Fusion Imaging Study Of Sacroiliac Joint In Ankylosing Spondylitis

Objective In this study,we aimed to verify the methodology and feasibility of fusion imaging of the sacroiliac joints of ankylosing spondylitis patients and assess the possible factors impacting the fusion process.The success of US and computed tomography(CT)/US and Magnetic Resonance Imaging(MRI)image fusion in sacroiliac joints is the precondition for assessing the sacroiliac joint disorders of ankylosing spondylitis patients via fusion imaging.Besides,acquaint with the anatomical characteristics of sacroiliac joint helps to have a deeper understanding in the regularities of tissues distribution indifferent levels of sacroiliac joint.Finally,evaluate the effect of US-CT image fusion of the SIJs of patients to locate the active inflammatory activity as visualized by CDUS in these patients to confirm the sources of abnormal vascularization.Methods We performed US-CT and US-MRI fusion imaging of SIJs with 84 inpatients and 30 controls.Image fusion process were performed at the cross-sectional levels of the first,second and third posterior sacral foramina(level1,level2,level3,respectively).Possible factors impacting the fusion process were considered including the lesion classes of SIJ,the skinfold thickness of the sacral region and the cross-sectional levels of the first,second and third posterior sacral foramina.Image fusion success rates at the 3 levels in the patient group and control group were compared to access the feasibility of US-CT/US-MRI image fusion in sacroiliac joints;the anatomy of three pelvises was examined.One SIJ was opened to expose the full view of the SIJ.The other SIJ was cut into cross-sectional slices according to 3 levels and then observe the intra-articular tissues.An interventional test guided by US and a histological examination were performed on the third SIJ to locate the tissues viewed by US.After successful US-CT image fusion of patients,CDUS was performed to detect abnormal blood flow signals and to estimate their positions.The located abnormal signals were grouped into 3 regions according to the 3 levels.The interior of the SIJ and the area surrounding the SIJ were used to describe the location of these signals cross-sectionally.Results Data showed high success rates of image fusion of US-CT at the 3 levels in the patient group and the control group.However,no significant differences were observed between the two groups at the 3 levels(all P>0.05);Success rates of image fusion of US-MRIT1 WI and US-MRIT2 WI in patient group at the 3 levels were much lower than the US-CT.There were also no significant differences between the two groups at the 3 levels(all P>0.05).In the cases of US-CT image fusion,the differences in the imaging success rates between the 4 classes of SIJ lesions were not significant at any level(P = 0.136,P = 0.708,and P = 0.311 for levels 1,2,and 3,respectively).Furthermore,a difference in the mean skinfold thickness at each of the 3 SIJ levels was observed between the successful and failed cases in both the patients’ and control group.The gross anatomy and the sectional anatomy procedures revealed that the actual synovial joint of the SIJ was positioned anteriorly and that the interosseous sacroiliac ligament was the main connection at the posterosuperior portion of the SIJ and the actual synovial joint of the SIJ gradually increased in size from its superior region to its inferior region but that the ligaments decreased in size at the back of the SIJ.Histological examination indicated that regardless of whether steel balls were placed superficially or deep,the tissues surrounding the balls at levels 1 and 2 were ligaments,whereas the tissue at level 3 was synovial membrane;The differences in abnormal blood flow signals among the 3 regions were significant(χ~2 = 9.101,P = 0.011).These data indicated that abnormal blood flow signals were significantly more likely to occur surrounding the SIJs than within level 1 or 2;conversely,abnormal signals were more likely to occur within level 3 than surrounding the SIJs.Combined the fused US-CT image with anatomical characteristics of sacroiliac joint,the locations of abnormal blood flow signals are initially confirmed,which suggested the intraligamentous inflammation and/or intracapsular inflammation of the sacroiliac joint.Conclusion In this study,we established the methodology of fusion imaging of the sacroiliac joints.The results suggested that US-CT is feasible with sacroiliac joints of ankylosing spondylitis patients;the skinfold thickness was identified as the main factor affecting the success rates.US-CT fusion imaging can be used to locate abnormal blood flow signals in the sacroiliac joints of ankylosing spondylitis patients with active sacroiliitis as visualized by CDUS.Abnormal blood flow signals at different levels indicate the occurrence of inflammation in different tissues of the posterior sacroiliac joint.US-CT imaging may provide a new visual perspective for imaging performance on ankylosing spondylitis patients and may be helpful in the diagnosis of AS patients,particularly at the early stages of ankylosing spondylitis.Technical limitations of US-MRI fusion still need to be resolved in the further studies.