E4676. 3D Steady State Free Precession in Fetal MRI: A Useful Adjunctive Sequence
Authors
Kantheera Leesmidt;
University of California San Diego
Amanda Liu;
University of California San Diego
Rachelle Durand;
University of California San Diego
Yi Li;
University of California San Diego
Poder Liina;
University of California San Diego
Orit Glenn;
University of California San Diego
Jesse Courtier;
University of California San Diego
Background
Fetal MRI has become a valuable noninvasive method for evaluating congenital anomalies of the fetus and can serve as an important adjunct to the prenatal ultrasound (US), which enhances diagnostic confidence and accuracy. Three-dimensional SSFP imaging provides high spatial resolution and excellent details based on the T2-T1 ratio of the tissues. A prior study by Griffiths, et al. utilized the 3D SSFP sequence to assess fetal brain anatomy and pathology; however, the diagnostic utility for other fetal MRI findings is not well described.
Educational Goals / Teaching Points
1) Review 3D SSFP sequence in fetal MRI; highlight interesting use cases and key imaging features for diagnosis; understand limitations of this technique; and review considerations for imaging at 3T versus 1.5T MRI. 2) Gain tips for image optimization.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
We provide our acquisition protocol at 3 T for the 3D SSFP sequence and provide illustrative cases showing specific pearls and pitfalls of this sequence. Additionally, we discuss image optimization techniques. Fetal MRI has become a valuable noninvasive method for evaluating congenital anomalies of the fetus and can serve as an important adjunct to the prenatal ultrasound (US), which enhances diagnostic confidence and accuracy. MRI has disadvantageous susceptibility to motion artifacts, which is challenging for fetal MRI. The single-shot T2-weighted (SST2W) sequence has been the majority for fetal MRI examinations. Fetal brain studies using MRI techniques have been reported over the past decade, and other fetal MRI findings have been less reviewed. Three-dimensional fast imaging employing steady-state acquisition (3D-FIESTA) imaging provides high spatial resolution and excellent details based on the T2-T1 ratio of the tissues. Although 3D-FIESTA has been introduced for assessing fetal brain anatomy and pathology, the diagnostic utility for further fetal congenital anomalies is less well described. Fetal MRI examinations performed at 1.5 and 3 T is controversial. At present, 1.5-T MRI is far more commonly used. Although 3-T MRI has higher signal-to-noise ratio and spatial resolution, heating from higher radiofrequency has been mainly a safety concern. Fetal 1.5- and 3-T MRI examinations were found to have equivalent energy metrics in one study; however, further modification for 3-T sequences may be required to keep the lowest energy delivered to the patient. In addition, 3-T MRI is more susceptible to motion and fluid-wave-related artifacts. MRI sequences that allow higher quality images are fundamental to fetal imaging performed at 3 T. This review focuses on 3D-FIESTA imaging applied to the fetal MRI examinations and how to generate clinically valuable information.
Conclusion
1) The 3D SSFP sequence is a useful adjunct for fetal imaging. 2) 3-T MRI is preferred for fetal imaging when available. 3) Compared to 1.5-T MRI, 3-T MRI has more fluid-wave-related artifacts. Thus, 1.5-T MRI is preferable in cases of polyhydramnios.
