In vivo whole-blood T versus HbO calibration by modulating blood oxygenation level in the femoral vein through intermittent cuff occlusion.

PURPOSE

To investigate the feasibility of estimating calibration constants (K and T ) in vivo for converting whole-blood T to blood hemoglobin oxygen saturation (HbO ) according to the Luz-Meiboom model, 1/T2=1/T2o+K(1-HbO2)2, where K and T are relaxivity and transverse relaxation time of fully saturated blood, respectively.

METHODS

A range of HbO values was achieved in the superficial femoral vein with intermittent cuff occlusion in seven healthy adults (four males) to establish a calibration curve between blood T and HbO at 1.5T. HbO was derived via MR susceptometry, a technique previously validated, and the transverse relaxation time was quantified with an optimized T -prepared balanced steady-state free precession pulse sequence. To evaluate the accuracy of the in vivo calibration method, T and HbO were quantified in the superior sagittal sinus in six additional subjects and compared with susceptometry.

RESULTS

Two sets of gender-specific calibration constants were derived, one for each gender corresponding to hematocrits of 0.47 ± 0.02 for males and 0.38 ± 0.01 for females, yielding K/T  = 41 Hz/260 ms and 26 Hz/280 ms, respectively. The in vivo calibration returned physiologically plausible superior sagittal sinus SvO values (65 ± 5% HbO ), and there was no significant difference between the results from the two methods (average difference -0.3% HbO ).

CONCLUSION

The results show feasibility of performing in vivo calibration for converting whole-blood T to HbO . The proposed approach bypasses the involved and cumbersome processes associated with in vitro calibration. Magn Reson Med 79:2290-2296, 2018. © 2017 International Society for Magnetic Resonance in Medicine.