Abstract
BackgroundThis study investigated whether changing a tumor's oxygenation would alter tumor metabolism, and thus uptake of 18F-FDG (fluorine-18 deoxyglucose), a marker for glucose metabolism using positron emission tomography (PET).ResultsTumor-bearing mice (squamous cell carcinoma) maintained at 37°C were studied while breathing either normal air or carbogen (95% O2, 5% CO2), known to significantly oxygenate tumors. Tumor activity was measured within an automatically determined volume of interest (VOI). Activity was corrected for the arterial input function as estimated from image and blood-derived data. Tumor FDG uptake was initially evaluated for tumor-bearing animals breathing only air (2 animals) or only carbogen (2 animals). Subsequently, 5 animals were studied using two sequential 18F-FDG injections administered to the same tumor-bearing mouse, 60 min apart; the first injection on one gas (air or carbogen) and the second on the other gas. When examining the entire tumor VOI, there was no significant difference of 18F-FDG uptake between mice breathing either air or carbogen (i.e. air/carbogen ratio near unity). However, when only the highest 18F-FDG uptake regions of the tumor were considered (small VOIs), there was a modest (21%), but significant increase in the air/carbogen ratio suggesting that in these potentially most hypoxic regions of the tumor, 18F-FDG uptake and hence glucose metabolism, may be reduced by increasing tumor oxygenation.ConclusionTumor 18F-FDG uptake may be reduced by increases in tumor oxygenation and thus may provide a means to further enhance 18F-FDG functional imaging.
Highlights
This study investigated whether changing a tumor's oxygenation would alter tumor metabolism, and uptake of 18F-FDG, a marker for glucose metabolism using positron emission tomography (PET)
While altered glucose metabolism is a unique feature of neoplastic growth, there are other factors associated with the tumor micro-environment that are in marked contrast to normal tissues
Non-invasive techniques, such as Overhauser-enhanced magnetic resonance imaging (OMRI) [8] and electron paramagnetic resonance imaging (EPRI) [9,10], are being evaluated to avoid the obstacles encountered with the polarographic electrode
Summary
This study investigated whether changing a tumor's oxygenation would alter tumor metabolism, and uptake of 18F-FDG (fluorine-18 deoxyglucose), a marker for glucose metabolism using positron emission tomography (PET). 18F-FDG (fluorine-18 deoxyglucose) has become widely used as a radiolabeled marker for positron emission tomography (PET) imaging of solid tumors. In some regions of the body, the predictive power for identifying cancer using 18F-FDG approaches 95% [1,2]. The vascular architecture in tumor tissue is abnormal and differs greatly from normal tissues, resulting in altered blood flow and the development of tumor hypoxia. The presence of tumor hypoxia is thought to represent a barrier for effective cancer treatment for both radiation and chemotherapy [3,4,5,6]. The ability to identify and quantify tumor hypoxia is limited. Non-invasive techniques, such as Overhauser-enhanced magnetic resonance imaging (OMRI) [8] and electron paramagnetic resonance imaging (EPRI) [9,10], are being evaluated to avoid the obstacles encountered with the polarographic electrode
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