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.

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.

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 Using Magnetic Resonance Imaging

Quantitative Susceptibility Mapping Using Magnetic Resonance Imaging
Author: Tian Liu
Publisher:
Total Pages: 154
Release: 2011
Genre:
ISBN:

Magnetic susceptibility is an intrinsic tissue property that reflects underlying concentration of iron, calcification or contrast agents, which are useful for the investigation of a wide range of physiological or pathological conditions. Due to this promising outlook, there has been a long-standing interest in quantifying magnetic susceptibility. Although methods to quantify susceptibility of certain material samples have been proposed in the past, a practical means to measure an arbitrary susceptibility distribution in a living organism was lacking. Consequently, many of the potential applications were still in speculation. This thesis reports a framework that allows quantitative mapping of magnetic susceptibility in human brain using magnetic resonance imaging (MRI). Two major building blocks were proposed to overcome the technical hurdles. First, a background field removal method was developed to obtain the magnetic field of interest free of contamination from background sources. Second, two independent methods were proposed to solve a classical ill-posed inverse problem of determining susceptibility sources from measured magnetic field. With these technical developments, quantitative susceptibility mapping was realized. Its utility was demonstrated in a molecular MRI application, where identification and quantification of iron-based contrast agents are now feasible, and in cerebral MRI, where susceptibility provides a more objective measurement of hemorrhage, allowing cross-center comparisons and longitudinal studies.

Quantitative Magnetic Resonance Imaging

Quantitative Magnetic Resonance Imaging
Author: Nicole Seiberlich
Publisher: Academic Press
Total Pages: 1094
Release: 2020-11-18
Genre: Computers
ISBN: 0128170581

Quantitative Magnetic Resonance Imaging is a ‘go-to’ reference for methods and applications of quantitative magnetic resonance imaging, with specific sections on Relaxometry, Perfusion, and Diffusion. Each section will start with an explanation of the basic techniques for mapping the tissue property in question, including a description of the challenges that arise when using these basic approaches. For properties which can be measured in multiple ways, each of these basic methods will be described in separate chapters. Following the basics, a chapter in each section presents more advanced and recently proposed techniques for quantitative tissue property mapping, with a concluding chapter on clinical applications. The reader will learn: The basic physics behind tissue property mapping How to implement basic pulse sequences for the quantitative measurement of tissue properties The strengths and limitations to the basic and more rapid methods for mapping the magnetic relaxation properties T1, T2, and T2* The pros and cons for different approaches to mapping perfusion The methods of Diffusion-weighted imaging and how this approach can be used to generate diffusion tensor maps and more complex representations of diffusion How flow, magneto-electric tissue property, fat fraction, exchange, elastography, and temperature mapping are performed How fast imaging approaches including parallel imaging, compressed sensing, and Magnetic Resonance Fingerprinting can be used to accelerate or improve tissue property mapping schemes How tissue property mapping is used clinically in different organs Structured to cater for MRI researchers and graduate students with a wide variety of backgrounds Explains basic methods for quantitatively measuring tissue properties with MRI - including T1, T2, perfusion, diffusion, fat and iron fraction, elastography, flow, susceptibility - enabling the implementation of pulse sequences to perform measurements Shows the limitations of the techniques and explains the challenges to the clinical adoption of these traditional methods, presenting the latest research in rapid quantitative imaging which has the possibility to tackle these challenges Each section contains a chapter explaining the basics of novel ideas for quantitative mapping, such as compressed sensing and Magnetic Resonance Fingerprinting-based approaches

Components of Variance

Components of Variance
Author: D.R. Cox
Publisher: CRC Press
Total Pages: 181
Release: 2002-07-30
Genre: Mathematics
ISBN: 1482285940

The components of variance is a notion essential to statisticians and quantitative research scientists working in a variety of fields, including the biological, genetic, health, industrial, and psychological sciences. Co-authored by Sir David Cox, the pre-eminent statistician in the field, this book provides in-depth discussions that set forth the essential principles of the subject. It focuses on developing the models that form the basis for detailed analyses as well as on the statistical techniques themselves. The authors include a variety of examples from areas such as clinical trial design, plant and animal breeding, industrial design, and psychometrics.

Susceptibility Weighted Imaging in MRI

Susceptibility Weighted Imaging in MRI
Author: E. Mark Haacke
Publisher: John Wiley & Sons
Total Pages: 817
Release: 2014-03-25
Genre: Medical
ISBN: 111814807X

MRI Susceptibility Weighted Imaging discusses the promising new MRI technique called Susceptibility Weighted Imaging (SWI), a powerful tool for the diagnosis and treatment of acute stroke, allowing earlier detection of acute stroke hemorrhage and easier detection of microbleeds in acute ischemia. The book is edited by the originators of SWI and features contributions from the top leaders in the science. Presenting an even balance between technical/scientific aspects of the modality and clinical application, this book includes over 100 super high-quality radiographic images and 100 additional graphics and tables.