Metal artifact reduction in musculoskeletal magnetic resonance imaging

Modern low-field MRI

This narrative review explores recent advancements and applications of modern low-field (≤ 1 Tesla) magnetic resonance imaging (MRI) in musculoskeletal radiology. Historically, high-field MRI systems (1.5 T and 3 T) have been the standard in clinical practice due to superior image resolution and signal-to-noise ratio. However, recent technological advancements in low-field MRI offer promising avenues for musculoskeletal imaging. General principles of low-field MRI systems are being introduced, highlighting their strengths and limitations compared to high-field counterparts. Emphasis is placed on advancements in hardware design, including novel magnet configurations, gradient systems, and radiofrequency coils, which have improved image quality and reduced susceptibility artifacts particularly in musculoskeletal imaging. Different clinical applications of modern low-field MRI in musculoskeletal radiology are being discussed. The diagnostic performance of low-field MRI in diagnosing various musculoskeletal pathologies, such as ligament and tendon injuries, osteoarthritis, and cartilage lesions, is being presented. Moreover, the discussion encompasses the cost-effectiveness and accessibility of low-field MRI systems, making them viable options for imaging centers with limited resources or specific patient populations. From a scientific standpoint, the amount of available data regarding musculoskeletal imaging at low-field strengths is limited and often several decades old. This review will give an insight to the existing literature and summarize our own experiences with a modern low-field MRI system over the last 3 years. In conclusion, the narrative review highlights the potential clinical utility, challenges, and future directions of modern low-field MRI, offering valuable insights for radiologists and healthcare professionals seeking to leverage these advancements in their practice.

Characterization of spatial integrity with active and passive implants in a low-field magnetic resonance linear accelerator scanner

Background and Purpose

Standard imaging protocols can guarantee the spatial integrity of magnetic resonance (MR) images utilized in radiotherapy. However, the presence of metallic implants can significantly compromise this integrity. Our proposed method aims at characterizing the geometric distortions induced by both passive and active implants commonly encountered in planning images obtained from a low-field 0.35 T MR-linear accelerator (LINAC).

Materials and Methods

We designed a spatial integrity phantom defining 1276 control points and covering a field of view of 20x20x20 cm3. This phantom was scanned in a water tank with and without different implants used in hip and shoulder arthroplasty procedures as well as with active cardiac stimulators. The images were acquired with the clinical planning sequence (balanced steady-state free-precession, resolution 1.5x1.5x1.5 mm3). Spatial integrity was assessed by the Euclidian distance between the control point detected on the image and their theoretical locations. A first plane free of artefact (FPFA) was defined to evaluate the spatial integrity beyond the larger banding artefact.

Results

In the region extending up to 20 mm from the largest banding artefacts, the tested passive and active implants could cause distortions up to 2 mm and 3 mm, respectively. Beyond this region the spatial integrity was recovered and the image could be considered as unaffected by the implants.

Conclusions

We characterized the impact of common implants on a low field MR-LINAC planning sequence. These measurements could support the creation of extra margin while contouring organs at risk and target volumes in the vicinity of implants.

Magnetic resonance imaging quality in the context of a knee-spanning external fixator placed inside the MR bore: a literature review

After emergent assessment of potentially limb-threatening injuries in knee dislocation or multi-ligament knee injury patients, magnetic resonance imaging is necessary to visualize ligamentous structures and plan for soft tissue repair. However, the application of a knee-spanning external fixator may introduce artifact and reduce overall image quality, which can limit the evaluation of soft tissue injury. As a result, the utility of MRI in the context of a knee-spanning external fixator has been called into question. Signal-to-noise ratio, contrast-to-noise ratio, and qualitative scales have been used to assess image quality of MRI in the context of a knee-spanning external fixator. Despite the potential for artifact, studies have demonstrated that useful diagnostic information may be obtained from MRI in the presence of an external fixator. This review examines the general principles of anatomical assessment, magnetic field strength, device composition and design, radiofrequency coil use, and MRI sequences and artifact reduction as they pertain to MRI in the presence of a knee-spanning external fixator.

Portable magnetic resonance imaging of patients indoors, outdoors and at home

Mobile medical imaging devices are invaluable for clinical diagnostic purposes both in and outside healthcare institutions. Among the various imaging modalities, only a few are readily portable. Magnetic resonance imaging (MRI), the gold standard for numerous healthcare conditions, does not traditionally belong to this group. Recently, low-field MRI technology companies have demonstrated the first decisive steps towards portability within medical facilities and vehicles. However, these scanners' weight and dimensions are incompatible with more demanding use cases such as in remote and developing regions, sports facilities and events, medical and military camps, or home healthcare. Here we present in vivo images taken with a light, small footprint, low-field extremity MRI scanner outside the controlled environment provided by medical facilities. To demonstrate the true portability of the system and benchmark its performance in various relevant scenarios, we have acquired images of a volunteer's knee in: (i) an MRI physics laboratory; (ii) an office room; (iii) outside a campus building, connected to a nearby power outlet; (iv) in open air, powered from a small fuel-based generator; and (v) at the volunteer's home. All images have been acquired within clinically viable times, and signal-to-noise ratios and tissue contrast suffice for 2D and 3D reconstructions with diagnostic value. Furthermore, the volunteer carries a fixation metallic implant screwed to the femur, which leads to strong artifacts in standard clinical systems but appears sharp in our low-field acquisitions. Altogether, this work opens a path towards highly accessible MRI under circumstances previously unrealistic.

Metal Artefact Reduction Sequences (MARS) in Magnetic Resonance Imaging (MRI) after Total Hip Arthroplasty (THA)

Background

In the past, radiographic imaging was of minor relevance in the diagnosis of periprosthetic joint infections (PJI). Since metal artefact reduction sequences (MARS) are available, magnetic resonance imaging (MRI) has become a promising diagnostic tool for the evaluation of hip arthroplasty implants. The purpose of the present study was to evaluate the efficacy of MARS-MRI in comparison to established diagnostic tools to distinguish between aseptic failure and PJI.

Methods

From July 2018 to September 2019, 33 patients classified as having an aseptic joint effusion were recruited into the study. The group included 22 women and 11 men with a mean age of 70.4 ± 13.7 (42–88) years. In the same period, 12 patients were classified as having a PJI. The group consisted of 9 women and 3 men with a mean age of 72.5 ± 10.6 (54–88) years. MARS-MRI was conducted using the optimized parameters at 1.5 T in a coronal and axial STIR (short-tau-inversion recovery), a non-fat-saturated T2 in coronal view and a non-fat-saturated T1 in transverse view in 45 patients with painful hip after total hip arthroplasty (THA). Normally distributed continuous data were shown as mean ± standard deviation (SD) and compared using student's t-test. Non-normally distributed continuous data were shown as mean and compared using the Mann–Whitney U test.

Results

Synovial layering and muscle edema were significant features of periprosthetic joint infection, with sensitivities of 100% and specifities of 63.0—75.0%. The combined specifity and sensitivity levels of synovial layering and muscular edema was 88.0% and 90.0%. Granulomatous synovitis was a significant feature for aseptic failure, with 90.0% sensitivity and 57.0% specifity.

Conclusion

MARS-MRI is as suitable as standard diagnostic tools to distinguish between aseptic failure and PJI in patients with THA. Further studies with larger patient numbers have to prove whether MARS-MRI could be integral part of PJI diagnostic.

[Imaging of the musculoskeletal system using low-field magnetic resonance imaging]

BACKGROUND

Magnetic resonance imaging (MRI) plays a crucial role in musculoskeletal imaging. The high prevalence and pain-related suffering of patients pose a particular challenge concerning availability and turnover times, respectively. Low-field (≤ 1.0 T) MRI has the potential to fulfill these needs. However, during the past three decades, high field systems have increasingly replaced low field systems because of their limitations in image quality. Recent technological advancements in high-performance hard- and software promise musculoskeletal imaging with adequate quality at lower field strengths for several regions and indications.

OBJECTIVES

The goal is to provide insight into the advantages and disadvantages of low-field musculoskeletal imaging, discuss the current literature, and include our first experiences with a modern 0.55 T MRI.

MATERIALS AND METHODS

This review is based on research in various literature databases and our own musculoskeletal imaging experiences with a modern 0.55 T scanner.

CONCLUSION

Most publications pertaining to musculoskeletal imaging at low-field strength MRI are outdated, and studies regarding the diagnostic performance of modern low-field MRI systems are needed. These new systems may complement existing high-field systems and make MRI more accessible, even in low-income countries. From our own experience, modern low-field MRI seems to be adequate in musculoskeletal imaging, especially in acute injuries.

Clinical utility of accelerated MAVRIC-SL with robust-PCA compared to conventional MAVRIC-SL in evaluation of total hip arthroplasties

OBJECTIVE

To compare the diagnostic performance of a conventional metal artifact suppression sequence MAVRIC-SL (multi-acquisition variable-resonance image combination selective) and a novel 2.6-fold faster sequence employing robust principal component analysis (RPCA), in the MR evaluation of hip implants at 3 T.

MATERIALS AND METHODS

Thirty-six total hip implants in 25 patients were scanned at 3 T using a conventional MAVRIC-SL proton density-weighted sequence and an RPCA MAVRIC-SL proton density-weighted sequence. Comparison was made of image quality, geometric distortion, visualization around acetabular and femoral components, and conspicuity of abnormal imaging findings using the Wilcoxon signed-rank test and a non-inferiority test. Abnormal findings were correlated with subsequent clinical management and intraoperative findings if the patient underwent subsequent surgery.

RESULTS

Mean scores for conventional MAVRIC-SL were better than RPCA MAVRIC-SL for all qualitative parameters (p < 0.05), although the probability of RPCA MAVRIC-SL being clinically useful was non-inferior to conventional MAVRIC-SL (within our accepted 10% difference, p < 0.05), except for visualization around the acetabular component. Abnormal imaging findings were seen in 25 hips, and either equally visible or visible but less conspicuous on RPCA MAVRIC-SL in 21 out of 25 cases. In 4 cases, a small joint effusion was queried on MAVRIC-SL but not RPCA MAVRIC-SL, but the presence or absence of a small effusion did not affect subsequent clinical management and patient outcome.

CONCLUSION

While the overall image quality is reduced, RPCA MAVRIC-SL allows for significantly reduced scan time and maintains almost equal diagnostic performance.

Magnetic Resonance Imaging of the Knee in the Presence of Bridging External Fixation: A Comparative Experimental Evaluation of Four External Fixators, Including Dolphix®

Performing MR investigation on patients instrumented with external fixators is still controversial. The aim of this study is to evaluate the quality of MR imaging of the knee structures in the presence of bridging external fixators. Different cadaveric lower limbs were instrumented with the MR-conditional external fixators Hofmann III (Stryker, Kalamazoo, MI, USA), Large external Fixator (DePuy Synthes, Raynham, MA, USA), XtraFix (Zymmer, Warsaw, IN, USA) and a newer implant of Ketron Peek CA30 and ERGAL 7075 pins, Dolphix^®, (Citieffe, Bologna, Italy). The specimens were MR scanned before and after the instrumentation. The images were subjectively judged by a pool of blinded radiologists and then quantitatively evaluated calculating signal intensity, signal to noise and contrast to noise in the five regions of interest. The area of distortion due to the presence of metallic pins was calculated. All the images were considered equally useful for diagnosis with no differences between devices (p > 0.05). Only few differences in the quantification of images have been detected between groups while the presence of metallic components was the main limit of the procedure. The mean length of the radius of the area of distortion of the pins were 53.17 ± 8.19 mm, 45.07 ± 4.33 mm, 17 ± 5.4 mm and 37.12 ± 10.17 mm per pins provided by Zimmer, Synthes, Citieffe and Stryker, respectively (p = 0.041). The implant of Ketron Peek CA30 and ERGAL 7075 pins showed the smallest distortion area.

Improving MR Image Quality in Patients with Metallic Implants

The number of implanted devices such as orthopedic hardware and cardiac implantable devices continues to increase with an increase in the age of the patient population, as well as an increase in the number of indications for specific devices. Many patients with these devices have or will develop clinical conditions that are best depicted at MRI. However, implanted devices containing paramagnetic or ferromagnetic substances can cause significant artifact, which could limit the diagnostic capability of this modality. Performing imaging with MRI when an implant is present may be challenging, and there are numerous techniques the radiologist and technologist can use to help minimize artifacts related to implants. First, knowledge of the presence of an implant before patient arrival is critical to ensure safety of the patient when the device is subjected to a strong magnetic field. Once safety is ensured, the examination should be performed with the MRI system that is expected to provide the best image quality. The selection of the MRI system includes multiple considerations such as the effects of field strength and availability of specific sequences, which can reduce metal artifact. Appropriate patient positioning, attention to MRI parameters (including bandwidth, voxel size, and echo), and appropriate selection of sequences (those with less metal artifact and advanced metal reduction sequences) are critical to improve image quality. Patients with implants can be successfully imaged with MRI with appropriate planning and understanding of how to minimize artifacts. This improves image quality and the diagnostic confidence of the radiologist. ^©RSNA, 2021.

Imaging Assessment of the Postoperative Spine: An Updated Pictorial Review of Selected Complications

Imaging of the postoperative spine requires the identification of several critical points by the radiologist to be written in the medical report: condition of the underlying cortical and cancellous bone, intervertebral disc, and musculoskeletal tissues; location and integrity of surgical implants; evaluation of the success of decompression procedures; delineation of fusion status; and identification of complications. This article presents a pictorial narrative review of the most common findings observed in noninstrumented and instrumented postoperative spines. Complications in the noninstrumented spine were grouped in early (hematomas, pseudomeningocele, and postoperative spine infection) and late findings (arachnoiditis, radiculitis, recurrent disc herniation, spinal stenosis, and textiloma). Complications in the instrumented spine were also sorted in early (hardware fractures) and late findings (adjacent segment disease, hardware loosening, and implant migration). This review also includes a short description of the most used diagnostic techniques in postoperative spine imaging: plain radiography, ultrasound (US), computed tomography (CT), magnetic resonance (MR), and nuclear medicine. Imaging of the postoperative spine remained a challenging task in the early identification of complications and abnormal healing process. It is crucial to consider the advantages and disadvantages of the imaging modalities to choose those that provide more accurate spinal status information during the follow-up. Our review is directed to all health professionals dealing with the assessment and care of the postoperative spine.

Metallic Implants in MRI - Hazards and Imaging Artifacts

BACKGROUND

 Magnetic resonance imaging (MRI) is an examination method for noninvasive soft tissue imaging without the use of ionizing radiation. Metallic implants, however, may pose a risk for the patient and often result in imaging artifacts. Due to the increasing number of implants, reducing these artifacts has become an important goal. In this review, we describe the risks associated with implants and provide the background on how metal-induced artifacts are formed. We review the literature on methods on how to reduce artifacts and summarize our findings.

METHOD

 The literature was searched using PubMed and the keywords "MRI metal artifact reduction", "metallic implants" and "MRI artefacts/artifacts".

RESULTS AND CONCLUSION

 The MRI compatibility of implants has to be evaluated individually. To reduce artifacts, two general approaches were found: a) parameter optimization in standard sequences (echo time, slice thickness, bandwidth) and b) specialized sequences, such as VAT, OMAR, WARP, SEMAC and MAVRIC. These methods reduced artifacts and improved image quality, albeit at the cost of a (sometimes significantly) prolonged scan time. New developments in accelerated imaging will likely shorten the scan time of these methods significantly, such that routine use may become feasible.

KEY POINTS

  · Metallic implants may pose a risk for patients and often cause artifacts.. · Imaging artifacts can be reduced by parameter optimization or special sequences.. · Metal artifacts are reduced with a lower TE, smaller voxel size, larger matrix, and higher bandwidth.. · SPI, STIR, VAT, SEMAC, MAVRIC, and MAVRIC-SL are specialized MR sequences that can reduce artifacts further..

CITATION FORMAT

· Peschke E, Ulloa P, Jansen O et al. Metallic Implants in MRI - Hazards and Imaging Artifacts. Fortschr Röntgenstr 2021; 193: 1285 - 1293.

Shoulder MR Imaging and MR Arthrography Techniques: New Advances

MR imaging is the standard diagnostic modality that provides a comprehensive and accurate assessment for both osseous and soft-tissue pathologic conditions of the shoulder. This article discusses standard MR imaging and arthrography protocols used routinely in clinical practice, as well as more innovative sequences and reconstruction techniques, facilitated by the increasing availability of high-field-strength magnets and multichannel phased array surface coils and incorporation of artificial intelligence. These exciting innovations allow for a more detailed and diagnostic imaging assessment, improvements in image quality, and more rapid image acquisition.

Value of standard radiographs, computed tomography, and magnetic resonance imaging of the lumbar spine in detection of intraoperatively confirmed pedicle screw loosening-a prospective clinical trial

BACKGROUND CONTEXT

Pedicle screw loosening is common after spinal fusion and can be associated with pseudoarthrosis and pain. With suspicion of screw loosening on standard radiographs, CT is currently considered the advanced imaging modality of choice. MRI with new metal artifact reduction techniques holds potential to be sensitive in detection of screw loosening. The sensitivity and specificity of either of the imaging modalities are yet clear.

PURPOSE

To evaluate the sensitivity and specificity of three different image modalities (standard radiographs, CT, and MRI) for detection of pedicle screw loosening.

STUDY DESIGN/SETTING

Cross-sectional diagnostic study.

PATIENT SAMPLE

Forty-one patients (159 pedicle screws) undergoing revision surgeries after lumbar spinal fusion between August 2014 and April 2017 with preoperative radiographs, CT, and MRI with spinal metal artifact reduction (STIR WARP and TSE high bandwidth sequences).

OUTCOME MEASURES

Sensitivity and specificity in detection of screw loosening for each imaging modality.

METHODS

Screw torque force was measured intraoperatively and compared with preoperative screw loosening signs such as peri-screw edema in MRI and peri-screw osteolysis in CT and radiographs. A torque force of less than 60 Ncm was used to define a screw as loosened.

RESULTS

Sensitivity and specificity in detection of screw loosening was 43.9% and 92.1% for MRI, 64.8% and 96.7% for CT, and 54.2% and 83.5% for standard radiographs, respectively.

CONCLUSIONS

Despite improvement of MRI with metal artifact reduction MRI technique, CT remains the modality of choice. Even so, CT fails to detect all loosened pedicle screws.

Overcoming metallic artefacts from orthopaedic wrist volar plating on a low-field MRI scanner

PURPOSE

To quantitatively compare the artefact reduction between standard and metallic artefact reduction (MAR) fast spin echo (FSE) T2 sequences in a low-field magnetic resonance imaging (MRI) scanner (0.3 T) in patients with titanium volar wrist plating.

MATERIALS AND METHODS

Sixteen patients with fractures of the distal radius, treated with titanium volar wrist plating and screws, were examined using a dedicated 0.3 T MRI scanner. Coronal standard FSE T2, FSE T2 high bandwidth (HiBW) and FSE T2 view angle tilting (VAT) sequences were performed. Metallic artefact volume, consisting of both "black" and "bright" artefacts, was calculated for each sequence. Quantitative differences were compared using repeated measures ANOVA test (P < 0.05).

RESULTS

FSE T2 HiBW and FSE T2 VAT showed a significant reduction in artefact volume compared to the standard sequence. Differences between the artefact volume of the standard FSE T2, HiBW and VAT sequences were statistically significant for both the "black" and "bright" artefacts (P < 0.0001). Differences between the 1.5 HiBW and VAT sequences were statistically significant (black P < 0.0001, bright P < 0.0302).

CONCLUSIONS

MAR sequences significantly reduced metallic artefacts in vivo using a 0.3 T MRI scanner.

Material-Dependent Implant Artifact Reduction Using SEMAC-VAT and MAVRIC: A Prospective MRI Phantom Study

OBJECTIVE

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

MRI anatomical preoperative evaluation of distally based peroneus brevis muscle flap in reconstructive surgery of the lower limb

BACKGROUND

The distally based peroneus brevis muscle flap has proved to be a simple solution for small- to moderate-sized wounds of the lower limb. The length of the muscle belly suitable for coverage is a crucial parameter. In this study, we evaluated the capability of 3D MRI of the lower limb to measure it preoperatively.

METHODS

Between 2008 and 2017, 32 patients with lower limb defects underwent preoperative MRI to measure the peroneus brevis muscle length. All patients underwent reconstruction, and the muscle was measured again intraoperatively during surgical dissection. Surgical measurements were then compared to the MRI ones.

RESULTS

MRI measures of the peroneus brevis muscle belly ranged from 9 to 21 cm (μ = 14.44 ± 3.43 cm), and intraoperative measures ranged from 9 to 20 cm (μ = 14.2 ± 2.3 cm). Thirty of 32 intraoperative measures corresponded to the MRI ones (variation = ± 1 cm, r = 0.92, p = 0.002). One patient showed an intraoperative muscle length 3 cm shorter than the MRI measure, and another patient had intraoperative muscle length 3 cm longer than the MRI one. All flaps survived, and no secondary local flap coverage was required, with no flap-related complication, limited donor site morbidity, and acceptable patient discomfort.

CONCLUSIONS

The reverse peroneus brevis muscle flap is a versatile alternative to free flap reconstruction in small- to moderate-sized defects of the lower limb. Preoperative 3D MRI is accurate to evaluate the anatomy of the muscle when performed by an expert radiologist. In our experience, it should become part of preoperative workup before performing a peroneus brevis flap procedure.

The effects of a common stainless steel orthodontic bracket on the diagnostic quality of cranial and cervical 3T- MR images: a prospective, case-control study

OBJECTIVES

To evaluate the effect of orthodontic stainless steel brackets and two different types of archwires on the diagnostic quality of 3-T MR images.

METHODS

This prospective, case-control study was conducted following Strengthening the Reporting of Observational Studies in Epidemiology guidelines. The recruitment was conducted among orthodontic patients. 80 subjects, requiring MRI for the presence of temporomandibular disorders, were enrolled and divided into four groups: 20 patients using aligners (control group); 20 patients with stainless steel brackets without archwires; 20 patients with stainless steel brackets and nickel-titanium archwires; and 20 patients with stainless steel brackets and stainless steel archwires. Two experts in neuroradiology evaluated the images to determine the amount of distortion in 6 regions and 48 districts. A score was subjectively assigned according to a modified receiver operating characteristic method of distortion classification. Any disagreement was resolved through consensus seeking; when this was not possible, a third neuroradiologist was consulted. The following statistical methods were used: descriptive statistics, Cohen's kappa coefficient (k), Kruskal-Wallis test, pairwise comparisons using the Dunn-Bonferroni approach. The significance was set at p ≤ 0.05.

RESULTS

The presence of stainless steel brackets with or without archwires negatively influenced MRI of the cervical region, paranasal sinuses, head and neck region, and cervical vertebrae but did not influence MRI of brain and temporomandibular joint regions.

CONCLUSIONS

Patients with a stainless steel multibracket orthodontic appliance should remove it before cervical vertebrae, cervical region, paranasal sinuses, and head and neck MRI scans. The brain and temporomandibular joint region MRI should not require the removal of such appliances.

Magnetic resonance imaging susceptibility artifacts in the cervical vertebrae and spinal cord related to monocortical screw-polymethylmethacrylate implants in canine cadavers

OBJECTIVE To characterize and compare MRI susceptibility artifacts related to titanium and stainless steel monocortical screws in the cervical vertebrae and spinal cord of canine cadavers. SAMPLE 12 canine cadavers. PROCEDURES Cervical vertebrae (C4 and C5) were surgically stabilized with titanium or stainless steel monocortical screws and polymethylmethacrylate. Routine T1-weighted, T2-weighted, and short tau inversion recovery sequences were performed at 3.0 T. Magnetic susceptibility artifacts in 20 regions of interest (ROIs) across 4 contiguous vertebrae (C3 through C6) were scored by use of an established scoring system. RESULTS Artifact scores for stainless steel screws were significantly greater than scores for titanium screws at 18 of 20 ROIs. Artifact scores for titanium screws were significantly higher for spinal cord ROIs within the implanted vertebrae. Artifact scores for stainless steel screws at C3 were significantly less than at the other 3 cervical vertebrae. CONCLUSIONS AND CLINICAL RELEVANCE Evaluation of routine MRI sequences obtained at 3.0 T revealed that susceptibility artifacts related to titanium monocortical screws were considered mild and should not hinder the overall clinical assessment of the cervical vertebrae and spinal cord. However, mild focal artifacts may obscure small portions of the spinal cord or intervertebral discs immediately adjacent to titanium screws. Severe artifacts related to stainless steel screws were more likely to result in routine MRI sequences being nondiagnostic; however, artifacts may be mitigated by implant positioning.

MRI compatibility of several early transition metal based alloys and its influencing factors

Magnetic resonance imaging (MRI) compatibility of three early transition metal (ETM) based alloys was assessed in vitro with agarose gel as a phantom, including Zr-20Nb, near-equiatomic (TiZrNbTa)₉₀ Mo₁₀ and Nb-60Ta-2Zr, together with pure tantalum and L605 Co-Cr alloy for comparison. The artifact extent in the MR image was quantitatively characterized according to the maximum area of 2D images and the total volume in reconstructed 3D images with a series of slices under acquisition by fast spin echo (FSE) sequence and gradient echo (GRE) sequence. It was indicated that the artifacts extent of L605 Co-Cr alloy with a higher magnetic susceptibility (χ_v ) was approximately 3-fold greater than that of the ETM-based alloys with χ_v in the range of 160-250 ppm. In the ETM group, the MRI compatibility of the materials can be ranked in a sequence of Zr-20Nb, pure tantalum, (TiZrNbTa)₉₀ Mo₁₀ and Nb-60Ta-2Zr. In addition, using a rabbit cadaver with the implanted tube specimens as a model for ex vivo assessment, it was confirmed that the artifact severity of Nb-60Ta-2Zr alloy is significantly reduced in comparison with the L605 alloy. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 377-385, 2018.

Does a titanium sleeve reduce the frequency of pseudotumors in metal-on-metal total hip arthroplasty at 5-7years follow-up?

INTRODUCTION

Little is known about pseudotumor frequency and risk factors for pseudotumor formation among different types of metal-on-metal (MoM) hip arthroplasties. A lower release of chromium and cobalt have been reported in MoM hip arthroplasties with a titanium sleeve compared to MoM designs without a titanium sleeve, but yet it is unknown whether a titanium sleeve reduces the pseudotumor frequency. We conducted a cross-sectional study to investigate: 1) pseudotumor frequency, 2) risk factors of pseudotumor formation 3) and correlations between pseudotumors, serum metal-ions, implant position, and clinical symptoms.

HYPOTHESIS

We expected a lower pseudotumor frequency in MoM hip articulation with a titanium sleeve than reported in MoM hip articulation designs using chromium-cobalt sleeve.

MATERIALS AND METHOD

A consecutive series of 41 patients/49 hips (31 males), mean age 52 (28-68) years, participated in a 5.5±0.5 (4-6.5) year follow-up study of their M2a_Magnum hip articulation (Biomet Inc., Warsaw, Indiana, USA). Patients were evaluated with magnetic resonance imaging (MRI), measurements of serum metal-ions, plain radiographs, and clinical outcome measures of Harris Hip Score (HHS) and Oxford Hip Score (OHS).

RESULTS

Eighteen of 47 hips (38%) had MRI-verified pseudotumors, all cystic, with a mean dimension of 10.6×25.6×41mm. Digital measurements on plain radiographs revealed a higher cup anteversion in patients with a pseudotumor of mean 28.4°±5.05° compared to mean 23.5°±6.5° in patients without a pseudotumor (P=0.009). Serum metal-ion concentrations, acetabular cup inclination and measures of HHS and OHS were similar between patients with and without a pseudotumor (P>0.46).

CONCLUSION

At 5.5±0.5years after surgery, MRI-verified cystic pseudotumors were frequently observed in M2a_Magnum hip articulations despite the use of titanium sleeves. The pseudotumors were related to high cup anteversion angles but not related to high serum metal-ions or clinical symptoms.

LEVEL OF EVIDENCE

IV: cross-sectional study.

Technical Considerations: Best Practices for MR Imaging of the Foot and Ankle

There are many challenges involved in obtaining diagnostic MR images of the foot and ankle. The complex anatomy and morphology, with curved and angular structures localized to the periphery of the body, make for an inherent challenge, let alone if an added level of complexity, such as orthopedic instrumentation, is added. This review outlines the technical considerations best designed to produce diagnostic images of the foot and ankle, with an emphasis on the postoperative state, including imaging in the presence of metal.

Metallic implant geometry and susceptibility estimation using multispectral B0 field maps

PURPOSE

To estimate the susceptibility and the geometry of metallic implants from multispectral imaging (MSI) information, to separate the metal implant region from the surrounding signal loss region.

THEORY AND METHODS

The susceptibility map of signal-void regions is estimated from MSI B₀ field maps using total variation (TV) regularized inversion. Voxels with susceptibility estimates above a predetermined threshold are identified as metal. The accuracy of the estimated susceptibility and implant geometry was evaluated in simulations, phantom, and in vivo experiments.

RESULTS

The proposed method provided more accurate susceptibility estimation compared with a previous method without TV regularization, in both simulations and phantom experiments. In the phantom experiment where the actual implant was 40% of the signal-void region, the mean estimated susceptibility was close to the susceptibility in literature, and the precision and recall of the estimated geometry was 85% and 93%. In vivo studies in subjects with hip implants also demonstrated that the proposed method can distinguish implants from surrounding low-signal tissues, such as cortical bone.

CONCLUSION

The proposed method can improve the delineation of metallic implant geometry by distinguishing metal voxels from artificial signal voids and low-signal tissues by estimating the susceptibility maps. Magn Reson Med 77:2402-2413, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Artifacts Affecting Musculoskeletal Magnetic Resonance Imaging: Their Origins and Solutions

Among articles within the radiology literature, few present the manifestations of magnetic resonance imaging artifacts in a clinically oriented manner. Recognizing such artifacts is imperative given the increasing clinical use of magnetic resonance imaging and the emphasis by the American Board of Radiology on practical physics applications. The purpose of this article is to present magnetic resonance physics principles visually and conceptually in the context of common musculoskeletal radiology artifacts and their solutions, described using nonmathematical explanations.

MRI evaluation of the knee with non-ferromagnetic external fixators: cadaveric knee model

INTRODUCTION

The advent of MRI-compatible external fixation devices has made the use of MRI possible in patients who have been treated with external fixation. However, although there have been multiple studies determining the safety of MRI scans with external fixator devices, there are no studies determining the artifact effect these devices can have on the MRI image. The purpose of our study was to evaluate the effect of two popular brands (Stryker and Synthes) of MRI-compatible external fixators on the diagnostic capacity of a knee MRI. We hypothesize that (1) MRI images would have higher noise due to the presence of an external fixator and (2) images of high diagnostic capacity will be obtainable in the presence of each external fixator spanning the knee.

METHODS

Using seven cadaveric knees, a study was performed to analyze MRI images taken in the presence each external fixator. Scans taken with no external fixator present served as controls. Signal-to-noise ratios (SNRs) were measured at five anatomic structures. These structures were compared as a quantitative measure of image quality. A qualitative analysis was also performed using a five-point grading scale to assess the influence of metal artifact on the quality of the images. Each scan was graded by three blinded musculoskeletal radiologists focusing on six key anatomic structures.

RESULTS

A reduction in SNR was identified on the external fixator group compare to the control groups at the patella tendon, MM and PCL. Qualitative scoring by three expert radiologists showed no difference in ability to identify the six key anatomic landmarks between the Stryker, Synthes and control images.

CONCLUSION

Although the presence of external fixation devices does increase the noise artifact in MRI scans, patients treated with these external fixators can undergo MRI of local structures with high likelihood of obtaining diagnostic quality images.

Metal-induced artifacts in computed tomography and magnetic resonance imaging: comparison of a biodegradable magnesium alloy versus titanium and stainless steel controls

OBJECTIVE

To evaluate metal artifacts induced by biodegradable magnesium--a new class of degradable biomaterial that is beginning to enter the orthopedic routine--on CT and MRI compared to standard titanium and steel controls.

METHODS

Different pins made of titanium, stainless steel, and biodegradable magnesium alloys were scanned using a second-generation dual-energy multidetector CT and a 1.5-T MR scanner. In CT, quantitative assessment of artifacts was performed by two independent readers by measuring the noise in standardized regions of interest close to the pins. In MRI, the artifact diameter was measured. Interobserver agreement was evaluated using intraclass correlation coefficients. Artifacts were compared using Mann Whitney U tests.

RESULTS

In comparison to stainless steel, biodegradable magnesium alloys induced significantly fewer artifacts in both 1.5-T MRI (p = 0.019-0.021) and CT (p = 0.003-0.006). Compared to titanium, magnesium induced significantly less artifact-related noise in CT (p = 0.003-0.008). Although artifacts were less on MRI for biodegradable magnesium compared to titanium, this result was not statistically significant.

CONCLUSION

Biodegradable magnesium alloys induce substantially fewer artifacts in CT compared to standard titanium and stainless steel, and fewer artifacts in MRI for the comparison with stainless steel.

Evaluating the progression of osteolysis after total knee arthroplasty

Osteolysis around the knee following total knee arthroplasty continues to be a leading cause for revision total knee arthroplasty. Risk factors for periprosthetic knee osteolysis are associated with excessive polyethylene wear and include, but may not be limited to, malalignment of the mechanical axis, early-generation polyethylene sterilization techniques, excessive backside polyethylene wear, metal-backed patellar components, patient age, and an elevated body mass index. The initial diagnosis of osteolysis is frequently discovered on routine surveillance radiographs. The location, size, progressive nature, and associated symptomatology of the defect guides treatment. Surgical indications and timing are predicated on the risk of failure with continued observation. Advanced imaging helps to quantitate the size and location of osteolytic lesions as accurately as possible and aids in preoperative planning. When deciding whether surgery or management with continued radiographic surveillance is indicated, a global assessment of the character and progression of the osteolysis must be weighed with the risk factors associated with the patient.

MR imaging near metallic implants using MAVRIC SL: initial clinical experience at 3T

RATIONALE AND OBJECTIVES

To compare the effectiveness of multiacquisition with variable resonance image combination selective (MAVRIC SL) with conventional two-dimensional fast spin-echo (2D-FSE) magnetic resonance (MR) techniques at 3T in imaging patients with a variety of metallic implants.

MATERIALS AND METHODS

Twenty-one 3T MR studies were obtained in 19 patients with different types of metal implants. Paired MAVRIC SL and 2D-FSE sequences were reviewed by two radiologists and compared for in-plane and through-plane metal artifact, visualization of the bone implant interface and surrounding soft tissues, blurring, and overall image quality using a two-tailed Wilcoxon signed rank test. The area of artifact on paired images was measured and compared using a paired Wilcoxon signed rank test. Changes in patient management resulting from MAVRIC SL imaging were documented.

RESULTS

Significantly less in-plane and through-plane artifact was seen with MAVRIC SL, with improved visualization of the bone-implant interface and surrounding soft tissues, and superior overall image quality (P = .0001). Increased blurring was seen with MAVRIC SL (P = .0016). MAVRIC SL significantly decreased the image artifact compared to 2D-FSE (P = .0001). Inclusion of MAVRIC SL to the imaging protocol determined the need for surgery or type of surgery in five patients and ruled out the need for surgery in 13 patients. In three patients, the area of interest was well seen on both MAVRIC SL and 2D-FSE images, so the addition of MAVRIC had no effect on patient management.

CONCLUSIONS

Imaging around metal implants with MAVRIC SL at 3T significantly improved image quality and decreased image artifact compared to conventional 2D-FSE imaging techniques and directly impacted patient management.

MRI findings following metal on metal hip arthroplasty and their relationship with metal ion levels and acetabular inclination angles

Following the global recall of all ASR metal on metal hip products, our aim was to correlate MRI findings with acetabular inclination angles and metal ion levels in patients with these implants. Both cobalt and chromium levels were significantly higher in the presence of a periprosthetic fluid collection. There was no association between the presence of a periprosthetic mass, bone marrow oedema, trochanteric bursitis or greater levels of abductor muscle destruction for cobalt or chromium. There was no association between the level of periprosthetic tissue reaction and the acetabular inclination angle with any of the pathologies identified on MRI. The relationship between MRI pathology, metal ion levels and acetabular inclination angles in patients with ASR implants remains unclear adding to the complexity of managing patients.

Using the dGEMRIC technique to evaluate cartilage health in the presence of surgical hardware at 3T: comparison of inversion recovery and saturation recovery approaches

OBJECTIVE

To evaluate the effect of metal artifact reduction techniques on dGEMRIC T(1) calculation with surgical hardware present.

MATERIALS AND METHODS

We examined the effect of stainless-steel and titanium hardware on dGEMRIC T(1) maps. We tested two strategies to reduce metal artifact in dGEMRIC: (1) saturation recovery (SR) instead of inversion recovery (IR) and (2) applying the metal artifact reduction sequence (MARS), in a gadolinium-doped agarose gel phantom and in vivo with titanium hardware. T(1) maps were obtained using custom curve-fitting software and phantom ROIs were defined to compare conditions (metal, MARS, IR, SR).

RESULTS

A large area of artifact appeared in phantom IR images with metal when T(I) ≤ 700 ms. IR maps with metal had additional artifact both in vivo and in the phantom (shifted null points, increased mean T(1) (+151 % IR ROI(artifact)) and decreased mean inversion efficiency (f; 0.45 ROI(artifact), versus 2 for perfect inversion)) compared to the SR maps (ROI(artifact): +13 % T(1) SR, 0.95 versus 1 for perfect excitation), however, SR produced noisier T(1) maps than IR (phantom SNR: 118 SR, 212 IR). MARS subtly reduced the extent of artifact in the phantom (IR and SR).

CONCLUSIONS

dGEMRIC measurement in the presence of surgical hardware at 3T is possible with appropriately applied strategies. Measurements may work best in the presence of titanium and are severely limited with stainless steel. For regions near hardware where IR produces large artifacts making dGEMRIC analysis impossible, SR-MARS may allow dGEMRIC measurements. The position and size of the IR artifact is variable, and must be assessed for each implant/imaging set-up.

Evaluation of intraorbital prosthetic pigmentation using 0.3 and 1.5 Tesla magnetic resonance imaging and computed tomography

PURPOSE

To investigate the magnetic susceptibility artifact associated with pigmented intraorbital prosthetics when performing magnetic resonance imaging (MRI) and computed tomography (CT). Potential artifact reduction techniques were also investigated.

STUDY DESIGN

Prospective study.

METHODS

Five different-colored 20-millimeter small animal silicone intraorbital prosthetics and two equine prosthetics were evaluated using 0.3 and 1.5 Tesla (T) MRI and CT. MRI sequences included T1- (T1WI) and T2-weighted spin echo (T2WI), T2 gradient echo (T2*), short tau inversion recovery (STIR), and fluid-attenuated inversion recovery (FLAIR). When present, artifact size was measured using computerized software by three separate observers. Artifact reduction techniques included alterations in receiver bandwidth, field of view, slice thickness, and matrix size.

RESULTS

The ferrous brown-pigmented prosthetic resulted in a magnetic susceptibility artifact with MRI. No artifact was observed on CT images. Interobserver variability was not statistically significant. For both the 0.3T and 1.5T MRI, the T2* sequence exhibited the largest artifact surface area followed by T2WI, T1WI, STIR, and FLAIR. Decreasing slice thickness showed a decrease in artifact size; however, this difference was not statistically significant.

CONCLUSIONS

The ferrous substances in the brown intraorbital prosthetic resulted in a significant magnetic susceptibility artifact when performing MRI. Artifact reduction techniques did not significantly decrease artifact surface area. The use of ferrous brown-pigmented prosthetics and their potential to affect future MR imaging studies should be adequately discussed with pet owners.

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.

SEMAC-VAT and MSVAT-SPACE sequence strategies for metal artifact reduction in 1.5T magnetic resonance imaging

OBJECTIVES

To evaluate the ability of four magnetic resonance imaging (MRI) techniques to correct for metallic artifacts. These techniques consisted of 3 2D techniques and one 3D technique. In 2D imaging the techniques View Angle Tilting (VAT), Slice Encoding for Metal Artifact Correction (SEMAC) and a technique that employed a combination of the first two (SEMAC-VAT) were evaluated. In 3D imaging the technique Multiple Slab acquisition with VAT based on a SPACE sequence was evaluated (MSVAT-SPACE).

MATERIALS AND METHODS

Agarose phantoms and tissue phantoms with two commonly used metal implants (stainless steel and titanium) as well as two volunteers with metal implants were imaged at 1.5T. All phantoms and volunteers were imaged using VAT, SEMAC, SEMAC-VAT and MSVAT-SPACE techniques, as well as 2D and 3D conventional imaging techniques. Each technique was optimized for different image contrast mechanisms. Artifact reduction was quantitatively assessed in the agarose phantoms by volumetric measurement. Image quality was qualitatively assessed by blinded reads employing two readers. Each reader independently viewed the tissue phantom images and in vivo human images. Statistical analysis was performed using a Friedman test, Wilcoxon test and weighted Cohen's kappa test.

RESULTS

T1-weighted, T2-weighted, PD-weighted and STIR image contrasts were successfully implemented with the evaluated artifact reduction sequences in both the phantom experiments and in vivo images. For all evaluated image contrasts and both metal implants, a reduction in the volume of metal artifacts was seen when compared with 2D conventional acquisitions. The 2D metal artifact volumes on average were reduced by 49% ± 16%, 56% ± 15% and 63% ± 15% for VAT, SEMAC and SEMAC-VAT acquisitions respectively. When Friedman and Wilcoxon tests were applied the difference in metal artifact volume was found to be statistically significant when VAT, SEMAC and SEMAC-VAT were compared with the 2D conventional techniques. In 3D imaging on average MSVAT-SPACE reduced metal artifact volume compared with the 3D conventional imaging technique by 72% ± 23% for all evaluated image contrasts and both metal implants. The metal artifact volume differences were statistically significant when MSVAT-SPACE was compared with the 3D conventional technique. The blinded reads demonstrated that SEMAC-VAT and MSVAT-SPACE had distinctly superior quality compared with conventional acquisitions. Quality was measured in terms of artifact size, distortions, image quality and visualization of bone marrow and soft tissues adjacent to metal implants. This was the case for both tissue phantom images and human images with good interobserver agreement.

CONCLUSIONS

SEMAC-VAT (2D) and MSVAT-SPACE (3D) demonstrated a consistent, marked reduction of metal artifacts for different metal implants and offered flexible image contrasts (T1, T2, PD and STIR) with high image quality. These techniques likely will improve the evaluation of postoperative patients with metal implants.

Magnetic resonance imaging of the postoperative hip

Magnetic resonance imaging (MRI) is ideally suited to imaging the patient with painful hip arthroplasty due to its superior soft tissue contrast, multiplanar capabilities, and lack of ionizing radiation. MRI is the most accurate imaging modality in the assessment of periprosthetic osteolysis and wear-induced synovitis, and can also assess regional tendons and neurovascular structures. This article discusses the technical aspects of MRI around metallic implants as well as the appearance of potential complications following hip arthroplasty, including osteolysis, wear-induced synovitis, infection, hemarthrosis, fracture, loosening, component displacement, heterotopic ossification, tendinopathy, and neurovascular impingement. The specific complication of metal hypersensitivity following metal-on-metal prostheses is reviewed.

MRI analysis of the component-bone interface after TKA

PURPOSE

The aim of the study is to describe and characterize the implant-bone interface of femoral, tibial and patellar components after TKA using magnet resonance imaging (MRI).

SCOPE

Fifty-five patients who underwent MRI modified to reduce artifacts after TKA were identified retrospectively from medical records. This included 27 TKA with a zirconium femoral component and 28 TKA with conventional cobalt/chrome/molybdenum alloy component (CoCrMo). The MRIs were evaluated by two blinded, independent investigators and Cohen's Kappa was applied to determine the interobserver reliability. Excellent visibility, interobserver agreement and reliability was found for the interface of the tibial components, patellar buttons, and for femoral components made of zirconium. Conventional CoCrMo components caused significant artifact that interfered with the evaluation of the interface of femoral components.

CONCLUSION

MRI performed with a special protocol allows good reproducibility of analysis of implant-bone interface at tibia and patella after TKA. The femoral interface was visualized for components made of zirconium. Conventional CoCrMo femoral components caused considerable artifact and interfered with the evaluation of the femoral interface. MRI tailored to reduce metallic susceptibility artifact can be a helpful tool for evaluation of prosthesis bone interface and may be helpful for the diagnosis of component loosening.

Spinal fusion-hardware construct: Basic concepts and imaging review

The interpretation of spinal images fixed with metallic hardware forms an increasing bulk of daily practice in a busy imaging department. Radiologists are required to be familiar with the instrumentation and operative options used in spinal fixation and fusion procedures, especially in his or her institute. This is critical in evaluating the position of implants and potential complications associated with the operative approaches and spinal fixation devices used. Thus, the radiologist can play an important role in patient care and outcome. This review outlines the advantages and disadvantages of commonly used imaging methods and reports on the best yield for each modality and how to overcome the problematic issues associated with the presence of metallic hardware during imaging. Baseline radiographs are essential as they are the baseline point for evaluation of future studies should patients develop symptoms suggesting possible complications. They may justify further imaging workup with computed tomography, magnetic resonance and/or nuclear medicine studies as the evaluation of a patient with a spinal implant involves a multi-modality approach. This review describes imaging features of potential complications associated with spinal fusion surgery as well as the instrumentation used. This basic knowledge aims to help radiologists approach everyday practice in clinical imaging.

Practical application of iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) imaging in minimizing metallic artifacts

Iterative decomposition of water and fat with echo asymmetry and the least-squares estimation (IDEAL) is a recently developed method for robust separation of fat and water with very high signal-to-noise-ratio (SNR) efficiency. In contrast to conventional fat-saturation methods, IDEAL is insensitive to magnetic field (B0 and B1) inhomogeneity. The aim of this study was to illustrate the practical application of the IDEAL technique in reducing metallic artifacts in postoperative patients with metallic hardware. The IDEAL technique can help musculoskeletal radiologists make an accurate diagnosis particularly in musculoskeletal imaging by reducing metallic artifacts, enabling the use of contrast enhancement, improving SNR performance, and providing various modes of MR images with one scan parameter.

Magnetic resonance imaging features of preserved vs divided and repaired piriformis during total hip arthroplasty: a randomized controlled trial

The aim of this study was to compare the muscle grade and bulk of the divided and repaired piriformis tendon by the standard posterior approach with the preserved tendon by a piriformis-sparing (PS) approach, in total hip arthroplasty. Twenty-two patients were randomized to either approach. Patients received preoperative and 3 months and 2 years postoperative magnetic resonance imaging scans. Patients and evaluators were blinded to allocation. There was significantly less deterioration in piriformis muscle grade (P = .029) and bulk (P = .015) in the PS group at 3 months. At 2 years, only the difference in grade remained significant (P = .001). There was no difference in Oxford hip scores. In conclusion, a PS approach avoids the marked wasting and deterioration in muscle grade that occurs postoperatively in the standard posterior approach.

Peripheral nerve surgery: the role of high-resolution MR neurography

High-resolution MRN is becoming increasingly available due to recent technical advancements, including higher magnetic field strengths (eg, 3T), 3D image acquisition, evolution of novel fat-suppression methods, and improved coil design. This review describes the MRN techniques for obtaining high-quality images of the peripheral nerves and their small branches and imaging findings in normal as well as injured nerves with relevant intraoperative correlations. Various microsurgical techniques in peripheral nerves, such as neurolysis, nerve repairs by using nerve grafts, and conduits are discussed, and MRN findings of surgically treated nerves are demonstrated.

MRI after arthroplasty: comparison of MAVRIC and conventional fast spin-echo techniques

OBJECTIVE

The goal of this study was to evaluate the quality of images obtained with a prototype imaging technique, multiacquisition variable-resonance image combination (MAVRIC), compared with fast spin-echo (FSE) images in the evaluation of patients who have undergone hip, shoulder, or knee arthroplasty.

MATERIALS AND METHODS

MRI with metal-artifact reduction FSE and MAVRIC sequences was performed in the care of 122 patients who had undergone 74 hip, 27 shoulder, and 21 knee arthroplasties. The FSE and MAVRIC images were subjectively graded for visualization of the synovium, prosthesis-bone interface, and hip abductors or supraspinatus tendon. The presence of synovitis, osteolysis, or supraspinatus tendon tear was recorded.

RESULTS

Visualization of the synovium was significantly better on MAVRIC images than on FSE images of the hip (p < 0.0001), shoulder (p < 0.01), and knee (p < 0.01). Synovitis was detected only on the MAVRIC images of nine subjects (12%) who had undergone hip arthroplasty and five subjects (18%) who had undergone shoulder arthroplasty. Visualization of the periprosthetic bone was significantly better on MAVRIC images of the hip (p < 0.0001), shoulder (p < 0.0001), and knee (p < 0.01). Osteolysis was detected only on the MAVRIC images of 12 subjects (16%) who had undergone hip arthroplasty, six (22%) who had undergone shoulder arthroplasty, and five (24%) who had undergone knee arthroplasty. Visualization of the supraspinatus tendon was significantly better on MAVRIC images (p < 0.0001). Supraspinatus tendon tears in 12 subjects (44%) were detected only on MAVRIC images.

CONCLUSION

MAVRIC complements the information on FSE images after arthroplasty and is a useful additional sequence, particularly when there is concern about synovitis, periprosthetic osteolysis, or the presence of a supraspinatus tendon tear.

Radiology of the resurfaced hip

Hip resurfacing arthroplasty is an increasingly common procedure for osteoarthritis. Conventional radiographs are used routinely for follow-up assessment, however they only provide limited information on the radiological outcome. Various complications have been reported in the scientific literature although not all are fully understood. In an effort to investigate problematic or failing hip resurfacings, various radiological methods have been utilized. These methods can be used to help make a diagnosis and guide management. This paper aims to review and illustrate the radiographic findings in the form of radiography, computerized tomography (CT), magnetic resonance imaging (MRI), and ultrasound of both normal and abnormal findings in hip resurfacing arthroplasty. However, imaging around a metal prosthesis with CT and MRI is particularly challenging and therefore the potential techniques used to overcome this are discussed.

Catastrophic polyethylene failure diagnosed with magnetic resonance imaging in a painful total knee arthroplasty

Determining the etiology of a painful knee after arthroplasty can be extremely challenging. Traditionally, orthopedists relied mainly on physical examination, laboratory results, serial radiographs, and 3-phase bone or indium-labeled white blood cell scans; however, recent advances in magnetic resonance imaging (MRI) software have given orthopedists another powerful tool in their diagnostic armamentarium. We provide the MRI software modification technique for metallic artifact reduction as well as present a novel case in which MRI was used to diagnose catastrophic polyethylene postfailure in a posterior cruciate ligament substituting knee. Although the role for MRI in the postarthroplasty knee has yet to be clearly defined, its utility in working up a painful arthroplasty when history, physical examination, and other diagnostic utilities fail to provide answers is clearly demonstrated in this case.

Iliopsoas tendonitis due to the protrusion of an acetabular component fixation screw after total hip arthroplasty

Postoperative pain after total hip arthroplasty can have a wide range of underlying causes. Iliopsoas tendonitis secondary to the impingement of this tendon is a relatively rare cause of pain after arthroplasty. This condition is characterized by pain on active flexion and an absence of signs or symptoms of loosening or infection. In this report, we describe the case of a patient who had signs and symptoms of iliopsoas tendonitis secondary to the protrusion of an acetabular fixation screw through the ilium after primary total hip arthroplasty. Nonoperative treatment was ineffective, and the patient ultimately underwent surgical removal of the screw. The severity of the patient's symptoms decreased significantly after the operation.

Metal-related artifacts in instrumented spine. Techniques for reducing artifacts in CT and MRI: state of the art

The projectional nature of radiogram limits its amount of information about the instrumented spine. MRI and CT imaging can be more helpful, using cross-sectional view. However, the presence of metal-related artifacts at both conventional CT and MRI imaging can obscure relevant anatomy and disease. We reviewed the literature about overcoming artifacts from metallic orthopaedic implants at high-field strength MRI imaging and multi-detector CT. The evolution of multichannel CT has made available new techniques that can help minimizing the severe beam-hardening artifacts. The presence of artifacts at CT from metal hardware is related to image reconstruction algorithm (filter), tube current (in mA), X-ray kilovolt peak, pitch, hardware composition, geometry (shape), and location. MRI imaging has been used safely in patients with orthopaedic metallic implants because most of these implants do not have ferromagnetic properties and have been fixed into position. However, on MRI imaging metallic implants may produce geometric distortion, the so-called susceptibility artifact. In conclusion, although 140 kV and high milliamperage second exposures are recommended for imaging patients with hardware, caution should always be exercised, particularly in children, young adults, and patients undergoing multiple examinations. MRI artifacts can be minimized by positioning optimally and correctly the examined anatomy part with metallic implants in the magnet and by choosing fast spin-echo sequences, and in some cases also STIR sequences, with an anterior to posterior frequency-encoding direction and the smallest voxel size.