
Contents
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4.1 Introduction 4.1 Introduction
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4.2 Why ultra-fast fMRI? 4.2 Why ultra-fast fMRI?
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4.3 Requirements for BOLD fMRI acquisition methods 4.3 Requirements for BOLD fMRI acquisition methods
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4.3.1 Echo time (TE) optimization 4.3.1 Echo time (TE) optimization
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4.3.2 The effect of field homogeneity on optimum TE values and BOLD signal 4.3.2 The effect of field homogeneity on optimum TE values and BOLD signal
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4.3.3 Intra-scan motion: signal stability 4.3.3 Intra-scan motion: signal stability
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4.4 Gradient echo methods 4.4 Gradient echo methods
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4.4.1 FLASH sequences 4.4.1 FLASH sequences
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4.4.2 Echo planar imaging 4.4.2 Echo planar imaging
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4.4.3 Limitations of EPI sequences 4.4.3 Limitations of EPI sequences
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4.4.4 3D gradient echo methods 4.4.4 3D gradient echo methods
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4.5 Spin echo methods 4.5 Spin echo methods
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4.5.1 Multiple echo sequences 4.5.1 Multiple echo sequences
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4.5.2 Spin echo EPI 4.5.2 Spin echo EPI
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4.6 Alternative k-space trajectories for fast MRI 4.6 Alternative k-space trajectories for fast MRI
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4.6.1 Spiral trajectories 4.6.1 Spiral trajectories
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4.6.2 Projection reconstruction 4.6.2 Projection reconstruction
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4.7 Advanced fMRI methods with reduced k-space coverage 4.7 Advanced fMRI methods with reduced k-space coverage
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4.7.1 Keyhole fMRI techniques 4.7.1 Keyhole fMRI techniques
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4.7.2 Half-Fourier 4.7.2 Half-Fourier
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4.7.3 Sensitivity encoding (SENSE) 4.7.3 Sensitivity encoding (SENSE)
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4.7.4 UNFOLD 4.7.4 UNFOLD
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4.8. Concluding remarks 4.8. Concluding remarks
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Acknowledgements Acknowledgements
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Notes Notes
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References References
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Cite
Abstract
Brain activation is known to lead to enhanced perfusion which, together with other physiological changes, results in a decreased deoxyhaemoglobin concentration in regions of neuronal activity. This effect is referred to as the blood oxygenation level dependent (BOLD) effect. The main purpose of this chapter is to outline the acquisition methods for ultra-fast BOLD functional magnetic resonance imaging (fMRI). It helps to explain the basics of echo planar imaging and alternative ultra-fast imaging techniques, discusses possible artefacts and pitfalls, and also studies the requirements for BOLD fMRI acquisition methods, focusing on echo planar imaging (EPI). The chapter discusses the two basic types of spin echo sequences that have been employed for fMRI studies, namely multiple echo sequences and spin echo EPI. The methods discussed traverse k-space in a rectilinear fashion. Moreover, the chapter also describes promising recent developments and mentions that ultra-fast 3D methods are under development which will potentially provide better signal-to-noise ratio and BOLD contrast per unit time than EPI, and which are also less sensitive to inflow effects.
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