Pos0421 Mri-Based Synthetic Ct Is Superior to Conventional Mri for the Detection of Structural Lesions in Postpartum Women After 5 Year Follow-Up

Background: Recently, a novel imaging technique has been introduced to detect structural lesions in sacroiliac joints, addressing the challenges associated with the evaluation of these lesions on routine T1-weighted MRI scans. MRI-based synthetic CT (sCT) allows detection of structural lesions like erosions with CT-like accuracy, all while eliminating the need for CT-related radiation exposure. Previously, we reported on the presence of SpA-like lesions in postpartum women, showing high prevalence of bone marrow edema (BME), while the presence of structural lesions was low in these subjects. Objectives: To compare structural lesions identified on routine MRI to lesions identified on sCT in postpartum women, 5 years after given birth. Methods: Synthetic CT images were reconstructed with commercially available software (BoneMRI Pelvic Region, version 1.5; MRIguidance). The software reconstructed sCT images from 3D T1-GRE images using a deep learning method based on the U-net architecture 1. MRI scan protocol contained Short Tau Inversion Recovery and T1-weighted sequences. Both MRI and sCT were available in 18 women. The sCT images were assessed by 2 readers and the MRI by 3 readers. Results are based on the consensus of at least 2 readers, within a modality. Both sCT and MRI were assessed separately for the presence of absence of erosions, fatty lesions and ankylosis per sacroiliac joint quadrant. This resulted in a maximum score of 144 quadrants per structural lesions. Taking into account that ankylosis always occurs in 2 quadrants. Descriptive data were presented on quadrant level. Results: Both MRI and sCT were available in 18 women with a mean age of 35.4 years (SD 2.6), all of whom were HLA-B27 negative. Mean BMI was 20.7 kg/m2 (SD 1.6). Six (33%) of these women reported back pain. On MRI, 1 quadrant with erosions was reported, compared to 5 quadrants with erosions seen on sCT. However, none of these erosions were seen on both modalities. Three quadrants with sclerosis were reported on MRI and sCT, compared to 26 quadrants with sclerosis seen on sCT only. No ankylosis was reported on MRI, nor on sCT. Conclusion: Overall, few structural lesions were seen in patients 5 years postpartum both on MRI and on sCT/bone MRI. Nevertheless, when comparing MRI to sCT, sclerosis and -to a lesser extent- erosions were more frequently accounted for in the latter. sCT combines the sensitivity for detection of structural lesions of CT, with the established benefits of MRI, displaying unprecedented opportunities for use in clinical practice. REFERENCES: 1 Jans et al. Radiology 2021 Feb;298(2):343-349. 2 Ronneberger O et al. MICCAI 2015. Lecture Notes in Computer Science 2015(9351); 234–241. Acknowledgements: NIL. Disclosure of Interests: None declared.