Minimizing artifacts caused by metallic implants at MR imaging: experimental and clinical studies.

Abstract

OBJECTIVE. The purpose ofthis studywasto investigate theeffectof metallicimplantposi tioning on MR imaging artifacts, to determine the optimal imaging conditions for minimizing ar tifacts, and to show the usefulness of artifact-minimizing methods in imaging of the knee.MATERIALS AND METHODS. Using MR imagesof experimentalphantoms(tita nium alloy and stainless steel screws), we compared the magnitude of metal-induced artifacts for various pulse sequences, different imaging parameters for the fast spin-echo sequence, and different imaging parameters for several incremental angles between the long axis of the screw and the direction of the main magnetic field. In clinical MR imaging of knees with me tallic implants (n = 19), we assessed geometric distortion of anatomic structures to compare the influence of different pulse sequences (n = 19), frequency-encoding directions (n = 7), and knee positions (n = 15).RESULTS. Titanium alloy screwsconsistentlyproducedsmallerartifactsthan did stain less steel screws. In experimental MR studies, artifacts were reduced with fast spin-echo Se quences, with a screw orientation as closely parallel to the main magnetic field as possible, and, particularly. with smaller voxels that correlated positively with artifact size (R2 = .88, p < .01). In clinical MR studies, fast spin-echo MR imaging obscured articular structures less than did spin-echo imaging (8/19 patients). In particular, the anteriorâ€"posterior frequency-encod ing direction (3/7 patients) and the flexion position of the knee (5/15 patients) were effective in reducing artifacts. CONCLUSION.MR artifactscan be minimizedby optimally positioningin the magnet subjects with metallic implants and by choosing fast spin-echo sequences with an anterior posteriorfrequency-encoding directionandthe smallestvoxel size.

MRI Predicts ALVAL and Tissue Damage in Metal-on-Metal Hip Arthroplasty

“…Two-dimensional fast spin echo (FSE) images were obtained in three planes using modifications to the pulse parameters to reduce susceptibility artifact. A wider receiver bandwidth and oversampling in the frequency encoding axis were used to increase the strength of the readout gradient [29]; the voxel size was reduced, thereby improving spatial resolution; and the number of signals averaged was increased to increase the signal-to-noise ratio [12]. Multiacquisition variable-resonance image combination (MAVRIC) was used in the coronal plane to reduce susceptibility artifact by combining multiple data sets acquired at frequency bands offset from the center proton frequency [12] (Fig.…”

Magnetic resonance imaging of the postoperative hip

“…Technical options available on most MR units to reduce magnetic susceptibility include use of a wider receiver bandwidth, thereby increasing the strength of the readout gradient (16,17). Orienting the frequency-encoding direction along the longitudinal axis of the prosthesis will further subjectively minimize the susceptibility artifact from the surrounding anatomy (14).…”

“…Orienting the frequency-encoding direction along the longitudinal axis of the prosthesis will further subjectively minimize the susceptibility artifact from the surrounding anatomy (14). Decreasing voxel size improves spatial resolution, helping to better define the interface between the arthroplasty and surrounding structures (17). Increasing the number of excitations will increase the scan time, but will also increase image signal-to-noise ratio (SNR).…”

Magnetic resonance imaging and gynecological devices

“…As far as the image is concerned, it can be identified as a hypointensity of focal signal, surrounded by a hyperintense halo, which can be associated to several levels of distortion in the surrounding tissue [5]. The size and shape of the artifact depend on the size, shape, orientation and nature of the metal, as well as the sequences used in the exam [6]. The artifact created by a ferromagnetic object is larger than that originated by a nonferromagnetic object [7] -the stronger the ferromagnetic nature of the object, the more intense the registered signal will be.…”

“…The artifact created by a ferromagnetic object is larger than that originated by a nonferromagnetic object [7] -the stronger the ferromagnetic nature of the object, the more intense the registered signal will be. Technically speaking, magnetic susceptibility artifacts are more prominent in gradient-echo and echoplanar sequences, and we may try to reduce them using a smaller voxel, shorter echo time, or larger bandwidth or even performing the exam with equipment featuring a lower-intensity magnetic field [6].…”