Clinical Physiology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
Diagnostic Radiology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
Magn Reson Med. 2023 Dec;90(6):2472-2485. doi: 10.1002/mrm.29821. Epub 2023 Aug 15.
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.
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).
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.
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.
通过系统评估误差源，最终使 T 准备 bSSFP 进行的准确、精确的胎儿无创氧饱和度（sO ）测量更广泛可用，以潜在降低心血管畸形和胎儿生长受限的围产儿死亡率。
在体模中采集 T 准备 bSSFP 数据；在成人的大脑上矢状窦、升主动脉和降主动脉以及主肺动脉中流动的血液中；以及在胎儿降主动脉和脐静脉中。评估 T 与 T 双参数或三参数曲线拟合技术、SSFP 读出、重聚时间延迟（τ）、恒流和脉动血流以及 T 恢复的影响之间的关系。此外，在健康胎儿和患有心血管畸形的胎儿（妊娠 32-38 周）的降主动脉和脐静脉中量化胎儿 T 和 sO 的变异性。
在体模中，三参数拟合无论在相位视野（FOV）<4 ms（即<2%）内都很准确，而在±30 Hz 失谐之外 T 被高估（最多 23 ms/10%；p=0.001）。在成人主动脉中，τ=16 ms 时，T 在较高血流速度和脉动时被低估（-41 ms/-17%；p=0.008）。在胎儿中，与三参数拟合相比，双参数拟合高估了 T（+33 ms/+18%；p=0.03）。胎儿降主动脉 T 的变异性为 18 ms/15%，脐静脉为 28 ms/14%。由此估计的 sO 变异性在胎儿降主动脉中约为 10%（sO 值的 15%）。
由于 T 拟合技术、失谐、流速以及图像采集之间的 T 恢复不足导致的误差可以通过使用包括饱和准备图像的三参数拟合来减轻，这些图像近似于无限 T 准备时间、充分覆盖胎儿和胎盘的匀场以及通过修改采集参数。然而，胎儿血液 T 和 sO 的变异性表明，目前尚不能使用这些方法来预测疾病。
