Evaluation of cartilage surface injuries using 3D-double echo steady state (3D-DESS): effect of changing flip angle from 40° to 90°

Utility of axial magnetic resonance images for detecting meniscal ramp lesions associated with anterior cruciate ligament injuries

Background

Ramp lesions (RLs), associated with anterior cruciate ligament (ACL) injuries, should be repaired to ensure postoperative knee stability. However, it is difficult to identify all RLs before surgery using conventional sagittal magnetic resonance (MR) images and arthroscopy from the anterior, medial, and lateral portals that are usually used during ACL reconstruction. We report the effectiveness of axial images for detecting RL.

Methods

From January 2018, a total of 316 knees underwent primary ACL reconstruction with preoperative magnetic resonance imaging (MRI) examination at our hospital. Among these, 149 knees, which required meniscal suturing at the same time, were retrospectively investigated. This study evaluated 22 knees with confirmed RLs around the posterior horn of the medial meniscus. The effectiveness of the preoperative sagittal and axial MR images for detecting RL was assessed. With the MR image, a three-dimensional double-echo steady-state image with a flip angle of 25° was reconstructed into the sagittal and axial planes, respectively. Reconstructed images with 3-mm slices for sagittal slices and 1-mm slices for axial sections were used. The diagnosis was made based on the presence of RL (RL was present, RL may be present, and RL was not present) by four knee surgeons with more than 10 years of experience.

Results

Approximately 53% of knee cases were diagnosed with RLs using sagittal images. Meanwhile, a diagnosis was achieved using axial images in 89% of cases.

Conclusion

Axial MRI may be superior in detecting RLs.

Three-dimensional double-echo steady-state (3D-DESS) magnetic resonance imaging of the knee: establishment of flip angles for evaluation of cartilage at 1.5 T and 3.0 T

BACKGROUND

The effect of flip angle (FA) on synovial fluid and cartilage signal and on image contrast using three-dimensional double-echo steady-state (3D-DESS) sequence have only been performed with 1.0-T but not with 1.5-T or 3.0-T scanners.

PURPOSE

To identify the FA that gives the maximum synovial fluid and cartilage values, and to identify the FA at which maximum values of synovial fluid-cartilage contrast-to-noise ratio (CNR) in 3D-DESS sequences when 1.5-T and 3.0-T scanners are used.

MATERIAL AND METHODS

Using 3D-DESS with water-excitation pulse, mid-sagittal plane images of the knees of 10 healthy volunteers (5 men, 5 women; age range, 21-42 years) were obtained with FA varying from 10° to 90°. Synovial fluid signals, cartilage signals, and background were measured at each FA, and the FA that gave the highest synovial fluid and cartilage values was obtained. Synovial fluid-cartilage CNR was also calculated, and the FA that gave the largest CNR was obtained.

RESULTS

At 1.5 T, the maximum synovial fluid signal was at FA 90°, and the maximum cartilage signal was at FA 30°. Synovial fluid-cartilage CNR was highest at FA 90° (P < 0.05). At 3.0 T, the maximum synovial fluid signal was at FA 90°, and the maximum cartilage signal was at FA 20°. Synovial fluid-cartilage CNR was highest at FA 90° (P < 0.05).

CONCLUSION

In order to improve the visibility of cartilage itself, FA settings of 30° at 1.5 T and 20° at 3.0 T are apparently ideal. For observing the cartilage surface, the most effective FA setting is 90° for both 1.5 T and 3.0 T.