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 T1 and T2* 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° and 20°) 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 T1 (DESPOT1 ) was used to quantify the mean water T1 of the lungs, intraabdominal organs, and muscle, and the mean water and lipid T1 of AT. IDEAL T2* maps were used to quantify the T2* values of the lungs, intraabdominal organs, and muscle. STATISTICAL TESTS: F-tests were performed to assess the T1 and T2* changes of each analyzed tissue as a function of GA. RESULTS: No tissue demonstrated a significant change in T1 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 T2* 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 T1 of the investigated tissues is relatively stable over 28-38 weeks GA, while the T2* change in spleen and muscle decreases significantly in that period. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 2.

Water-fat magnetic resonance imaging of adipose tissue compartments in the normal third trimester fetus.

BACKGROUND: Assessment of fetal adipose tissue gives information about the future metabolic health of an individual, with evidence that the development of this tissue has regional heterogeneity. OBJECTIVE: To assess differences in the proton density fat fraction (PDFF) between fetal adipose tissue compartments in the third trimester using water-fat magnetic resonance imaging (MRI). MATERIALS AND METHODS: Water-fat MRI was performed in a 1.5-T scanner. Fetal adipose tissue was segmented into cheeks, thorax, abdomen, upper arms, forearms, thighs and lower legs. PDFF and R2* values were measured in each compartment. RESULTS: Twenty-eight women with singleton pregnancies were imaged between 28 and 38 weeks of gestation. At 30 weeks' gestation (n=22), the PDFF was statistically different between the compartments (P<0.0001), with the highest PDFF in cheeks, followed by upper arms, thorax, thighs, forearms, lower legs and abdomen. There were no statistical differences in the rate of PDFF change with gestational age between the white adipose tissue compartments (P=0.97). Perirenal brown adipose tissue had a different PDFF and R2* compared to white adipose tissue, while the rate of R2* change did not significantly change with gestational age between white adipose tissue compartments (P=0.96). CONCLUSION: Fetal adipose tissue accumulates lipids at a similar rate in all white adipose tissue compartments. PDFF variances between the compartments suggest that accumulation begins at different gestational ages, starting with cheeks, followed by extremities, trunk and abdomen. Additionally, MRI was able to detect differences in the PDFF between fetal brown adipose tissue and white adipose tissue.

The application of in utero magnetic resonance imaging in the study of the metabolic and cardiovascular consequences of the developmental origins of health and disease.

Observing fetal development in utero is vital to further the understanding of later-life diseases. Magnetic resonance imaging (MRI) offers a tool for obtaining a wealth of information about fetal growth, development, and programming not previously available using other methods. This review provides an overview of MRI techniques used to investigate the metabolic and cardiovascular consequences of the developmental origins of health and disease (DOHaD) hypothesis. These methods add to the understanding of the developing fetus by examining fetal growth and organ development, adipose tissue and body composition, fetal oximetry, placental microstructure, diffusion, perfusion, flow, and metabolism. MRI assessment of fetal growth, organ development, metabolism, and the amount of fetal adipose tissue could give early indicators of abnormal fetal development. Noninvasive fetal oximetry can accurately measure placental and fetal oxygenation, which improves current knowledge on placental function. Additionally, measuring deficiencies in the placenta's transport of nutrients and oxygen is critical for optimizing treatment. Overall, the detailed structural and functional information provided by MRI is valuable in guiding future investigations of DOHaD.

Measuring fetal adipose tissue using 3D water-fat magnetic resonance imaging: a feasibility study.

Purpose: Analysis of fetal adipose tissue volumes may provide useful insight towards assessment of overall fetal health, especially in cases with abnormal fetal growth. Here, we assess whether fetal adipose tissue volume can be reliably measured using 3D water-fat MRI, using a quantitative assessment of the lipid content of tissues.Materials and methods: Seventeen women with singleton pregnancies underwent a fetal MRI and water-only and fat-only images were acquired (modified 2-point Dixon technique). Water and fat images were used to generate a fat signal fraction (fat/(water + fat)) from which subcutaneous adipose tissue was segmented along the fetal trunk. Inter-rater (three readers) and intrarater reliability was assessed using intraclass-correlation coefficients (ICC) for 10 image sets. Relationships between adipose tissue measurements and gestational age and estimated fetal weight percentiles were examined.Results: The ICC of the inter-rater reliability was 0.936 (p < .001), and the ICC of the intrarater reliability was 0.992 (p < .001). Strong positive correlations were found between adipose tissue measurements (lipid volume, lipid volume/total fetal volume, mean fat signal fraction) and gestational age.Conclusions: 3D water-fat MRI can reliably measure volume and quantify lipid content of fetal subcutaneous adipose tissues.

Altered maternal and placental lipid metabolism and fetal fat development in obesity: Current knowledge and advances in non-invasive assessment.

Abnormal maternal lipid profiles, a hallmark of increased maternal adiposity, are associated with pregnancy complications such as preeclampsia and gestational diabetes, and offspring long-term metabolic health is impacted as the consequence of altered fetal growth, physiology and often iatrogenic prematurity. The metabolic changes associated with maternal obesity and/or the consumption of a high-fat diet effecting maternal lipid profiles and metabolism have also been documented to specifically affect placental function and may underlie changes in fetal development and life course disease risk. The placenta plays a critical role in mediating nutritional signals between the fetus and the mother. As obesity rates in women of reproductive age continue to increase, it is becoming evident that inclusion of new technologies that allow for a better understanding of early changes in placental lipid transport and metabolism, non-invasively in maternal circulation, maternal tissues, placenta, fetal circulation and fetal tissues are needed to aid timely clinical diagnosis and treatment for obesity-associated diseases. This review describes pregnancy lipid homeostasis, with specific reference to changes arising from altered maternal body composition on placental and fetal lipid transport and metabolism. Current technologies for lipid assessments, such as metabolomics and lipidomics may be impacted by labour or mode of delivery and are only reflective of a single time point. This review further addresses how established and novel technologies for assessing lipids and their metabolism non-invasively and during the course of pregnancy may guide future research into the effect of maternal metabolic health on pregnancy outcome, placenta and fetus.

Comparison of modified two-point dixon and chemical shift encoded MRI water-fat separation methods for fetal fat quantification.

BACKGROUND: Fetal fat is indicative of the energy balance within the fetus, which may be disrupted in pregnancy complications such as fetal growth restriction, macrosomia, and gestational diabetes. Water-fat separated MRI is a technique sensitive to tissue lipid content, measured as fat fraction (FF), and can be used to accurately measure fat volumes. Modified two-point Dixon and chemical shift encoded MRI (CSE-MRI) are water-fat separated MRI techniques that could be applied to imaging of fetal fat. Modified two-point Dixon has biases present that are corrected in CSE-MRI which may contribute to differences in the fat measurements. PURPOSE: To compare the measurement of fetal fat volume and FF by modified two-point Dixon and CSE-MRI. STUDY TYPE: Cross-sectional study for comparison of two MRI pulse sequences. POPULATION: Twenty-one pregnant women with singleton pregnancies. FIELD STRENGTH/SEQUENCE: 1.5T, modified two-point Dixon and CSE-MRI. ASSESSMENT: Manual segmentation of total fetal fat volume and mean FF from modified 2-point Dixon and CSE-MRI FF images. STATISTICAL TESTS: Reliability was assessed by calculating the intraclass correlation coefficient (ICC). Agreement was assessed using a one-sample t-test on the fat measurements difference values (modified two-point Dixon - CSE-MRI). The difference scores were tested against a value of 0, which would indicate that the measurements were identical. RESULTS: The fat volume and FF measured by modified two-point Dixon and CSE-MRI had excellent reliability, demonstrated by ICCs of 0.93 (P < 0.001) and 0.90 (P < 0.001), respectively. They were not in agreement, with CSE-MRI giving mean fat volumes 180 mL greater and mean FF 3.0% smaller than modified two-point Dixon. DATA CONCLUSION: The reliability between modified two-point Dixon and CSE-MRI indicates that either technique can be used to compare fetal fat measurements in different participants, but they are not in agreement possibly due to uncorrected biases in modified two-point Dixon. LEVEL OF EVIDENCE: 4 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018.