Regional dynamic signal changes during controlled hyperventilation assessed with blood oxygen level-dependent functional MR imaging.
OBJECTIVE
To quantitate the amplitude changes and temporal dynamics of regional functional MR imaging signals during voluntary hyperventilation using blood oxygen level-dependent contrast echo-planar imaging.


METHODS
Seven male subjects were studied during voluntary hyperventilation (PetCO2 = 20 mm Hg) regulated by capnometry. Measurements were made on multisection echo-planar MR images obtained with parameters of 1000/66 (repetition time/echo time), flip angle of 30 degrees, and voxel size of 3 x 3 x 5 mm3. Sensitivity of the functional MR imaging signal to changes in PetCO2, time delays in relation to PetCO2 changes, and time constants of functional MR imaging signal changes were assessed on a region-by-region basis.


RESULTS
Within 20 seconds of starting hyperventilation, rapid and substantial decreases in the functional MR imaging signal (by as much as 10%) were measured in areas of gray matter, which were significantly greater than the modest changes observed in white matter. Regional-specific effects in areas of the frontal, occipital, and parietooccipital cortex were stronger than in subcortical regions or in the cerebellum. Signal decreases measured with functional MR imaging were significantly delayed with respect to the reduction in PetCO2. Apparent differences between regional time constants did not reach statistical significance.


CONCLUSIONS
Regional and gray-white matter differences in functional MR imaging signal changes during controlled hyperventilation may reflect differences in metabolic activity, vascular regulation, and/or capillary density. When measuring brain activation with functional MR imaging, arterial PCO2 differences due to unregulated respiration may confound interpretation of activation-related functional MR imaging signal changes.
Posse
S
S
Institute of Medicine, Research Center Jülich GmbH, Germany.
Olthoff
U
U
Weckesser
M
M
Jäncke
L
L
Müller-Gärtner
H W
HW
Dager
S R
SR
D000328:Adult; D001921:Brain / Q000098:blood supply*; D001931:Brain Mapping; D002245:Carbon Dioxide / Q000097:blood*; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D006985:Hyperventilation / Q000503:physiopathology*; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000097:blood*; D012016:Reference Values; D014655:Vascular Resistance / Q000502:physiology
D002245:Carbon Dioxide; D010100:Oxygen