting that nonheme iron depositionlikely ferric iron (Sun et al, 2015)-is the dominant source of QSM alterations due to aging. Demyelination could, however, play a more active role in modulating QSM alterations (Fukunaga et al, 2010; Stüber et al, 2014).…”

“…Finally, susceptibility-weighted imaging (SWI) yields nonlocal measures that are difficult to interpret in biological terms (Pfefferbaum et al, 2009). To circumvent such limitations, a new contrast referred to as quantitative susceptibility mapping (QSM) has been proposed (de Rochefort et al, 2008;Kressler et al, 2010). QSM can measure magnetic susceptibility from MRI scans using standard commercial scanners Wang and Liu, 2015).…”

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.…”

Computational Analysis: A Bridge to Translational Stroke Treatment

“…However, cellular density cannot be adequately determined using visual methods, hampering true quantitative measurements of replication. Recent studies have attempted to quantify the amount of iron, hence the number of NSCs, using susceptibility weighted images (SWI) and maps [ 75 ] . While location is important, the number, density, and replication of these NSCs are equally critical.…”

“…42.7 ) are promising and are currently being validated using immunohistochemical staining [ 77,78 ] . We have extended this method to detect iron-labeled NSCs from SWI which we expect will have increased detectability due to the exquisite sensitivity of SWI to enhance detection of iron particles within NSCs [ 75 ] .…”