Spine. Volume 35(2), 15 January 2010, pp 252-256

Minimizing Ferromagnetic Artifact With Metallic Lumbar Total Disc Arthroplasty Devices at Adjacent Segments: Technical Note

Marshman, Laurence A. G. MD, FRCSN*; Strong, Graeme BSc, PgDip†; Trewhella, Matthew FRCR‡; Kasis, Ata MRCS*; Friesem, Tai MD*. From the Departments of *Spinal Surgery, †Magnetic Resonance Imaging, and ‡Radiology, University Hospital of North Tees, Hardwick, Stockton. © 2010 Lippincott Williams & Wilkins, Inc.

Study Design. Technical report.

Objective. To minimize the gross artifact associated with a conventional metallic lumbar total disc arthroplasty (TDA) device on a conventional high field-strength (1.5 Tesla [T]) magnetic resonance imaging (MRI) scanner.

Summary of Background Data. Gross artifact is often apparent with ferromagnetic metallic TDA devices on conventional high field-strength MRI scanners. Such artefact completely obliterates MRI assessment at the operated level, and usually obscures visualization of adjacent segments. Because adjacent segment preservation is a raison d'être of spinal TDA, clarity of imaging at this latter level is imperative. A failure to image adjacent segments may presage investigations, which are either invasive (e.g., myelography) or associated with significant radiation hazard (e.g., computed tomography), both with significantly less diagnostic sensitivity. This could negatively direct TDA choice with certain TDAs.

Methods. Progressive modifications to specific imaging parameter settings were sought on a conventional high field-strength (1.5T) closed-bore scanner to match the minimal artefact previously observed on a lower field-strength (0.3T) open scanner. Direct comparisons were made between each modified protocol image obtained initially using a phantom; however, routine postoperative MRIs were subsequently obtained in n = 40 patients following lumbar TDA insertion.

Results. Key parameter modifications were required in the receive bandwidth, the strength of the frequency encoding gradient, as well as in the echo train length. The use of higher specification “focused gradients” was also avoided. The overall effect was to reduce the slew rate of the gradients, which limited artefact due to a decrease in phase dispersion. Such appearances effectively matched with those previously obtained on the low field-strength (0.3T) open scanner in n = 40 patients.

Conclusion. Relatively simple modifications to MRI parameter settings can be made on conventional high field-strength (1.5T) closed-bore scanners, which minimize metal artifact and enhance imaging of adjacent segments with ferromagnetic TDA devices. Such modifications effectively match appearances to those obtained with outmoded low field-strength (0.3T) open-bore scanners.

total disc arthroplasty ferromagnetic artifact