Quantification of 1.5 T T1 and T2* Relaxation Times of Fetal Tissues in Uncomplicated Pregnancies

Background Despite its many advantages, experience with fetal magnetic resonance imaging (MRI) is limited, as is knowledge of how fetal tissue relaxation times change with gestational age (GA). Quantification of fetal tissue relaxation times as a function of GA provides insight into tissue changes during fetal development and facilitates comparison of images across time and subjects. This, therefore, can allow the determination of biophysical tissue parameters that may have clinical utility. Purpose To demonstrate the feasibility of quantifying previously unknown T-1 and T-2* relaxation times of fetal tissues in uncomplicated pregnancies as a function of GA at 1.5 T. Study Type Pilot. Population Nine women with singleton, uncomplicated pregnancies (28-38 weeks GA). Field Strength/Sequence All participants underwent two iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL-IQ) acquisitions at different flip angles (6 degrees and 20 degrees) at 1.5 T. Assessment Segmentations of the lungs, liver, spleen, kidneys, muscle, and adipose tissue (AT) were conducted using water-only images and proton density fat fraction maps. Driven equilibrium single pulse observation of T-1 (DESPOT1) was used to quantify the mean water T-1 of the lungs, intraabdominal organs, and muscle, and the mean water and lipid T-1 of AT. IDEAL T-2* maps were used to quantify the T-2* values of the lungs, intraabdominal organs, and muscle. Statistical Tests F-tests were performed to assess the T-1 and T-2* changes of each analyzed tissue as a function of GA. Results No tissue demonstrated a significant change in T-1 as a function of GA (lungs [P = 0.89]; liver [P = 0.14]; spleen [P = 0.59]; kidneys [P = 0.97]; muscle [P = 0.22]; AT: water [P = 0.36] and lipid [P = 0.14]). Only the spleen and muscle T-2* showed a significant decrease as a function of GA (lungs [P = 0.67); liver [P = 0.05]; spleen [P < 0.05]; kidneys [P = 0.70]; muscle [P < 0.05]). Data Conclusion These preliminary data suggest that the T-1 of the investigated tissues is relatively stable over 28-38 weeks GA, while the T-2* change in spleen and muscle decreases significantly in that period. Level of Evidence 3 Technical Efficacy Stage 2

Automated summary

This pilot study aimed to quantify the T-1 and T-2* relaxation times of fetal tissues in relation to gestational age, showing relatively stable T-1 values across tissues over 28-38 weeks GA, while the T-2* values of the spleen and muscle decreased significantly during this period.