ABSTRACT
Objective Using MRI compatible OxyLiteTM fiber-optic microprobes to verify the reliability of detecting the oxygenation changes in rats C6 glioma by BOLD fMRI with non- hemodynamic response function (non-HRF) post-processing algorithm. Methods A total of 20 male SD rats were used to establish the subcutaneous C6 glioma model. GRE-EPI BOLD fMRI scans were performed in the tumor-bearing rats with Carbogen inhalation after anatomic scans using 1.5 T MR imaging system with Micro-47 microscopic coil. Fiber-optic microprobes were implanted in tumor to acquire the dynamic pO2 indications during BOLD fMRI scan.“Oxy-localization map”and“oxy-amplitude map”were generated from BOLD functional image data by non-HRF post-processing algorithm analysis. A ROI about 1.5 mm on a side centered to the tip of microprobe was defined on the MRI morphological image, and then was copied onto the“oxy-localization map”and“oxy-amplitude map”to extract the values of significant re-oxygenation (T), percent BOLD signal change (ΔPSC). The mean difference of pO2(ΔpO2) measured by fiber-optic microprobes before(pO2-Air)and after (pO2-Car)Carbogen inhalation in the ROI areas was calculated. Correlation analysis was madebetween cov (T value, Δ pO2) and cov (ΔPSC value, Δ pO2). The difference between pO2-Air and pO2-Car were tested by Mann Whitney U test. Results pO2 was successfully measured and recorded from 23 points in tumor using fiber-optic microprobe during the BOLD fMRI scan. The analysis results both of physiological and functional imaging parameters were as follows: pO2-Air=2.285(19.056) mmHg,pO2-Car=14.701(48.390)mmHg,ΔpO2=8.107(33.557)mmHg,ΔPSC=0.402(2.192)%,T=2.025 (8.293). (1) 10 points were identified clearly in parenchyma area of tumor. The mean value of pO2 during air inhalation [19.462(21.511)mmHg] significantly increased after Carbogen inhalation [59.904(56.710)mmHg] (U=14.000,P=0.007). (2) 5 points were identified in tumor necrosis area. The mean value of pO2 during air inhalation [0.149(0.479)mmHg] showed no significant change comparing with Carbogen inhalation[0.273 (8.050)mmHg](U=9.000,P=0.465). (3) 8 points were identified in the boundary of tumor parenchyma and necrosis areas. Among which, 5 showed the similar pO2 change to that located in tumor necrosis area, 2 showed the similar to the tumor parenchyma. However, the pO2 showed continuously decrease after Carbogen inhalation in the last 1 point. TheΔpO2 measured from the total of 23 points correlated positively toΔPSC and T value extracted from the corresponding ROI (r=0.660,0.576,P<0.01). TheΔpO2 measured from 10 points in tumor parenchyma correlated positively to ΔPSC(r=0.717,P=0.020). Conclusion“Oxy-localization map”and“oxy-amplitude map”generated from BOLD fMRI combined with non-HRF post-processing algorithm could show reliably not only the location but also the extent where the re-oxygenation occurred within tumor.