Regular articleComparison of fMRI activation at 3 and 1.5 T during perceptual, cognitive, and affective processing
Introduction
Functional magnetic resonance imaging (fMRI) is now widely used to study brain function and dysfunction. Due to their wide availability, 1.5 T systems are currently used in a majority of fMRI studies. Increasingly, however, fMRI studies are being conducted at field strengths of 3 T or higher. Recent research has demonstrated that exquisite spatial resolution can be obtained with functional imaging at higher field strength in a manner that was not possible at 1.5 T. For example, researchers have demonstrated high-resolution maps of ocular dominance columns Cheng et al 2001, Menon et al 1997 and retinotopy within the lateral geniculate nucleus (Ugurbil et al., 1999). Many of the early studies comparing brain activation at 1.5 T with higher fields focused on examining signal increases in the visual Gati et al 1997, Turner et al 1993 and motor (Yang et al., 1999) cortices. No information, however, is available on the relative gain, or the comparability of data, obtained at higher field strengths for regions other than the visual and motor cortices. In this study we examine qualitative and quantitative differences in the patterns of activation observed at 3 and 1.5 T during sensory, cognitive, and affect-processing tasks.
For fMRI, a major advantage of using higher fields derives from the fact that the rate of transverse relaxation, R2* = 1/T2*, scales as the square of the external magnetic field for small blood vessels and capillaries, whereas the change is linear for large blood vessels (Gati et al., 1997). Since the blood oxygen level-dependent (BOLD) contrast originates from the intravoxel magnetic field inhomogeneity induced by paramagnetic deoxyhemoglobin, higher fields should result in improved sensitivity related primarily to BOLD changes in capillary beds in response to neural activity Kruger et al 2001, Ugurbil et al 1999. Thus, theoretical considerations indicate that higher fields should result in improved sensitivity and spatial specificity for detection of task-related brain activation. Furthermore, since BOLD signal changes at 1.5 T are rather small (on the order of a few percent), it is thought that higher field strengths of 3 T or more should significantly enhance the ability to reliably detect signals of interest.
Four published studies to date have directly compared changes in task-related fMRI activation at 1.5 T and higher field strengths Gati et al 1997, Kruger et al 2001, Turner et al 1993, Yang et al 1999. Two of these studies focused on the visual cortex, one on the motor cortex, and a fourth on the visual and motor cortices. Turner et al. (1993) compared activation in the visual cortex at 1.5 and 4 T during photic stimulation and reported an increase of approximately 300% in an eight-voxel (5 mm2) region at 4 T. More recent studies have taken scanner noise and physiological fluctuations into account and have reported more modest increase in signal. Gati et al. (1997) found a 70% increase in average percentage signal change in cortical gray matter activation during photic stimulation. Yang et al. (1999) examined activation in the motor cortex during a finger-tapping task and found that at 4 T, compared with 1.5 T, there was a 70% increase in the number of voxels activated and a 20% higher average t score for the activated voxels. Kruger et al. (2001) examined motor and visual cortex activation at 3 T, compared with 1.5 T. They found a 44% increase in the number of voxels activated in the primary motor cortex and 36% more voxels were activated in the visual cortex compared with activation during a checkerboard reversal task (Kruger et al., 2001). Taken together, these studies suggest that higher field strength provides an advantage for functional imaging of primary sensory and motor cortices. The extent to which signal gains of the type found in primary sensory and motor cortices might extend to association cortices, e.g., the prefrontal and parietal cortex, is not known. This is an important question to examine since fMRI is now extensively used to study cognitive function and dysfunction.
A second major issue that has not been addressed in studies to date is the comparative extent of susceptibility artifacts at higher field strengths. Susceptibility artifacts result from abrupt changes in magnetic susceptibility that occur across tissue interfaces such as the border between air-filled sinuses and brain parenchyma or between bone and brain parenchyma (Ojemann et al., 1997). Brain regions closest to such borders are especially prone to BOLD signal loss due to this artifact. Brain regions that are affected by these artifacts include the orbitofrontal cortex, hippocampus, amygdala, and anterior, inferolateral temporal pole Devlin et al 2000, Lipschutz et al 2001, Ojemann et al 1997. No study to date has examined differences in activation at different magnetic field strengths using tasks that are known to involve brain regions that are prone to susceptibility artifact.
In this study, we examined differences in activation at 1.5 and 3 T using three different tasks that are known to activate distinct brain regions. We used a visual perception task known to reliably activate striate and extrastriate cortices DeYoe et al 1994, Watson et al 1993, a working memory task known to reliably activate the prefrontal and parietal association cortices Smith and Jonides 1997, Smith and Jonides 1998, and an affect-processing task known to reliably activate the amygdala Breiter et al 1996, Yang et al 2002. A random effects model was used to examine differences in activation obtained at the two field strengths. The results of this analysis were used to isolate the precise voxels that showed statistically significant differences in activation between the two field strengths. For each task, we examined the increased sensitivity for detection of activation at 3 T; by “activation” we mean voxels for which the z scores exceed a specified threshold. Finally, we also examined the effect of susceptibility artifacts on amygdala activation at the two field strengths.
Section snippets
Subjects
Fourteen right-handed subjects (aged 17–25, mean age = 21.21 years, SD = 2.16; 7 male) participated in the study after giving written informed consent. fMRI data were acquired for each subject as he or she performed three different tasks involving visual perception, working memory, and affect-processing in scanners with 1.5- and 3-T magnetic field strengths. Both task order and scanner order were randomized and counterbalanced in this within-subjects design. Each subject was presented with the
Activation
Significant activation was observed in the striate, extrastriate, and posterior parietal cortex at both 3 and 1.5 T, with more extensive activation at 3 T (Fig. 1). A direct comparison of activations using random effects analysis revealed a greater number of activated voxels at 3 T in the striate cortex (VI) and extrastriate regions (V2 and V3) (Fig. 2). Significant between-scanner differences were detected in 896 voxels; 3811 voxels were activated at 1.5 T, implying an increase in activation
Discussion
During both the visual perception and visuospatial working memory tasks significantly greater cortical activation was observed at 3 T, compared with 1.5 T. Increased activation at 3 T was most dramatic in frontal and parietal cortices during the working memory task. Compared with an increase in visual cortex activation of about 23% during the visual perception task, increases in activated voxels of 78% in the prefrontal cortex and 59% in the parietal cortex were observed during the working
Acknowledgements
This research was supported by NIH Grants HD40761, MH62430, RR09784, and MH19908, and grants from the Norris Foundation, and the Lucas Imaging Center.
References (52)
- et al.
Functional magnetic resonance imaging of facial affect recognition in children and adolescents
J. Am. Acad. Child Adolesc. Psychiatry
(1999) - et al.
Response and habituation of the human amygdala during visual processing of facial expression
Neuron
(1996) - et al.
Emotion and motivationthe role of the amygdala, ventral striatum, and prefrontal cortex
Neurosci. Biobehav. Rev.
(2002) - et al.
Human ocular dominance columns as revealed by high-field functional magnetic resonance imaging
Neuron
(2001) - et al.
Compensation of susceptibility-induced signal loss in echo-planar imaging for functional applications
Magn. Reson. Imaging
(2000) - et al.
Compensation of susceptibility-induced BOLD sensitivity losses in echo-planar fMRI imaging
NeuroImage
(2002) - et al.
Susceptibility-induced loss of signalcomparing PET and fMRI on a semantic task
NeuroImage
(2000) - et al.
Functional magnetic resonance imaging (FMRI) of the human brain
J. of Neurosci. Methods
(1994) - et al.
Common regions of the human frontal lobe recruited by diverse cognitive demands
Trends Neurosci.
(2000) Localization of function all over again
NeuroImage
(2000)
Reliability and validity of MRI measurement of the amygdala and hippocampus in children with fragile X syndrome
Psychiatry Resv75
Robust smoothness estimation in statistical parametric maps using standardized residuals from the general linear model
NeuroImage
Assessing study-specific regional variations in fMRI signal
NeuroImage
Functional brain activation during cognition is related to FMR1 gene expression
Brain Res.
Functional MRI of the human amygdala?
NeuroImage
The prefrontal cortexno simple matter
NeuroImage
Working memory for letters, shapes, and locationsfMRI evidence against stimulus-based regional organization in human prefrontal cortex
NeuroImage
Anatomic localization and quantitative analysis of gradient refocused echo-planar fMRI susceptibility artifacts
NeuroImage
Combining spatial extent and peak intensity to test for activations in functional imaging
NeuroImage
An fMRI investigation of cortical contributions to spatial and nonspatial visual working memory
NeuroImage
Functional MRI reveals left amygdala activation during emotion
Psychiatry Res.
Working memorya view from neuroimaging
Cogn. Psychol.
Automated anatomical labeling of activations in SPM using a macroscopic anatomical parcellation of the MNI MRI single-subject brain
NeuroImage
Comparison of 3D BOLD functional MRI with spiral acquisition at 1.5 and 4.0 T
NeuroImage
The amygdala and reward
Nat. Rev. Neurosci.
Matching patterns of activity in primate prefrontal area 8a and parietal area 7ip neurons during a spatial working memory task
J. Neurophysiol.
Cited by (111)
Design science and neuroscience: A systematic review of the emergent field of Design Neurocognition
2023, Design StudiesCitation Excerpt :The type of brain imaging tool and the tool's technical specifications, such as its data resolution, varied across studies. For fMRI, better spatial resolution can be obtained with functional imaging at higher field strengths of 3T compared to 1.5T (Krasnow et al., 2003). The majority of the Design Science studies were executed in a 3T MRI scanner (Fu et al., 2019; Goucher-Lambert et al., 2018a, 2019; Goucher-Lambert & McComb, 2019; Hay et al., 2019), while two studies were conducted with a 1.5T instrument (Alexiou et al., 2009, 2011).
Cortical and subcortical contributions to interference resolution and inhibition – An fMRI ALE meta-analysis
2021, Neuroscience and Biobehavioral ReviewsThe Mediodorsal Thalamus: An Essential Partner of the Prefrontal Cortex for Cognition
2018, Biological Psychiatry