SEMAC-VAT MR Imaging Unravels Peri-instrumentation Lesions in Patients With Attendant Symptoms After Spinal Surgery

Abstract

The study aimed for evaluating the diagnostic value of a 2D Turbo Spin Echo (TSE) magnetic resonance (MR) imaging sequence implanted slice-encoding metal artifact correction (SEMAC) and view-angle tilting (VAT) in patients with spinal instrumentation.Sixty-seven consecutive patients with an average age of 59.7 ± 17.8 years old (range: 32–75 years) were enrolled in this study. Both sagittal, axial T1-weighted and T2-weighted MRI images were acquired with a standard TSE sequence and a high-bandwidth TSE sequence implemented the SEMAC and VAT techniques. Three continuous sections around the instrumentation in axial and sagittal images were selected for quantitative evaluation. The measurement included cumulative areas of signal void on axial images and the length of spinal canal obscuration on sagittal images. Three radiologists independently evaluated all images blindly. The inter-observer reliability was evaluated with inter-class coefficient. We defined patients with discomfortable symptoms caused by spinal instrumentation as spinal instrumentation adverse reaction.Visualizations of all periprosthetic anatomic structures were significantly better for SEMAC-VAT compared with standard imaging. For axial images, the area of signal void at the level of the instrumentation were statistically reduced with SEMAC-VAT TSE sequences than with standard TSE sequences for T2-weighted images (9.9 ± 2.6 cm2 vs 29.8 ± 14.7 cm2, P < 0.001). For sagittal imaging, the length of spinal canal obscuration at the level of the instrumentation was reduced from 5.2 ± 2.0 cm to 1.2 ± 0.6 cm on T2-weighted images (P < 0.001), and from 4.8 ± 2.1 cm to 1.1 ± 0.5 cm on T1-weighted images with SEMAC-VAT sequences (P < 0.001). Interobserver agreement for visualization of anatomic structures and image quality was good for both SEMAC-VAT (k = 0.77 and 0.68, respectively) and standard (k = 0.74 and 0.80, respectively) imaging. The number of abnormal findings noted on SEMAC images (59 findings) was significantly higher than detected on standard images (40 findings). The incidence rate of spinal instrumentation adverse reaction was 38.81%.MR images with SEMAC-VAT can significantly reduce metal artifacts for spinal instrumentation and improve delineation of the instrumentation and periprosthetic region. Furthermore, SEMAC-VAT technique can improve diagnostic accuracy in patients with post-instrumentation spinal diseases.

Advances in MRI around metal

“…For metal artifact reduced imaging of the spine, the frequency‐encoding direction should be positioned along the long axis of the pedicle screws in sagittal and transverse images (anterior–posterior) . The utility of SEMAC for artifact reduction in spine imaging has been demonstrated in several studies . SEMAC sequences enabled significantly improved periprosthetic visualization of the pedicles, vertebral body, dural sac, and neural foramina .…”

“…New carbon stabilization systems produce fewer artifacts on CT and MRI. Besides the aforementioned complications, typical clinical queries are postoperative intradural or epidural hematoma, abscess or tumor, spondylodiscitis, neuroforaminal stenosis, disc protrusion, or myelopathy …”

Basic and Advanced Metal-Artifact Reduction Techniques at Ultra-High Field 7-T Magnetic Resonance Imaging—Phantom Study Investigating Feasibility and Efficacy

“…All pulse sequences in our study setup completed scanning without failure on the ultra-high field MRI scanner, proving the technical feasibility of applying the well-known methods of metal-artifact reduction—both basic sequence optimizations (eg, increasing the receive bandwidth) and advanced techniques (ie, VAT and SEMAC) 7 . At lower field strengths (≤3-T MRI), the value of these techniques in artifact reduction around metal has been widely investigated and proven 7,18,22,27,38,42,45–48 . One recent experimental study quantified metal-induced artifacts around various implants at 7-T MRI for 3-dimensional sequences, zero echo time sequences, and diffusion weighted imaging.…”

3D MRI of the Spine

“…53 They have been most extensively studied in the evaluation of joint replacements, but some investigations were performed using these sequences in the postoperative spine. [52][53][54][55] SEMAC T1-weighted and STIR sequences significantly decreased susceptibility artifact with improved visualization of bone lesions, nerve root compression, soft tissue edema, and periprosthetic osteolysis compared with equivalent high-bandwidth 2D sequences in postoperative spine patients at 3 T. 54 Studies examining SEMAC sequences in patients with spinal instrumentation showed that periprosthetic anatomy was better demonstrated and postoperative complications were visualized more often 56 or with greater confidence. 57 A study evaluating a MAVRIC variant at 3 T showed L5 nerve root impingement, where conventional sequences did not, in a patient with foot drop following internal fixation of a pelvic fracture.…”