Purpose: To examine the in vivo relationship between fluorine 18 fluorodeoxyglucose (FDG) uptake, as measured with positron emission tomography (PET), and functional tumor vasculature, as measured with dynamic contrast material-enhanced magnetic resonance (MR) imaging, in patients with liver metastases of colorectal cancer.
Materials and methods: All patients provided written informed consent, and the study was approved by the institutional review board. A total of 26 patients (12 men and 14 women; mean age, 59 years) who were suspected of having liver metastases of histologically proved colorectal cancer and underwent work-up for liver metastasectomy were included. Patients underwent whole-body FDG PET, and tumor-to-nontumor ratio of FDG uptake in metastases was calculated. Dynamic contrast-enhanced MR imaging was performed, and the rate constant k(ep) (s(-1)) of gadopentetate dimeglumine uptake in metastases was determined. Pimonidazole was used to determine tumor hypoxia and vascular density of metastases. To assess the relationship between FDG uptake, rate constant k(ep) of gadopentetate dimeglumine uptake, hypoxic fraction, and vascular density, the Pearson correlation coefficient was calculated.
Results: Negative correlation between tumor-to-nontumor ratio of FDG uptake and rate constant k(ep) was observed (r = -0.421, P = .082). No correlation between tumor hypoxia and tumor-to-nontumor ratio of FDG uptake or rate constant k(ep) was found. A positive correlation was observed between vascular density and rate constant k(ep) (r = 0.458, P = .034) but not between tumor-to-nontumor ratio of FDG uptake.
Conclusion: Negative correlation between tumor-to-nontumor ratio of FDG uptake and rate constant k(ep) suggests that lower values of gadopentetate dimeglumine uptake imply an acutely reduced supply of oxygen, which necessitates a higher uptake of glucose to maintain tumor energy levels. The positive correlation of vascular density with rate constant k(ep), but not with tumor-to-nontumor ratio of FDG uptake, emphasizes the potential of dynamic contrast-enhanced MR imaging to enable measurement of tumor vascularity in vivo and its additional value compared with ex vivo methods.