Phantom based qualitative and quantitative evaluation of artifacts in MR images of metallic hip prostheses.

To develop methods for qualitative and quantitative evaluation of MRI artifacts near metallic prostheses, and to compare the efficiency of different artifact suppression techniques with different types of hip prostheses

Comparisons of slice-encoding metal artifact correction and view-angle tilting magnetic resonance imaging and traditional digital radiography in evaluating chronic hip pain after total hip arthroplasty

Purpose: The aims of this study were (1) to compare the areas of metal-induced artifacts and definition of periprosthetic structures between patients scanned with the slice-encoding metal artifact correction and view-angle tilting (SEMAC-VAT) turbo-spin-echo (TSE) prototype and those scanned with the standard TSE magnetic resonance (MR) sequences and (2) to further clarify the superiority of the SEMAC-VAT MR imaging technique at detecting lesions in patients after total hip arthroplasty (THA), compared with digital radiography (DR). Materials and methods: A total of 38 consecutive patients who underwent THA were referred to MR imaging at our institution. All patients suffered from chronic hip pain postoperatively. Twenty-three patients of the 38 were examined with a 1.5-T MR scanner using a SEMAC-VAT TSE prototype and standard TSE sequence, and the remaining 15 patients were examined with the same 1.5-T MR scanner, but using the SEMAC-VAT TSE prototype only. The traditional DR imaging was also performed for all patients. Two radiologists then independently measured the area of metal-induced artifacts and evaluated the definition of both the acetabular and femoral zones based on a three-point scale. Finally, the positive findings of chronic hip pain after THA based on SEMAC-VAT TSE MR imaging and traditional DR imaging were compared and analysed. Results: The areas of metal-induced artifacts were significantly smaller in the SEMAC-VAT TSE sequences than those in the standard TSE sequences for both the T1-weighted (p < 0.001) and T2-weighted (p < 0.001) turbo inversion recovery magnitude images. In addition, 28 patients showed a series of positive signs in the SEMAC-VAT images that were not observed in the traditional DR images. Conclusion: Compared with the standard TSE MR imaging, SEMAC-VAT MR imaging significantly reduces metal-induced artifacts and might successfully detect most positive signs missed in the traditional DR images. Translational potential of this article: The main objective of this research was to show that MR sequences from the SEMAC-VAT TSE prototype provide a significant advantage at detecting lesions in patients after THA because of the excellent soft-tissue resolution of the MR imaging. SEMAC-VAT MR can evaluate chronic hip pain after THA and determine the cause, which can help the clinician decide on whether a surgical revision is needed

Reduction of Metal Artifacts in Patients with Total Hip Arthroplasty with Slice-encoding Metal Artifact Correction and View-Angle Tilting MR Imaging

Purpose: To compare the new "warp" sequence (slice-encoding metal artifact correction [SEMAC], view-angle tilting [VAT], and increased bandwidth) for the reduction of both through-plane and in-plane magnetic resonance (MR) artifacts with current optimized MR sequences in patients with total hip arthroplasty (THA). Materials and Methods: The institutional review board issued a waiver for this study. Forty patients with THA were prospectively included. SEMAC, VAT, and increased bandwidth were applied by using the warp turbo-spin-echo sequence at 1.5 T. Coronal short tau inversion-recovery (STIR)-warp and transverse T1-weighted warp (hereafter, T1-warp) images, as well as standard coronal STIR and transverse T1-weighted sequence images optimized with high bandwidth (STIR-hiBW and T1-hiBW), were acquired. Fifteen additional patients were examined to compare the T1-warp and T1-hiBW sequence with an identical matrix size. Signal void was quantified. Qualitative criteria (distinction of anatomic structures, blurring, and noise) were assessed on a five-point scale (1, no artifacts; 5, not visible due to severe artifacts) by two readers. Abnormal imaging findings were recorded. Quantitative data were analyzed with a t test and qualitative data with a Wilcoxon signed rank test. Results: Signal void around the acetabular component was smaller for STIR-warp than STIR-hiBW images (21.6 cm(2) vs 42.4 cm(2); P = .0001), and for T1-warp than T1-hiBW images (17.6 cm(2) vs 20.2 cm(2); P = .0001). Anatomic distinction was better on STIR-warp compared with STIR-hiBW images (1.9-2.8 vs 3.6-4.6; P = .0001), and on T1-warp compared with T1-hiBW images (1.3-2.8 vs 1.8-3.2; P < .002). Distortion, blurring, and noise were lower with warp sequences than with the standard sequences (P = .0001). Almost half of the abnormal imaging findings were missed on STIR-hiBW compared with STIR-warp images (55 vs 105 findings; P = .0001), while T1-hiBW was similar to T1-warp imaging (50 vs 55 findings; P = .06). Conclusion: STIR-warp and T1-warp sequences were significantly better according to quantitative and qualitative image criteria, but a clinically relevant artifact reduction was only present for STIR images. © RSNA, 2012

Knee implant imaging at 3 Tesla using high-bandwidth radiofrequency pulses

BACKGROUND: To investigate the impact of high-bandwidth radiofrequency (RF) pulses used in turbo spin echo (TSE) sequences or combined with slice encoding for metal artifact correction (SEMAC) on artifact reduction at 3 Tesla in the knee in the presence of metal. METHODS: Local transmit/receive coils feature increased maximum B1 amplitude, reduced SAR exposition and thus enable the application of high-bandwidth RF pulses. Susceptibility-induced through-plane distortion scales inversely with the RF bandwidth and the view angle, hence blurring, increases for higher RF bandwidths, when SEMAC is used. These effects were assessed for a phantom containing a total knee arthroplasty. TSE and SEMAC sequences with conventional and high RF bandwidths and different contrasts were tested on eight patients with different types of implants. To realize scan times of 7 to 9 min, SEMAC was always applied with eight slice-encoding steps and distortion was rated by two radiologists. RESULTS: A local transmit/receive knee coil enables the use of an RF bandwidth of 4 kHz compared with 850 Hz in conventional sequences. Phantom scans confirm the relation of RF bandwidth and through-plane distortion, which can be reduced up to 79%, and demonstrate the increased blurring for high-bandwidth RF pulses. In average, artifacts in this RF mode are rated hardly visible for patients with joint arthroplasties, when eight SEMAC slice-encoding steps are applied, and for patients with titanium fixtures, when TSE is used. CONCLUSION: The application of high-bandwidth RF pulses by local transmit coils substantially reduces through-plane distortion artifacts at 3 Tesla. J. Magn. Reson. Imaging 2014

3-T MRI implant safety: heat induction with new dual-channel radiofrequency transmission technology

We aimed to investigate whether different transmission settings of the dual-transmit technology may influence the amount of heat induction around an implant material dependent on its location within the magnetic field. Metallic hip implants were positioned in the magnet of a 3-T scanner at various lateral offset positions in relation to the magnetic axis in a body-phantom tank filled with polyacrylic acid gel. The temperature increase close to the implants was measured during turbo spin-echo scanning using dual-channel parallel radiofrequency (RF) transmission with circular in comparison to elliptic RF polarization. Circularly polarized transmission (CPT) induced higher temperature increases (maximum 6.2 °C) than elliptically polarized transmission (EPT) (maximum 1.5 °C). The heat induction was dependent on the distance to the isocenter with increased heating by increased distance to the isocenter. EPT showed lower heating around implants compared to the CPT as commonly used in single-transmission system; further, less heating was observed for both transmission settings closer to the magnet isocenter

MR imaging with metal artifact-reducing sequences and gadolinium contrast agent in a case-control study of periprosthetic abnormalities in patients with metal-on-metal hip prostheses.

To apply and compare magnetic resonance imaging (MRI) metal artifact reducing sequences (MARS) including subtraction imaging after contrast application in patients with metal-on-metal (MoM) hip prostheses, investigate the prevalence and characteristics of periprosthetic abnormalities, as well as their relation with pain and risk factors

STIR sequence with increased receiver bandwidth of the inversion pulse for reduction of metallic artifacts

OBJECTIVE: The purpose of this study was to evaluate a STIR sequence with an optimized inversion pulse that entails use of increased receiver bandwidth for metal artifact reduction. CONCLUSION: Image distortion, artifacts, insufficient fat suppression, and detection of relevant findings improved with the STIR optimized inversion pulse, which was associated with significant artifact reduction