Optimization of Scan Time in MRI for Total Hip Prostheses: SEMAC Tailoring for Prosthetic Implants Containing Different Types of Metals

Deligianni, Xeni; Bieri, Oliver; Elke, R.; Wischer, Thorsten; Egelhof, Thomas

doi:10.1055/s-0041-104893

Cited by 13 publications

(10 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Standard SEMAC sequences (without CS) had been frequently acquired with 6 to 12 SESs. [7][8][9][36][37][38] Therefore 11,19,and 27 SESs were assessed in this study. More SESs were associated with higher SNR, reduced metal artifacts, and improved imaged quality, but images showed more severe ripple artifacts and had longer acquisition and reconstruction times; 19 SESs were identified to be sufficient for optimal artifact reduction.…”

Section: Discussionmentioning

confidence: 99%

Improved Visualization of Juxtaprosthetic Tissue Using Metal Artifact Reduction Magnetic Resonance Imaging

et al. 2019

View full text Add to dashboard Cite

OBJECTIVES The purpose of this study was to identify an optimal imaging protocol for metal artifact reduced magnetic resonance imaging by application of different imaging and postprocessing parameters in compressed sensing slice-encoding for metal artifact correction (CS-SEMAC) and to test it in patients with total hip arthroplasty (THA). MATERIALS AND METHODS In an experimental setup, a phantom consisting of a standard THA embedded in gadolinium-containing agarose was scanned at 1.5 T. Pulse sequences included coronal short tau inversion recovery (STIR), T1-weighted (w), and T2-w CS-SEMAC sequences. All pulse sequences were acquired with 11, 19, and 27 slice-encoding steps (SESs), respectively. For each raw dataset, postprocessing was performed with variations of the parameters: (1) number of iterations (5, 10, 20, 30, 50) and (2) normalization factor (0.0005, 0.001, 0.002, 0.003, 0.005). Following, in clinical magnetic resonance scans of patients with THA, identical STIR, T1-w, and T2-w pulse sequences with 11 and 19 SESs were acquired and were postprocessed similarly with variations in parameters. Semiquantitative outcome measures were assessed on a 5-point scale (1 = best, 5 = worst). The overall best image quality was determined. Signal-to-noise ratio and contrast-to-noise ratio were calculated. Statistical analyses included descriptive statistics, t-tests, multivariate regression models, and partial Spearman correlations. RESULTS Scan times varied between 2:24 (T2-w, 11 SESs) and 8:49 minutes (STIR, 27 SESs). Reconstruction times varied between 3:14 minutes (T1-w, 11 SESs, 5 iterations) and 85:00 minutes (T2-w, 27 SESs, 50 iterations). Signal-to-noise ratio and contrast-to-noise ratio increased with increasing SESs, iterations, and normalization factor. In phantom scans, artifact reduction was optimal with an intermediate normalization factor (0.001) and improved with higher SESs and iterations. However, iterations greater than 20 did not improve artifact reduction or image quality further. On the contrary, ripple artifacts increased with higher SESs and iterations. In clinical scans, up to 20 iterations reduced blurring of the image; no further reduction was observed with iterations greater than 20. A normalization factor of 0.001 or 0.002 was best for reduction of blurring, whereas the soft tissue contrast was better and the distortion of soft tissue was less severe with lower normalization factors. Overall best soft tissue image quality was found for STIR and T1-w images with 19 SESs, 10 iterations, and a normalization factor of 0.001, and for T2-w images with 11 SESs, 10 iterations, and a normalization factor of 0.0005. CONCLUSIONS Optimized advanced acceleration and reconstruction algorithms of CS-SEMAC have been identified to reduce metal artifacts in patients with THA enabling imaging with clinically feasible acquisition and reconstruction times.

show abstract

Section: Discussionmentioning

confidence: 99%

Improved Visualization of Juxtaprosthetic Tissue Using Metal Artifact Reduction Magnetic Resonance Imaging

et al. 2019

View full text Add to dashboard Cite

show abstract

“…This phantom study systematically evaluated the effectiveness of SEMAC-VAT and MAVRIC for metal artifact reduction at 3 T. The size of various types of artifacts was compared between different prosthetic materials and different contrast weightings. Earlier studies focused on qualitative assessment [21][22][23] or quantitative measurements 18,[24][25][26] of metal artifact reduction with dedicated sequences. To our best knowledge, this is the first study comparing SEMAC-VAT and MAVRIC at 3 T. In line with the literature, artifacts in the present study were most severe in case of SS, followed by CoCr, Ti, and oxZi, 8,[17][18][19] which can be explained with the different magnetic susceptibility of these materials.…”

Section: Discussionmentioning

confidence: 99%

Material-Dependent Implant Artifact Reduction Using SEMAC-VAT and MAVRIC

et al. 2017

View full text Add to dashboard Cite

The aim of this study was to compare the degree of artifact reduction in magnetic resonance imaging achieved with slice encoding for metal artifact correction (SEMAC) in combination with view angle tilting (VAT) and multiacquisition variable resonance image combination (MAVRIC) for standard contrast weightings and different metallic materials. Methods: Four identically shaped rods made of the most commonly used prosthetic materials (stainless steel, SS; titanium, Ti; cobalt-chromium-molybdenum, CoCr; and oxidized zirconium, oxZi) were scanned at 3 T. In addition to conventional fast spin-echo sequences, metal artifact reduction sequences (SEMAC-VAT and MAVRIC) with varying degrees of artifact suppression were applied at different contrast weightings (T1w, T2w, PDw). Two independent readers measured in-plane and through-plane artifacts in a standardized manner. In addition, theoretical frequency-offset and frequency-offset-gradient maps were calculated. Interobserver agreement was assessed using intraclass correlation coefficient. Results: Interobserver agreement was almost perfect (intraclass correlation coefficient, 0.86-0.99). Stainless steel caused the greatest artifacts, followed by CoCr, Ti, and oxZi regardless of the imaging sequence. While for Ti and oxZi rods scanning with weak SEMAC-VAT showed some advantage, for SS and CoCr, higher modes of SEMAC-VAT or MAVRIC were necessary to achieve artifact reduction. MAVRIC achieved better artifact reduction than SEMAC-VAT at the cost of longer acquisition times. Simulations matched well with the apparent geometry of the frequency-offset maps. Conclusions: For Ti and oxZi implants, weak SEMAC-VAT may be preferred as it is faster and produces less artifact than conventional fast spin-echo. Medium or strong SEMAC-VAT or MAVRIC modes are necessary for significant artifact reduction for SS and CoCr implants. Key Points: • The amount of MR artifacts strongly depends on the prosthetic material. • The effectiveness of SEMAC-VAT and MAVRIC depends on the prosthetic material and the contrast weighting. • Stainless steel and cobalt-chromium-molybdenum require higher modes of SEMAC-VAT and MAVRIC compared with titanium or oxidized zirconium.

show abstract

“…The amount of SEMAC steps may be chosen individually for each scan. The larger the area of field inhomogeneities, the more slice‐encoding steps need to be selected . Reducing these steps reduces scan time.…”

Section: Hardware and Pulse Sequencesmentioning

confidence: 99%