Compensation of susceptibility-induced signal loss in echo-planar imaging for functional applications☆

Cordes, Dietmar; Turski, Patrick A.; Sorenson, James A.

doi:10.1016/s0730-725x(00)00199-5

Cited by 64 publications

(51 citation statements)

References 31 publications

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“…Finally, regardless of the model to be tested, we propose that future fMRI studies of the hippocampus should include some estimate of susceptibility artifact. Recent work by Devlin et al (2000) and Cordes et al (2000) has shown that susceptibility artifact is not limited to the temporal pole or lateral temporal regions and our study confirms that it can significantly impact regional analyses of hippocampal function.…”

Section: Discussionsupporting

confidence: 85%

“…Devlin et al (2000) compared PET and fMRI directly, using a nearly identical semantic task, and found that anteromedial temporal activation was detected with PET, but not with fMRI. Cordes et al (2000) showed susceptibility-induced signal loss in the parahippocampal and amygdala regions while a subject mentally rehearsed a gymnastics routine. Because the hippocampus rises superiorly from anterior to posterior, one would expect greater susceptibility-induced signal loss in the anterior (inferior) relative to the posterior (superior) hippocampus.…”

Section: Introductionmentioning

confidence: 99%

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Regional analysis of hippocampal activation during memory encoding and retrieval: fMRI study

et al. 2002

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ABSTRACT:Investigators have recently begun to examine the differential role of subregions of the hippocampus in episodic memory. Two distinct models have gained prominence in the field. A potential confounding factor in these fMRI studies, however, is that susceptibility artifact may differentially reduce signal in the anterior versus the posterior hippocampus. In the present study, we examined activation differences between hippocampal subregions during encoding and retrieval of words and interpreted our findings within the context of these two models. We also examined the extent to which susceptibility artifact affects the analysis and interpretation of hippocampal activation by demonstrating its differential effect on the anterior versus the posterior hippocampus. Both voxel-by-voxel and region-of-interest analyses were conducted, allowing us to quantify differences between the anterior and posterior aspects of the hippocampus. We detected significant hippocampal activation in both the encoding and retrieval conditions. Our data do not provide evidence for regional anatomic differences in activation between encoding and retrieval. The data do suggest that, even after accounting for susceptibility artifact, both encoding and retrieval of verbal stimuli activate the middle and posterior hippocampus more strongly than the anterior hippocampus. Finally, this study is the first to quantify the effects of susceptibility-induced signal loss on hippocampal activation and suggests that this artifact has significantly biased the interpretation of earlier fMRI studies. Hippocampus 2003;13:164 -174.

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Section: Discussionsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Regional analysis of hippocampal activation during memory encoding and retrieval: fMRI study

et al. 2002

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“…In EEG-fMRI of epileptic patients, it is preferable to scan the whole brain, since the generator of scalp spikes may, within reason, be anywhere. Other strategies include optimisation of the slice orientation [Deichmann et al, 2003;Ojemann et al, 1997], the use of diamagnetic materials to correct for field perturbations [Wilson et al, 2002], and zshimming methods, which apply refocusing pulses to correct for local field inhomogeneities in the slice selection direction [e.g., Cordes et al, 2000, Gu et al, 2002. All of these techniques have drawbacks, such as precluding whole brain coverage, reducing the temporal resolution, reducing the BOLD contrast to noise ratio, or, in the case of passive diamagnetic shims, discomfort for the patient during the course of a 90-min scanning session.…”

Section: Discussionmentioning

confidence: 99%

EEG‐fMRI of focal epileptic spikes: Analysis with multiple haemodynamic functions and comparison with gadolinium‐enhanced MR angiograms

Bagshaw

Aghakhani

Bénar

et al. 2004

Human Brain Mapping

211

210

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Combined EEG-fMRI has recently been used to explore the BOLD responses to interictal epileptiform discharges. This study examines whether misspecification of the form of the haemodynamic response function (HRF) results in significant fMRI responses being missed in the statistical analysis. EEG-fMRI data from 31 patients with focal epilepsy were analysed with four HRFs peaking from 3 to 9 sec after each interictal event, in addition to a standard HRF that peaked after 5.4 sec. In four patients, fMRI responses were correlated with gadolinium-enhanced MR angiograms and with EEG data from intracranial electrodes. In an attempt to understand the absence of BOLD responses in a significant group of patients, the degree of signal loss occurring as a result of magnetic field inhomogeneities was compared with the detected fMRI responses in ten patients with temporal lobe spikes. Using multiple HRFs resulted in an increased percentage of data sets with significant fMRI activations, from 45% when using the standard HRF alone, to 62.5%. The standard HRF was good at detecting positive BOLD responses, but less appropriate for negative BOLD responses, the majority of which were more accurately modelled by an HRF that peaked later than the standard. Co-registration of statistical maps with gadolinium-enhanced MRIs suggested that the detected fMRI responses were not in general related to large veins. Signal loss in the temporal lobes seemed to be an important factor in 7 of 12 patients who did not show fMRI activations with any of the HRFs.

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“…For social semantics, there were clusters of activation in the left superior and medial frontal gyri, left inferior and middle frontal gyri, and right medial frontal gyrus. Visual inspection of the functional images suggested that the absence of activation of orbito-frontal regions was due to signal dropout (see Figure 2), this was most likely due to susceptibility artifact from the nasal sinuses (Cordes, Turski, & Sorenson, 2000).…”

Section: Imaging Datamentioning

confidence: 99%

Category-Specific Representations of Social and Nonsocial Knowledge in the Human Prefrontal Cortex

Wood

Romero

Makale

et al. 2003

Journal of Cognitive Neuroscience

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Abstract& Complex social behavior and the relatively large size of the prefrontal cortex are arguably two of the characteristics that distinguish humans from other animals. Grafman presented a framework concerning how the prefrontal cortex (PFC) controls complex behavior using stored structured event complexes (SECs). We report behavioral and imaging data from a modified go/no-go paradigm in which subjects had to classify words (semantic) and phrases (SEC) according to category. In experimental trials, subjects classified items according to social or nonsocial activity; in control trials, they classified items according to font. Subjects were faster to classify social than nonsocial semantic items, with the reverse pattern evident for the social and nonsocial SEC items. In addition, the conditions were associated with different patterns of PFC activation. These results suggest that there are different psychological and neural substrates for social and nonsocial semantic and SEC representations. &

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Compensation of susceptibility-induced signal loss in echo-planar imaging for functional applications☆

Cited by 64 publications

References 31 publications

Regional analysis of hippocampal activation during memory encoding and retrieval: fMRI study

Regional analysis of hippocampal activation during memory encoding and retrieval: fMRI study

EEG‐fMRI of focal epileptic spikes: Analysis with multiple haemodynamic functions and comparison with gadolinium‐enhanced MR angiograms

Category-Specific Representations of Social and Nonsocial Knowledge in the Human Prefrontal Cortex

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