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Comprehensive evaluation of wrist kinematics using 3D real-time MRI
Ye Tian1, Abhijit J. Chaudhari2, and Krishna S. Nayak1
1Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA, United States, 2Department of Radiology, University of California Davis, Davis, CA, United States

Synopsis

Keywords: Functional/Dynamic, MSK, wrist, low-field, real-time

Motivation: A thorough understanding of wrist kinematics and kinetics is essential for diagnosing and treating wrist pain and instability. Current MRI methods are limited to tracking just a few thick slices and therefore use hand supports to restrict motion to pre-selected, simplified orientations.

Goal(s): To develop a 3D real-time MRI method at 0.55T for comprehensive evaluation of wrist kinematics.

Approach: A bSSFP 3D stack-of-spiral sequence with long spiral readout was implemented for evaluating wrist kinematics during maneuvers.

Results: Comprehensive 3D coverage at 10 frames/second was achieved without any restriction on wrist motion, providing measurements of ligament intervals in 3D and during active wrist motion.

Impact: The proposed 3D real-time method can potentially improve diagnosis of wrist injury and dysfunction and treatment planning, by providing a unique 3D evaluation of wrist kinematics and kinetics during the performance of clinically-important maneuvers involved in activities of daily living.

Introduction

There is currently an incomplete understanding of wrist kinematics and kinetics when performing routine tasks as part of activities of daily living. Therefore, wrist instability, resulting from trauma or injury, is difficult to diagnose and treat. Dynamic MRI (1-4) or CT (5) have been employed for these assessments, with MRI being the preferred modality as it is part of routine clinical care. However, current dynamic MRI methods are limited to 2D (1,3) or 3D (2) acquisitions with limited spatial coverage. To address this, the hand and arm are restrained to move in only a few pre-determined planes (2, 3), significantly reducing degrees of freedom. This arrangement makes it challenging to resolve and understand off-plane motion of wrist tissues during clinically-relevant maneuvers such as dart-throw (DT) and wrist flexion-extension (FE) (6).

The new generation of mid-field MRI scanners (0.1-1.0T) (7,8) have substantially reduced B0 inhomogeneity and specific absorption rate (SAR), enabling the use of spiral balanced steady-state free precession (bSSFP) sequences with longer readouts and greater flexibility in the flip angle selection, while avoiding banding artifacts and exceeding SAR limitation. These advancements have the potential to greatly enhance the capabilities of real-time MRI, by providing more spatial coverage at a higher temporal resolution.

In this study, we implemented a real-time 3D bSSFP pulse sequence that combines a non-selective hard-pulse and a stack-of-spiral readout. This pulse sequence achieves exceptional scan efficiency for wrist imaging, allowing us to capture 3D real-time wrist movements at a frame rate of 10 frames/second. This approach permits a wide range of wrist maneuvers, including radial-ulnar deviation (RUD), DT, and FE, all without the need to restrict hand movement during the imaging process.

Methods

Pulse sequence
Figure 1 illustrates the 3D golden-angle stack-of-spiral sampling pattern. By using a non-selective hard-pulse (TRF=0.7ms) and long spiral readout (Tread=6.48 ms), this pulse sequence has an acquisition duty cycle of 77% (Tread/TR), which is much larger than Cartesian or radial acquisitions (~30-40%).

Data acquisition
Experiments were performed on a whole-body 0.55T system (prototype MAGNETOM Area, Siemens Healthineers, Erlangen Germany) with high-performance shielded gradients (45 mT/m amplitude, 200 T/m/s slew rate). RTHawk real-time interactive platform (Vista.ai, Palo Alto, California) was used to program the pulse sequence, perform online reconstruction for preliminary quality check, and acquire the data. One healthy adult male volunteer was scanned, under a protocol approved by our IRB.

Two body-6 coils were used for data reception as illustrated in Figure 2. The volunteer was asked to kneel at the back of the scanner and extend his right arm to the scanner iso-center. Three different maneuvers were performed: RUD, FE, and DT, with each maneuver performed at a speed of 8-10 seconds per repetition for two repetitions. Scan parameters were TE/TR=0.46/8.42ms, Tread=6.48ms, flip angle=60o, FOV=22x22x8cm3, and voxel size=1.4x1.4x4mm3. Resonance frequency was tuned to imaging fat (-80Hz relative to water at 0.55T) to offer a positive contrast between bone marrow and ligament gaps. Real-time 3D images were reconstructed offline by spatiotemporally constrained reconstruction (STCR) (9), with the regularization parameters empirically chosen to balance the temporal blurring and residual aliasing.

Analysis
From images of the RUD and DT maneuvers, the scapholunate (SL) interval were measured in 3D. Similarly, the distance between the proximal and distal poles of the scaphoid along the volar cortex during the FE maneuver was determined.

Results

Figure 3 shows the central slices of real-time movies of RUD. Figure 4 shows 3D rendering of RUD. Figure 5 shows 3D rendering of DT. The SL interval assessment appeared to be more consistent across the range-of-motion with the DT maneuver (6.05mm versus 6.00mm at the extremas) compared to the RUD maneuver (3.25mm versus 4.37mm at the extremas). The distance between the scaphoid proximal and distal poles was 11.91mm.

Discussion

This work presents a 3D real-time method to capture wrist movements at a frame rate of 10 frames/second. The use of non-selective excitation pulses and a relatively large imaging FOV ensured complete wrist coverage during the full range-of-motion, resolved in three-dimensions. With comprehensive wrist coverage, collected data can be visualized and evaluated in 4D (x,y,z,t), without restriction on maneuvers or range of motion. Intra-articular morphometrics can be assessed from the proposed method. The use of image registration or segmentation could potentially improve the 4D visualization further and may enable motion compensated reconstruction to further allow even higher spatial and temporal resolution. Further study will also evaluate the method in patients with dynamic wrist instability.

Conclusion

Real-Time 3D imaging of the moving wrist is feasible at 0.55T, without movement restriction, and achieving 1.4x1.4x4mm3 spatial and 100ms temporal resolution.

Acknowledgements

We acknowledge research support from Siemens Healthineers, and grant support from the National Institutes of Health (R21 HL159533 and U01 HL167613) and National Science Foundation (Award 1828736).

References

1. Chaudhari AJ, Lim Y, Cui SX, Bayne CO, Szabo RM, Boutin RD, Nayak KS. Real-Time MRI of the Moving Wrist at 0.55 Tesla. British Journal of Radiology; 2023 Nov;96(1151):20230298.

2. Shaw CB, Foster BH, Borgese M, Boutin RD, Bateni C, Boonsri P, et al. Real-time three-dimensional MRI for the assessment of dynamic carpal instability. PLoS One. 2019;14(9):e0222704.

3. Boutin RD, Buonocore MH, Immerman I, Ashwell Z, Sonico GJ, Szabo RM, et al. Real-time magnetic resonance imaging (MRI) during active wrist motion--initial observations. PLoS One. 2013;8(12):e84004.

4. Wilms LM, Radke KL, Abrar DB, Frahm J, Voit D, Thelen S, et al. Dynamic assessment of scapholunate ligament status by real-time magnetic resonance imaging: an exploratory clinical study. Skeletal Radiol. 2023.

5. Leng S, Zhao K, Qu M, An KN, Berger R, McCollough CH. Dynamic CT technique for assessment of wrist joint instabilities. Med Phys. 2011;38 Suppl 1(Suppl 1):S50.

6. Moritomo H, Apergis EP, Herzberg G, Werner FW, Wolfe SW, Garcia-Elias M. 2007 IFSSH committee report of wrist biomechanics committee: biomechanics of the so-called dart-throwing motion of the wrist. J Hand Surg Am. 2007;32(9):1447-53.

7. Campbell-Washburn AE, Ramasawmy R, Restivo MC, Bhattacharya I, Basar B, Herzka DA, et al. Opportunities in Interventional and Diagnostic Imaging by Using High-Performance Low-Field-Strength MRI. Radiology. 2019;293(2):384-93.

8. Guenthner C, Peereboom SM, Dillinger H, McGrath C, Albannay MM, Vishnevskiy V, et al. Ramping down a clinical 3 T scanner: a journey into MRI and MRS at 0.75 T. MAGMA. 2023.

9. Adluru G, McGann C, Speier P, Kholmovski EG, Shaaban A, Dibella EV. Acquisition and reconstruction of undersampled radial data for myocardial perfusion magnetic resonance imaging. J Magn Reson Imaging. 2009;29(2):466-73.

Figures

Figure 1. Sampling pattern. The data acquisition is a 3D stack-of-spiral with golden angle kx-ky rotation and kz undersampling. (a) Kx-ky variable density spiral trajectory. The trajectory rotates by 222.5o every 12 TRs. (b) Kz sampling pattern. For each 12 TRs, the kz partition starts form one edge of the k-space and goes to the other edge, with 2x undersampling in the peripheral k-space and fully sampling in the center of k-space. The undersampling pattern has an interleaved pattern between adjacent 12 TRs. (c) Kx-ky spiral initial rotation angle.

Figure 2. Coil setups. We used two body-6 coils to acquire data with different setups to allow for different movements. In both setups, the coils or hand were supported to allow the wrist being placed at the magnet iso-center for best image quality. (a) coil setup for RUD and FE manuvers. One body-6 (bottom) was placed right below the iso-center, and another body-6 (top) was placed ~16 cm above, allowing enough space for movements. (b) coil setup for the DT maneuver. Two body-6 were placed to form a triangular tent shape to allow more flexible movement in the vertical direction.

Figure 3. Selected slices of radial-ulnar maneuver. Real-time 3D images were reconstructed at 100 ms/frame and a voxel size of 0.7x0.7x1.4 mm3. The center 10 slices covering the scaphoid and lunate are shown. The interaction between the carpal bones as well as the ligaments movements are clearly depicted. With a complete 4D coverage, the through-plane motion is also fully captured, allowing 3D reformatting to visualize the motion in an arbitrary angle (not shown). Video is displayed with a 5x acceleration.

Figure 4. Dynamic volume rendering of radial-ulnar maneuver. Video shows the dynamic visualizations of the radial-ulnar maneuver from the superior and the left side viewpoints. The video also shows volume cut-through views that better reveal the carpal bones movements inside the wrist. The volumetric rendering of dynamic data is made possible by the efficient 3D stack-of-spiral data acquisition, which fully displays the wrist movement in real-time. Note that the video quality is compromised due to high compression.

Figure 5. Dynamic volume rendering of dart-throw maneuver. Video shows the dynamic visualizations of the dart-throw maneuver from the right side and the superior viewpoints. The draft-throw maneuver has been found to be clinically meaningful in assessing wrist pathology. The efficient stack-of-spiral acquisition used in this study can fully capture the 3D motion in the draft-throw maneuver in real-time, and in combination with other maneuvers it is possible to offer an improved evaluation of wrist instability resulting from ligament injuries.

Proc. Intl. Soc. Mag. Reson. Med. 32 (2024)
0767
DOI: https://doi.org/10.58530/2024/0767