Imaging of Sacroiliac Joints.

The central role of imaging in diagnosing disorders affecting the sacroiliac joints (SIJs) necessitates a comprehensive understanding of the advantages, limitations, and potential pitfalls of the imaging techniques that can be used. In this article, the anatomy and biomechanics of SIJs are exposed, outlining their unique features, particularly the division into anteroinferior cartilaginous and postero-superior ligamentous parts. Overall, the goal of this article is to offer a comprehensive understanding of imaging techniques, anatomic complexity, and diagnostic considerations relevant to SIJs disorders, facilitating accurate diagnosis and patient management in clinical practice and research.

Prognostic value of hypermetabolic bone sarcoidosis observed by 18F-fluorodeoxyglucose positron emission tomography.

OBJECTIVES: Sarcoidosis is a multisystemic granulomatosis diagnosed mainly in young adults.18F-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) is useful in sarcoidosis cases to search for a biopsiable site or assess disease activity.18F-FDG PET-CT can reveal bone hypermetabolism in sarcoidosis patients, even in the absence of osteoarticular symptoms. The aim of this study was to describe metabolic bone involvement in sarcoidosis patients and to evaluate its prognostic impact. METHODS: This was an observational, comparative, retrospective, monocentric study. Inclusion criteria were a confirmed diagnosis of sarcoidosis according to the World Association of Sarcoidosis and Other Granulomatous Diseases (WASOG) criteria and at least one 18F-FDG PET-CT scan during follow-up. Metabolic bone involvement of sarcoidosis was defined as focal bone hypermetabolism with no argument for a differential diagnosis of bone 18F-FDG uptake. Patients with and without bone involvement were compared. RESULTS: Among the 175 included patients, 32 (18%) had metabolic bone involvement of sarcoidosis. The metabolic bone involvement was mainly axial and mostly without bone abnormalities on CT. Metabolic bone involvement was associated with intrathoracic and extrathoracic lymph node involvement and with a higher number of organs involved. Patients with metabolic bone involvement more frequently received corticosteroids, methotrexate and tumor necrosis factor (TNF)-α inhibitors and a higher number of treatments. Relapse of sarcoidosis occurred sooner in patients with metabolic bone involvement. CONCLUSION: These results suggest that metabolic bone involvement is associated with more diffuse and more severe sarcoidosis.

ZTE MR-based attenuation correction in brain FDG-PET/MR: performance in patients with cognitive impairment.

OBJECTIVE: One of the main challenges of integrated PET/MR is to achieve an accurate PET attenuation correction (AC), especially in brain acquisition. Here, we evaluated an AC method based on zero echo time (ZTE) MRI, comparing it with the single-atlas AC method and CT-based AC, set as reference. METHODS: Fifty patients (70 ± 11 years old, 28 men) underwent FDG-PET/MR examination (SIGNA PET/MR 3.0 T, GE Healthcare) as part of the investigation of suspected dementia. They all had brain computed tomography (CT), 2-point LAVA-flex MRI (for atlas-based AC), and ZTE-MRI. Two AC methods were compared with CT-based AC (CTAC): one based on a single atlas, one based on ZTE segmentation. Impact on brain metabolism was evaluated using voxel and volumes of interest-based analyses. The impact of AC was also evaluated through comparisons between two subgroups of patients extracted from the whole population: 15 patients with mild cognitive impairment and normal metabolic pattern, and 22 others with metabolic pattern suggestive of Alzheimer disease, using SPM12 software. RESULTS: ZTE-AC yielded a lower bias (3.6 ± 3.2%) than the atlas method (4.5 ± 6.1%) and lowest interindividual (4.6% versus 6.8%) and inter-regional (1.4% versus 2.6%) variabilities. Atlas-AC resulted in metabolism overestimation in cortical regions near the vertex and cerebellum underestimation. ZTE-AC yielded a moderate metabolic underestimation mainly in the occipital cortex and cerebellum. Voxel-wise comparison between the two subgroups of patients showed that significant difference clusters had a slightly smaller size but similar locations with PET images corrected with ZTE-AC compared with those corrected with CT, whereas atlas-AC images showed a notable reduction of significant voxels. CONCLUSION: ZTE-AC performed better than atlas-AC in detecting pathologic areas in suspected neurodegenerative dementia. KEY POINTS: • The ZTE-based AC improved the accuracy of the metabolism quantification in PET compared with the atlas-AC method. • The overall uptake bias was 21% lower when using ZTE-based AC compared with the atlas-AC method. • ZTE-AC performed better than atlas-AC in detecting pathologic areas in suspected neurodegenerative dementia.