Purpose : To discuss the application of 3D UTE sequence and 2 kinds of routine 2D sequences in children’s knee MRI examination.

Materials and methods : 5 children with knee MRI examination between March 2023 and May 2023 were enrolled in our study , including 4 cases of male and 1 case of female . Their age range was from 6 years old to 14 years old . The United Imaging uMR570 scanner was chosen and T1WI FSE sequence , PDWI FSE FS sequence , 3D UTE sequence were all scanned with the knee special coil for every child . The main parameters of 3D UTE sequence were as follows : TR=7ms, TE1=0.09ms-0.16ms , TE2=4.48ms , Flip Angle=8 , scan time was about 5 min . 3 kinds of  images were generated from 3D UTE scanning , including short TE images ( from TE1 sequence ) , long TE images ( from TE2 sequence ) , SUB images ( the images of TE1 sequence subtracted those of TE2 sequence ) . Because of the scanning direction in 3D UTE sequence was horizontal axis , multiplanar reformation was made after scanning . On all sagittal images , ROIs were set in cartilages of distal femur , proximal tibia and patella . What’s more , ROIs were set in anterior cruciate ligament and posterior cruciate ligament . SNRs were calculated from above 3 kinds of cartilages and 2 kinds of ligaments . In statistical analysis , paired t test or Wilcoxon rank sum test was made in SNRs between short TE images of 3D UTE sequence and T1WI FSE sequence , between long TE images of 3D UTE sequence and PDWI FSE FS sequence .

Results : SNRs in cartilages of distal femur , proximal tibia and patella , in anterior cruciate ligament and posterior cruciate ligament were as follows . The SNRs on short TE sequence of 3D UTE images were 15.5±5.02 , 16.2±4.58 , 18.32±6.12 , 17.4±5.54 , 21.7±4.38 , respectively , on T1WI FSE images were 9.0±3.59 , 10.8±4.87 , 13.27±3.62 , 6.6±4.56 , 3.9±3.43 , respectively , with statistically significant differences (P＜0.05) . The SNRs on long TE sequence of 3D UTE images were 10.3±2.76 , 11.2±3.12 , 19.1±2.85 , 12.6±3.57 , 5.94±2.42 , respectively , on PDWI FSE FS images were 4.2±0.78 , 5.2±0.53 , 4.9±0.69 , 3.5±0.82 , 3.22±0.64 , respectively , with statistically significant differences (P＜0.05) . The SNRs on SUB images were 4.92±1.63 , 4.24±1.30 , 3.09±1.53 , 6.73±3.26 , 5.68±2.13 , respectively.

Conclusions : (1) In cartilages of distal femur , proximal tibia and patella , in anterior cruciate ligament and posterior cruciate ligament measured in our study , SNRs on short TE sequence of 3D UTE images were higher than those of T1WI FSE images and SNRs on long TE sequence of 3D UTE images were higher than those of PDWI FSE FS images . (2) A third SUB images were generated from 3D UTE sequence and could provide more information for diagnosing children’s knee diseases.