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

PURPOSE

To ultimately make accurate and precise fetal noninvasive oxygen saturation (sO ) measurements by T -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 -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 was assessed in relation to T two- or three-parameter curve-fitting techniques, SSFP readout, refocusing time delay (τ), constant and pulsatile blood flow, and impact of T recovery. Further, fetal T and sO 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 was overestimated (up to 23 ms/10%; p = 0.001) beyond ±30 Hz off-resonance. In the adult aorta, T was underestimated during higher blood flow velocities and pulsatility for τ = 16 ms (-41 ms/-17%; p = 0.008). In fetuses, two-parameter fitting overestimated T compared with three-parameter fitting (+33 ms/+18%; p = 0.03). T variability was 18 ms/15% in the fetal descending aorta and 28 ms/14% in the umbilical vein. The resulting estimated sO variability was ∼10% (15% of sO value) in the fetal descending aorta.

CONCLUSIONS

Errors due to T -fitting techniques, off-resonance, flow velocity, and insufficient T recovery between image acquisitions could be mitigated by using three-parameter fitting with included saturation-prepared images approximating infinite T -preparation time, adequate shimming covering the fetus and placenta, and by modifying acquisition parameters. Variability in fetal blood T and sO , however, indicate that it is currently not feasible to use these methods for prediction of disease.