Journal of magnetic resonance imaging : JMRI
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J Magn Reson Imaging · Jun 2006
ReviewDesign and analysis of fMRI studies with neurologically impaired patients.
Functional neuroimaging can be used to characterize two types of abnormality in patients with neurological deficits: abnormal functional segregation and abnormal functional integration. In this paper we consider the factors that influence the experimental design, analysis, and interpretation of such studies. With respect to experimental design, we emphasize that: 1) task selection is constrained to tasks the patient is able to perform correctly, and 2) the most sensitive designs entail presenting stimuli of the same type close together. ⋯ At the second level (between subjects), inference should be based on between-subjects variance. Provided that these and other constraints are met, deficits in functional segregation are indicated when activation in one or a set of regions is higher or lower in patients relative to control subjects. In contrast, deficits in functional integration are implied when the influence of one brain region on another is stronger or weaker in patients relative to control subjects.
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J Magn Reson Imaging · Jun 2006
ReviewRole of fMRI in the decision-making process: epilepsy surgery for children.
Functional MRI (fMRI) is increasingly being used to evaluate children and adolescents who are candidates for surgical treatment of intractable epilepsy. It has the advantage of being noninvasive and well tolerated by young people. By identifying important functional regions within the brain, including unpredictable patterns of functional reorganization, it can aid in surgical decision-making. ⋯ We describe how fMRI, used in conjunction with conventional investigative methods such as neuropsychological assessment, MRI, and electrophysiology, can 1) help to improve functional outcome by enabling resective surgery that spares functional cortex, 2) guide surgical intervention by revealing when reorganization of function has occurred, and 3) show when abnormal cortex is also functionally active, and hence that surgery may not be the best option. Altogether, these roles have reduced the need for invasive procedures that can be both risky and distressing for young people with epilepsy. In our experience, fMRI has significantly contributed to the decision-making process, and improved the counseling and management of young people with intractable epilepsy.
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Neuroimaging in recent years has greatly contributed to our understanding of a wide range of aspects related to central neurological diseases. These include the classification and localization of disease, such as in headache; the understanding of pathology, such as in Parkinson's disease (PD); the mechanisms of reorganization, such as in stroke and multiple sclerosis (MS); and the subclinical progress of disease, such as in amyotrophic lateral sclerosis (ALS). ⋯ Nevertheless, functional imaging does enable the formulation of neurobiological hypotheses that can be tested clinically, and thus is well suited for testing classic clinical hypotheses about how the brain works. Understanding the mechanisms and sites of pathology, such as has been achieved in cluster headaches, facilitates the development of new therapeutic strategies.
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J Magn Reson Imaging · Jun 2006
ReviewPrinciples of magnetic resonance assessment of brain function.
MRI has advanced to being one of the major tools for the assessment of brain function. This review article examines the basic principles that underpin these measurements. The main emphasis is on the characteristics and detection of blood oxygen level dependent (BOLD) contrast. ⋯ The second section of the article deals with the imaging characteristics of BOLD in terms of the attainable spatial resolution and linear system characteristics. In the third section, practical BOLD imaging is examined for choice of pulse sequence, resolution, echo time (TE), repetition time (TR), and flip angle. The final section touches on other MRI approaches that are relevant to cognitive neuroimaging, in particular the measurement of blood flow, blood volume, resting state fluctuations in the BOLD signal, and measures of connectivity using diffusion tensor imaging and fiber-tracking.
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Functional MRI (fMRI) has tremendous clinical potential that is as yet unrealized. There are tremendous unmet medical needs that fMRI could address with significant benefit to human health. However, both medical and technical barriers prevent this benefit from accruing today. ⋯ However, the real challenge lies in the medical realm, and this will require multidisciplinary and interdisciplinary work since the technical aspects of fMRI are ahead of the medical aspects. This can be seen in a range of diseases from Alzheimer's disease to schizophrenia to ischemic stroke: in each case our ability to image changes with fMRI outstrips our ability to do anything useful for the patient with them. Diagnostic imaging will always be linked in the clinic to therapeutic choices, and therefore the most powerful approach to link fMRI more directly to the clinic will be to tie fMRI to therapy development and implementation.