Simultaneous Estimation of Bone Morphology and Fat Fraction Using General-purpose Magnetic Resonance Imaging

Background / Purpose

Intravertebral fat degeneration may be a potential risk factor for bone fractures. Previously, measurements of vertebral morphological changes and fat fraction have been performed separately. However, separate measurements can lead to positioning errors, and with regard to X-ray examinations, an added factor of radiation exposure also exists. Our developed method allows for the simultaneous evaluation of bone morphology and fat fraction using magnetic resonance imaging (MRI), addressing the concerns mentioned above.

Methods

All examinations were performed on a 1.5 T MRI system. To obtain a bone image, multi-echo images with in-phase (i.e., echo time [TE], comprising 4 TE, ranged from 4.6–18.4 ms) were acquired. We generated a bone image by applying an inversion process to the sum of the four images. Additionally, by setting the initial TE of the multi-echo image to the opposed phase (i.e., TE, 2.3 ms), the fat fraction was calculated on a pixel-by-pixel basis. Furthermore, a field map was used to correct the inhomogeneity of the magnetic field within the in-plane using MATLAB 2023b.

Results

Images that enabled the evaluation of bone morphology similar to X-ray computed tomography were obtained from MRI. Using the in-phase images from multi-echo MRI also made it possible to evaluate trabecular bone. Additionally, opposed-phase images were used to calculate fat fraction images. By incorporating the field map into the analysis, obtaining a more accurate image of the fat fraction was possible without magnetic field inhomogeneity.

Conclusion

This method can be completed in a single imaging session, with minimal burden on the participant and no positional displacement, in a clinically useful manner.