Test-Retest Analysis With Functional MR of the Activated Area in the Human Visual Cortex

PURPOSE To investigate the intersubject and intrasubject variability of the activated area in the visual cortex with functional MR imaging. METHODS Double-section gradient-echo MR images were acquired at 1.5 T in 28 healthy volunteers using the fast low-angle shot (FLASH) technique. Visual stimulation was obtained with light-emitting diode (LED) goggles. Eighteen volunteers were studied twice. The size of the activated areas in the visual cortex and the increase in signal were measured. A reproducibility ratio for size (R[size]) and for location (R[overlap]) was calculated on a scale of 0.0 to 1.0. RESULTS Activation was seen in 89% of the subjects. The size of the activated area was widely variable among subjects: mean, 460 +/- 284 mm2; range, 0 to 1029 mm2 in the first study in all volunteers. Signal increases ranged from 3.2% to 10.9%, with a mean of 6.6 +/- 1.7%. The mean values of intrasubject variability testing were R(size) = 0.83 +/- 0.16 and R(overlap) = 0.31 +/- 0.11. CONCLUSION Functional MR imaging with the FLASH technique is useful in identifying certain cortical areas that have quite variable locations among subjects. This study provides reference data for the intrasubject and intersubject variability of the activation pattern of the visual cortex.