Download or read book Towards Absolutely Quantitative Phase Contrast Magnetic Resonance Imaging written by Matthew Joseph Middione and published by . This book was released on 2013 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Phase Contrast Magnetic Resonance Imaging (PC-MRI) is a non-invasive clinical imaging technique used primarily for measuring blood velocity and flow throughout the major blood vessels of the cardiovascular system. PC-MRI uses magnetic field gradients to impart zero phase to stationary spins and a non-zero phase to moving spins. The phase measurements provide quantitative information that is useful during the diagnosis and treatment of many cardiovascular diseases. Blood flow measurements obtained using PC-MRI hold an advantage over other techniques, namely echocardiography and catheterization, due to its ability to reduce lifetime radiation exposure, provide accurate and direct quantification of flow, and it's non-invasiveness. Despite decades of research, our ability to measure blood flow with PC-MRI is still hampered by quantitative inaccuracies leading to clinically significant errors, which dampens clinical enthusiasm for the technique. Nevertheless PC-MRI continues to be a compelling clinical technique because of the need to non-invasively measure flow in a wide range of clinical contexts. Frequently inconsistent PC-MRI measurements, however, continue to be a source of clinical frustration and in order for PC-MRI to become an absolutely quantitative measure of flow, both the accuracy and precision of these measurements must be improved. Herein an analysis of the effects of chemically shifted perivascular fat; time efficient velocity encoding; region-of-interest contouring; and the use of convex gradient optimization is conducted in an effort towards developing absolutely quantitative PC-MRI. In Chapter 4 we explore the phase errors associated with chemically shifted perivascular fat. Stationary perivascular fat, which surrounds most vessels throughout the cardiovascular system, can impart a significant chemical shift-induced phase error in PC-MRI. This chemical shift error does not subtract in phase difference processing, unlike other off-resonance phase errors, but can be minimized significantly with proper parameter selection. The chemical shift induced phase errors largely depend on both the receiver bandwidth and the echo time (TE). The amount of chemically shifted fat pixels that shift into the vessel can be reducedby increasing the receiver bandwidth while the use of an in-phase TE (TE_IN) will ensure that fat and water resonances are in-phase with slow flowing blood near the vessel wall, which minimizes the resulting errors in the calculated velocity. Computational simulations and both in vitro and in vivo experiments are used to show that the use of a high bandwidth and TE_IN significantly improves intra-subject flow agreement compared to a more clinically standard low receiver bandwidth and the minimum available TE (TE_MIN). In Chapter 5 we explore a time efficient chemical shift reduction strategy. The minimum available TE_IN at 3T field strength (TE_IN, MIN = 2.46ms), however, may not be routinely achievable with standard flow-encoding methods. Hence, we developed a novel method for flow encoding in PC-MRI, which uses the slice select gradientand a time-shifted refocusing gradient lobe for velocity encoding. Velocity encoding with the slice select refocusing gradient (SSRG) enables the use of TE_IN, MIN at 3T for time-efficient reduction of chemical shift-induced phase errors in PC-MRI, whereas this can't be achieved with bi-polar or flow compensated/flow encoded PC-MRI. In vivo measurements were acquired to show that PC-MRI measurements obtained using SSRG with a high receiver bandwidth and TE_IN, MIN significantly improves intra-subject flow agreement compared to a conventional clinical sequence, which uses a low receiver bandwidth and TE_MIN. This approach also increases temporal resolution and signal-to-noise ratio by 35% and 33%, respectively. In Chapter 6 we explore time efficient velocity encoding and the capabilities of convex gradient optimization in PC-MRI in chapter 7. Conventional PC-MRI pulse sequences use time inefficient velocity encoding methods along with trapezoidal and triangular gradient lobes, which do not make optimal use of the available gradient hardware. Convex gradient optimization (CVX) can be used to minimize PC-MRI gradient waveform durations subject to both gradient hardware and pulse sequence constraints. CVX PC-MRI with TE_IN, MIN provides more accurate measurements of blood flow and velocity through the reduction of chemical shift-induced phase errors and increased sequence efficiency, which can provide either higher spatial or higher temporal resolution. Another potential source of error in PC-MRI flow quantification occurs during image analysis. In Chapter 8 we analyze the errors associated with ROI contouring in PC-MRI. PC-MRI blood flowmeasurements require a region-of-interest (ROI) to be manually contoured to encompass the vessel lumen, but this process is subjective and prone to error. A systematic analysis of ROI contouring was used to evaluate the impact of overestimating and underestimating the ROI size on PC-MRI flow measurements. ROIs that overestimate the vessel lumen/wall boundary contribute a lower magnitude total flow error compared to ROIs that underestimate the same boundary. Reducing errors arising from chemically shifted perivascular fat, implementing time efficient velocity encoding, increasing spatiotemporal resolution through the use of convex gradient optimization, and careful analysis of ROI contours all help move us towards absolutely quantitative PC-MRI.
Download or read book Quantitative Magnetic Resonance Imaging written by Nicole Seiberlich and published by Academic Press. This book was released on 2020-11-18 with total page 1094 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Download or read book Fast Quantitative Magnetic Resonance Imaging written by Guido Buonincontri and published by Morgan & Claypool Publishers. This book was released on 2020-02-20 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: Among medical imaging modalities, magnetic resonance imaging (MRI) stands out for its excellent soft-tissue contrast, anatomical detail, and high sensitivity for disease detection. However, as proven by the continuous and vast effort to develop new MRI techniques, limitations and open challenges remain. The primary source of contrast in MRI images are the various relaxation parameters associated with the nuclear magnetic resonance (NMR) phenomena upon which MRI is based. Although it is possible to quantify these relaxation parameters (qMRI) they are rarely used in the clinic, and radiological interpretation of images is primarily based upon images that are relaxation time weighted. The clinical adoption of qMRI is mainly limited by the long acquisition times required to quantify each relaxation parameter as well as questions around their accuracy and reliability. More specifically, the main limitations of qMRI methods have been the difficulty in dealing with the high inter-parameter correlations and a high sensitivity to MRI system imperfections. Recently, new methods for rapid qMRI have been proposed. The multi-parametric models at the heart of these techniques have the main advantage of accounting for the correlations between the parameters of interest as well as system imperfections. This holistic view on the MR signal makes it possible to regress many individual parameters at once, potentially with a higher accuracy. Novel, accurate techniques promise a fast estimation of relevant MRI quantities, including but not limited to longitudinal (T1) and transverse (T2) relaxation times. Among these emerging methods, MR Fingerprinting (MRF), synthetic MR (syMRI or MAGIC), and T1‒T2 Shuffling are making their way into the clinical world at a very fast pace. However, the main underlying assumptions and algorithms used are sometimes different from those found in the conventional MRI literature, and can be elusive at times. In this book, we take the opportunity to study and describe the main assumptions, theoretical background, and methods that are the basis of these emerging techniques. Quantitative transient state imaging provides an incredible, transformative opportunity for MRI. There is huge potential to further extend the physics, in conjunction with the underlying physiology, toward a better theoretical description of the underlying models, their application, and evaluation to improve the assessment of disease and treatment efficacy.
Download or read book M1 Space Under Sampling Fast Phase Contrast Magnetic Resonance Imaging written by Da Wang and published by . This book was released on 2017 with total page 117 pages. Available in PDF, EPUB and Kindle. Book excerpt: Phase Contrast Magnetic Resonance Imaging (PC-MRI) is one of the primary means for quantification of blood flow and velocity. In conventional PC-MRI, the Flow Compensated (FC) and the three-directional (3D) Flow Encoded (FE) images are acquired in an interleaved fashion, and each directional blood flow velocity is encoded in the phase difference between each directional FE and the FC data. This acquisition strategy often limits its achievable temporal sampling period and temporal footprint. Temporal sampling period and temporal footprint are two important indices govern the measurement accuracy of the maximum peak velocity. The underestimation of the maximum peak velocity due to long temporal sampling period and long temporal footprint may result in misdiagnosis of a number of clinical diseases, such as artery stenosis. In the conventional 4D flow PC-MRI, each cardiac phase requires four acquisitions (i.e. one FC and 3D FE, FC/3FE) to update the 3D velocity vector field. Thus, the temporal sampling period and temporal footprint of 4D flow PC-MRI equal to 4*TR*Views-per-segment. Using a small views-per-segment (VPS) can achieve a decreased temporal sampling period and temporal footprint but concomitantly increase the total scan time. So far, fast PC-MRI techniques are majorly implemented to compensate the increase of the total acquisition time. In this work, we first introduce the gradient first moment (M1) space under-sampling, which aims to reduce the number of the four samples (FC and 3D FE) required for 4D flow reconstruction. This is the unique advantage of M1-space under-sampling over conventional fast PC-MRI techniques. It can improve both the temporal sampling period and temporal footprint without increasing the total scan time or reduce the total scan time with fixed temporal sampling period and temporal footprint. Furthermore, the M1-space is a novel dimension to accelerate 4D flow scans, so it can be combined with K-space, K-t-space, temporal dimension fast PC-MRI techniques to achieve further acceleration. In Chapter 2, we propose a technique to use sliding window temporal view sharing of the FC data (FCVS) to accelerate PC-MRI. The technique aims to accelerate certain PC-MRI applications, such as assessment of volumetric blood flow in the carotid arteries, intracranial vessels and peripheral vessels, where the physiological motion is minor and the FC background phase is not expected to change significantly over time. In this regard, the conventional PC-MRI acquisition strategy is redundant since it repetitively acquires the similar FC data for each cardiac phase. Especially the FC data does not contain dynamic flow velocity information. The FCVS technique achieves two-fold acceleration compared to standard through-plane encoding (FC/FE) PC-MRI. More importantly, the FCVS approach improves both the temporal sampling period and temporal footprint, which are very important for accurate velocity and flow quantification. Computational simulations and both retrospective and prospective in vivo studies demonstrated that the FCVS technique provides more accurate maximum peak velocity measurement while maintaining the measurement accuracy of total volumetric flow compared with conventional FCFE technique. In Chapter 3, we propose a 4D flow PC-MRI strategy, which is completely free of FC data acquisition and achieves 4/3-fold acceleration. In this technique, we hypothesize that the velocity direction (not magnitude) remains relatively unchanged within two cardiac phases (~100-150ms) during the cardiac cycle. The velocity direction consistency constraint enables the FC background phase calculation based on 3D FE data. Thus, the four M1-space samples (FC/3FE) have been reduced to three samples (3FE). The HOTFEO achieves 4/3-fold acceleration. However, the velocity direction consistency constraint has two ill conditions: the two consecutive velocities equal to each other and they are along the diagonal direction in the logical encoding coordinate. To address these problems, we propose to use a hybrid one- and two-sided flow encoding only (HOTFEO) strategy. More specifically, that is to use FE acquisition pattern with alternating polarity (i.e. two-sided FE) in the Y-direction (FEy) in addition to using single polarity (i.e. one-sided) FEx and FEz. The HOTFEO pattern can address the two ill conditions by converting the underdetermined constraint into convex function optimizations. The HOTFEO technique can also significantly increase the accuracy of FC background calculation and result in more accurate maximum peak velocity and total volumetric flow measurement. In Chapter 4, we propose a two-fold accelerated 4D flow PC-MRI technique with hybrid one- and two-sided flow encoding and velocity spectrum separation (HOTSPA). There are three components in the HOTSPA technique: 1) the two-sided FE has been applied in two of the three FE directions; 2) the one-sided FE has been applied in the remaining FE direction; 3) the FC data is not explicitly acquired. The two-sided FE strategy provides a 0/ linear phase modulation in the temporal dimension. In the Fourier velocity spectrum domain, the spectrum of temporal modulated velocity waveform will be shifted by half of the frequency support and separated from the spectrum of FC or one-sided FE waveform. The HOTSPA technique then separates the Fourier velocity spectra into components for FC background phase and 3D velocity waveforms. The combinations of the acquired data enable 3D velocity calculations based on two M1-space samples instead of four samples as conventional 4D flow PC-MRI. The HOTSPA technique can be used to either improve the temporal sampling period and temporal footprint or reduce the total scan time. The approach has been demonstrated to provide more accurate maximum peak velocity and total volumetric flow measurements. The M1-space under-sampling is a novel and promising technique to accelerate PC-MRI. First, it can improve both temporal sampling period and temporal footprint by reducing the M1-space samples. Second, it can accelerate 4D flow independently or it can be applied on phase images after finishing other fast PC-MRI technique reconstructions, such as compressed sensing, parallel imaging, non-Cartesian trajectory, thus allowing their combination to achieve further acceleration. In Chapter 4, we will introduce the balanced four-point flow encoding strategy, which can achieve four-fold acceleration using HOTSPA technique. The M1-space under-sampling can significantly improve the measurement accuracy of velocity and flow quantifications or reduce the total scan time, especially for 4D flow applications.
Download or read book Understanding Phase Contrast MR Angiography written by Joseph Suresh Paul and published by Springer. This book was released on 2015-12-12 with total page 99 pages. Available in PDF, EPUB and Kindle. Book excerpt: Providing many unique MATLAB codes and functions throughout, this book covers the basics of Magnetic Resonance Imaging (MRI), leading to an in-depth understanding of the concepts and tools required for analysis and interpretation of Phase Contrast MR Angiography (PC-MRA). The concept of PC-MRA is often difficult, but essential for practicing engineers and scientists working in MR related areas. The concepts are better understood by uniquely combining the physical principles of fluid flow and MR imaging, laid out by modeling the theory and applications using a commonly used software tool MATLAB®. The book starts with a detailed theory of PC-MRA followed by a description of various image processing methods, including detailed MATLAB codes used for their implementation. The flow concepts in the context of MR imaging are explained using MATLAB based simulations.
Download or read book Rapid Phase contrast Magnetic Resonance Imaging Using Spiral Trajectories and Parallel Imaging written by J. A. Steeden and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Phase contrast (PC) MRI is a proven method of measuring blood flow in the clinical environment. Traditionally, PCMR data is acquired using cardiac gated Cartesian sequences. However, these sequences are time consuming and difficult to perform in patients with irregular heart rates. The work of my thesis covers three alternative PC sequences, all using undersampled spiral sequences with SENSE reconstruction algorithms. The first piece of work investigates real-time spiral PCMR. The spiral flow sequence was validated at rest by comparing stroke volumes in the aorta of healthy volunteers, against a retrospectively gated Cartesian sequence. By combining flow data with simultaneous blood pressure measurements during exercise, this sequence was used to quantify the hemodynamic response to physical stress. The second piece of work investigates improvements in spatial or temporal resolution for real-time PCMR, by splitting the acquisition of flow-compensated and flow-encoded data into separate short blocks. The data is then retrospectively matched in cardio-respiratory space, to remove background phase offsets. This sequence was validated (at rest) in an adult population. The improved spatial resolution was shown to provide more accurate flow measurements than standard real-time flow measurements, in a paediatric population. The third piece of work investigates prospectively triggered spiral PCMR to achieve high spatio-temporal resolution, within a short breath-hold. Flow volumes, regurgitation fraction and shunt ratios were compared from a high spatial-resolution, free breathing retrospectively gated Cartesian sequence with 3 averages (~2.5 minute scan time), a low spatial-resolution breath-hold retrospectively gated Cartesian sequence (~20 second scan time), and the (high spatial-resolution) prospectively triggered spiral sequence (~6 second scan time). It was shown that accurate flow measurements can be made in the aorta, pulmonary artery and pulmonary branches, within manageable breath-hold times for children and sick adults. This sequence may improve patient compliance and increase patient throughput.
Download or read book Adult Hydrocephalus written by Daniele Rigamonti and published by Cambridge University Press. This book was released on 2014-02-06 with total page 331 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides guidelines for managing this grossly underdiagnosed and undertreated condition, focusing on early detection and timely, effective interventions.
Download or read book Rapid Phase contrast Magnetic Resonance Imaging Using Spiral Trajectories and Parallel Imaging written by Jennifer Anne Steeden and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Principles of Magnetic Resonance Imaging written by Yi Wang and published by CreateSpace. This book was released on 2012-10-03 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: Principles of Magnetic Resonance Imaging provides a contemporary introduction of the fundamental concepts of MRI and connects these concepts to the latest MRI developments. Graphic illustrations are used to clarify underlying biophysical processes, simplified calculations are derived to add precision in appreciating abstract concepts, and insightful interpretations are presented for biomedical information in MRI signal. This book contains three parts. I. Section the body into voxels, which describes the Fourier encoding matrix for an imaging system, realization of Fourier encoding using the gradient field in magnetic resonance, and k-space sampling. II. What's in a voxel, which examines the effects of the biophysical processes in a voxel on MRI signal. Intuitive biophysical models are developed for MRI signal dependence on Spin fluctuation in thermal microenvironment, which leads to T1/T2 relaxation rates reflecting cellular contents in a water voxel. Micro- and macro physiological motion, which includes diffusion, perfusion, flow and biomechanical motion. Molecular electron response to the B0 field, which leads to magnetic susceptibility and chemical shift. III. How to operate MRI, which describes MRI safety issue, hardware, software, MRI scanning and routine MRI protocols. This book also uses basic concepts to demonstrate and expose students to the latest technological innovations in MRI, including: B1+ B1- mapping, Electric property tomography (EPT), Quantitative susceptibility mapping (QSM), Chemical exchange saturation transfer (CEST), Contrast agents, Molecular MRI, Spin tagging (SPAMM and DENSE), MR elastography, Parallel imaging including SENSE and GRAPPA, Compressed sensing and Bayesian approach.
Download or read book Accuracy and Reproducibility in Phase Contrast Magnetic Resonance Imaging written by Per Thunberg and published by . This book was released on 2004 with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Quantitative Magnetic Resonance Flow Imaging written by Jill Fredrickson and published by . This book was released on 1997 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical and Experimental Study of Three Imaging Advancements in Phase Contrast Magnetic Resonance Imaging written by Longchuan Li and published by . This book was released on 2007 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt: The SR PC-MR data showed significantly better representation of the velocity-time waveform as assessed by lower root-mean-square (RMS) errors (9.0+/-1.0% vs. 24.0+/-0.2%, p<0.005). Overestimation of peak velocity was dramatically attenuated using Self Reference compared to the conventional approach (2.8+/-0.4% vs. 16.9+/-6.4%, p<0.005). An average of 119.4 +/- 26.6% (p<0.005) SNR was realized in both in vitro and in vivo SR PC-MR data compared to conventional scans.
Download or read book Fluorine Magnetic Resonance Imaging written by Ulrich Flogel and published by CRC Press. This book was released on 2016-10-26 with total page 462 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the past decade, fluorine (19F) magnetic resonance imaging (MRI) has garnered significant scientific interest in the biomedical research community owing to the unique properties of fluorinated materials and the 19F nucleus. Fluorine has an intrinsically sensitive nucleus for MRI. There is negligible endogenous 19F in the body and thus there is no background signal. Fluorine-containing compounds are ideal tracer labels for a wide variety of MRI applications. Moreover, the chemical shift and nuclear relaxation rate can be made responsive to physiology via creative molecular design. This book is an interdisciplinary compendium that details cutting-edge science and medical research in the emerging field of 19F MRI. Edited by Ulrich Flögel and Eric Ahrens, two prominent MRI researchers, this book will appeal to investigators involved in MRI, biomedicine, immunology, pharmacology, probe chemistry, and imaging physics.
Download or read book Analysis and Improvements in Magnetic Resonance Phase Contrast Flow Imaging written by Craig Alan Hamilton and published by . This book was released on 1992 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Theory Of Quantitative Magnetic Resonance Imaging written by Hernan J. Jara and published by . This book was released on 2010 with total page 265 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Quantitating Peripheral Blood Flow written by Constantino Santiago Peña and published by . This book was released on 1994 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Biomedical Technology written by Peter Wriggers and published by Springer. This book was released on 2017-08-29 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides an overview of new mathematical models, computational simulations and experimental tests in the field of biomedical technology, and covers a wide range of current research and challenges. The first part focuses on the virtual environment used to study biological systems at different scales and under multiphysics conditions. In turn, the second part is devoted to modeling and computational approaches in the field of cardiovascular medicine, e.g. simulation of turbulence in cardiovascular flow, modeling of artificial textile-reinforced heart valves, and new strategies for reducing the computational cost in the fluid-structure interaction modeling of hemodynamics. The book’s last three parts address experimental observations, numerical tests, computational simulations, and multiscale modeling approaches to dentistry, orthopedics and otology. Written by leading experts, the book reflects the remarkable advances that have been made in the field of medicine, the life sciences, engineering and computational mechanics over the past decade, and summarizes essential tools and methods (such as virtual prototyping of medical devices, advances in medical imaging, high-performance computing and new experimental test devices) to enhance medical decision-making processes and refine implant design. The contents build upon the International Conference on Biomedical Technology 2015 (ICTB 2015), the second ECCOMAS thematic conference on Biomedical Engineering, held in Hannover, Germany in October 2015.
