Metal-related artifacts in instrumented spine. Techniques for reducing artifacts in CT and MRI: state of the art

Abstract

The projectional nature of radiogram limits its amount of information about the instrumented spine. MRI and CT imaging can be more helpful, using cross-sectional view. However, the presence of metal-related artifacts at both conventional CT and MRI imaging can obscure relevant anatomy and disease. We reviewed the literature about overcoming artifacts from metallic orthopaedic implants at high-field strength MRI imaging and multi-detector CT. The evolution of multichannel CT has made available new techniques that can help minimizing the severe beam-hardening artifacts. The presence of artifacts at CT from metal hardware is related to image reconstruction algorithm (filter), tube current (in mA), X-ray kilovolt peak, pitch, hardware composition, geometry (shape), and location. MRI imaging has been used safely in patients with orthopaedic metallic implants because most of these implants do not have ferromagnetic properties and have been fixed into position. However, on MRI imaging metallic implants may produce geometric distortion, the so-called susceptibility artifact. In conclusion, although 140 kV and high milliamperage second exposures are recommended for imaging patients with hardware, caution should always be exercised, particularly in children, young adults, and patients undergoing multiple examinations. MRI artifacts can be minimized by positioning optimally and correctly the examined anatomy part with metallic implants in the magnet and by choosing fast spin-echo sequences, and in some cases also STIR sequences, with an anterior to posterior frequencyencoding direction and the smallest voxel size.

Three-Dimensional Characterization of Tissue-Engineered Constructs by Contrast-Enhanced Nanofocus Computed Tomography

“…This lower quantification limit was directly related to the artifacts introduced by the metallic scaffolds used in this work. 47 For other scaffold materials, however, it is anticipated that the lower quantification threshold of CE-nano-CT will further decrease, since material-dependent artifacts will be reduced compared to the worst-case scenario described here.…”

Non-invasive biomechanical characterization of intervertebral discs by shear wave ultrasound elastography: a feasibility study

“…The presence of a rigid segment in the column seems to accelerate the natural aging of adjacent intervertebral discs, but in particular if those discs had asymptomatic disc degeneration prior to surgery (Ishihara et al, 2004). Elastography could help detect these discs, especially since it is not affected by artefacts induced by the presence of metal-like implants, as is the case with computerized tomography and magnetic resonance (Stradiotti et al, 2009).…”

CT Provides Precise Size Assessment of Implanted Titanium Alloy Pedicle Screws

“…2 The maximum width measured on a CT scan for a 7-mm screw is shown. purpose but has been shown to produce significant metal artifact when imaging stainless steel implants, making image interpretation difficult [2,14,17,24,26]. Since volume, or size, of implant adversely affects image quality, surgeons can choose to downsize spinal implants trading fixation strength for improved postoperative imaging capability [26,31].…”

“…Since volume, or size, of implant adversely affects image quality, surgeons can choose to downsize spinal implants trading fixation strength for improved postoperative imaging capability [26,31]. Another option is to use titanium implants, which have been shown to produce less bloom artifact [14,26,31]. However, to our knowledge, no study has addressed whether increasing size of titanium implants exhibit similar degradation of postoperative imaging.…”

“…Plain radiographs may show gross screw malposition, but advanced imaging is required to truly verify screw position in three dimensions [1]. Numerous authors have reported significant metal artifact when imaging stainless steel implants with CT or MRI making image interpretation difficult [2,14,17,24,26]. The degree of artifact produced is dependent on the cross-sectional area of the implant imaged.…”