Application of High Dielectric Constant Pads in 3T Fetal MRI

Background Introduction

With the advancement of medical imaging technology, fetal MRI (Magnetic Resonance Imaging) is increasingly being used in prenatal diagnosis. Compared to ultrasound, MRI provides higher soft tissue resolution and contrast, offering significant advantages in imaging complex structures such as the fetal brain, lungs, and spine. However, as magnetic field strength increases, 3T MRI faces two major technical challenges in fetal imaging: first, image quality degradation due to dielectric effects, and second, an increase in Specific Absorption Rate (SAR). The rise in SAR not only poses potential thermal risks to the fetus and mother but may also limit the adjustment of imaging parameters, thereby affecting image quality and scan time.

To address these issues, researchers have begun exploring the application of High Dielectric Constant (HDC) pads in 3T fetal MRI. By modulating the wavelength of the radiofrequency field, HDC pads can improve the homogeneity of the radiofrequency field, reduce dielectric artifacts, and lower SAR values. Although previous electromagnetic simulation studies have demonstrated the potential of HDC pads in 3T MRI, their practical application in pregnant women has not been fully validated. Therefore, this study aims to evaluate the clinical effectiveness of HDC pads in improving image quality and reducing SAR in 3T fetal MRI.

Source of the Paper

This paper was co-authored by Zhengyang Zhu, Xunwen Xue, Tang Tang, and others, with the research team affiliated with Nanjing Drum Tower Hospital, affiliated with Nanjing University, Shenzhen Institutes of Advanced Technology of the Chinese Academy of Sciences, United Imaging Healthcare Group, and other institutions. The paper was published in 2025 in the Journal of Magnetic Resonance Imaging under the title “Improving Image Quality and Decreasing SAR with High Dielectric Constant Pads in 3T Fetal MRI.”

Research Process and Results

Study Participants and Experimental Design

This prospective single-center observational study recruited 168 pregnant participants, of whom 128 underwent Balanced Steady-State Free Precession (bSSFP) scanning, and 40 underwent Single-Shot Fast Spin-Echo (SSFSE) scanning. Participants’ clinical characteristics included gestational age (GA), amniotic fluid index (AFI), abdominal circumference (AC), body mass index (BMI), and fetal position.

Design and Preparation of HDC Pads

The research team designed a high dielectric constant material composed of barium titanate (BaTiO3) and heavy water (D2O) in a 4:1 ratio, which was filled into 10 plastic bags measuring 350 mm × 40 mm × 15 mm, ultimately forming the HDC pad. The relative permittivity and conductivity of the pad were 223.699 and 0.372 S/m, respectively.

MRI Scanning and Image Analysis

All participants were first scanned in axial, coronal, and sagittal planes with the assistance of the HDC pad, followed by repeat scans after removing the pad. Image quality analysis included quantitative analysis (signal-to-noise ratio, SNR, and contrast-to-noise ratio, CNR) and qualitative analysis (scoring of overall image quality, dielectric artifacts, and diagnostic confidence by three radiologists). Additionally, whole-body total SAR values were recorded.

Key Results

1. Improved Image Quality:

   • In the bSSFP sequence, the use of the HDC pad increased SNR by an average of 41.45% and CNR by an average of 54.05%.
     
   • In the SSFSE sequence, SNR increased by an average of 258.76%, and CNR increased by an average of 459.55%.
     
   • Qualitative analysis showed significant improvements in overall image quality, reduction in dielectric artifacts, and diagnostic confidence with the use of the HDC pad.

2. Reduction in SAR Values:

   • In the bSSFP sequence, whole-body total SAR decreased by 32.60%.
     
   • In the SSFSE sequence, whole-body total SAR decreased by 15.40%.

3. Correlation Between Clinical Characteristics and Image Quality Changes:

   • The study found no significant correlation between changes in image quality and participants’ clinical characteristics (e.g., gestational age, amniotic fluid index, abdominal circumference).

Conclusion and Significance

This study demonstrates that the use of HDC pads in 3T fetal MRI can significantly improve image quality, reduce dielectric artifacts, and lower SAR values. These findings provide strong support for the clinical application of HDC pads, particularly in enhancing the safety and imaging quality of fetal MRI.

Research Highlights

1. Innovation: This study is the first to validate the effectiveness of HDC pads in 3T fetal MRI in a clinical setting, bridging the gap between previous electromagnetic simulation studies and practical applications.
2. Practicality: The design of the HDC pad is simple and easy to operate, significantly improving image quality and safety without increasing scan complexity.
3. Broad Applicability: The results indicate that HDC pads perform well in pregnant women with different gestational ages, abdominal circumferences, and fetal positions, demonstrating broad clinical potential.

Future Outlook

Although this study has achieved positive results, some limitations remain. For example, the HDC pad is a homemade device, and its reproducibility and standardized production require further research. Additionally, future studies could explore the effectiveness of HDC pads in other MRI sequences and their compatibility with MRI equipment from different manufacturers.

The findings of this study provide new insights into the technical improvement of 3T fetal MRI and are expected to be widely applied in clinical practice in the future.