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Magnetic resonance imaging in stroke
  1. J M Wardlaw

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    Stephen Davis, Marc Fisher, Steven Warach, eds. Cambridge: Cambridge University Press 2003, pp 266, £80.00. ISBN 0-521-80683-6

    This book does much more than its title would suggest. Although mainly concerned with magnetic resonance imaging (MRI) in stroke, the text actually covers single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging as well and containing one of the best chapters ever written on computed tomography (CT) in stroke. The approach and content reflect the predominance of neurologists among the editors and authors, with only a few radiologists, and is really aimed at neurologists and stroke physicians.

    The scene is set in the first chapter with a discussion of the limitations of clinical diagnosis of stroke and the specific role that imaging can play in diagnosing the type and cause of stroke. There is a superb chapter on CT in acute stroke, which exemplifies how the role of imaging in any diagnostic process should be evaluated. Separately, there is a chapter on CT evaluation of cerebral blood flow, a useful and practical introduction to MRI, discussion of conventional structural MR techniques such as T2, FLAIR, and gradient echo sequences, and a section on MR angiography. Much of the rest of the book (about half of it) is given over to diffusion and perfusion MRI, including its evaluation in animal models, concepts of identifying the ischaemic penumbra, evaluation of transient ischaemic attacks, selection of patients for new therapies and drug development trials, and finally a chapter on MR spectroscopy and a (very short) chapter on functional MR after stroke.

    Although written by MR enthusiasts, the text is tempered with some discussion of the drawbacks of MR, such as poorer patient accessibility (compared with CT) and problems of metallic foreign bodies. It also makes the point that, despite the huge interest in MR diffusion and perfusion imaging, the precise thresholds of defining irreversibly damaged tissue and tissue at risk are yet to be determined. Some aspects of stroke MRI are not dealt with in much detail, for example classification or interpretation of white matter lesions (frequently found in stroke patients), or the identification and interpretation of microhaemorrhages on MR and how they might influence decisions regarding stroke treatment, or on using diffusion imaging to identify lesions in patients with milder strokes or at later time intervals after acute stroke (that is, not just the first few hours). There is very little on practical issues (perhaps reflecting the neurology rather than the radiology approach) such as how one assesses a stroke patient who is unable to speak prior to MR to make sure that it is safe for the patient to go into the magnet, and how one manages the patient while in the magnet with respect to factors such as oxygenation.

    Some of the authors express personal views that not all readers will agree with. For example, in the chapter on assessment of a transient ischemic attack (TIA), the authors suggest that the definition of a TIA should be changed to one based on the presence or absence of certain imaging features. Although this clearly represents a personal opinion expressed by the authors, my objection to changing a classification that is so fundamental to stroke epidemiology and clinical practice is that only those with access to an MR scanner with diffusion imaging would be able to correctly diagnose a TIA using this new classification. Not only that, but the diagnosis of TIA might be dependent on the ability of the local radiologist or clinician to spot subtle features of recent ischaemia on diffusion, and on the timing of scanning after symptom onset.

    I found it a little disappointing that a proportion of the perfusion images were presented in black and white when this is one technique which really requires colour display for proper interpretation and appreciation.

    In summary, this is a useful textbook, particularly for neurologists or stroke physicians who need to understand more about imaging and its role in patient characterisation, decision making, and assessment of treatments in acute stroke. It’s not just about MR and everybody with an interest in stroke should read the chapter on clinical efficacy of CT in acute cerebral ischaemia. At just over 250 pages it is easily digestible and yet also a useful reference. At £80.00 I think compared with other books on MR and on stroke it represents good value for money.