Dynamic changes in oxygenation of intracranial tumor and contralateral brain during tumor growth and carbogen breathing: a multisite EPR oximetry with implantable resonators.
BACKGROUND
Several techniques currently exist for measuring tissue oxygen; however technical difficulties have limited their usefulness and general application. We report a recently developed electron paramagnetic resonance (EPR) oximetry approach with multiple probe implantable resonators (IRs) that allow repeated measurements of oxygen in tissue at depths of greater than 10mm.


METHODS
The EPR signal to noise (S/N) ratio of two probe IRs was compared with that of LiPc deposits. The feasibility of intracranial tissue pO(2) measurements by EPR oximetry using IRs was tested in normal rats and rats bearing intracerebral F98 tumors. The dynamic changes in the tissue pO(2) were assessed during repeated hyperoxia with carbogen breathing.


RESULTS
A 6-10 times increase in the S/N ratio was observed with IRs as compared to LiPc deposits. The mean brain pO(2) of normal rats was stable and increased significantly during carbogen inhalation in experiments repeated for 3months. The pO(2) of F98 glioma declined gradually, while the pO(2) of contralateral brain essentially remained the same. Although a significant increase in the glioma pO(2) was observed during carbogen inhalation, this effect declined in experiments repeated over days.


CONCLUSIONS
EPR oximetry with IRs provides a significant increase in S/N ratio. The ability to repeatedly assess orthotopic glioma pO(2) is likely to play a vital role in understanding the dynamics of tissue pO(2) during tumor growth and therapies designed to modulate tumor hypoxia. This information could then be used to optimize chemoradiation by scheduling treatments at times of increased glioma oxygenation.
EPR Center for the Study of Viable Systems, Department of Radiology, Dartmouth Medical School, Hanover, NH 03755, United States. Huagang.Hou@Dartmouth.edu
Huagang
H
Hou
Ruhong
R
Dong
Hongbin
H
Li
Benjamin
B
Williams
Jean P
JP
Lariviere
S K
SK
Hekmatyar
Risto A
RA
Kauppinen
Nadeem
N
Khan
Harold
H
Swartz
D000818:Animals; D001932:Brain Neoplasms / Q000378:metabolism* / Q000473:pathology; D002245:Carbon Dioxide / Q000378:metabolism*; D049108:Cell Enlargement; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D015336:Molecular Probe Techniques / Q000295:instrumentation*; D018670:Monitoring, Ambulatory / Q000295:instrumentation; D010092:Oximetry / Q000295:instrumentation*; D010100:Oxygen / Q000378:metabolism*; D019736:Prostheses and Implants; D051381:Rats; D011916:Rats, Inbred F344
D002245:Carbon Dioxide; C011700:carbogen; D010100:Oxygen