Participants
- After approval by the institutional review board,
a total of 38 patients who were already referred for knee arthroscopy in our institution,
were invited to participate in this prospective study and were evaluated with a preoperative MRI of the knee to be operated.
MRI Acquisition
- All knees were imaged with the same 1.5T MRI unit (Philips Achieva 1.5T MRI System,
Philips Medical Systems,
Best,
The Netherlands) using an 8-channel SENSE knee coil.
Both standard 2D and 3D TSE techniques were acquired in the same day.
Routine 2D TSE MRI consisted in 3 sequences,
all acquired with SPAIR (spectral attenuated inversion recovery,
a high uniform fat saturation method which uses adiabatic spectral saturation pulses): 1) sagittal Iw TSE (repetition time (TR) 2342 ms,
echo time (TE) 50 ms,
224 x 176 matrix,
16 x 16 cm field of view (FOV),
4 mm slice thickness,
4 number of excitations (NEX),
echo train length (ETL) 14,
bandwidth 395 Hz/pixel,
acquisition time 2 minutes 43 seconds); 2) coronal Iw TSE (TR 2342 ms,
TE 50 ms,
224 x 176 matrix,
16 x 16 cm FOV,
4 mm slice thickness,
4 NEX,
ETL 14,
bandwidth 386 Hz/pixel,
acquisition time 2 minutes 30 seconds); and 3) axial Iw TSE (TR 3045 ms,
TE 50 ms,
224 x 176 matrix,
16 x 16 cm FOV,
4 mm slice thickness,
4 NEX,
ETL 14,
bandwidth 429 Hz/pixel,
acquisition time 3 minutes).
The total acquisition time for routine 2D TSE MRI was 8 minutes 13 seconds.
- The 3D TSE sequence was also acquired with the SPAIR technique in the sagittal plane (source images),
with Iw contrast and nearly isotropic voxels (0.6 x 0.6 x 0.7 mm),
with the following parameters: TR 2500 ms,
TE 35 ms,
300 x 258 matrix,
18 x 18 cm FOV,
1 NEX,
ETL 65,
and bandwidth 255 Hz/pixel.
The total time acquisition for the 3D sagittal sequence (source images) was 5 minutes.
- The source images were used to create sagittal,
coronal,
and axial reformatted images of the knee joint with 1.5 mm slice thickness,
which were used for the 3D TSE MRI assessment of the knee.
The post-processing of the 3D TSE sequence (VISTA) was performed by a fellowship in musculoskeletal radiology on the imaging workstation immediately after the MRI examination.
MRI Assessment
- The interpretation of both techniques (2D and 3D MRI) was separately and independently made by two musculoskeletal radiologists,
being the first reader a senior radiologist with more than ten years of experience and the second reader a fellow in musculoskeletal radiology with one-year experience.
They were blinded to the medical and surgical history of the patient or any other information regarding the indication for the MRI. The time frame between the 2D and 3D readings was one month.
- The medial and lateral menisci were evaluated according to the presence or absence of a meniscal tear.
A meniscal tear was defined as an abnormal signal extending into the articular surface of the meniscus on at least two sagittal or coronal consecutive slices.
Intrameniscal degenerative changes were not considered as meniscal tears.
- Both anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were analyzed according to the presence or absence of tears,
regardless of being partial or complete tears.
Arthroscopic knee surgery
- All knee arthroscopies were performed within a maximum period of three days after the MRI,
and in 80% of the cases the arthroscopy was performed on the same day of the MRI. The knee arthroscopies were performed by one of two experienced knee surgeons at our institution with 5 and 20 years of practice,
respectively.
Analytic Approach
- The sensitivity,
specificity,
and accuracy for the detection of meniscal and cruciate ligaments tears were calculated separately for each MRI technique,
taking prompt surgical findings (arthroscopy) as the reference standard.
- The data from the independent assessment of both readers were analyzed separately and then combined when calculating sensitivity and specificity to increase statistical power for a comparison between 3D-TSE and the standard 2D-TSE MR protocol.
- Kappa statistics (k) were used to measure interobserver agreement between readers for determining the presence or absence of meniscal and cruciate ligament tears.
K was also calculated to measure intraobserver agreement between both methods (2D-TSE versus 3D-TSE) for each reader.
- The differences between 3D-TSE and the routine 2D-TSE MR techniques were calculated for dichotomized values (presence or absence of pathology) with 95% confidence intervals using the Fisher’s test,
and were considered to be statistically significant when the p-value was less than 0.05.