4 Tesla gradient recalled echo characteristics of photic stimulation‐induced signal changes in the human primary visual cortex

Ravi S. Menon, Seiji Ogawa, David W. Tank, Kǎmil Uǧurbil

Research output: Contribution to journalArticle

321 Scopus citations

Abstract

Multi‐echo measurements of photic stimulation‐induced signal changes in human visual cortex were made at 4 Tesla in order to quantify the nature of the signal change and its vascular origin, and to determine the optimum echo time for detection of the changes. Utilizing high resolution images, two distinct regions (ascribed to be microvasculature and visible venous vessels) were identified as giving rise to the signal increase. The fractional signal changes in gray matter areas depended linearly on echo time (TE) in the range of 10 to 60 ms and extrapolated to virtually zero for TE = 0, indicating that in‐flow effects secondary to stimulation‐induced blood flow increases were negligible in our functional imaging studies; instead, signal change due to photic stimulation originated from the increase in the apparent transverse relaxation rate, 1/T2*. This decrease in (1/T2*, brought about by the alterations in hemodynamic parameters, was 1.3 ± 0.4 s−1 for gray matter and 3.0 ± 0.7 s−1 (averaged over 10 individuals) for venous vessels visible in the images. The optimum choice of echo time was found to be TE ≥ T2*.

Original languageEnglish (US)
Pages (from-to)380-386
Number of pages7
JournalMagnetic Resonance in Medicine
Volume30
Issue number3
DOIs
StatePublished - Sep 1993

All Science Journal Classification (ASJC) codes

  • Radiology Nuclear Medicine and imaging

Keywords

  • functional MR
  • human brain function
  • human brain mapping
  • visual cortex

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