3-T MRI advancing on ultrasound for imaging fetal abnormalities

Does higher field strength increase risk?

Although ultrasound remains the primary imaging modality used in prenatal imaging, fetal MRI is playing an increasing role in further evaluation of fetuses suspected of congenital anomalies. As 3-T MRI scanners become more common due to their improved image signal-to-noise ratio and anatomical detail, the benefits of 3-T MRI must be weighed against potential risks to the fetus that may result from the higher field strength.

"MRI is playing an increasingly important role in the assessment of complex prenatal disease," said Kathleen E. Carey, MD, Mayo Clinic, Jacksonville, FL. "The use of stronger 3-T field strengths may allow for improved visualization of subcutaneous fat and osseous structures, including the hands and feet of the developing fetus."

The study is featured in an electronic exhibit at the ARRS 2015 Annual Meeting in Toronto.

Abstract

Pediatric Imaging

E1144. Fetal MRI: Case Series and Discussion of Risks Versus Benefits of Using 3 T Versus 1.5 T

Carey K1, Chetan S.2 1. Mayo Clinic, Jacksonville, Fl; 2. Nemours Childrens Hospital, Jacksonville, Fl

Background Information: Although ultrasound remains the primary imaging modality used in prenatal imaging, fetal MRI is playing an increasing role in further evaluation of fetuses suspected of congenital anomalies. First attempted in the 1980s, MRI in pregnancy has maintained a steady growth rate. Recent studies have demonstrated that fetal MRI not only provides good detail of normal fetal anatomy and allows characterization of suspected anomalies but also may alter the diagnosis provided by ultrasound, uncovering fetal anomalies earlier and more accurately. In this presentation, we will provide a series of interesting fetal MRI cases that highlight the diagnostic capabilities of fetal MRI with a focus on the corresponding role in fetal intervention or management of pregnancy. Currently, clinical MRI is most frequently performed on 1.5-T MRI systems, but 3-T scanners are becoming more common around the world as the search for improved image signal-to-noise ratio and anatomic detail grows. This developmental opportunity must be weighed against potential risks to the fetus, taking into account the specific absorption rate. We will provide insight into the challenges faced with the performance and interpretation of fetal MRI at various field strengths and review the current evidence on safety.

Educational Goals/Teaching Points : We present a series of fetal MRI cases and discuss the anatomic and imaging findings, indication for MRI, diagnosis, and impact on patient management. We discuss the benefits and limitations of fetal MRI at 1.5-T and 3-T field strengths and briefly consider future advanced imaging, including spectroscopy and diffusion tensor imaging.

Key Anatomic/Physiologic Issues and Imaging Findsings/Techniques : We will present a series of fetal MRI examinations from a tertiary care hospital demonstrating various congenital anomalies and neoplasms involving the CNS. Fetal MRI at our institution is performed on a Signa HDXT 1.5-T scanner (GE Healthcare). Sequences are monitored in real time by the radiologist at the scanner and manipulated to determine optimal imaging planes during the scan. T2-weighted HASTE (TR/TE, 1500/60; 4-mm slice thickness) sequences are obtained in the axial, coronal, and sagittal planes with respect to the fetus. This sequence is primarily suited for assessment of fetal anatomy and pathology. Images are obtained typically after 18-20 weeks of gestation. No gadolinium is used given the risk to the fetus.

Conclusion: Although ultrasound remains the initial imaging study required in the evaluation of the fetus, MRI is playing an increasingly important role in the assessment of complex prenatal disease. It is important to be aware of the indications and limitations of fetal MRI at 1.5 T as well as higher field strengths as the diagnostic community continues to move in the direction of 3 T.