Magnetic resonance imaging (MRI) can now provide maps of human brain function with high spatial and temporal resolution. We aimed to establish whether this noninvasive technique could also map the cortical activation that occurs during focal seizures. In order to do this, we used a conventional 1.5-tesla clinical MRI system for the investigation of a 4-year-old boy suffering from frequent partial motor seizures of his right side. We acquired FLASH images (TE = 60 msec) every 10 seconds over intervals of 10 minutes and derived activation images by subtracting baseline images from images obtained during clinical seizures. Functional MRI revealed sequential activation associated with specific gyri within the left hemisphere with each of five consecutive clinical seizures, and also during a period that was not associated with a detectable clinical seizure. The activated regions included gyri that were structurally abnormal. We concluded that functional MRI can provide new insights into the dynamic events that occur in the epileptic brain and their relationship to brain structure.

Diffusion tensor fiber tracking potentially can give information about in vivo brain connectivity. However, this technique is difficult to validate due to the lack of a gold standard. Fiber tracking reliability will depend on the quality of the data and on the robustness of the algorithms used. Information about the effects of various anatomical and image acquisition parameters on fiber tracking reliability may be used in the design of imaging sequences and of tracking algorithms. In this study, tracking was performed on two different simulated models to study the effects on tracking quality of SNR, anisotropy, curvature, fiber cross-section, background anisotropy, step size, and interpolation. Tracking was also performed on volunteer data to assess the relevance of the simulations to real data. Our results show that, in general, tracking with high SNR and high anisotropy using interpolation and a low step size gives the most reliable results. In recent years, diffusion tensor MRI (DT-MRI) has emerged as a promising tool for the study of the microscopic properties of tissue (1-7). In particular, it can be used to infer the directionality of the white matter fiber architecture within a voxel. With this information, studies of human white matter connectivity (fiber tracking) in vivo are now feasible, although a number of issues remain to be addressed.Due to the lack of a relevant gold standard, validation of DT-MRI fiber tracking is not straightforward. It has been shown in the optic nerve of the rat (2) and in the myocardium of the rabbit (3) that the direction of fastest diffusion, as measured by DT-MRI, does correspond to the orientation of the fibers. Fiber tracking has been performed in rat and human brain, and the results have been compared to the corresponding anatomical atlases (4 -7). However, there is a need for alternative methods to assess DT-MRI fiber tracking algorithms, and simulations on synthetic data in which the fiber geometry is known exactly can provide a means of doing this.A further issue is that the limitations and requirements of DT-MRI fiber tracking have not been fully assessed. Fiber tracking relies on the use of good-quality diffusionweighted images, together with a suitable algorithm to generate the tracks. However, acquisition of a set of images with sufficiently high quality is time-consuming, and in practice quality is usually compromised to allow shorter scan times. Different tracking algorithms may be susceptible to noise, partial volume effects, motion artifacts, etc., to varying degrees. It is therefore essential to establish which structures can be tracked reliably, and under what conditions this can be achieved. Simulations can provide a means of assessing these issues as well.Lori et al. (8) recently presented results using an algorithm proposed by Conturo et al. (6) showing the importance of the signal-to-noise ratio (SNR) for reliable tracking. Basser et al. (7) assessed the behavior of their own algorithm in a range of specific situations (for example, crossing and "kissi...

This studs examined the cognitive manifestations of frontallobe 'hfarction in a population of children with sickle cell disease ( S O ) . Forty-one patients with SCD underwent MRI.