MRI-based Quantification of Ossification Centers in the Human Fetal Atlas and Axis Vertebrae

Background: Although fetal MRI has been increasingly widely used in clinical and research settings, quantitative studies specifically targeting the ossification centers of the atlas and axis remain scarce. This study aims to quantitatively assess the ossification centers of the atlas and axis in fetuses using Magnetic Resonance Imaging (MRI) and establish standardized reference data for prenatal evaluation. Materials and Methods: This study included 41 human fetuses (24 males and 17 females) at 17 to 42 weeks of gestation, collected after spontaneous abortion or preterm birth that met ethical standards. High-resolution imaging was obtained by an MRI scanner. Three-dimensional volumetric data of the ossification centers were obtained and analyzed using the 3D Slicer software. Morphometric parameters, which included the 3D maximum diameter, projection surface area, and volume, were measured. Statistical analysis was conducted with SPSS 23, and growth dynamics were evaluated by regression models. Results: Analysis shows that the ossification centers of the atlas and axis increase proportionally with gestational age, and there is a significant correlation between age and measurement parameters. The average 3D maximum diameter, projected surface area, and volume show consistent growth patterns, with no significant differences between genders. The linear regression model is the best at describing developmental dynamics, with high coefficients of determination for all parameters (R 2>0.70). Discussion: This study indicates that the ossification centers of the fetal atlas and axis increase proportionally with gestational age, and a high correlation is observed in all morphological measurement parameters. Compared with ultrasound or CT, MRI has been proven to be a superior non-invasive imaging method that can provide high-resolution three-dimensional data for detailed evaluation of the fetal cervical spine without radiation exposure. The lack of gender-based differences supports the use of a unified growth model. These normative data provide valuable benchmarks for detecting cervical dysplasia. Although the sample size and cross-sectional design are relatively limited, this study provides clinically applicable growth references that may aid in the early diagnosis of congenital spinal abnormalities. Conclusion: This study provides standardized morphometric data for the main ossification centers of the atlas and axis in human fetuses. These findings contribute to a better understanding of fetal cervical spine development and establish a reference framework for early detection of congenital abnormalities. In addition, the research findings emphasize that MRI is a reliable and non-invasive tool for the detailed assessment of fetal skeletal maturity.