Study Of Synthetic Magnetic Resonance (MAGIC) Combined With Diffusion Tensor Imaging (DTI) To Evaluate The Maturity Of Anterior Cruciate Ligament Grafts

Objective: To analyze the feasibility and reliability of synthetic magnetic resonance(MAGIC)combined with diffusion tensor imaging(DTI)in evaluating the maturity of anterior cruciate ligament(ACL)grafts,and to further analyze the variation trend of the derived parameters of two kinds of magnetic resonance techniques in the process of graft remodeling.Methods: 1.Feasibility analysis of synthetic magnetic resonance(MAGIC)combined with diffusion tensor imaging(DTI)to evaluate the maturity of ACL grafts: Thirty patients who underwent ACL reconstruction of autogenous tendon graft in the Second Affiliated Hospital of Guangxi Medical University from March 2020 to March 2021 were collected as the subjects for this observation,including 23 males and 7 females,with an average age of 30.6 years.Postoperative time was 13.6±4.1 months,and the grafts of 27 patients were complete.Three patients had graft tears(all followed a standardized rehabilitation exercise program).All patients underwent T1 WI,PDWI,STIR,DTI and MAGIC sequence scans at 10-15° knee flexion,of which 15 patients underwent 3 axial MAGIC and DTI scans on the same day,and the magnetic resonance imaging system repositioned the coil after each acquisition.After image acquisition,one physician measured the SNR and CNR of articular fluid,articular cartilage,meniscus,bone marrow,muscle and graft respectively on synthetic MRI and conventional MRI images to compare the quality of two kinds of MRI images.Two physicians independently evaluated the structural abnormality of knee joint on synthetic MRI and conventional MRI images,including the integrity of meniscus,articular cartilage,graft and whether the subchondral bone was bone edema.The detection rate of structural abnormality of knee joint was compared between the two kinds of MRI images.DTT fiber tracking: DTI images were fused with PDWI images,and then regions of interest(ROIs)were drawn on the PDWI images.Three ROIs were placed on the axial position and two ROIs were placed on the sagittal position.The fiber bundles of five ROIs were tracked simultaneously,and the FA threshold was adjusted for fiber bundle tracking.ROIs with appropriate area were drawn at roughly the same position in the middle segment of the graft on the three groups of axial images of MAGIC and DTI,and each parameter was measured to further evaluate the accuracy of parameters of MAGIC and DTI.Pair t-test was used to analyze the differences of SNR and CNR between synthetic MRI and conventional MRI images,and Kappa test was used to analyze the comparison of the abnormal detection rate of knee joint structure between synthetic MRI and conventional MRI images.Intra-group correlation coefficient(ICC)was used to analyze the consistency of three synthetic MRI and DTI parameters on the same day,and to evaluate the accuracy of synthetic MRI and DTI parameters.2.Analyzing the change of the magnetic resonance(NMR)derivative parameters during graft remodeling: collected in March,2020-March 2021 the second affiliated hospital of guangxi medical university do autogenous tendon graft ACL revascularization 40 patients as the observation object,40 patients were successful operation,graft survival,and all patients follow standardized rehabilitation exercise plan.Among them,there were 31 males and 9 females,with an average age of 32.9 years.Postoperative time ranged from 6 to 18 months,with an average postoperative time of 12.8 months.All patients underwent three examinations every three months,during which no history of severe trauma was reported.In addition,18 healthy subjects(14 males and 4females,with an average age of 28.8 years)were recruited as the control group.All participants underwent T1 WI,PDWI,DTI and MAGIC sequence scans after knee flexion of 10-15°.After the image acquisition of all patients(three times)and volunteers,the appropriate area of ROIS was drawn on the tendon at roughly the same position of the grafts for three times to measure each parameter.In the control group,ROIS with appropriate area was drawn on the pure ligament of ACL to measure each parameter.Single factor repeated measurement ANOVA analysis of variance was used to analyze the changes of parameters of DTI and MAGIC every three months,and LSD multiple comparison method was used to compare and analyze the differences of data of each parameter three times in pairs.Results: 1:(1)The SNR of articular fluid of synthetic T1 WI images was higher than that of conventional T1 WI images(t=3.36,P=0.008),and the SNR of meniscus was lower than that of conventional T1 WI images(t=-5.81,P <0.001).The SNR of articular fluid and muscle in synthetic PDWI images were higher than those in conventional PDWI images(t=3.84,P=0.003,t=2.29,P=0.042).SNR of joint fluid in synthetic STIR images was higher than that in conventional STIR images(t=3.35,P=0.007),and SNR of meniscus and bone marrow in synthetic STIR images was lower than that in conventional STIR images(t=-4.91,P < 0.001,t=-7.89,P < 0.001).(2)The CNR of synthetic T1 WI images was generally higher than that of conventional T1 WI images,except for the CNR muscular-bone marrow and CNR cartilaginous meniscus(t=1.37,P=0.197,t=0.02,P=0.986).CNR articular fluid-cartilage,CNR articular fluid-menisus and CNR articular fluid-graft in synthetic PDWI and STIR images were higher than those in conventional PDWI and STIR images(t=3.23,P=0.007,t=3.43,P=0.005,t=3.43,P=0.005;T =3.1,P=0.009,t=3.3,P=0.006,t=3.21,P=0.007).(3)The detection rate of structural abnormality of knee joint by synthetic MRI and conventional MRI is highly consistent,but the detection rate of cartilage wear is moderately consistent.(4)Fibrous tracts could be reconstructed in all 27 patients,which basically matched the morphology and movement of ACL grafts.In 3 cases,the graft was broken and the structure of the fibrous bundle was disordered.The reconstruction effect was related to the setting of fiber tracking parameters(such as FA threshold)and the number and location of ROIs placed.The tracing effect of some graft fiber tracts was not ideal,with discontinuity and segment breaking.(5)The intra-group correlation coefficients(ICC)of quantitative parameters(T1,T2,PD,FA,ADC)in the three groups of the grafts of 15 patients were 0.861,0.770,0.955,0.822 and 0.828(P < 0.001 for the five groups).2:(1)There were statistically significant differences in T1 values among the three groups(1175±324ms,1097±230ms and 1040±194ms,and 1019±335ms in the control group),F=3.7,P=0.044;The difference in T2 value between the three groups was statistically significant(50.7±3.1ms,44.2±1.3ms and 43.5±0.9ms,and 43.6±5.6ms in the control group),F=4.7,P=0.030.There was significant difference in PD value between the three groups(37.9± 2.5PU,35.3± 2.3PU and 31.4± 2.3PU,control group 20.5±3.6PU),F=9.6,P < 0.001;The difference in FA value between the three groups was statistically significant(0.433±0.091,0.389±0.057 and 0.380±0.058,and0.383±0.025 in the control group),F=7.8,P=0.003;There were significant differences in ADC values among the three groups(2.19±0.30×10-3mm2/s,2.42±0.39×10-3mm2/s and 2.55±0.48×10-3mm2/s,and 2.64±0.35×10-3mm2/s in the control group),F=9.5,P < 0.001.(2)Pairwise comparison of the three groups of parameters: the differences of T2,FA and ADC values between the first and the second were statistically significant(P=0.037,0.004,0.007),while the differences between the second and the third were not statistically significant(P=0.483,0.298,0.130).There was no statistically significant difference between the first and second PD values(P=0.145),while there was statistically significant difference between the second and third PD values(P=0.006).There was statistically significant difference in T1 value between the first and the third time(P=0.035),while there was no statistically significant difference between the other two groups(P=0.095,0.229).(3)The parameters of the three times were close to the values of the control group.When the data was collected for the third time(postoperative time for all cases was longer than 12 months),T2 and FA values changed little,while PD and ADC values changed greatly with the extension of postoperative time.Conclusions: Our study confirms the potential of synthetic magnetic resonance(MAGIC)combined with diffusion tensor imaging(DTI)to monitor the extent of remodeling of human anterior cruciate ligament grafts,and the MR derived parameters of the grafts indicate remodeling over 12 months.