Quantitative susceptibility mapping in the human fetus to measure blood oxygenation in the superior sagittal sinus
To present the feasibility of performing quantitative susceptibility mapping (QSM) in the human fetus to evaluate the oxygenation (SvO2) of cerebral venous blood in vivo.
Susceptibility weighted imaging (SWI) data were acquired from healthy pregnant subjects (n = 21, median = 31.3 weeks, interquartile range = 8.8 weeks). The susceptibility maps were generated from the SWI-phase images using a modified QSM processing pipeline, optimised for fetal applications. The processing pipeline is as follows: (1) mild high-pass filtering followed by quadratic fitting of the phase images to eliminate background phase variations; (2) manual creation of a fetal brain mask that includes the superior sagittal sinus (SSS); (3) inverse filtering of the resultant masked phase images using a truncated k-space approach with geometric constraint. Further, the magnetic susceptibility, ∆χv and corresponding putative SvO2 of the SSS were quantified from the generated susceptibility maps. Systematic error in the measured SvO2 due to the modified pipeline was also studied through simulations.
Simulations showed that the systematic error in SvO2 when using a mask that includes a minimum of 5 voxels around the SSS and five slices remains < 3% for different orientations of the vessel relative to the main magnetic field. The average ∆χv in the SSS quantified across all gestations was 0.42 ± 0.03 ppm. Based on ∆χv, the average putative SvO2 in the SSS across all fetuses was 67% ± 7%, which is in good agreement with published studies.
This in vivo study demonstrates the feasibility of using QSM in the human fetal brain to estimate ∆χv and SvO2.
• A modified quantitative susceptibility mapping (QSM) processing pipeline is tested and presented for the human fetus.
• QSM is feasible in the human fetus for measuring magnetic susceptibility and oxygenation of venous blood in vivo.
• Blood magnetic susceptibility values from MR susceptometry and QSM agree with each other in the human fetus.
KeywordsMagnetic resonance imaging Brain Second trimester
Magnetic susceptibility difference between fully oxygenated and deoxygenated fetal blood
Brain Extraction Tool
Quantitative susceptibility mapping
Venous oxygen saturation
Specific absorption rate
Superior sagittal sinus
Dr. Romero has contributed to this work as part of his official duties as an employee of the United States Federal Government.
This research was supported, in part, by the Perinatology Research Branch (PRB), Program for Perinatal Research and Obstetrics, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, U.S. Department of Health and Human Services (NICHD/NIH/DHHS); in part, with Federal funds from NICHD/NIH/DHHS under Contract No. HHSN275201300006C; and an STTR grant from the NHLBI number 1R42HL112580- 01A1.
Compliance with ethical standards
The scientific guarantor of this publication is Dr. Jaladhar Neelavalli.
Conflict of interest
The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.
Statistics and biometry
No complex statistical methods were necessary for this paper.
Written informed consent was obtained from all subjects (patients) in this study.
Institutional review board approval was obtained.
Study subjects or cohorts overlap
The imaging data used in this manuscript has been used in part previously in an earlier manuscript (Yadav et al ), which evaluated fetal blood oxygenation as a function of gestational age in a larger cohort. This manuscript, on the other hand, focuses on demonstrating the applicability of a novel technique in the human fetus for in vivo blood oximetry and compares the results with those obtained using the standard model-dependent method. We find that the results affirm the applicability of both methods for in vivo fetal blood susceptometry and oximetry.
• Performed at one institution
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