MRI-based Synthetic CT in the Detection of Structural Lesions in Patients with Suspected Sacroiliitis: Comparison with MRI

Abstract

MUSCULOSKELETAL IMAGINGM RI of the sacroiliac (SI) joints is the imaging standard used to detect sacroiliitis in patients with spondyloarthritis (1). Bone marrow edema of the SI joints plays a key role in diagnosis but has limited sensitivity (65%) and specificity (75%) (1-3). Erosions of the SI joints are less prevalent in the setting of spondyloarthritis, with lower sensitivity (54%) but much higher specificity (95%) (2). T1-weighted MRI scans are obtained to depict structural lesions, such as erosions, which are notoriously difficult to demonstrate (2,4).CT also demonstrates erosions, as it enables clear visualization of bone due to its much higher x-ray attenuation. The combined use of MRI and CT is applied in radiation therapy planning (5) and orthopedic surgery (6,7). However, performing both CT and MRI increases patient burden, adds ionizing radiation, and introduces complex workflows. It would be useful to generate synthetic CT (sCT) data demonstrating bone anatomy from MRI scans. Different techniques to generate sCT data were developed in the past decade, mainly for radiation therapy guidance (8,9) and PET/MRI attenuation correction (10,11).In this study, we evaluate an sCT data generation method aiming at specific visualization of the osseous morphology by Hounsfield unit estimation (12). The MRI-based sCT is a deep learning-based technology, performing three-dimensional (3D) MRI to CT mapping and generating CT-like images from an axial 3D T1-weighted radiofrequency spoiled multiple gradient-echo (T1MGE) sequence. This technology was clinically validated in the cervical spine and pelvis (12-14).

CT-like images of the sacroiliac joint generated from MRI using susceptibility-weighted imaging (SWI) in patients with axial spondyloarthritis

“…Statistical analysis was performed using SPSS (V.27.0.0.0). 6 While other novel MRI sequences such as volumetric interpolated breath-hold examination (VIBE) and MRI-based synthetic CT have been shown to be superior to T1 in detecting erosions in the SIJ, [9][10][11] they do not allow direct visualisation of the cortical and trabecular bone structure and, thus, still suffer from typical MRI shortfalls. VIBE, for example, is a gradient echo sequence with an undesired T2* effect that causes a signal loss in the vicinity of calcium crystals, resulting in the typical stark contrast of soft tissue and bone.…”

Deep learning based synthetic‐CT generation in radiotherapy and PET: A review

“…For example, Kawahara et al 222 proposed to generate synthetic dual-energy CT from CT to assess the body material composition using 2D paired GANs. Also, commercial solutions start to be evaluated for the generation of DL-based sCT from MRI for lesion detection of suspected sacroiliitis 223…”

Anatomical Joint Form Variation in Sacroiliac Joint Disease: Current Concepts and New Perspectives

“…Therefore, the optimal diagnostic approach to anatomical variation-induced stress consists of a CT scan to detect whether an anatomical variation is present and an MRI to assess the pathophysiological stress reactions of the bone, mainly in the form of bone marrow edema. However, recent developments in imaging techniques such as dual-energy CT (for detection of bone marrow lesions) [31,32] or direct depiction of the bone in MRI, e.g., with synthetic CT [33], have the potential to improve the diagnostic workup. So far, classification of sacroiliac joint form in Images adapted with the authors' permission from [22] radiography has not been attempted.…”