Brain incorporation of 11C-arachidonic acid, blood volume, and blood flow in healthy aging: a study with partial-volume correction.
PET with 11C-arachidonic acid (AA) can be used to quantify neural signaling related to phospholipase A2 (PLA2). Animal studies suggest reduction in the activity of this signaling system with age. The aim of this study was to evaluate the effect of healthy aging on brain incorporation of 11C-AA, before and after partial-volume correction (PVC).


METHODS
Absolute measurements of cerebral blood flow (CBF) were obtained in 8 young and 7 old healthy subjects (mean age +/- SD, 27 +/- 5 y and 65 +/- 9 y) with bolus injection of 15O-water. About 15 min later, dynamic 60-min 3-dimensional scans were acquired after the injection of 11C-AA. Radioactivity frames of 11C-AA were corrected for head motion and registered to magnetic resonance (MR) images. A 3-segment (3S) and a 2-segment (2S) PVC was applied pixel-by-pixel to the activity frames. For the 3S method, the white matter value was estimated using a new automatic method by extrapolating the activity values of pixels with white matter membership > 0.99. Parametric images of the brain incorporation rate of 11C-AA (K*) and cerebral blood volume (Vb), as well as CBF, were generated and regional gray matter values were obtained.


RESULTS
Among cortical areas, there were no significant differences (uncorrected P < 0.05) in K* or Vb absolute values between young and old subjects before or after PVC. A significant reduction of CBF was detected in the frontal cortex of the elderly group. After normalization to the global gray average, K*, Vb, and CBF values revealed significant reductions in the frontal lobe of old subjects; none of these differences were significant after PVC.


CONCLUSIONS
These results confirm previous PET findings that brain function at rest is minimally affected by healthy aging. Proper PVC methodology is of critical importance in accurate quantitative assessment of PET physiologic measures.
Giovacchini
Giampiero
G
Brain Physiology and Metabolism Section, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892-1180, USA.
Lerner
Alicja
A
Toczek
Maria T
MT
Fraser
Charles
C
Ma
Kaizong
K
DeMar
James C
JC
Herscovitch
Peter
P
Eckelman
William C
WC
Rapoport
Stanley I
SI
Carson
Richard E
RE
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000465:Algorithms; D016718:Arachidonic Acid / Q000493:pharmacokinetics*; D001783:Blood Flow Velocity; D001811:Blood Volume Determination / Q000379:methods; D001921:Brain / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D002250:Carbon Radioisotopes; D002560:Cerebrovascular Circulation; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008954:Models, Biological; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012016:Reference Values
D002250:Carbon Radioisotopes; D019275:Radiopharmaceuticals; D016718:Arachidonic Acid; D010741:Phospholipases A; D054467:Phospholipases A2