Usefulness of metal artifact reduction with WARP technique at 1.5 and 3T MRI in imaging metal-on-metal hip resurfacings

Abstract

WARP proved useful in imaging metal-on-metal hip resurfacings at 1.5T as well as 3T with better image quality surrounding the implants. At 3T imaging could be considerably accelerated without losing diagnostic quality.

Advances in MRI around metal

“…However, unless the field inhomogeneities are very mild, artifact size is smaller and artifact reduction is more effective at 1.5T; therefore, overall image quality in patients with metal implants is superior at 1.5T (Fig. ) . By applying these advanced techniques in clinical practice, a sufficient in‐plane and through‐plane metal artifact reduction is achieved for most types of modern metal implants.…”

7-T clinical MRI of the shoulder in patients with suspected lesions of the rotator cuff

“…Image quality was assessed in consensus by two radiologists separately for each patient and each sequence using Likert scales [23][24][25]. For this issue, the presence of artifacts was rated on a 5-point scale: score 5 = excellent image quality without any artifacts; score 4 = very good image quality with hardly definable artifacts/artifacts out of region of interest (i.e., pulmonary); score 3 = few artifacts without affection of diagnostic image quality; score 2 = moderate artifacts with affection of diagnostic image quality/overall reduced signal-to-noise ratio; score 1 = severe artifacts with non-diagnostic image quality.…”

Magnetic resonance imaging of the knee: An overview and update of conventional and state of the art imaging

“…The WARP package (Fig. b) available on some scanners combines high bandwidth parameters with VAT . Slice encoding for metal artifact correction (SEMAC) is a package available on some scanners, which adds phase‐encoding steps to the slice selection direction to decrease artifact in the through‐plane direction, which can be combined with the ability of VAT to decrease displacement of the in‐plane dimension .…”

“…40 The larger gradient amplitude associated with higher readout bandwidth reduces spatial distortion, by reducing the relative size of the metal-induced magnetic field gradients, while the shorter data sampling time enabled by the larger gradient amplitude reduces signal loss due to intravoxel dephasing in the presence of these background gradients. Factors that decrease voxel size such as either increasing the matrix, decreasing slice thickness, or decreasing the field of view will also reduce artifact by reducing intravoxel signal dephasing, 41,42 albeit at the cost of decreased signalto-noise ratio (SNR). Increasing the echo train length will also reduce metal artifact, albeit at the expense of lower SNR and image blurring.…”

“…6b) available on some scanners combines high bandwidth parameters with VAT. 42 Slice encoding for metal artifact correction (SEMAC) is a package available on some scanners, 43 which adds phaseencoding steps to the slice selection direction to decrease artifact in the through-plane direction, which can be combined with the ability of VAT to decrease displacement of the in-plane dimension. 39 The multiacquisition variableresonance image combination (MAVRIC) package available on some machines 43 uses spectrally overlapping 3D acquisitions to decrease the encoding errors typically seen with metal artifact.…”