Objective: To evaluate the clinical value of low-dose semicoronal computerized tomography (CT) of sacroiliac joints (SIJ) in the early diagnosis of ankylosing spondylitis (AS).
Methods: Patients who were diagnosed with AS and had received axial CT examination of SIJs over the past 2 years were recruited. All of them simultaneously underwent a low-dose semicoronal CT of SIJs. The clinical data were recorded. Radiation dose was compared between low-dose CT and the previous conventional axial CT. Image quality of low-dose CT was assessed and correlation between image quality and weight or body mass index (BMI) was analyzed. CT images of the two groups were graded by modified New York criteria, the Lee criteria and the Innsbruck criteria. The kappa coefficient was used to assess the consistency of grading between the two groups.
Results: Thirty-three patients were enrolled in this study. The effective dose (ED) of semicoronal SIJ CT was 3.37 mSv which was 49% lower than conventional axial CT (6.56 mSv). Lower dose had the potential protection of gonads. The quality of images in male patients with BMI<25 kg/m(2) and all female patients were good or excellent. There was a significant negative correlation between image quality and BMI (r=-0.746, P=0.000; r=-0.784, P=0.000; respectively). All patients were diagnosed as sacroiliitis by modified New York criteria and the grading of two groups was consistent. The consistency of grading between two groups was satisfactory no matter which classification criteria was used. (k=0.897 with Lee criteria; k=0.814 with Innsbruck criteria; P>0.05).
Conclusions: The radiation dose of semicoronal SIJ CT is significantly lower than that of the conventional axial CT with comparable efficacy of diagnosis.