Reproducibility and postprocessing of gradient-echo functional MRI to improve localization of brain activity in the human visual cortex

Moser, Ewald; Teichtmeister, C.; Diemling, Markus

doi:10.1016/0730-725x(96)00095-1

Cited by 58 publications

(29 citation statements)

References 13 publications

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“…2 and 4). This is an important point in the previously mentioned discussion about fixed or data-dependent thresholds (26). Our results support the view that individually adapted thresholds are a reasonable means of analyzing single subject data to get comparable results for several individuals and to increase intra-individual reliability.…”

Section: Discussionsupporting

confidence: 76%

“…With qualitative indices in particular, the results are strictly dependent upon whether fixed statistical thresholds (23)(24)(25)(26) or data-dependent thresholds (26 -28) have been employed. The choice of threshold depends on the statistical analysis strategy, whether it is exploratory or confined to an a priori hypothesis about activations in some pre-specified regions (29,30).…”

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confidence: 99%

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Assessment of reliability in functional imaging studies

Specht

Willmes

Shah

et al. 2003

Magnetic Resonance Imaging

120

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Purpose:To investigate the reliability of functional magnetic resonance imaging (fMRI), an approach for mapping and quantifying reliably activated voxels was developed. Materials and Methods:First, a SPM99 analysis was performed, and the resulting statistical maps were taken as the basis for subsequent analyses of reliability. Several approaches were demonstrated using 1) a voxel-wise intraclass correlation coefficient (ICC); 2) an analysis of scatter plots, calculating the correlation of contrast t-values for pairs of activation maps; and 3) the ratio of overlapping volumes as suggested in the literature. The methods were applied to an fMRI study in which subjects were asked to vary their attentional effort during watching a flickering checkerboard pattern with varying letters in the center. The subjects had to ignore or attend to the presentation, or they had to detect a target letter within the checkerboard. Results:The imaging data showed good reliability in terms of ICC for regions of visual processing, as well as for frontal areas, especially in the letter detection task. Furthermore, the size of reliable clusters depended on the presumed attentional effort of the subjects. Conclusion:Application of the method demonstrated that the activation due to visual stimulation could also be detected very consistently during a no-attend condition, but the reliability of the activations were best during the attended tasks. THIS PAPER DESCRIBES statistical techniques employed for functional magnetic resonance imaging (fMRI) studies that allow assessment of the reliability of activations. The detected signal change in the time course caused by the BOLD effect (blood oxygenation level dependence) is an indirect measurement of neural activity. The BOLD effect can be attenuated because of several underlying technical, physiological, and psychological phenomena. The signal change of about 2%-5% is not much higher than the general noise components in the fMRI time series. The amount of activation can also be affected by remaining motion after realignment, as noted by Casey et al (1) in a comparison of fMRI results across four institutes, whereas the activation maps are in general similar between institutes, modalities, and analysis methods (2).However, use of the fMRI technique for clinical purposes requires reliable results within single subjects measured at different times, for comparisons between subjects or patients, as well as for diagnostic examinations. Aguirre and coworkers (3) compared the variability of BOLD responses within and between subjects and found a higher variability in the shape of responses between subjects than within. McGonigle et al (4) investigated the same subject in several repeated measurements and concluded that single-subject results could lead to erroneous interpretations. This should be taken into account in preoperative planning for which fMRI is becoming more and more important (5). The relationship between neural activity and the signal change is also still a matter of discussion. Arthurs ...

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Section: Discussionsupporting

confidence: 76%

mentioning

confidence: 99%

Assessment of reliability in functional imaging studies

Specht

Willmes

Shah

et al. 2003

Magnetic Resonance Imaging

120

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“…fMRI therefore gives a map of the brain regions involved in task performance and indicates part of the mechanisms of that brain activation. It has demonstrated reproducibility and reliability for visual, motor, and cognitive tasks (27,28), and we designed our study to eliminate any intraindividual variation from day to day (29).…”

Section: Discussionmentioning

confidence: 99%

The Effect of Acute Hypoglycemia on Brain Function and Activation

et al. 2001

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The authors' aim was to examine the regional anatomy of brain activation by cognitive tasks commonly used in hypoglycemia research and to assess the effect of acute hypoglycemia on these in healthy volunteers. Eight right-handed volunteers performed a set of cognitive tasks-finger tapping (FT), simple reaction time (SRT), and four-choice reaction time (4CRT)-twice during blood oxygen level-dependent (BOLD) functional magnetic resonance imaging of the brain on two occasions. In study 1 (n ‫؍‬ 6), plasma glucose was maintained at euglycemia (5 mmol/l) throughout. In study 2 (n ‫؍‬ 6), plasma glucose was reduced to 2.5 mmol/l for the second set. Performance of the tasks resulted in specific group brain activation maps. During hypoglycemia, FT slowed (P ‫؍‬ 0.026), with decreased BOLD activation in right premotor cortex and supplementary motor area and left hippocampus and with increased BOLD activation in left cerebellum and right frontal pole. Although there was no significant change in SRT, BOLD activation was reduced in right cerebellum and visual cortex. The 4CRT deteriorated (P ‫؍‬ 0.020), with reduction in BOLD activation in motor and visual systems but increased BOLD signal in a large area of the left parietal association cortex, a region involved in planning. Hypoglycemia impairs simple brain functions and is associated with task-specific localized reductions in brain activation. For a task with greater cognitive load, the increased BOLD signal in planning areas is compatible with recruitment of brain regions in an attempt to limit dysfunction. Further investigation of these mechanisms may help devise rational treatment strategies to limit cortical dysfunction during acute iatrogenic hypoglycemia. Diabetes 50:1618 -1626, 2001

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“…Motion correction was not performed on the data before the analysis because of the small number of slices. Instead, in order to eliminate the signal intensity changes due to stimulation-related motion, center of mass (COM) analysis was performed (24). If the COM position changed as function of time coincidentally with the BOLD response time course, the data were rejected.…”

Section: Functional Mri Analysismentioning

confidence: 99%

MR perfusion, diffusion and BOLD imaging of methotrexate‐exposed swine brain

Mäkiranta

Lehtinen

Jauhiainen³

et al. 2002

Magnetic Resonance Imaging

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Purpose: To evaluate the methotrexate (MTX)-exposed swine brain, functional magnetic resonance imaging (MRI), including perfusion, diffusion, and blood-oxygen-level-dependent (BOLD) contrast imaging, was used. Material and Methods:Juvenile pigs received either 2 ϫ 5 g/m 2 , or 5 ϫ 2 g/m 2 MTX intravenously within one month. MRI was performed (sedative: propofol) before (14 -17 kg, N ϭ 6) and after (21-27 kg, N ϭ 4) the MTX exposure. Also, age-matched controls (22-27 kg, N ϭ 4) were imaged. Results:After the MTX exposure, reduced (from 2%-4% to 0%-1%) or negative (-2% to -3%) BOLD responses were detected; apparent diffusion coefficient (ADC) or relative perfusion values did not change. Conclusion:This study suggests that MTX-related changes in the brain may be detected as changes in flow-metabolism coupling as reduced or negative response (for somatosensory activation) in the BOLD contrast MRI. The contrast agent perfusion MRI, without absolute quantification, may not show global damage in brain perfusion related to the MTX exposure in the swine model used. ADC (in one direction) may not indicate MTX-related changes in the brain. FUNCTIONAL MAGNETIC RESONANCE imaging (MRI) (including perfusion, diffusion, and blood-oxygen-leveldependent [BOLD] imaging) may allow early detection of brain injury before clear anatomic abnormalities (1). Such defects may include microcirculation, water homeostasis, and neuronal activation. Brain microcirculation is typically measured by T 2 *-weighted perfusion imaging with a paramagnetic contrast agent. However, the absolute values of mean transit time (MTT), regional cerebral blood volume (rCBV), and regional cerebral blood flow (rCBF) can only be obtained if the arterial input function is known, which is difficult (1,2). An easier but less accurate way is to calculate relative values between the different anatomic areas. Apparent diffusion coefficient (ADC) is related to extracellular water volume and energy metabolism (3,4). BOLD contrast MRI utilizes paramagnetic deoxyhemoglobin as an endogenous contrast agent in T 2 *-weighted activation studies (5-7). Alterations in BOLD response may correspond to changes in flow-metabolism coupling during local neuronal activation in the brain.Methotrexate (MTX) has several effects on cerebral metabolism causing i) demyelination, ii) deterioration in vascular endothelium, iii) synthesis of excitatory neurotransmitters, and iv) decrease in cerebral glucose metabolism (CMR glu ) (8 -14). MTX induces deficits in brain perfusion in several brain areas detected with Single Photon Emission Computed Tomography (SPECT) and positron emission tomography (PET) studies (15,16). Also, MTX may sometimes induce white matter changes in the anatomic .The purpose of the present study was to show how MTX-related changes in the brain affect different functional MRI parameters. Our hypothesis was that functional MRI could show MTX-related changes in brain functionality, i.e., changes in rCBF ratios, MTT ratios, ADC, and BOLD response after the MTX exposure. MATER...

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Reproducibility and postprocessing of gradient-echo functional MRI to improve localization of brain activity in the human visual cortex

Cited by 58 publications

References 13 publications

Assessment of reliability in functional imaging studies

Assessment of reliability in functional imaging studies

The Effect of Acute Hypoglycemia on Brain Function and Activation

MR perfusion, diffusion and BOLD imaging of methotrexate‐exposed swine brain

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