Abstract
BackgroundThis study compares the frequency and distribution of increased activity on 18 F-fluoride PET/CT with the presence of bone marrow edema on whole-body MR imaging in the spine and sacroiliac joints (SIJ) of patients with active ankylosing spondylitis (AS).MethodsTen patients (6 men and 4 women), between 30 and 58 years old (median 44) with active AS, were prospectively examined with both whole-body MRI and 18 F-fluoride PET/CT. Patients fulfilled modified NY criteria and had a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) of at least 4. Increased radiotracer uptake in PET/CT and bone marrow edema in whole-body MRI of spine and SIJ was evaluated independently by two blinded observers for each modality. Kappa statistics were used to compare interobserver agreement as well as scores of consensus reading of the two imaging modalities.ResultsAnalysis of interobserver agreement for PET/CT yielded a kappa value of 0.68 for spinal lesions and of 0.88 for SIJ lesions. The corresponding kappa values for the MRI modality were 0.64 and 0.93, respectively. More spinal lesions were detected by MRI in comparison to PET/CT (68 vs. 38), whereas a similar number of SIJ quadrants scored positive in both modalities (19 vs. 17). Analysis of agreement of lesion detection between both imaging modalities yielded a kappa value of only 0.25 for spinal lesions and of 0.64 for SIJ lesions.ConclusionIncreased 18 F-fluoride uptake in PET/CT is only modestly associated with bone marrow edema on MRI in the spine and SIJ of patients with AS, suggesting different aspects of bone involvement in AS.
Highlights
This study compares the frequency and distribution of increased activity on 18 F-fluoride PET/CT with the presence of bone marrow edema on whole-body MR imaging in the spine and sacroiliac joints (SIJ) of patients with active ankylosing spondylitis (AS)
Interobserver agreement for F PET/CT and MRI of spinal lesions Reader agreement was assessed by kappa statistics for each imaging modality
The results of the present descriptive pilot study suggest that the radiotracer uptake detected by F PET/CT in the spine and SIJ of patients with AS is only marginally associated with the concomitant MRI evidence of inflammation
Summary
This study compares the frequency and distribution of increased activity on 18 F-fluoride PET/CT with the presence of bone marrow edema on whole-body MR imaging in the spine and sacroiliac joints (SIJ) of patients with active ankylosing spondylitis (AS). The current paradigm involves resolution of an inflammatory lesion and its replacement by fat tissue followed by cartilage metaplasia and osteoproliferation through endochondral ossification [7,8]. This is exemplified by the observation that syndesmophytes seem to preferentially develop at fatty degenerated vertebral corners after resolution of inflammation [9,10]. We compared the distribution of the lesions with the inflammation detected as bone marrow edema on short tau inversion recovery (STIR) sequences by whole-body MRI in the same patients
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