Ex-Vivo Validation of Blood Oxygen Level-Dependent Cardiovascular Magnetic Resonance (BOLD-CMR): the Role of Haemodilution of Arterial and Venous Blood on Signal Intensity

BACKGROUND: Oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) becomes more and more utilized in the field, thus it is important to assess confounders that may alter image results. Contrast changes are mainly caused by changes of deoxyhaemoglobin (dHb), and thus are dependent on haemoglobin concentration (cHb) and on oxygen saturation (sO2). Importantly, during long or repeated experiments, changes in fluid status may alter cHb, potentially introducing further variability. The primary objective of this in vitro study was to investigate the relationship between Hb, sO2 and changes in signal intensity (SI). METHODS: Arterial blood of dogs ventilated with 100% oxygen was obtained to study the singular effect of haemodilution, while venous blood was used to assess the combined effects of both haemodilution and desaturation. The blood was diluted in 10% increments with isotonic saline up to 50%. Oxygenation-sensitive T2* weighted images were obtained using a cardiac sequence at 3 Tesla and SI was compared to the blood gas analysis of all samples. RESULTS: Arterial blood remained fully saturated at each dilution while venous blood showed a decrease in absolute dHb content and an increase in sO2 with increasing dilutions, which was significantly correlated to changes in SI (R1⁄40.62; p<0.001). Both the arterial and venous blood demonstrated a decrease in cHb levels as dilutions increased. There was a corresponding negative correlation between SI and cHb for venous (R1⁄40.43; p1⁄40.009) and arterial blood (R1⁄40.53; p1⁄40.002). Arterial blood had a significant elevation difference in SI in comparison to venous samples (p<0.001) at the same dilutions. A drop in cHb of 23% venous (p1⁄40.035) or 28% arterial blood (p1⁄40.041) was required to yield a significant difference in SI at 10% dilution increments. CONCLUSION: With decreasing haemoglobin concentration at physiological levels, the SI in oxygenation-sensitive images changes despite similar oxygenation. Therefore, in experiments with suspected changes in fluid status, signal intensity changes in oxygenation-sensitive CMR images may have to be corrected for changes in haemoglobin concentration. 089 ALTERATIONS OF MYOCARDIAL OXYGENATION DURING VOLUNTARY APNEA IN PATIENTS WITH OBSTRUCTIVE SLEEP APNEA SYNDROME: A STUDY USING OXYGENATION-SENSITIVE CARDIOVASCULAR MR