Advances in Quantitative Susceptibility Mapping for Human Brain

Advances in Quantitative Susceptibility Mapping for Human Brain
Author: Ashmita De
Publisher:
Total Pages: 0
Release: 2022
Genre: Brain
ISBN:

Quantitative Susceptibility Mapping (QSM) is an emerging postprocessing method, computed from phase images, which is finding wide application in quantifying iron content in healthy and pathological tissue. However, QSM is still not commonly used in clinical practice. This thesis discusses the challenges that come during the application of QSM to patient studies and makes advances to solve problems such as long acquisition times, motion, and works towards finding more applications for QSM. The focus for this work is on stroke applications where methods such as Susceptibility Weighted Imaging (SWI) and Time-of-Flight (TOF) MR Angiography (MRA) are already used.SWI finds one application in the study of hemorrhage, and it has been shown in previous studies that QSM can be reconstructed from the single echo SWI sequence. However, whole brain SWI requires an acquisition time of about 5 mins which is often too long for hemorrhagic patients to remain still inside the scanner. In Chapter 2, a rapid single-shot Echo-planar Imaging (EPI) sequence with acquisition time of 0.45 mins was applied to subjects with intracerebral hemorrhage (ICH) which enabled rapid measurement of ICH area and mean magnetic susceptibility, with reduced motion as compared to standard SWI. EPI requires minimal additional acquisition time and hence can be incorporated into iron tracking studies in ICH.Motion effects cause artifacts in magnitude as well as phase images. Hence, Chapter 3 investigates the quantitative effects of movement and respiratory fluctuations on QSM in the brain. QSM was found to be more sensitive to motion caused by movement than magnitude images and thus post-processing motion correction or faster sequences may be beneficial for QSM applications. However, respiratory fluctuations did not cause statistically significant differences in susceptibility values in group study; although, these variations might be considered important in individual follow-up studies.SWI is widely used in the study of veins, hematoma, lesions etc. However, since it uses filtered phase for its computation, SWI has certain limitations such as artifacts arising from phase wraps, blooming effects, dependence of phase value on the orientation of object with main magnetic field etc. In order to overcome SWI limitations, a new method called quantitative susceptibility weighted imaging also known as true susceptibility weighted imaging (tSWI), has been recently introduced which uses susceptibility maps instead of filtered phase. Chapter 4 aims at optimizing tSWI parameters for strong susceptibility sources like hemorrhage and investigates the benefits and limitations of tSWI for hemorrhages. In hemorrhage, tSWI minimizes both blooming effects and phase wrap artifacts observed in SWI. However, unlike SWI, tSWI requires an alteration in the threshold limits for best hemorrhage depiction that greatly differs from the standard values. tSWI can be used as a complementary technique for visualizing hemorrhages along with SWI.It is always desirable to obtain maximum information from a single acquisition. Hence in Chapter 5, a new sequence has been introduced to simultaneously compute TOF-MRA, QSM, SWI and transverse relaxation rate R2* while maintaining all the key features of standard TOF-MRA such as multiple overlapping thin slab acquisition (MOTSA), ramped RF pulses and venous saturation. The effect of these TOF features on QSM and SWI was studied. The proposed sequence with the TOF features provided TOF-MRA and SWI with similar CNRs to standard methods. The mean susceptibility values for brain structures had no significant susceptibility variation between the proposed and standard methods as well. Thus, this sequence is able to provide similar TOF-MRA to standard TOF methods while enabling additions of SWI, R2* and QSM.

Quantitative Susceptibility Mapping in Human Brain

Quantitative Susceptibility Mapping in Human Brain
Author: Hongfu Sun
Publisher:
Total Pages: 152
Release: 2015
Genre: Brain mapping
ISBN:

Quantitative susceptibility mapping (QSM) is an emerging magnetic resonance imaging (MRI) method that provides image contrast based on an important underlying brain tissue property. It is derived from the phase images from a gradient echo sequence, and overcomes the orientation dependency problem associated with phase imaging. However, QSM from gradient echo phase involves complicated image processing for reconstruction. This thesis explores technical challenges in QSM and provides advanced methods to solve them. Methods are introduced for background phase removal and fast QSM and then applied in three QSM applications: functional MRI studies, validation of QSM for deep grey matter iron in multiple sclerosis subjects and evaluation of QSM in patients with intracranial hemorrhage. One of the biggest challenges in QSM reconstruction is the removal of background phase. A novel method that makes use of the harmonic property of background field and Tikhonov regularization is presented in Chapter 2. The method is named RESHARP (Regularized Enabled Sophisticated Harmonic Artifact Reduction for Phase data). It is shown to be effective and robust in removal background phase while reserving local phase contrast. QSM has been proposed as a direct brain iron mapping technique for deep grey matter. However, most of the susceptibility to iron correlations are estimated using a brain iron study more than 50 years ago. A postmortem study is performed by measuring brain iron levels using Perls' ferric iron staining and comparing with susceptibilities in multiple sclerosis brain, which is presented in Chapter 3. High linear correlations between Perls' optical density and QSM were found in three subjects studied, leading to the conclusion that ferritin-iron is the main susceptibility source in deep GM which can be measured with QSM. Fast acquisition of QSM is also demonstrated in Chapter 4 using high resolution single-shot gradient echo-planar imaging (EPI). It reduces scan time from using regular gradient echo imaging of ~ 6mins to only 7 secs. Deep grey matter iron contrasts using EPI are found to be similar to traditional full scan. As an application of fast QSM with EPI, QSM extraction from regular fMRI studies is illustrated in Chapter 5, which also use gradient EPI. A single mean QSM from fMRI time series is derived for deep grey matter, which enables QSM application from any standard fMRI study. Heme-iron is highly concentrated in intracranial hemorrhage and changes its form with blood degradation, which makes it a perfect candidate for QSM application. However, gradient echo images in the clinic typically are obtained from a single echo with long echo time, which impedes QSM due to the fast signal decay within and around hemorrhage. A new method is presented in Chapter 6 that isolates the ICH dipole field followed by susceptibility superposition using multiple boundaries for background field removal. This method significantly reduces artifacts and makes susceptibility measurement of ICH feasible. In conclusion, this thesis has proposed methods to solve QSM reconstruction challenges, illustrated and validated its clinical value and power as a new contrast mechanism for MRI.

Robust Phase Pre-processing for Quantitative Susceptibility Mapping

Robust Phase Pre-processing for Quantitative Susceptibility Mapping
Author: Alex Ensworth
Publisher:
Total Pages:
Release: 2021
Genre:
ISBN:

"Quantitative susceptibility mapping (QSM) is a technique in magnetic resonance imaging (MRI) that translates the signal produced by an MRI scanner into values of magnetic susceptibility related to the structures that are being scanned. MRI scanners record complex signal with a magnitude and a phase component. Through theory based on electromagnetism, it can be shown that the phase data produced by the MRI scanner is directly related to the magnetic susceptibility of the structures being scanned. The process in which we relate phase back to susceptibility is called QSM. However, there are many complications that make this inverse problem troublesome, and as a result it lacks a ground truth. QSM has many applications: in the brain alone, the magnetic susceptibility can be an indicator of myelination, microbleeds, iron metabolism and can be used to detect and track many neurological diseases such as Parkinson’s, Huntington’s and Multiple Sclerosis.The goals of this thesis are as follows: to develop a foundation of MRI physics with a focus on the development of phase data and multi-echo MRI sequences; to review the literature of QSM, with a focus on the pre-processing steps; to provide a comparison of spatial unwrapping techniques currently available in the field of QSM; and to introduce a novel temporal unwrapping approach to the QSM pipeline and to evaluate its effectiveness. Throughout this work, the phase unwrapping step was examined in detail. Specifically, six spatial unwrapping techniques were investigated for both their accuracy in unwrapping phase and if they are subject to phase unwrapping errors. To do so, the wrapped data and unwrapped results were compared via a line profile, and thus eliminating techniques that modify phase beyond pure 2pi unwrapping. The remaining techniques were investigated further for unwrapping failures by using the remainder of the QSM pipeline to look for any catastrophic effects and to assess their overall quality. Of the six techniques, it was found that only quality guided region growing (QGRG) did not modify phase and was without any major phase unwrapping failures. In addition, temporal unwrapping was investigated. This is the offset of phase maps by 2pi jumps between successive echoes in a multi-echo sequence, due to the nature in which the data is recorded and spatially unwrapped. We devised a temporal unwrapping algorithm to correct for this artifact. We found that our temporal unwrapping algorithm caught every instance of temporal wraps present and correctly resolved them. In addition, when temporal wraps were not present, the algorithm did not modify the data in any way. When temporal wraps were ignored, we found that the resulting QSM images were typically unrecognisable. We conclude that in order to accurately unwrap phase data without modifying it and without unwrapping failures, a combination of the QGRG spatial unwrapping technique and our temporal unwrapping technique is required.The findings of this research provide insight on one of the fundamental steps of the QSM pipeline, leading to a more accurate QSM image. Accurate QSM will lead to results that are more reproducible and will allow for QSM to be incorporated into studies that require reproducibility across many different datasets, and to get us close to a more robust and accurate measurement"--

Quantitative Susceptibility Mapping (QSM) Reconstruction from MRI Phase Data

Quantitative Susceptibility Mapping (QSM) Reconstruction from MRI Phase Data
Author: Sara Gharabaghi
Publisher:
Total Pages: 87
Release: 2020
Genre: Computer science
ISBN:

Quantitative susceptibility mapping (QSM) is a powerful technique that reveals changes in the underlying tissue susceptibility distribution. It can be used to measure the concentrations of iron and calcium in the brain both of which are linked with numerous neurodegenerative diseases. However, reconstructing the QSM image from the MRI phase data is an ill-posed inverse problem. Different methods have been proposed to overcome this difficulty. Still, the reconstructed QSM images suffer from streaking artifacts and underestimate the measured susceptibility of deep gray matter, veins, and other high susceptibility regions. This thesis proposes a structurally constrained Susceptibility Weighted Imaging and Mapping (scSWIM) method to reconstruct QSM for multi-echo, multi-flip angle data collected using strategically acquired gradient echo (STAGE) imaging. scSWIM performs a single step regularization-based reconstruction technique that takes advantage of the unique contrast of the STAGE T1 weighted enhanced (T1WE) image to extract reliable geometry constraints to protect the basal ganglia from over-smoothing. Furthermore, the multi-echo, multi-flip angle data from STAGE can all be used to improve the contrast-to-noise ratio in QSM through a weighted averaging scheme. scSWIM was tested on both simulated and in vivo data. Results show that the unique contrast and tissue boundaries from T1WE and an earlier approach called iterative SWIM enable the accurate definition of the edges of high susceptibility regions. scSWIM achieved the best overall root mean squared error and structural similarity index metrics as well as the lowest deviation from the expected susceptibility in deep gray matter compared to other published methods. Finally, susceptibility measurements of the basal ganglia extracted from the scSWIM data for a cohort of Parkinson's disease patients and healthy control subjects were in agreement with the literature.

Quantitative Susceptibility Mapping in the Human Brain

Quantitative Susceptibility Mapping in the Human Brain
Author: Diana Khabipova
Publisher:
Total Pages: 193
Release: 2016
Genre:
ISBN:

Mots-clés de l'autrice: MRI ; magnetic resonance imaging ; QSM ; quantitative susceptibility mapping ; apparent transversal relaxation rate ; longitudinal relaxation rate ; transversal relaxation rate ; human brain.

Handbook of Pediatric Brain Imaging

Handbook of Pediatric Brain Imaging
Author: Hao Huang
Publisher: Academic Press
Total Pages: 582
Release: 2021-10-27
Genre: Computers
ISBN: 0128166428

Handbook of Pediatric Brain Imaging: Methods and Applications presents state-of-the-art research on pediatric brain image acquisition and analysis from a broad range of imaging modalities, including MRI, EEG and MEG. With rapidly developing methods and applications of MRI, this book strongly emphasizes pediatric brain MRI, elaborating on the sub-categories of structure MRI, diffusion MRI, functional MRI, perfusion MRI and other MRI methods. It integrates a pediatric brain imaging perspective into imaging acquisition and analysis methods, covering head motion, small brain sizes, small cerebral blood flow of neonates, dynamic cortical gyrification, white matter tract growth, and much more. Presents state-of-the-art pediatric brain imaging methods and applications Shows how to optimize the pediatric neuroimaging acquisition and analysis protocols Illustrates how to obtain quantitative structural, functional and physiological measurements