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. The ΔpO2 measured from the total of 23 points correlated positively to ΔPSC and T value extracted from the corresponding ROI (r=0.660, 0.576, P<0.01). The ΔpO2 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. Key words: Glioma; Magnetic resonance imaging; Animal experimentation
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