Magnetic resonance spectroscopy in stroke

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 T ₂-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.