Utility of blood oxygen level dependent magnetic resonance imaging in the evaluation of tissue oxygenation patterns of prostate cancer.

Abstract

198 Background: Tumor hypoxia is associated with worse pathologic features and oncological outcomes. Blood Oxygen Level Dependent (BOLD) MRI evaluates changes in endogenous contrast generated by paramagnetic deoxy-hemoglobin to non-invasively evaluate tissue oxygenation. Prior attempts using carbogen-based (95%O2 + 5%CO2) imaging were limited by patient tolerance. We present the first-in-man evaluation of a novel oxygen breathing challenge technique to monitor tissue oxygenation with BOLD MRI in patients with prostate cancer. Methods: Following IRB approval, 10 patients with clinically localized prostate cancer scheduled for radical prostatectomy underwent preoperative imaging with a 3-Tesla MRI scanner. Images were acquired using a 6-element SENSE body transmit coil and endorectal receive coil. T2* signal intensity is dependent on the concentration of deoxy-hemoglobin. Signal intensity measurements were obtained at different time points. Shorter T2* times imply the presence of hypoxia. Dynamic T2* maps were acquired while subjects breathed air for 2 mins followed by oxygen (15 l/min). Results: 10 patients (median age: 59 years (range 48-73), median PSA 6.9 ng/ml (range 2.5-25), with prostate cancer (Gleason sum 6- 7, 8-9 in 7 and 3 patients respectively) underwent BOLD MRI within 3 weeks of definitive management with a robotic assisted laparoscopic prostatectomy. All patients tolerated BOLD MRI with oxygen challenge without difficulty. Evaluation of BOLD MRI revealed wide variation in T2* values within the prostates from a median of 14.7 ± .71 ms to 44.5 ± 3.3ms. Surrounding muscle T2* values were similar for all patients, indicating that heterogeneous values were specific to each patient’s prostate. Shorter T2* values were seen in Gleason 6-7 than Gleason 8- 9 cancers, indicating more hypoxic areas in these tumors. HIF-1α staining was strongly positive in all tumors. Conclusions: BOLD MRI with oxygen challenge is well tolerated in patients and is a feasible noninvasive technique to study tissue oxygenation in tumors. Differential oxygenation patterns of prostates appear to correlate with pathological features. Further testing is needed to validate these findings.