Feasibility Study Of MR Ultrashort Echo Time Imaging For The Assessment Of Knee Cartilage And Its Damage

Objectives: To image knee osteochondral specimens and healthy volunteers using magnetic resonance(MR)ultrashort echo time imaging with pointwise encoding time reduction with radial acquisition combined fat suppression(PETRA-FS)sequence to determine whether it can reveal non-calcified cartilage,including the deep radial layer,and to assess its effectiveness in cartilage damage diagnosis.Materials and Methods: PETRA-FS imaging was performed on 58 osteochondral specimens of the lower femur and upper tibia to observe the depth of cartilage injury involvement and to assess whether cartilage hypersignal was continuous and whether cartilage hypersignal was present.Kappa values were used to assess interobserver agreement.At the end of the MR scan,each osteochondral tissue was cut at a randomly selected level with approximately 0.5 cm width.Retrieved material orientation was marked and distance from the edge of tissue was recorded.The tissue was fixed in 10%formaldehyde solution and then decalcified with 10% ethylenediaminetetraacetic acid for3–4 weeks.The decalcified osteochondral tissue was obtained perpendicular to the articular cartilage,and subsequently embedded,sectioned,and stained with hematoxylin-eosin.Cartilage morphology was observed microscopically to assess whether the cartilage was damaged,and to record the depth of the damage.The composition of signal intensity of bone-chondral isolated specimens was observed using pathological findings as the standard;the sensitivity,specificity and reliability of PETRA-FS sequence for the diagnosis of cartilage injury were assessed.The efficacy of the PETRA-FS sequence in diagnosing cartilage injury was evaluated using the subject operating characteristic(ROC)curve and the area under the ROC curve(AUC).Twenty-nine healthy volunteers with a total of 58 knee joints were recruited to undergo FS FSE PDWI sequence and ultrashort echo time PETRA-FS sequence scans to measure patellar cartilage and femoral cartilage thickness,assess the difference in cartilage thickness shown by the two sequences and observe their signal characteristics,and evaluate the advantage of MR Ultrashort echo sequence showing cartilage.Results:1、Knee osteochondral specimensHistological diagnosis of cartilage injury was made in 38 cases and undamaged in 20 cases.Continuous cartilage high signal was seen on PETRA-FS sequence images in 20 cases without cartilage damage(No damage to the tangential,transitional and deep layers of cartilage,n=20).In 11 cases,cartilage damage reached the tangential layer(Equivalent to damage to remove part of the tangential layer),and PETRA-FS sequence images showed continuous cartilage high signal(n=11),among which 6 cases showed slight wavy changes on the cartilage surface,and 5 cases had smooth cartilage surface without diagnosed damage.In 7 cases,cartilage damage reached the transitional layer(Equivalent to damage to the tangential and partially transitional layers)with limited cartilage thinning on PETRAFS sequence images,and continuous cartilage high signal was also seen(n=7).In 13 cases,cartilage damage reached the radial layer,including 8 cases in which it reached the deep radial layer(Equivalent to the removal of tangential,transitional layers and partially deep layers)with significant cartilage thinning on PETRA-FS sequence images,and continuous cartilage high signal still visible(n=13).In 3 cases,cartilage damage reached the calcified cartilage layer(Equivalent to the removal of tangential,transitional and deep layers),and PETRA-FS sequence images showed limited cartilage high signal disappearance of the entire layer with cartilage high signal discontinuity(n=3).In 4 cases with cartilage defects,PETRA-FS sequence images did not show a high signal.PETRA-FS sequence showed 37 cases of cartilage damage and 21 cases of no damage among 58 specimens,kappa value of0.75.Using histological results as the gold standard,PETRA-FS sequence had a sensitivity of 87.00%,specificity of 80.00%,kappa value of 0.81,and an area under the ROC curve(AUC)of 0.83 for cartilage injury diagnosis.2、Healthy volunteersFS FSE PDWI sequences showed normal cartilage,and no abnormal cartilage signal or morphology was seen.PETRA-FS sequence images showed that the signals of knee cartilage were stratified,and the shallow layer showed medium-high signals,which corresponded to the signals of cartilage shown in FS FSE PDWI sequence images.PETRAFS sequence images showed high signal in the deep cartilage,while FS FSE PDWI sequence images showed very low signal,which was indistinct from the subchondral bone and could not be distinguished.The FS FSE PDWI sequence and PETRA-FS sequence showed patellar cartilage thicknes(4.18±0.89 vs 5.34±0.88,t=3.94,P<0.05);femoral cartilage thicknes(2.89±0.46 vs 3.52±0.67,t=3.26,P<0.05),the differences were statistically significant,the PETRA-FS sequence showed that cartilage thickness was greater than that shown by FS FSE PDWI sequences were shown.Conclusion: MR ultrashort echo time imaging PETRA-FS sequence can show noncalcified cartilage,including the deep radial layer(conventional MR Images showed very low signal).The PETRA-FS sequence is of great diagnostic value in the diagnosis of cartilage injuries.