Evaluation of metal artifacts in clinical MR images of patients with total hip arthroplasty using different metal artifact-reducing sequences.

PURPOSE: To evaluate the distortion and artifact area of metal in MR images and to compare artifact reduction using different metal artifact-reducing sequences in patients with metal-on-metal (MoM) and non-MoM total hip prostheses. MATERIALS AND METHODS: Thirty-six MoM and 15 non-MoM prostheses were examined in a 1.5-T MR scanner using T1-weighted (T1-w) sequences: turbo spin echo (TSE) high-readout bandwidth (hiBW), T1-w; TSE view angle tilting (VAT), T1-w; TSE VAT + slice encoding for metal artifact correction (SEMAC); short tau inversion recovery (STIR) hiBW or matched RF pulses (mRFp). Distortion was quantified using a new method measuring the acetabular roof angle (ARA). The artifact area was defined in the mid-coronal plane of the artifact. RESULTS: The T1 VAT + SEMAC sequence showed the least distortion compared to T1 VAT and T1-hiBW (150°, 127° and 102°, p < 0.001, in MoM; 152°, 143° and 128°, p ≤ 0.014, in non-MoM). The artifact area was smaller in MoM prostheses using the T1 VAT sequence compared to T1 hiBW and T1 VAT + SEMAC (2506 mm(2), 3160 mm(2) and 3214 mm(2), p < 0.001) and smaller in non-MoM prostheses using T1 VAT compared to T1-hiBW (4296 mm(2) and 4831 mm(2), p = 0.041). STIR-mRFp substantially reduced the artifact size compared with STIR-hiBW (MoM 4559 mm(2) and 6323 mm(2); non-MoM 5625 mm(2) and 8764 mm(2), p < 0.001). CONCLUSION: Metal artifacts in MR imaging examinations of hip prostheses can be evaluated for distortion using a distortion angle (ARA) and the degree of signal artifact as determined by measuring the largest cross-sectional artifact area. T1 VAT + SEMAC showed the least distortion; T1 VAT and STIR-mRFp were most efficient for reduction of the artifact area.

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.

OBJECTIVE: 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. MATERIALS AND METHODS: Fifty-two MoM prostheses (35 cases with pain and or risk factors, and 17 controls) in 47 patients were examined in a 1.5-T MR scanner using MARS: turbo spin echo (TSE) with high readout bandwidth with and without view angle tilting (VAT), TSE with VAT and slice encoding for metal artifact correction (SEMAC), short tau inversion recovery (STIR) with matched RF pulses, and post-contrast imaging. The relations of MRI findings to pain and risk factors were analyzed and in five revised hips findings from operation, histology, and MRI were compared. RESULTS: TSE VAT detected the highest number of osteolyses. Soft tissue mass, effusion, and capsular thickening were common, whereas osteolysis in acetabulum and femur were less frequent. Contrast enhancement occurred in bone, synovia, joint capsule, and the periphery of soft tissue mass. There was no significant relation between MRI findings and pain or risk factors. CONCLUSIONS: MARS and gadolinium subtraction imaging are useful for evaluation of complications to MoM prosthesis. TSE VAT had the highest sensitivity for osteolysis. Contrast enhancement might indicate activation of aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL). Pain, small head, or steep prosthesis inclination angle are not useful predictors of periprosthetic abnormalities, and wide indications for MR follow-up are warranted.

Assessment of perfusion in normal carpal bones with dynamic gadolinium-enhanced MRI at 3 Tesla.

PURPOSE: To investigate the normal enhancement patterns of the scaphoid, lunate, and capitate bones with dynamic contrast-enhanced magnetic resonance imaging (MRI). MATERIALS AND METHODS: The study was approved by the hospital's Ethics Committee. Nineteen volunteers (13 female, 6 male; mean age 38 years) were examined and all gave written consent. Perfusion was assessed at 3 Tesla using dynamic contrast-enhanced MRI. After two-dimensional (2D) motion correction of the data set, regions of interest were placed in the capitate, lunate, and distal and proximal pole of scaphoid bone and from the mean signal intensities (SI), the enhancement was computed. The four locations were compared for time to peak, delay time, maximum enhancement, and maximum slope using Friedman's two-way analysis of variance. RESULTS: Typical SI versus time curves revealed two components: a faster component with strong contrast enhancement and a slow component with prolonged enhancement. The mean value (standard deviation, SD) for maximum enhancement was 51 (33)% in the capitate, 54 (25)% in the lunate, 51 (34)% in the proximal pole and 51 (28)% in the distal pole of the scaphoid. The result of the Friedman test showed no significant difference (P < 0.05) in the perfusion variables between the capitate, lunate, and distal and proximal scaphoid bones. CONCLUSION: Assessment of perfusion in normal carpal bone using contrast-enhanced MRI is possible. Optimization of the method and understanding of the normal perfusion may allow evaluation of pathological conditions such as osteonecrosis.

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

PURPOSE: 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. METHODS: Three hip prostheses of cobalt-chromium, stainless steel, and titanium were embedded in agarose gel together with a rectilinear grid. Coronal MR images of the prostheses were acquired on a 1.5T scanner. Three pulse sequences were evaluated; TSE: a high-bandwidth turbo spin echo; VAT: TSE with view angle tilting, SEMAC: TSE with both VAT and slice distortion correction (6, 10 or 16 z-phase-encoding steps). Through-plane distortions were assessed as the length of visible gridlines, in-plane artifacts as the artifact area, and total artifacts by subtraction of an ideal, undistorted image from the actual image. RESULTS: VAT reduced in-plane artifacts by up to 50% compared to TSE, but did not reduce through-plane artifacts. SEMAC reduced through-plane artifacts by 60-80% compared to TSE and VAT. SEMAC in-plane artifacts were from 20% higher (6 encoding steps) to 50% lower (16 steps) than VAT. Total artifacts were reduced by 60-80% in the best sequence (SEMAC, 16 steps) compared to the worst (TSE). The titanium prosthesis produced 3-4 times lower artifact scores than the other prostheses. CONCLUSIONS: A rectilinear grid phantom is useful for qualitative and quantitative evaluation of artifacts provoked by different MRI protocols and prosthesis models. VAT and SEMAC were superior to TSE with high bandwidth. A proper number of z-encoding steps in SEMAC was critical. The titanium prosthesis caused least artifacts.