Abstract
Reports on spinal‐implant metallic artifacts in 7‐T magnetic resonance imaging (MRI) are lacking. Thus, we investigated the magnitude of metal artifacts derived from spinal implants in 7‐T MRI and analyzed the differences obtained with spinal rods manufactured from pure titanium, titanium alloy, and cobalt‐chrome (5.5‐mm and 6.0‐mm diameters and 50‐mm length). Following the American Society for Testing and Materials guidelines, we measured the artifact size and artifact volume ratio of each rod during image acquisition using 7‐T MRI scanners with three‐dimensional (3D) T1‐weighted and 3D T2* spoiled gradient echo (GRE), 3D T2‐weighted fast spin echo, zero echo time (ZTE), and diffusion‐weighted imaging sequences. Pure titanium and titanium alloy rods yielded significantly smaller artifacts than did cobalt‐chrome rods, with no significant difference between pure titanium and titanium alloy rods. The artifact sizes of the 5.5‐mm and 6.0‐mm diameter rods were similar. The artifact magnitude increased in the following sequence order: ZTE, 3D T2 fast spin echo, 3D T1 spoiled GRE, 3D T2* spoiled GRE, and diffusion‐weighted imaging. Artifacts obtained using the spin echo method were smaller than those obtained with the GRE method. Because the echo time in ZTE is extremely short, the occurrence of artifacts because of image distortion and signal loss caused by differences in magnetic susceptibility is minimal, resulting in the smallest artifacts. ZTE can be a clinically useful method for the postoperative evaluation of patients after instrumentation surgery, even with 7‐T MRI.
Highlights
We investigated whether the displacement forces caused by a static magnetic field and the heating induced by radiofrequency (RF) radiation are substantial for spinal implants in a 7-T field and reported on its safety[3] in accordance with the American Society for Testing and Materials (ASTM), which sets magnetic resonance imaging (MRI) compatibility standards.[4]
diffusion-weighted SEplanar imaging (DWI) did not yield accurate measurements of the artifact area because the artifact area exceeded the measurable range in all rods
This is because artifacts differ in shape with respect to the static magnetic field direction, as previously reported for imaging of stents using 1.5-T and 3-T MRI17; we propose that the size of artifacts could be attenuated by placing them parallel with respect to the static magnetic field direction, even at 7 T
Summary
Six different metal rods that are frequently used in spinal surgery in clinical practice were examined. The rods were manufactured from 14 cm FIGURE 1 Schematic illustration of the phantom. The container of the phantom is composed of acrylic and is filled with vegetable oil. The container size is 24 × 14 × 12 cm. Each metal implant was placed at the center of a nylon net within the phantom either of three types of metals: pure titanium, a titanium alloy, or cobalt-chrome (CD HORIZON SOLERA Spinal System, Medtronic, Minneapolis, Minnesota), with diameters of 5.5 or 6.0 mm; the length of all rods was 50 mm
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