Mukherji SK, Cons. Ed., Schaefer PW, Guest Ed. Neuroimaging Clinics of North America: Stroke Imaging. Theclinics.com 21(2):197-211. 12-month subscription: $314.00.
With the emergence of advanced imaging techniques in the evaluation of ischemic stroke, it is appropriate that an entire issue of the Neuroimaging Clinics of North America be devoted to Stroke Imaging. This 428-page volume, edited by Pam Schaefer, is co-authored by 35 contributors, and those include a combination of diagnostic neuroradiologists, interventional neuroradiologists, neurologists, and ophthalmologists. In this way the reader gets a sense of the many aspects of medical treatment and clinical care perspectives of stroke.
The volume starts off with the single most useful and commonly used imaging test for acute hemorrhage stroke—and that, of course, is CT—in the chapter entitled “Advanced CT Imaging for Hemorrhagic Stroke”. While most are familiar with these findings, a number of important points are emphasized, such as the CT angiography spot sign, subtle changes secondary to venous thrombosis, and scoring calculations for secondary intracerebral hemorrhage. Emphasis is placed on the detection of acute bleeding by CT at the time of admission, for therapeutic reasons.
Because of its more common availability, CT rather than MR may be more commonly employed for determining perfusion in acute ischemic stroke. Such is the topic in the book’s second chapter. The technique and technical parameters are described along with a comparison with MR perfusion. The advantages of pCT along with its disadvantage are nicely summarized. A very well written summary of radiation concerns and definition of pCT parameters help make this one of the more important chapters in this book. Five pages of image interpretation makes the theoretical to practical stick and there is some emphasis on the value of CTA-SI being flow- rather than strictly volume-related. Additionally, concerning pCT, relative vs. absolute CBF values are compared as are predictors of hemorrhage and hemorrhagic conversion.
A chapter on the variables to be considered during the time period within which one could consider the use of thrombolytic agents, adds to the overall context of the book. We learn of standardization issues in relation to pCT. Interesting and important concepts are illustrated on the effect of varying CBV threshold to most accurately predict final infarct area, along with the effect of various statistical packages. Those who want to read about research groups in stroke will find their group names and what they are working on in the third chapter of this book.
Successive chapters deal first with MRI and trials for emergency care ischemic stroke. Good imaging examples accompany the description of varying trials. There is some redundancy between this material and preceding and subsequent chapters, but this is to be expected in a multi-authored text. One legend (figure 1) is incorrectly described; however, the others are proper—we read of a term “malignant infarction”, which to this reviewer is a term seldom used in describing the characteristics of an infarction. The consequences of large volumes of restricted diffusion and delayed transit with thrombolytic therapy is reviewed. The actual ADC values for possible predictions of reversal of diffusion restriction receive attention in a portion of this chapter. The following chapter, “MR Perfusion in Acute Ischemic Stroke”, provides details on the hemodynamics of stroke along with technical parameters used in pMR. For those revising or intiating pMR protocols, up-to-date information is provided, and, in the next chapter, arterial spin labeling and its potential in stroke evaluation is described and illustrated.
Transient ischemia of the brain is summarized in a chapter where the diagnosis and what is termed risk stratification is described. Instructive cases are shown such as a DWI negative but a large area of hypoperfusion in a Tmax study in a patient with 2 episodes of TIA. Emphasized also is the fact that not infrequently clinically transient symptoms may actually show small, DWI-positive areas. The point is made of looking at TIAs with a tissue-based rather than simply a clinically based definition and how the risk changes when the tissue based definition is used. This is an important chapter.
In near follow-up to the chapter on TIAs comes one entitled “Imaging Stroke Patients with Unclear Onset Times”. Since many acute/subacute symptoms related to brain ischemia have undeterminable times which one can date the actual onset of symptoms, imaging them assumes an important role. Included also are examples of what are various scenarios for eligibility and ineligibility for TPA therapy. One reads here also of the theories relative to various times of the day when strokes are most likely to occur.
A detailed chapter on MR diffusion ischemic stroke covers the clinical applications of DWI along with the theoretical and mathematical basis for determining and calculating diffusion parameters. Many parts of this chapter are valuable, particularly the time changes of DWI over time following acute ischemic. The presence of pseudonormalization is shown and described in a valuable table. Included, also, are examples of other conditions which result in diffusion restrictions and correlative cases showing correlation between diffusion and fractional anisotropy.
Concluding chapters discuss intra-arterial therapy for stroke, evaluating extracranial carotid arteries with noninvasive technique (US, MRA, CTA), and various scoring methods for the triaging and prediction of outcomes of stroke.
Despite some redundancy in material between a number of chapters, this issue of the NICNA is extremely valuable and should be read by all those involved in evaluating patients with stroke symptoms, whether they are radiologists or those primarily in the care of neurology patients.
