Clinical fMRI

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145338/1/cpmia0600.pd

Quality Assurance for Clinical fMRI

The functional MRI (fMRI) procedure has several sources of variance that determine the success of the examination. These include the scanner, patient, and paradigm. As blood oxygenation level dependent (BOLD) contrast is a small effect, high signal‐to‐noise performance is mandatory. Because the preparation of a functional activation map requires averaging multiple images over time, the scanner must produce high temporal stability of the signal intensity. This unit presents the for achieving scanner stability. There are many determinants of such performance but not all possibilities need to be checked separately. An adequate approach has been to verify total system performance under the conditions of a functional MRI study on a phantom. This testing is done daily prior to patient studies.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145361/1/cpmia0602.pd

An fMRI study of saccadic and smooth pursuit eye movement control

PURPOSE. To compare the cortical networks that underlie oculomotor function in patients with age-related macular degeneration (AMD) with those in normally sighted control subjects, using functional magnetic resonance imaging (fMRI). METHODS. Six patients with bilateral geographic retinal atrophy due to AMD (age range, 55-83 years) were recruited for the study. The visual acuities of the patients ranged from 20/76 (0.58 logMAR) to 20/360 (1.26 logMAR). An additional six younger (age range, 22-31 years) and six older (age range, 54 -78 years) normally sighted individuals were recruited as control subjects. fMRI data were acquired on a 3.0-Tesla, scanner while subjects performed visually guided saccade (VGS) and smooth-pursuit (SmP) tasks. RESULTS. Contrasts between VGS and fixation on a stationary target identified a network of activation that included the frontal eye fields (FEFs), supplementary eye fields (SMA/SEFs), prefrontal cortex (PFC), intraparietal sulci (IPS), and the areas of the visual cortex (MT/V5, V2/V3, and V1) in control subjects and patients. A similar network was identified for comparisons between SmP and periods of fixation. Marked variability was observed in the performance of both tasks across all patients. For both tasks, the patients generally showed increased PFC and IPS activation, with decreased activation in visual cortex compared with the control subjects. The patients showed significantly increased activation of the FEFs and SMA/SEFs in the SmP task, compared with the control subjects. CONCLUSIONS. These data suggest that performance of both eye movement tasks required greater involvement of the cortical regions generally implicated in attention and effort in patients with AMD. (Invest Ophthalmol Vis Sci. 2008;49:1728 -1735) DOI:10.1167/iovs.07-0372 T he most common visual impairment in persons older than 50 years is a progressive loss of central visual function as a result of AMD. 1,2 It has been estimated that one in three individuals more than 75 years of age and 1 in 30 individuals more than 52 years of age are affected by AMD. 3 Previous research in our laboratory with patients having juvenile or age-related macular degeneration has demonstrated that good central visual acuity is critically important in performing everyday activities, such as reading, writing personal correspondence, and recognizing faces and expressions, and that patients with macular degeneration are impaired in these areas. 4 -8 Commonly, patients who are affected by AMD show some adaptation to their compromised visual system. This adaptation is observed clinically by the use of preferred retinal locations (PRLs) and viewing eccentrically outside of diseased foveae. The use of PRLs is effortful and fatiguing to the patients. Furthermore, many patients use different PRLs depending on the nature of the task. 9,10 Although adaptive in nature, the use of PRLs does not result in normal oculomotor function. For example, the reading rates of patients with AMD using PRLs are substantially lower than those of normally sighted subjects. 11-14 A potential reason for reduced function in patients using PRLs is abnormal scanning of text, which would involve unsteady fixation, and inaccurate saccadic and pursuit eye movements. The primary goal of the present study was to examine the cortical networks that underlie saccadic and pursuit eye movements in patients affected by AMD who use PRLs. To do this, patients and normally sighted control subjects performed saccadic and pursuit eye movement tasks interspersed with periods of central fixation while functional magnetic imaging data were acquired. This study provides insight into the downstream cortical consequences of retinal disease

Brain activation modulated by sentence comprehension.

The comprehension of visually presented sentences produces brain activation that increases with the linguistic complexity of the sentence. The volume of neural tissue activated (number of voxels) during sentence comprehension was measured with echoplanar functional magnetic resonance imaging. The modulation of the volume of activation by sentence complexity was observed in a network of four areas: the classical left-hemisphere language areas (the left laterosuperior temporal cortex, or Wernicke's area, and the left inferior frontal gyrus, or Broca's area) and their homologous righthemisphere areas, although the right areas had much smaller volumes of activation than did the left areas. These findings generally indicate that the amount of neural activity that a given cognitive process engenders is dependent on the computational demand that the task imposes. This study examines what it means to be "thinking harder" in the course of sentence comprehension, in terms of functional magnetic resonance imaging (fMRI)-measured brain activation. One of the challenges of brain science is to relate the dynamics of higher level cognition to the equally dynamic activity of brain-level events. A possible meeting ground between these two levels is the modLulation in the amount of neuronal activity (at the brain level) in a given task, measured as a function of the amount of computational demand that the task places on cognitive resources (1). In particular, we examined whether sentences that were more computationally demanding also engender more brain activation (2, 3). At the cognitive level, sentence comprehension requires combining information from a sequence of words and phrases, computing their syntactic and thematic relations, and using world knowledge to construct a representation of the sentence meaning. These processes require the consumption of computational resources to perform the comprehension operations and also to maintain the representations of the component word meanings, propositions, and relational structures in an activated state during the processing (1). At the brain level, sentence comprehension entails activation in a network of cortical areas, most prominent of which are the left laterosuperior temporal cortex (Wernicke's area) (4) and the left inferio