Introduction

As discussed in the previous chapter, a stroke is the rapidly developing loss of brain functions owing to a disturbance in the vessels supplying blood to the brain. This can be caused by ischemia (lack of blood supply) following thrombosis or embolism, or a hemorrhage. Acute stroke is a medical emergency, and imaging plays an important role in confirming (or otherwise) the clinical diagnosis of stroke, categorizing it as either ischemic or hemorrhagic, and identifying the underlying cause. Increasingly, imaging is also being used to guide therapeutic interventions and monitor their success. While traditionally X-ray computed tomography (CT) has been the imaging modality of choice (primarily because of its speed and widespread availability), MRI has been increasingly used because of its excellent contrast, high sensitivity and possibilities for multimodal acquisition (e.g., diffusion, perfusion, MR angiography, etc.). These topics are discussed in the following chapters.

Proton magnetic resonance spectroscopy (MRS) of the human brain was first demonstrated in the mid 1980s,[1–4] and shortly thereafter the first reports of its application to the study of human stroke appeared.[5,6] Although there have been reports of 31P,[7] 23Na,[8] and 13C [9] spectroscopy in human stroke, the majority of studies to date have utilized the proton nucleus, both because of its high sensitivity and the fact that proton MRS can be readily combined with conventional MRI without hardware modifications. Although the proton MRS studies performed in the early 1990s appeared to offer promise for diagnostic value in acute stroke, this modality has had relatively little impact for several reasons. The most important reason is the technical difficulty of performing it in a timely fashion in this patient population; secondly, much of the required clinical information is available from other (easier to perform) sequences, such as diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI), and T2-weighted MRI. Nevertheless, it is important to be aware of the spectroscopic correlates of acute and chronic infarction as, on occasion, MRS may be helpful in these clinical contexts.

Preface to the first edition

The advent of clinical MR imaging (MRI) in the 1980s heralded a new era in the ability to image the brain in vivo. MRI allows the detailed depiction of brain anatomy and pathology with unprecedented spatial resolution and soft-tissue contrast. It is also relatively safe and completely non-invasive. Nevertheless, the sensitivity and specificity with which structural MRI alone can define the wide range of neurological disease is limited.

The last decade has also seen the development of physiological MR techniques, whereby information concerning tissue function as well as structure is obtained. These techniques include diffusion, perfusion, and MR spectroscopy, which provide information on tissue ultra-structure, blood flow, and biochemistry, respectively. Information of this type supplements and complements that from clinical or structural imaging investigations, often providing important surrogate markers of disease pathophysiology or therapeutic response.

Preface to the second edition

In the 5 years since ‘Clinical MR Neuroimaging: Diffusion, Perfusion and Spectroscopy’ was published, physiological and functional neuro magnetic resonance (MR) techniques have continued to evolve. In addition to the increased use of diffusion (DWI) MRI, perfusion (PWI) MRI, and MR spectroscopy (MRS) in clinical practice, there has also been increased attention to techniques such as functional MRI (fMRI), permeability- and susceptibility-weighted (SWI) imaging. The second edition of ‘Clinical MR Neuroimaging’ has therefore been updated to reflect not only the latest developments in DWI, PWI and MRS, but also to include fMRI, permeability imaging, and SWI. The subtitle has been changed from ‘Diffusion, Perfusion and Spectroscopy’ to ‘Physiological and Functional Techniques’ to reflect this broadening of the subject material.

As in the earlier edition, the first section of the book describes the physical principles underlying each of these techniques, including potential associated artifacts and pitfalls. The second section addresses applications in different branches of clinical neuroscience. Chapters are grouped according to pathology, and are preceded by overviews that aim to place these methodologies in a broader clinical perspective. Further illustrative case studies have been added, including the ‘new’ as well as the ‘old’ techniques. Whereas SWI (e.g., for the exquisitely sensitive detection of hemorrhage or venous deoxygenation) and fMRI (for pre-surgical brain mapping) are clearly entering the clinical arena, other advanced methods (such as volumetric MRI, or magnetization transfer imaging) remain primarily in the research realm, and hence are not covered here.