SUMMARY:Texture analysis describes a variety of image-analysis techniques that quantify the variation in surface intensity or patterns, including some that are imperceptible to the human visual system. Texture analysis may be particularly well-suited for lesion segmentation and characterization and for the longitudinal monitoring of disease or recovery. We begin this review by outlining the general procedure for performing texture analysis, identifying some potential pitfalls and strategies for avoiding them. We then provide an overview of some intriguing neuro-MR imaging applications of texture analysis, particularly in the characterization of brain tumors, prediction of seizures in epilepsy, and a host of applications to MS.ABBREVIATIONS: ABSV ϭ absolute gradient value; AIS ϭ acute ischemic stroke; ANN ϭ artificial neural network; CIS ϭ clinically isolated syndrome; d ϭ distance; DCE ϭ dynamic contrastenhanced; FCD ϭ focal cortical dysplasia; FLAIR ϭ fluid-attenuated inversion recovery; f x ϭ second-order gray-level co-occurrence feature number "x"; GLCM ϭ gray-level co-occurrence matrix; GM ϭ gray matter; HT ϭ hemorrhagic transformation; LDA ϭ linear discriminant analysis; MGL ϭ mean gray level; MGR ϭ mean gradient; MS ϭ multiple sclerosis; MTR ϭ magnetization transfer ratio; NAWM ϭ normal-appearing white matter; N g ϭ number of gray levels; PCA ϭ principal components analysis; PPMS ϭ primary-progressive MS; RLM ϭ run-length matrix; ROC ϭ receiver-operator characteristic; ROI ϭ region of interest; RRMS ϭ relapsing-remitting MS; rtPA ϭ recombinant tissue plasminogen activator; SPMS ϭ secondary-progressive MS; SVM ϭ support vector machine; ϭ direction; VGL ϭ variance of gray levels; VGR ϭ variance gradient; WM ϭ white matter

Stepping-table digital subtraction contrast material-enhanced MR angiography has high accuracy compared with catheter angiography in patients with arterio-occlusive disease of the aorta and outflow vessels. These preliminary study results suggest that this technique may ultimately provide a safe, noninvasive, and cost-effective alternative to catheter angiography.

Background and Purpose-Age-related white matter disease (leukoaraiosis) clusters in bands in the centrum semiovale, about the occipital and frontal horns of the lateral ventricles, in the corpus callosum, and internal capsule. Cerebrovascular anatomy suggests that some of these locations represent border zones between arterial supply territories. We hypothesized that there are zones of reduced cerebrovascular reserve (susceptible to selective reductions in blood flow, ie, steal phenomenon) in the white matter of young, healthy subjects, the physiological correlate of these anatomically defined border zones. Furthermore, we hypothesized that these zones spatially correspond with the regions where the elderly develop leukoaraiosis. Methods-Twenty-eight healthy volunteers underwent functional MR mapping of the cerebrovascular response to hypercapnia. We studied 18 subjects by blood oxygen level-dependent MRI and 10 subjects by arterial spin labeling MRI. We controlled both end-tidal pCO 2 and pO 2 . All functional data was registered in Montreal Neurological Institute space and generated composite blood oxygen level-dependent MR and arterial spin labeling MR maps of cerebrovascular reserve. We compared these maps with frequency maps of leukoaraiosis published previously. Results-Composite maps demonstrated significant (90% CI excluding the value zero) steal phenomenon in the white matter. This steal was induced by relatively small changes in end-tidal pCO 2 . It occurred precisely in those locations where elderly patients develop leukoaraiosis. Key Words: cerebrovascular accident Ⅲ cerebrovascular disorders Ⅲ magnetic resonance imaging S ince the advent of CT, physicians and researchers have noted the prevalence of abnormality in the white matter of elderly human brain. Characterized by patchy or diffuse low density on CT images, and corresponding hyperintensity on T2-weighted MRIs, this abnormality histopathologically represents rarefaction of myelin, loss of axons and oligodendrocytes, dilatation of perivascular spaces, and mild gliosis. 1 It is simply called white matter disease, or leukoaraiosis, 2 literally meaning diminution of white matter density. Leukoaraiosis clusters in several locations: cigar-shaped bands in the deep white matter of the centrum semiovale, 3,4 in the white matter about the occipital and frontal horns of the lateral ventricles, [3][4][5] in the genu and splenium of the corpus callosum, 3,5 and in the posterior limb of the internal capsule. 4 Prevalence increases with age with some degree of leukoaraiosis in more than half of those older than 60 years of age. 6 It was initially considered a benign age-related change, but more recent studies suggest it may be associated with cognitive dysfunction 7 and the development of dementia. 8 Despite growing appreciation of its clinical significance, the pathogenesis of leukoaraiosis is poorly understood. 9 Evidence suggests an ischemic process, 10 but what causes the ischemia? Conclusions-ThisOne theory is based on a concept of "internal border zon...

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Purpose: To evaluate the reproducibility and gender differences in cerebrovascular reactivity (CVR) measurements obtained using the blood-oxygen level dependent (BOLD) response to controlled changes in end-tidal partial pressure of carbon dioxide (PETCO 2 ). Materials and Methods:We obtained ethical approval to image 19 healthy volunteers (10 men, 9 women) on a 1.5 Tesla (T) MRI scanner twice on two separate days using identical procedures. CVR images were generated by collecting BOLD MRI data during controlled changes in PETCO 2 induced by a sequential gas delivery system.Results: Using the intraclass correlation coefficient (ICC), we demonstrated excellent within-day CVR measures in gray matter (GM) (ICC ¼ 0.92) and white matter (WM) (ICC ¼ 0.88) regions, excellent between-day reproducibility in GM (ICC ¼ 0.81), and good between-day reproducibility in the WM (ICC ¼ 0.66). CVR values between men and women were significantly different in the GM and WM. Men exhibited a 22 6 2% greater CVR in GM and a 17 6 2% greater CVR in WM compared with females.Conclusion: Our results demonstrate the reliability of BOLD MRI CVR measurements obtained using a controlled cerebrovascular challenge. Using this technique, we also revealed significantly increased BOLD response to CO 2 in males compared with females.

The dynamics of BBB permeability after AIS in humans are not well understood. In the present study we measured the evolution of BBB permeability after AIS in humans using MRI. Patients presenting to our institution with a diagnosis of AIS underwent a single dynamic contrast-enhanced MRI (DCE-MRI) sequence to measure BBB permeability during their initial workup. Forty-two patients were included in the final analysis. The patient sample underwent DCE-MRI at a mean time of 23.8hrs after the onset of AIS symptoms (range: 1.3–90.7hrs). At all time-points the BBB permeability within the infarct region of the brain as defined on DWI/ADC was higher compared to the homologous region of the contralateral hemisphere (p<0.005). BBB permeability, expressed as a ratio of infarct permeability to contralateral permeability, was greatest at 6-48hrs after the onset of AIS. Although the data was not acquired longitudinally, these findings suggest that the permeability of the BBB is continually elevated following AIS, which contradicts previous assertions that BBB permeability after AIS follows a biphasic course. Knowledge of BBB dynamics following AIS may provide insight into future treatments for AIS, especially BBB stabilizing agents.

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T he disease burden of acute ischemic stroke (AIS) is rising in the United States and Canada. It is estimated that in the United States 795 000 people have a stroke each year, which amounts to $34 billion in medical expenses and lost productivity.1 Recent trials have shown the potential benefit of procedural thrombectomy in the management of AIS. 2 However, despite substantial research expenditures over the past 2 decades, there have been no new pharmacological agents for the initial treatment of AIS since the approval of recombinant tissue-type plasminogen activator in 1996. Recently, the role of the blood-brain barrier (BBB) in the pathogenesis of AIS has emerged as a focus for new therapeutic strategies. After the onset of AIS, the BBB is rapidly disrupted and this disruption persists for days through the acute and early subacute phases of AIS. The disruption of the BBB can be quantified as an increase in the permeability of the BBB (Figure 1). 4 In the setting of AIS, disruption of the BBB is thought to be a precursor to serious clinical consequences such as hemorrhagic transformation (HT), 5-7 which refers to the development of a hemorrhage within the ischemic brain tissue. Current research is attempting to elucidate the mechanisms of BBB disruption after AIS and develop therapeutic strategies to mitigate the clinical consequences of BBB disruption.Given these developments, a greater number of preclinical and clinical studies are incorporating assessment of BBB disruption into their study designs. Although assessment of BBB disruption may once have been technically difficult, a plethora of methods now exist to assess BBB disruption with relative ease in animal models and humans. When taken together, these methods cover a wide range of temporal and spatial resolutions and permit simultaneous assessment of cell morphology, protein expression and localization, cell electrophysiology, and gross neurological function. An awareness of the specifications and limitations of the methods of assessing BBB disruption is necessary to design effective studies and evaluate the literature.In the present review, we summarize the available methods of assessing BBB permeability in animal models and humans. We strive to highlight the relative strengths and weaknesses of these methods and provide suggestions for study design in stroke research. Finally, we discuss recent translational developments in assessing BBB disruption for the treatment of AIS. Ex Vivo Assessment of BBB DisruptionThe pioneering experiments of Max Lewandowsky first defined the BBB as a dynamic barrier separating the intravascular and extravascular compartments. This laid the groundwork for current methods of assessing BBB disruption in AIS animal models and human trials.8 All methods of assessing BBB disruption are common in their use of tracers, which can be either endogenous if they are naturally found in the blood or exogenous if introduced into the circulation by the experimenter. Table I in the online-only Data Supplement summarizes methods of ass...