MRI Studies Of Cartilage Abnormalities In Early Sacroiliitis In Ankylosing Spondylitis

PartⅠ MRI sequences comparison study for displaying sacroiliac jointcartilageObjective: To investigate whether the3D-FLASH-WE sequence couldshow the SIJ cartilage clearly, and further to validate the value of the waterexcitation technique in the SIJ cartilage examination.Methods: Bilateral SIJs of16healthy volunteers(9male and7female,age range20~30years, mean age25.1±3.6years) underwent MRI scanningwith four sequences including TSE-T1WI-FS, TSE-TSE-PDWI-FS,3D-FLASH-WE and3D-FLASH-FS. According to whether the image candistinguish cartilage in the sacral side and in the iliac side,whether the edge ofthe cartilage is clear, and to whether the the contrast between the cartilage andsurrounding structures is principle,we established six score standard (0,1,2...5points)and then we scored the images from each sequence.In addition, wemeasured, calculated and compared the signal to noise ratio (SNRs) of the SIJcartilage for different sequence, and compared the contrast to noise ratio (CNR)between the cartilage and cortical bone,and between cartilage and cancellousbone. The resulting data were statistically analyzed to compare foursequences.Results: Both3D-FLASH-WE and3D-FLASH-FS sequences got thehighest score results (both average score is4.67points), there was nosignificant difference (P=0.24), but obviously higher than the TSE-T1WI-FSand TSE-PDWI-FS sequence's score (P<0.05). The SNR of cartilage and theCNR between cartilage and bone cortex in3D-FLASH-WE,3D-FLASH-FSand TSE-T1WI-FS sequences are significantly higher than in theTSE-PDWI-FS sequence (P<0.05), but no significant difference among thethree sequences. The CNRs between cartilage and cancellous bone in both the 3D-FLASH-WE and the3D-FLASH-FS sequence are ignificantly higher thanthat in the TSE-T1WI-FS and TSE-PDWI-FS sequence (P<0.05),but nostatistical difference between in the two3D sequences (P=0.30).3D-FLASH-WE sequence scan time was significantly shorter than the3D-FLASH-FS sequence, respectively for3minutes4seconds and5minutes23seconds.Conclusion: Both the3D-FLASH-WE and the3D-FLASH-FS sequencescan show the SIJ cartilage more clearly than TSE-T1WI-FS andTSE-PDWI-FS, but the3D-FLASH-WE sequence is significantly faster thanthe3D-FLASH-FS sequence. It is recommended that the3D-FLASH-WEsequence is the best sequence for the SIJ cartilage examination.PartⅡ Preliminary MRI study of sacroiliac joint cartilage abnormalityin the patients with clinical symptoms supporting ankylosingspondylitis but without sacroiliac joint abnormality on CT.Objective: To study the MRI findings of sacroiliac joint cartilageabnormality in early sacroiliitis caused by ankylosing spondylitis(AS),andfurther to investigate the relationship between the cartilage change and thesubchondral bone changes in early sacroiliitis.Methods:79patients suspected AS with clinical symptoms but withnormal sacroiliac joint (SIJ) on CT were enrolled in the suspected early ASgroup (61male and18female, age range13~39years, mean age23.5years),66healthy volunteers (33male,33female,age range20~30years,mean age25.5years) and30patients (22male and8female, age range18~42years,mean age25years) confirmed AS sacroiliitis on CT were enrolled as thecontrols, all of the subjects underwent SIJ MRI scan with four sequencesincluding TSE-T1WI-FS, TSE-T2WI-FS,3D-FLASH-WE and STIR. The MRand CT images were observed and analysis to explore the MRI feature ofcartilage abnormality in early sacroiliitis, and to explore the relationshipbetween the cartilage abnormality and subchondral bone changes.Results: Normal SIJ cartilage of20to30-year-old healthy volunteers is linear high signal intensity covering the cortical surface in3D-FLASH-WEsequence, the sacral cartilage is thicker than iliac cartilage.89%of the normalSIJs has low signal gap between the sacral the iliac cartilage, and11%of thenormal SIJs the gap can not be displayed but the cartilage shape is regular andthe signal is hemogenous. We discoverd laminated appearance in the sacralcartilage of11%normal SIJs, as the shallow and deep zone is linear highsignal while the middle layer is low signal. There is short strip high signalextending from the cartilage to the subchondral bone in13%normal SIJs. ASOf all the44SIJs which have bone destruction on CT,9%have no bonemarrow oedema (BMO) signal;73%have bone destruction only in the ililuebut not in the sacrum,34%of which have cartilage abnormal in iliac side butthe cartilage in the sacrum side is normal; only27%had bone destruction inboth the sacrum and ilium and the ilium distruction was more serious. In26SIJs with early sacroiliitis (CT normal),96%of the BMO signal located in theilium and61%of which accompanied with BMO in the sacrum, and in onlyone SIJ, BMO lacated in the sacrum with nomal iliac. Only3%of the SIJswith BMO in T2WI and STIR sequence can be detected by3D-FLASH-WEsequence. We found four types of SIJ cartilage abnormalities in3D-FLASH-WE sequences, the first one is the cartilage shape irregularity anduneven thickness, the second is the gap between cartilage in the sacral andiliac side become unclear and even disappear, the third is the interface area ofcartilage and cortical become irregular, and the fourth is low signal defec incartilage within thet stove. Four types of cartilage abnormalities in MRIsacroiliitis group (CT normal but BMO on MRI) appear significantly higherthan in the patients with only symptoms(neither bone destruction nor BMO inSIJs)(P<0.05). The positive rate of the first three types of cartilageabnormalities have no difference between the SIJ sacroiliitis group and CTsacroiliitis group (SIJs have bone destruction on CT)(P=0.33,0.37,0.05),while the positive rate of the low signal defects in the MRI sacroiliitis group ishigher than that in CT sacroiliitis group (P<0.05). We found low signal defectin9%of the normal SIJs but not combined with other three types of cartilage abnormalities.Conclusion: Normal SIJs cartilage of20to30-year-old healthyvolunteers is displayed as continuous linear high signal in3D-FLASH-WEsequence, and low signal linear gap between the sacral and iliac cartilage canbe seen. However, low signal defect, gap disapearence, laminated appearanceor short strip high signal extending from the cartilage to the subchondral bonecan be found in the cartilage of part of the normal SIJs, with normal cartilagearound it. In3D-FLASH-WE sequence, it should be known as cartilagechange in early sacroiliitis that the cartilage shape appears irregular, combinewith or without surface unsmooth,low signal defect stove,irregular interfaceof bone and cartilage and gap disappearance. Before appearance of bonedestruction,most of the BMO of early sacroiliitis distributes in the ilium, thismay be one of the reasons why bone destruction in ilium appears earlier andmore serious than that in sacrum. Part of BMO appears earlier than bonedestruction.3D-FLASH-WE sequence is not sensitive to check out BMOdema.