Synopsis

2D TSE MRI is widely used for the evaluation of internal knee derangement but is time-consuming. Recently introduced 3D TSE acceleration strategies, such as CAIPIRINHA allow for fast sampling, and together with AutoAlign technology enable now fully automated one-button-push 3D MRI protocols in 10 minutes total scan time. In a prospective study of 150 subjects, we analyzed the frequencies of structural abnormalities, inter-reader reliability, inter-method concordance, diagnostic definitiveness, and interchangeability of 10-min 3D CAIPIRINHA SPACE TSE protocols and 20-min 2D TSE standard-of-reference protocols. Our results indicated that that 10-min 3D TSE protocols are at least equivalent to 20-min 2D TSE protocols for the diagnosis of internal derangement of the knee.

Introduction

MRI protocols for the evaluation of internal knee derangement include pulse sequence that are tailored for the morphological assessment of anatomic structures and fluid-sensitive pulse sequences that are tailored to maximize the conspicuity of findings with long T2 constants, such as inflammation, collections, and edema. 2D TSE pulse sequences can be acquired with a high in-plane spatial resolution, but a mandatory slice thickness of 2-4 mm prevents multiplanar reformations and requires the separate acquisition of multiple series of images in axial, sagittal and coronal orientation, which can be a time-consuming process and often requires total protocol acquisition times of 20 minutes. 3D TSE techniques yield substantially more MR signal and provide an opportunity to image which substantially higher spatial resolution.¹ The two phase-encoding directions of 3D SPACE provides an opportunity for bidirectional acceleration, which in combination with a shifted Controlled Aliasing In Parallel Imaging Results IN Higher Acceleration (CAIPIRINHA) sampling pattern² results in excellent image quality.³ CAIPIRINHA-accelerated 3D SPACE TSE with integrated anatomical landmark-based AutoAlign Knee technology⁴ provides automatic field-of-view and slice positioning and is capable of fully automated, one-button-push, high-resolution, 3D isotropic diagnostic knee MRI with intermediate- and T2SPAIR-weighted image contrasts and total acquisition times of approximately 10 minutes.

Purpose

Methods

Results

All MRI studies were successfully performed. Both readers diagnosed abnormalities with similar proportions regardless of the MRI technique or field strength (Figure 2). The inter-method concordance agreement (Figure 2) for matched diagnoses between 2D and 3D TSE was good to very good (kappa, 0.614 – 0.837) for meniscal and anterior cruciate ligament tears, areas of bone marrow edema, and fractures; whereas the concordance agreement was moderate for the detection and differentiation of partial- and full-thickness defects (kappa, 0.597 - 0.590). The readers' diagnostic definitiveness in diagnosing meniscal tears and cartilage defects was higher on 3D than 2D studies, and similar for 2D and 3D for the diagnosis of anterior cruciate ligament tears, bone marrow edema, and fractures (Figure 3A). In an interchangeability comparison using common pair exact match proportions (Figure 3B), 2D and 3D MRI were interchangeable for the diagnosis of medial collateral ligament tears, anterior cruciate ligament tears (Figure 4), and fractures; whereas the common pair exact match proportions were significantly (p < 0.01) higher for 3D TSE MRI when readers diagnosed medial and lateral meniscal tears (Figure 5) and bone marrow edema. The common pair exact match proportions for diagnosing cartilage defects was different for all combinations.

Discussion

Owing to the rising economic constraints and the demand of MRI for non-invasive diagnosis of internal knee derangement, there is a need for faster MRI acquisition without comprising diagnostic performance. 10-min 3D CAIPIRINHA SPACE TSE knee protocols offer an opportunity to shorten the table time for patients, increase institutional throughput, and potentially a path to compensate for decreasing reimbursements. The 10-min acquisition time was achieved through 2x2 acceleration with a shifted, bidirectional CAIPIRINHA undersampling in phase and partition encoding directions. This approach helped to minimize aliasing artifacts, reduce image noise, and provided a path to 4-fold acceleration without the need for image quality compromising acceleration strategies, including long echo trains, partial Fourier undersampling, and anisotropic data acquisition. Analyses of the frequencies of structural abnormalities, inter-reader reliability, inter-method concordance, diagnostic definitiveness, and interchangeability comparison indicate that 1.5 and 3T 3D CAIPIRINHA SPACE TSE protocols are at least equivalent to 2D TSE standard-of-reference protocols for the diagnosis of internal derangement of the knee.

Conclusion

Acknowledgements

References

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