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

Abstract

Objectives: The aim of this study was to demonstrate the feasibility and efficacy of basic (increased receive bandwidth) and advanced (view-angle tilting [VAT] and slice-encoding for metal artifact correction [SEMAC]) techniques for metalartifact reduction in ultra-high field 7-T magnetic resonance imaging (MRI). Materials and Methods: In this experimental study, we performed 7-T MRI of titanium alloy phantom models composed of a spinal pedicle screw (phantom 1) and an intervertebral cage (phantom 2) centered in a rectangular LEGO frame, embedded in deionized-water-gadolinium (0.1 mmol/L) solution. The following turbo spin-echo sequences were acquired: (1) nonoptimized standard sequence;(2) optimized, that is, increased receive bandwidth sequence (oBW); (3) VAT; (4) combination of oBW and VAT (oBW-VAT); and (5) SEMAC. Two fellowshiptrained musculoskeletal radiologists independently evaluated images regarding peri-implant signal void and geometric distortion (a, angle measurement and b, presence of circular shape loss). Statistics included Friedman test and Cochran Q test with Bonferroni correction for multiple comparisons. P values <0.05 were considered to represent statistical significance. Results: All metal-artifact reduction techniques reduced peri-implant signal voids and diminished geometric distortions, with oBW-VAT and SEMAC being most efficient. Compared with nonoptimized sequences, oBW-VAT and SEMAC produced significantly smaller peri-implant signal voids (all P ≤ 0.008) and significantly smaller distortion angles ( P ≤ 0.001). Only SEMAC could significantly reduce distortions of circular shapes in the peri-implant frame ( P ≤ 0.006). Notably, increasing the number of slice-encoding steps in SEMAC sequences did not lead to a significantly better metal-artifact reduction (all P ≥ 0.257). Conclusions: The use of basic and advanced methods for metal-artifact reduction at 7-T MRI is feasible and effective. Both a combination of increased receive bandwidth and VAT as well as SEMAC significantly reduce the peri-implant signal void and geometric distortion around metal implants.

7 T Musculoskeletal MRI

“…22,23 Recent advances in metal-artifact reduction at ultra-high-field strength have also made it possible to reduce peri-implant signal voids and geometric distortions in the presence of metal with a combination of increased receive bandwidth, view-angle tilting, as well as slice-encoding for metal artifact correction. 24 The extent of metal artifacts is directly proportional to the field strength. 25 Therefore, metal artifact techniques at 7 T MRI will help obtain a homogeneous signal intensity in patients undergoing 7 T MRI, for example, after ACL or tendon reconstructions.…”

Metal artifact reduction around cervical spine implant using diffusion tensor imaging at 3T: A phantom study

“…However, the limitations of DTI have been demonstrated in providing post-surgery information 4 . High-intensity geometric distortions arise due to the presence of metal in the imaging plane or in the adjacent plane, also known respectively as in-plane and through-plane artifacts 13,21 . It has been shown that the size and the intensity of metal-induced artifacts increase with magnetic eld strength and employed pulse sequence parameters such as the echo spacing and the receiver bandwidth 22 .…”

“…Even with these new improvements, postsurgical metallic implants typically induce dramatic magnetic eld inhomogeneities, leading to severe image distortions. The metal-induced artifact depends on the implant hardware (material, size, shape), the magnetic eld B0 strength, and MRI sequence 13 . Moreover, DTI is often performed using the single-shot Echo Planar Imaging pulse sequence (SS-EPI) due to its fast acquisition speed.…”

Assessment of a Functional Electromagnetic Compatibility Analysis of Near-Body Medical Devices Subject to Electromagnetic Field Perturbation

“…Living tissues can also diminish the image quality due to susceptibility discrepancies, such as those between soft tissues and air holes in the brain. Moreover, embedded matters within the body such as prostheses and particularly metallic ones can also weaken image quality [34][35][36][37][38][39][40]. The image modification due to metallic materials, which present susceptibility variations, depends on the size, the shape and the direction with respect to B 1 [27,29,33].…”