Factors affecting performance of fetal blood T-2 measurements for noninvasive estimation of oxygen saturation

Purpose: To ultimately make accurate and precise fetal noninvasive oxygen saturation (sO(2)) measurements by T-2-prepared bSSFP more widely available by systematically assessing error sources in order to potentially reduce perinatal mortality in cardiovascular malformations and fetal growth restriction. Methods: T-2-prepared bSSFP data were acquired in phantoms; in flowing blood in adults in the superior sagittal sinus, ascending and descending aorta, and main pulmonary artery; and in the fetal descending aorta and umbilical vein. T-2 was assessed in relation to T-2 two- or three-parameter curve-fitting techniques, SSFP readout, refocusing time delay (t), constant and pulsatile blood flow, and impact of T-1 recovery. Further, fetal T-2 and sO(2) variability were quantified in the descending aorta and umbilical vein in healthy fetuses and fetuses with cardiovascular malformation (gestational weeks 32-38). Results: In phantoms, three-parameter fitting was accurate irrespective of phase FOV (<4 ms; i.e., <2%), and T-2 was overestimated (up to 23 ms/10%; p = 0.001) beyond +/- 30 Hz off-resonance. In the adult aorta, T-2 was underestimated during higher blood flow velocities and pulsatility for t = 16 ms (-41 ms/-17%; p = 0.008). In fetuses, two-parameter fitting overestimated T-2 compared with three-parameter fitting (+33 ms/+18%; p = 0.03). T-2 variability was 18 ms/15% in the fetal descending aorta and 28 ms/14% in the umbilical vein. The resulting estimated sO(2) variability was similar to 10% (15% of sO(2) value) in the fetal descending aorta. Conclusions: Errors due to T-2-fitting techniques, off-resonance, flow velocity, and insufficient T-1 recovery between image acquisitions could be mitigated by using three-parameter fitting with included saturation-prepared images approximating infinite T-2-preparation time, adequate shimming covering the fetus and placenta, and by modifying acquisition parameters. Variability in fetal blood T-2 and sO(2), however, indicate that it is currently not feasible to use these methods for prediction of disease.

Automated summary

The purpose of this study was to evaluate the errors in fetal noninvasive oxygen saturation measurements and explore potential solutions for achieving accurate and precise results. The study examined T-2-prepared bSSFP data in various settings and assessed the impact of different factors on the accuracy of measurements. The findings indicate that although improvements can be made, it is currently not feasible to use these methods for predicting disease.