Ultrafast MRI: Techniques and Applications

ISBN-13: 9783642803864 / Angielski / Miękka / 2011 / 232 str.

J. Rg F. Debatin; Graeme C. McKinnon

Opis

The imaging potential of the MR experiment continues to evolve. In recent years, an increasing number of fast and ultrafast imaging strategies has been described. In this evolu tion the definition of the terms fast and ultrafast has been blurred. Hence they are frequently used interchangeably. The evolution of these methods has been based on two related, yet separate developments: an increasingly thorough understand ing of the complexities inherent to pulse sequence design and the increasing availability of stronger and faster gradient sys tems. The combination of these two factors has laid the foun dation for vast reductions of MRI data acquisition times. Min utes have been replaced by seconds. Beyond shortening MR examination times and thereby increasing patient throughput, a most significant consequence has been the ability to acquire complex MR image sets within the time confines of a single breath-hold. The constraints placed by the presence of respi ratory motion have thus been effectively eliminated. Ultrafast breath-held data acquisition strategies already represent the backbone of many abdominal, thoracic and even pelvic imaging protocols. The enhanced image quality permits full exploitation of the unsurpassed soft tissue contrast inherent to the MR experiment. Beyond improving the quality of ex isting applications, the implementation of ultrafast imaging techniques has permitted the exploration of new imaging in dications, particularly in the area of perfusion and diffusion as well as ultrafast 3D imaging."

Spis treści

1 The Physics of Ultrafast Magnetic Resonance Imaging.- 1 Introduction.- 2 Background Theory.- 2.1 The Spin Vector.- 2.2 Two-Dimensional Vectors and Complex Numbers.- 2.3 Complex Exponentials and Vector Rotation.- 2.4 Basics of 1D Fourier Transforms.- 2.5 Fourier Construction of a 1D Box.- 2.6 The Mathematics of Fourier Transforms.- 2.7 Aliasing or Undersampling.- 2.8 2D Fourier Transforms.- 2.9 2D Wave Functions.- 2.10 Fourier Construction of a 2D Object.- 3 MRI Basics.- 3.1 Resonance.- 3.2 Radiofrequency Field.- 3.3 Gradient Fields.- 3.4 Rotating Frame.- 3.5 Spin Excitation in a Gradient Field.- 3.6 Signal Detection in a Gradient Field.- 3.7 Spin Precession in a Gradient Field.- 3.8 A Pulse Sequence Diagram.- 3.9 Slice Selection.- 3.10 Phase Encoding.- 3.11 Frequency Encoding.- 3.12 Signal Reception.- 3.13 The MRI Signal.- 4 k-Space.- 4.1 Equations.- 4.2 Image Signal to Noise Ratio.- 5 k-Space Considerations for Ultrafast Imaging.- 5.1 k-Space Coverage and Image Resolution.- 5.2 K-Space Coverage and Field of View.- 5.3 Fractional K-Space Imaging.- 5.4 Half-Echo Verses Half-Nex.- 5.5 View Sharing.- 5.6 Zero Filling.- 6 Coherence Pathways.- 6.1 Controlling the Coherences.- 6.2 Coherence Pathway Diagram.- 7 Fast Gradient-Echo Imaging.- 7.1 Refocused Gradient-Echo Imaging.- 7.2 Spoiled Gradient-Echo Imaging.- 7.3 Reaching Steady State.- 7.4 Designing a Fast Gradient-Recalled Echo Sequence.- 7.4.1 Gradients.- 7.4.2 RF Pulse.- 7.4.3 Acquisition.- 7.4.4 Rewinder Gradient.- 7.4.5 Minimum Sequence Time.- 8 Planar k-Space Sampling Techniques.- 8.1 Echo-Planar Imaging.- 8.1.1 Multishot Echo-Planar Imaging.- 8.1.2 Asymmetric Echo-Planar Imaging.- 8.2 Spiral Imaging.- 8.3 Fast (Turbo) Spin-Echo Imaging.- 8.3.1 Multishot and Single-Shot Fast Spin-Echo Imaging.- 8.3.2 RF Phase Errors.- 9 Physiological Gating.- 9.1 Prospective and Retrospective Gating.- 9.2 Segmented K-Space.- 9.3 Navigator Gating and Motion Correction.- 10 Hardware Considerations.- 10.1 Gradient Slew Rate.- 10.1.1 dB/dT Limits.- 10.2 Gradient Strength.- 10.2.1 Maxwell Terms.- 10.2.2 Eddy Currents.- 10.3 Gradient Limited Imaging Speed.- 10.4 Sampling Bandwidth.- References.- 2 Ultrafast Magnetic Resonance Imaging of the Brain and Spine.- 1 Morphology.- 1.1 Magnetic Resonance Imaging of the Fetal Brain with HASTE.- 1.2 Ultrafast Multiple Sclerosis (MS) Plaque Imaging.- 1.3 Dynamic Evaluation of Cervical Spine Motion.- 2 Function.- 2.1 Functional MRI.- 2.1.1 Principle of BOLD Imaging.- 2.1.2 Practical Aspects of fMRI.- 2.1.3 Normal Results of Brain Activations.- 2.1.3.1 Cortical Activations in Normal Subjects.- 2.1.3.2 Central Activations in Normal Subjects.- 2.1.4 Clinical Applications of fMRI of the Brain.- 2.1.4.1 Presurgical Localization of Functional Areas.- 2.1.4.2 fMRI in Multiple Sclerosis (MS).- 2.2 Perfusion Imaging of the Brain.- 2.3 Diffusion-Weighted Imaging of the Brain.- 2.3.1 Application to the Early Diagnosis and Prognosis Determination of Stroke.- 2.3.2 Application to MS.- 2.4 Magnetization Transfer Imaging.- 2.4.1 Echo-Planar Generation of MT Maps.- 2.4.2 Evaluation of Demyelination in MS.- 2.4.3 Brain Malformations.- References.- 3 Ultrafast Magnetic Resonance Imaging of the Heart.- 1 Introduction.- 2 MRI in Myocardial Ischemia.- 2.1 Introduction.- 2.2 Review of Clinical Applications of MRI in Ischemic Heart Disease.- 2.3 Myocardial Perfusion Imaging.- 2.3.1 Image Acquisition.- 2.3.2 Flow Quantitation.- 2.3.3 Potential Applications.- 2.3.4 Stress MR Perfusion.- 2.4 MR Angiography of the Coronary Arteries.- 2.4.1 Image Acquisition.- 2.4.2 Coronary Flow Reserve.- 3 Myocardial Function.- 3.1 Introduction.- 3.2 Wall Motion Analysis.- 3.3 Correction for Respiratory Motion.- 3.3.1 Breath-Hold Segmented EPI.- 3.3.2 Real-Time Respiratory Navigator Gating.- 3.4 Myocardial Viability.- 3.5 Stress MRI.- 3.6 Summary.- References.- 4 Ultrafast Magnetic Resonance Imaging of the Vascular System.- 1 Introduction.- 2 Vascular Morphology.- 2.1 Contrast-Enhanced 3D MRA.- 2.1.1 Technical Aspects.- 2.1.1.1 Hardware Considerations.- 2.1.1.2 Pulse Sequence.- 2.1.1.3 Gadolinium Infusion.- 2.1.1.4 Image Interpretation.- 2.1.2 Clinical Applications.- 2.1.2.1 Pulmonary Arteries.- 2.1.2.2 Aorta.- 2.1.2.3 Extracranial Carotid Arteries.- 2.1.2.4 Renal Arteries.- 2.1.2.5 Celiac and Superior Mesenteric Arteries.- 2.1.2.6 Peripheral Arteries.- 2.1.2.7 Portal Venous System.- 2.2 Echo-Planar MRA.- 2.2.1 Technique Considerations.- 2.2.2 Applications of echo-planar MRA.- 2.2.2.1 Carotid Arteries.- 2.2.2.2 Renal Arteries.- 2.2.2.3 Trifurcation Arteries.- 2.2.2.4 Calf Veins.- 3 Vascular Function.- 3.1 PC Mapping: Technical Considerations.- 3.1.1 Spatial Averaging.- 3.1.2 Temporal Averaging.- 3.2 Applications of Ultrafast PC Imaging.- 3.2.1 Renal Arterial Flow Measurements.- 3.2.2 Mesenteric Ischemia.- References.- 5 Ultrafast Magnetic Resonance Imaging of the Abdomen.- 1 Introduction.- 2 Fast (Turbo) T2-Weighted Imaging.- 2.1 Technique Considerations.- 2.1.1 T2-Weighted Spin-Echo Sequence.- 2.1.2 Inversion Recovery.- 2.1.3 Fast (Turbo) Spin-Echo Sequences.- 2.1.4 Half-Fourier Acquisition Single-Shot Fast Spin-Echo Sequences.- 2.1.5 Fast Inversion Recovery.- 2.1.6 3D FSE Imaging.- 2.2 Applications of Fast T2-Weighted Imaging.- 2.2.1 Liver.- 2.2.2 Pancreas.- 2.2.3 Spleen.- 2.2.4 Kidneys.- 2.2.5 MR Cholangio-pancreatography.- 2.2.6 MR Pyeolgraphy.- 3 Fast 2D Gradient-Echo Imaging.- 3.1 Technique Considerations.- 3.1.1 Sequential GRE Acquisitions.- 3.1.2 Multiplanar GRE Acquisitions.- 3.2 T1-Weighted GRE Imaging.- 3.3 Dynamic Contrast-Enhanced GRE Imaging.- 3.3.1 Liver.- 3.3.2 Spleen.- 3.3.3 Pancreas.- 3.3.4 Kidneys.- 3.4 Phase-Shift Gradient-Echo Imaging.- 4 Ultrafast 3D Gradient-Echo Imaging.- 4.1 MR Colonography.- 4.2 MR Gastrography.- 5 Echo-planar Techniques.- References.

Blurb

The implementation of ultrafast MRI has dramatically impacted clinical MR practice. Faster image acquisition has resulted in greater patient throughput and higher image quality, particularly in regions subject to respiratory motion. In addition, ultrafast techniques proffer new insight into function and morphology of organ systems by providing the basis for cerebral perfusion and diffusion imaging as well as virtual 3D MR colonography and gastrography . The book attempts to bridge the gap dividing MR scientists into physicists and clinicians. It has been written for both. Based on schematic drawings, underlying pulse sequence designs and hardware considerations are illustrated. Strategies for implementing these techniques into clinical protocols are described for neurologic, cardiac, vascular and abdominal applications.