Keywords: Susceptibility/QSM, Susceptibility, Fat/Water Separation

Motivation: Gradient echo imaging using in-phase echoes has been proposed to simplify the fieldmap estimation in water–fat regions. The use of so-called effective multi-peak in-phase echo times allow for the bias-free QSM estimation in body regions in the presence of complex fat-models. Conventionally, the in-phase paradigm rigidly constrains the selection of echo times, often balancing acquisition speed, resolution, and SNR against one another. 

Goal(s): .

Approach: .

Results: This study demonstrates the feasibility of a nearly unrestricted selection of the first echo time, without introducing significant quantification bias. This advance allows for a more flexible and efficient imaging process.

Impact: This work introduces a simple, flexible and bias-free body QSM acquisition strategy based on so-called pseudo in-phase echos that allows for considerably faster acquisitions while simultaneously increasing the SNR efficiancy

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping, Total Field Inversion, Boundary Element method, Fast Multipole method

Motivation: The study aims to improve quantitative susceptibility mapping (QSM) precision at region of interest (ROI) boundaries where background field interference affects accuracy.

Goal(s): To introduce a novel boundary element method total field inversion (BEM-TFI) enhanced by the fast multipole method (FMM) for high-resolution QSM.

Approach: A comparative assessment of BEM-TFI technique was performed with traditional QSM methods, utilizing in-vivo data and simulated field maps to determine inversion quality and background field removal efficiency.

Results: Enhanced by FMM, the BEM-TFI method demonstrated significant improvements in accurately discerning tissue susceptibility from background noise, indicating a substantial advancement in the outcomes of QSM.

Impact: The BEM-TFI enhancement in QSM accuracy allows for more detailed characterization of the brain's cortex, potentially enriching neuroscientific research and elevating the quality of neuroimaging data.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping, Orientation-Adaptive, Latent Feature Editing, OA-iQSM

Motivation: The performances of most DL-QSM methods are limited to MRI phase data of pure-axial acquisition orientation. 

Goal(s): In this work, we would like to propose a novel DL-based end-to-end neural network for QSM reconstruction from phase data of arbitrary dipole orientations. 

Approach:  A novel Latent Feature Editing (LFE) module to learn the encoding of acquisition orientation vectors and seamlessly integrate them into the latent features of deep networks to make them orientation-adaptive. 

Results: Both simulated and in vivo experiments demonstrate that the proposed LFE module can result in desirable QSM images at arbitrary oblique head orientations. 

Impact: This work introduces a new DL paradigm, allowing researchers to develop innovative QSM methods without requiring a complete overhaul of their existing architectures.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping, Source Separation, DECOMPOSE, Multi-echo

Motivation: DECOMPOSE-QSM is a susceptibility source separation method that has the potential for many clinical applications. However, its sensitivity to input QSM acquisition parameters and reconstruction method, and its repeatability are unknown.

Goal(s): To investigate the performance and repeatability of DECOMPOSE-QSM with QSM calculated using various acquisition schemes and multiple dipole inversion methods.

Approach: Eight different QSM dipole-inversion methods were used as inputs for DECOMPOSE-QSM. Multi-echo GRE were acquired with different protocols to evaluate reproducibility and sensitivity to the acquisition.

Results: We reduced susceptibility contrast differences from different QSM methods by normalizing input susceptibilities. DECOMPOSE-QSM results were repeatable across different subjects.

Impact: We showed that, with normalization, inputting QSM from different inversion methods yields similar DECOMPOSE-QSM separation maps and that this technique is reproducible. Taking into account its sensitivity to different acquisition parameters will facilitate further clinical applications of DECOMPOSE-QSM.

Keywords: Data Processing, Aging

Motivation: Studies have demonstrated that iron accumulation rates in various gray matter nuclei are different throughout an individual’s lifetime, yet no study has quantitatively evaluated how the spatial distribution of brain iron might evolve with normal physiological development and aging.

Goal(s): This study was to investigate the change trajectories of spatially distribution of iron in the deep gray matter nuclei as a function of ageing using QSM. 

Approach: 3D texture analyses were performed on QSM maps to calculate the texture features using the GLCM.

Results: The quadratic regression results characterized differential age-dependent trajectories of texture features in gray matter of basal ganglia, midbrain and cerebellum. 

Impact: Quantitatively evaluated the spatial distribution properties of brain iron during lifespan might provide critical information for understand the brain development and aging, as well as predicting cognitive or neurodegenerative diseases.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping, Cortex orientation, Myelin concentration

Motivation: Effect of cortex orientation relative to the magnetic field can impede quantitative susceptibility mapping (QSM) from being established as a robust measurement of cortical pathology.

Goal(s): To identify the significance of cortical orientation effect in QSM and its underlying contribution from cortical myelin.

Approach: QSM was performed in eight healthy subjects at isotropic 0.75mm resolution at 3T. The relationship between QSM and cortical orientation was evaluated in cortical regions across the brain. The region-specific effect strength was correlated with region-average myelin approximation.

Results: Significant orientation effect was observed in most brain regions, including significant correlation between the region-specific effect strength and myelin estimation.

Impact: This study represents an initial effort to uncover the cortex orientation effect in cortical grey matter QSM result towards establishing QSM as a robust clinical tool for cortical pathology.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping, Vessels, Artifacts

Motivation: χ-separation is an advanced QSM method that provides para- and diamagnetic susceptibility maps. Despite its potential utilities, both maps reveal (erroneously) high intensity signals from vessels, hampering their applications and quantification. 

Goal(s): Proposing a vessel segmentation method designed for χ-separation by utilizing physical properties of vessel signals in χ-separation.  

Approach: Acquiring seeds by informing physics of vessels in χ-separation, and vessel geometry characteristics guided-region growing is implemented to generate vessel masks.

Results: Our method successfully creates vessel masks for both susceptibility maps and demonstrates to be robust to various input types. When applied to an ROI analysis, reduced variability in measurements was shown.

Impact: The novel vessel segmentation method utilizes physical properties of vessels in χ-separation for reliable and robust segmentation, providing substantially improved segmentation results. It may help us to improve downstream analysis when quantifying susceptibility of myelin or tissue iron excluding vessels.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping, subvoxel QSM

Motivation: Subvoxel QSM could be beneficial for assessing the knee cartilage but requires two separate sequences for reconstruction by using APART-QSM.

Goal(s): To achieve subvoxel QSM reconstruction of knee cartilage in a single scan. 

Approach: A multi-contrast framework was used to simultaneously estimate $$$T_1$$$, $$$T_2$$$ and $$$T_2^{*}$$$ mapping in one scan. The magnitude and phase images were generated based on the signal equation. The preprocessed phase and $$$R_2^{'}$$$(=$$$1/{T_2^*}$$$-$$$1/{T_2}$$$) were used for subvoxel QSM reconstruction. The results were compared with conventional approach using two sequences (GRE+MSE). 

Results: The subvoxel QSM results using the multi-contrast framework have good agreement with the conventional condition. 

Impact: The diamagnetic and paramagnetic susceptibility source separation of the knee cartilage could be achieved in a single scan using a multi-contrast framework. This technique can provide specific information to assess the tissue magnetic properties of the knee cartilage.

Keywords: Gray Matter, Quantitative Susceptibility mapping

Motivation: MRI signals have phase information from the GRE sequence, which reflects B0 field homogeneities. 

Goal(s):  Due to acquisition, the phase is converted from complex data, ranging from -π to π and causing visual discontinuities. However, previous learning-based approaches have difficulties processing 3D brain data directly. 

Approach: In this study, we introduced an unsupervised refinement based on Deep Image Prior to enhance the performance of the pre-trained networks (PHU-DIP), and the inference were performed on one simulated and one in vivo brain. 

Results: The PHU-DIP method corrected the misclassification regions from the pre-trained networks and exhibited the significant time-efficiency compared to conventional method.

Impact: The PHU-DIP provided a refinement scheme that help to improve the performance of a well-trained network. This technique could also be expanded onto other training modes and other pathological conditions. 

Keywords: Susceptibility/QSM, Susceptibility, High-resolution anatomy

Motivation: High-resolution χ-separation at 7T can delineate detailed structures related to iron and myelin concentrations in the brain. However, it has the challenge of requiring an R2 map, which is not practical at 7T due to SAR and scan time. 

Goal(s): Our objective is to generate high-resolution χ-separation maps at 7T.

Approach: An R2* 7T-to-3T conversion network to transform a 7T R2* map into its 3T counterpart is developed. Then, 𝜒-separation is processed via QSMnet, χ-sepnet-R2*, and resolution generalization.

Results: We successfully produced high-quality and high-resolution 𝜒-separation maps only from multi-echo gradient echo data at 7T.

Impact: This study suggests a solution for the technical challenge of requiring R2 map in 7T χ-separation, enabling high-resolution (=650 um) χ-separation. This may benefit the analysis of iron and myelin concentration changes in various neurodegenerative diseases through detailed structural examination.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping

Motivation: Quantitative Susceptibility Mapping (QSM) at 7-Tesla (7T) has been implicated to improve assessment of neurodegenerative disorders but has yet to be integrated into clinical practice.

Goal(s): We aimed to address the growing demand for a standardized and optimized QSM reconstruction protocol that enables accurate quantification of susceptibility, mitigates contaminating artifacts, and is clinically feasible. 

Approach: Here, we compared 32 end-to-end QSM processing pipelines and evaluated their performance.

Results: We show that reconstruction with Laplacian phase-unwrapping, RESHARP background field removal, and MEDI dipole inversion outperformed other pipelines in suppressing artifacts.

Impact: Our optimized pipeline results in a 7T QSM reconstruction with clear cortical and subcortical boundaries, and mitigates susceptibility artifacts. Furthermore, the comprehensive review of QSM processing algorithms highlights Laplacian, RESHARP, and MEDI as robust algorithms with reliable, consistent performance.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping, cognitive decline

Motivation: Brain iron content may play an important role in the development of Mild Cognitive Impairment (MCI) and dementia due to Alzheimer’s Disease (AD).

Goal(s): To investigate the utility of baseline brain iron levels, measured by quantitative susceptibility mapping (QSM), to predict time to onset of symptoms of MCI and global cognitive decline among older adults with normal cognition at baseline.

Approach: Cox regression models and linear mixed models were used.

Results: Higher brain iron levels in entorhinal cortex and putamen were associated with an earlier time to MCI onset and greater global cognitive decline, independent of the volume and amyloid of those regions.

Impact: Brain iron deposition assessed by QSM MRI may help predict risk of MCI onset and cognitive decline among cognitively normal individuals.

Keywords: Susceptibility/QSM, Susceptibility, Gray Matter/ Ex-Vivo Applications

Motivation:  Previous studies have demonstrated the correlations between iron and paramagnetic susceptibility and myelin and diamagnetic susceptibility. However, there has yet to be a quantitative layer-wise comparison with histology.

Goal(s):  Our objective is to validate laminar structures of χ-separation against histology in V1.

Approach:  In V1, we performed laminar profiling of χ-separation, iron-, and myelin histology. The profile was obtained by sampling points at 5% intervals along the cortical depth, oriented perpendicularly to the cortex.

Results: The cortical depth profile reveals that both χ_para with iron histology and χ_dia with myelin staining exhibit similar profiles and peaks at the location of the Gennari line.

Impact: By comparing the cortical depth profile in the V1 region including the location of the Gennari line between χ-separation and histology, we have confirmed that χ-separation (χ_para, χ_dia) accurately represents the quantitative amounts of iron and myelin with precision.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping

Motivation: White matter (WM) microstructure can affect estimation of WM susceptibility with QSM. However, as QSM fits all voxels at once, it is less understood how it affects estimation of surrounding tissue.

Goal(s): Our goal is to demonstrate the effect of a cylindrical microstructure on surrounding tissue in a digital phantom.

Approach: We synthesize a digital phantom with parallel rods surrounded by a rim with random dots. We estimate susceptibility with (QSM+) and without (QSM) account of microstructure.

Results: QSM is biased inside the rim, and this error spreads to the surrounding tissue characterized by a power law. QSM+ improved susceptibility fitting.

Impact: It may be important to account for microstructure in WM even though one may only be interested in analyzing surrounding tissue like gray matter. Failing to do so could lead to misinterpretation of tissue magnetic susceptibility.

Keywords: Susceptibility/QSM, Electromagnetic Tissue Properties

Motivation: While high-resolution quantitative susceptibility mapping (QSM) reveals unprecedented anatomical cytoarchitectures, delineation of certain substructures may be limited in regions containing both iron and myelin.

Goal(s): To demonstrate iron and myelin-specific anatomy inside human brain using sub-millimeter susceptibility source-separation (chi-separation).

Approach: Sub-millimeter multi-orientation QSM and chi-separation were obtained on postmortem human hemibrain at 7T. Capabilities of QSM, χ_para and χ_dia contrasts for delineating neuroanatomy were compared.

Results: While iron-rich substructures like line of Gennari can be readily identified in QSM, χ_dia helps reveal small fibers including striatal tracts, perforant pathway and fibers in cortical/subthalamic area.

Impact: Sub-millimeter susceptibility source separation images can delineate neuroanatomical substructures in the human brain with increasing specificity to iron or myelin related cytoarchitecture.

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping, Susceptibility source separation, R2* mapping, Artifact correction, Iron imaging, Myelin imaging

Motivation: An advanced quantitative susceptibility mapping (QSM) technique, χ-separation, requires tissue field map and R₂* to separate paramagnetic and diamagnetic components. As the background field is removed to acquire the tissue field map, the background R₂* needs to be removed to accurately estimate paramagnetic and diamagnetic susceptibility maps.

Goal(s): Investigate the effect of background R₂* correction on χ-separation.

Approach: The effect of background R₂* correction on χ-separation was tested by varying the background R₂* with multiple head orientations and k-space filtering.

Results: Background R₂* correction successfully reduced overestimation in χ-separation maps in different head orientations and low-pass filtering levels.

Impact: Background R₂* correction enables consistent χ-separation across different head orientations and k-space filtering.