Bulk volume susceptibility difference between deoxyhemoglobin and oxyhemoglobin for HbA and HbS: A comparative study

Abstract

Purpose: Sickle cell anemia is a blood disorder that alters the morphology and the oxygen affinity of the red blood cells. Cerebral oxygen extraction fraction measurements using quantitative BOLD contrast have been used for assessing inadequate oxygen delivery and the subsequent risk of ischemic stroke in sickle cell anemia. The BOLD signal in MRI studies relies on $\Delta {\chi }_{\mathrm{do}}$ , the bulk volume susceptibility difference between fully oxygenated and fully deoxygenated blood. Several studies have measured $\Delta {\chi }_{\mathrm{do}}$ for normal hemoglobin A (HbA). However, it is not known whether the value is different for sickle hemoglobin. In this study, $\Delta {\chi }_{\mathrm{do}}$ was measured for both HbA and sickle hemoglobin.

Methods: Six sickle cell anemia patients and 6 controls were recruited. Various blood oxygenation levels were achieved through in vivo manipulations to keep the blood close to its natural state. To account for the differences in oxygen affinity, Hill's equations were used to translate partial pressure of oxygen to oxygen saturation for HbA, sickle hemoglobin, and fetal hemoglobin (HbF) separately. The pH and PCO₂ corrections were performed. Temperature and magnetic field drift were controlled for. A multivariate generalized linear mixed model with random participant effect was used.

Results: Assuming that $\Delta {\chi }_{\mathrm{do}}$ is similar for HbA and HbF and that $\Delta {\chi }_{\mathrm{metHb}}$ is 5/4 of $\Delta {\chi }_{\mathrm{do}}$ for HbA, it was found that the $\Delta {\chi }_{\mathrm{do}}$ values for HbA and sickle hemoglobin were not statistically significantly different from each other.

Conclusion: The same $\Delta {\chi }_{\mathrm{do}}$ value can be used for both types of hemoglobin in quantitative BOLD analysis.

Keywords: blood; magnetic susceptibility; sickle cell anemia.