Bicomponent Mapping of Cortical Bone Using a New Interleaved UTE Imaging Sequence

ABSTRACT Purpose Ultrashort echo time (UTE) MRI enables direct imaging of cortical bone and quantification of its water compartments via bicomponent T 2 * modeling. However, conventional approaches require multiple separate dual‐echo scans due to limitations in gradient power. This approach is prone to inter‐scan inconsistencies such as motion and signal drift, which degrade fitting accuracy. This study proposes an interleaved dual‐echo acquisition sequence that acquires multiple echo time (TE) images in a single scan to improve bicomponent T 2 * quantification in cortical bone. Methods The proposed UTE sequence utilizes interleaved dual‐echo acquisitions with flexible TE spacings. This sequence was tested on five healthy subjects' tibial midshafts and compared to conventional separate dual‐echo scans with and without image registration. Bicomponent T 2 * modeling was performed, and fitting accuracy was evaluated using normalized‐root‐mean‐squared error (NRMSE). Three subjects were scanned three times to evaluate the scan repeatability. Results The interleaved method significantly reduced NRMSE (3.2% ± 2.3% vs. 6.2% ± 3.1%, p = 0.0231) and yielded lower and more stable T 2 * (T 2s *; 0.50 ± 0.10 ms vs. 0.76 ± 0.13 ms, p < 0.0001) and fraction (F s ; 78.2 ± 5.1 vs. 84.2% ± 7.1%, p = 0.0006) of short T 2 components compared to separate scans without registration. Image registration had a minimal improvement on mapping results for separate scans. Parameter maps from the interleaved scans confirmed more homogeneous distributions of T 2s * and F s with lower fitting errors. The much lower coefficients of variance of the interleaved scans demonstrated improved repeatability compared with separate scans. Conclusion The proposed interleaved UTE dual‐echo sequence improves the robustness of bicomponent T 2 * mapping of the cortical bone by reducing inter‐scan inconsistencies.