Echo time dependence of BOLD fMRI studies of the piriform cortex

Research output: Contribution to journalResearch articleContributedpeer-review

Contributors

  • Rainer Kopietz - , Ludwig Maximilian University of Munich (Author)
  • Jessica Albrecht - , Ludwig Maximilian University of Munich (Author)
  • Jennifer Linn - , Institute and Polyclinic of Diagnostic and Interventional Neuroradiology, Hospital of the Ludwig-Maximilians-University (LMU) Munich, Ludwig Maximilian University of Munich (Author)
  • Olga Pollatos - , Ludwig Maximilian University of Munich (Author)
  • Andrea Anzinger - , Ludwig Maximilian University of Munich (Author)
  • Tim Wesemann - , Ludwig Maximilian University of Munich (Author)
  • Gunther Fesl - , Ludwig Maximilian University of Munich (Author)
  • Thomas Stephan - , Ludwig Maximilian University of Munich (Author)
  • Hartmut Brückmann - , Ludwig Maximilian University of Munich (Author)
  • Martin Wiesmann - , Ludwig Maximilian University of Munich (Author)

Abstract

Background and Purpose: : In functional magnetic resonance imaging (fMRI) studies, brain areas that are commonly associated with the processing of olfactory stimuli, i.e., piriform cortex and orbitofrontal cortex, are often obscured by susceptibility-induced signal loss. The authors hypothesized that using a short echo time (TE) should not only reduce susceptibility artifacts but also increase the overall signal-to-noise ratio and allow to retrieve a blood oxygenation level-dependent (BOLD) signal in regions normally affected by these artifacts. Material and Methods: : Two sequences with TEs of 60 and 32 ms were compared using a 1.5-T MRI scanner: in a standard motor paradigm, activations of the contralateral motor cortex were measured. In an olfactory stimulation paradigm, activations in piriform cortex were compared. Results: : Reducing TE from 60 to 32 ms reduced the observed signal intensity changes in the motor paradigm by 51%. Concomitant to this, geometric distortions and signal dropout artifacts were decreased at orbitofrontal and temporomesial brain areas in both paradigms. Contrary to the authors' expectations, the signal intensity changes in the piriform cortex were also reduced by 48% in the olfactory paradigm. Moreover, piriform cortex activation was detected in less subjects at TE = 32 ms than at TE = 60 ms. Changes in cortical activation were significant in the right, but not in the left piriform cortex. Conclusion: : Although a shorter TE reduces signal dropouts due to susceptibility artifacts, this shorter TE is not sufficient to recover the BOLD signal from regions affected by susceptibility artifacts such as the piriform cortex. Thus, reducing the TE to the T2*of the investigated region is not an effective approach to improve the results of olfactory fMRI studies.

Details

Original languageEnglish
Pages (from-to)275-282
Number of pages8
JournalClinical neuroradiology
Volume19
Issue number4
Publication statusPublished - Dec 2009
Peer-reviewedYes

External IDs

PubMed 19936572

Keywords

Keywords

  • Echo time, FMRI, Olfaction, Piriform cortex, Susceptibility artifacts