The impact of hematocrit on oxygenation-sensitive cardiovascular magnetic resonance

Background: oxygenation-sensitive (os) cardiovascular magnetic resonance (cmr) is a promising utility in the diagnosis of heart disease. contrast in os-cmr images is generated through deoxyhemoglobin in the tissue,which is negatively correlated with the signal intensity (si). thus,changing hematocrit levels may be a confounder in the interpretation of os-cmr results. we hypothesized that hemodilution confounds the observed signal intensity in os-cmr images. methods: venous and arterial blood from five pigs was diluted with lactated ringer solution in 10 % increments to 50 %. the changes in signal intensity (si) were compared to changes in blood gases and hemoglobin concentration. we performed an os-cmr scan in 21 healthy volunteers using vasoactive breathing stimuli at baseline,which was then repeated after rapid infusion of 1 l of lactated ringer's solution within 5-8 min. changes of si were measured and compared between the hydration states. results: the % change in si from baseline for arterial (r = -0.67,p < 0.0001) and venous blood (r = -0.55,p = 0.002) were negatively correlated with the changes in hemoglobin (hb). si changes in venous blood were also associated with so2 (r = 0.68,p < 0.0001) and deoxyhb concentration (-0.65,p < 0.0001). in healthy volunteers,rapid infusion resulted in a significant drop in the hemoglobin concentration (142.5 ± 15.2 g/l vs. 128.8 ± 15.2 g/l; p < 0.0001). baseline myocardial si increased by 3.0 ± 5.7 % (p = 0.026) following rapid infusion,and in males there was a strong association between the change in hemoglobin concentration and % changes in si (r = 0.82,p = 0.002). after hyperhydration,the si response after hyperventilation was attenuated (hv,p = 0.037),as was the maximum si increase during apnea (p = 0.012). the extent of si attenuation was correlated with the reduction in hemoglobin concentration at the end of apnea (r = 0.55,p = 0.012) for all subjects and at maximal si (r = 0.63,p = 0.037) and the end of breath-hold (r = 0.68,p = 0.016) for males only. conclusion: in dynamic studies using oxygenation-sensitive cmr,the hematocrit level affects baseline signal intensity and the observed signal intensity response. thus,the hydration status of the patient may be a confounder for os-cmr image analysis. © 2016 the author(s).