Managing Patients With Unlabeled Passive Implants on MR Systems Operating Below 1.5 T.

The standard of care for managing a patient with an implant is to identify the item and to assess the relative safety of scanning the patient. Because the 1.5 T MR system is the most prevalent scanner in the world and 3 T is the highest field strength in widespread use, implants typically have "MR Conditional" (i.e., an item with demonstrated safety in the MR environment within defined conditions) labeling at 1.5 and/or 3 T only. This presents challenges for a facility that has a scanner operating at a field strength below 1.5 T when encountering a patient with an implant, because scanning the patient is considered "off-label." In this case, the supervising physician is responsible for deciding whether to scan the patient based on the risks associated with the implant and the benefit of magnetic resonance imaging (MRI). For a passive implant, the MRI safety-related concerns are static magnetic field interactions (i.e., force and torque) and radiofrequency (RF) field-induced heating. The worldwide utilization of scanners operating below 1.5 T combined with the increasing incidence of patients with implants that need MRI creates circumstances that include patients potentially being subjected to unsafe imaging conditions or being denied access to MRI because physicians often lack the knowledge to perform an assessment of risk vs. benefit. Thus, physicians must have a complete understanding of the MRI-related safety issues that impact passive implants when managing patients with these products on scanners operating below 1.5 T. This monograph provides an overview of the various clinical MR systems operating below 1.5 T and discusses the MRI-related factors that influence safety for passive implants. Suggestions are provided for the management of patients with passive implants labeled MR Conditional at 1.5 and/or 3 T, referred to scanners operating below 1.5 T. The purpose of this information is to empower supervising physicians with the essential knowledge to perform MRI exams confidently and safely in patients with passive implants. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 3.

Identifying Hidden Zones of the Far Posterior Cartilage of the Femoral Condyles Not Visible During Knee Arthroscopy.

OBJECTIVE: The purpose of this study was to compare standard knee arthroscopic and MRI findings and measurements for visualization of the femoral condyle articular cartilage. The hypothesis was that certain posterior cartilage defects identified with MRI may not be accessible with routine arthroscopy. MATERIALS AND METHODS: Six cadaveric knees were examined by routine arthroscopy through standard inferomedial and inferolateral portals. Suture anchors were inserted into the femoral condyles at 30°, 60°, 90°, and 120° of flexion as markers of the cartilage surface at the most posterior aspect of the condyle that could be accessed at each degree of flexion. Each specimen was then examined with 3-T MRI and gross dissection. Measurements were obtained and compared. RESULTS: During arthroscopy at 90° of knee flexion, only 5.83 mm of the medial femoral condyle and 6.83 mm of the lateral femoral condyle were visualized posterior to the anchor placed at 90° of flexion. These arthroscopic measurements were statistically significant underestimates of the actual amount of cartilage identified posterior to the 90° anchor at gross dissection (medial condyle, 44.20 mm; lateral condyle, 37.50 mm) and MRI (medial, 41.33 mm; lateral, 38.87 mm). This indicates that 85.9% of the medial and 81.8% of the lateral posterior articular cartilage of the femoral condyle seen at MRI were not visualized during arthroscopy. CONCLUSION: More than 80% of the articular cartilage proximal to the menisci seen at MRI is not visible during routine arthroscopy. This far posterior articular cartilage should be called the hidden zone.

Xenograft bone-patellar tendon-bone ACL reconstruction: a case series at 20-year follow-up as proof of principle.

PURPOSE: ACL reconstruction has a significant failure rate. To address the need for inexpensive strong tissue, a treatment process to "humanize" porcine tissue was developed and tested in primates and humans. This report describes the long-term outcomes from the first human clinical trial using a porcine xenograft ACL reconstruction device. METHODS: The study was performed with Z-Lig™ xenograft ACL device in 2003 as a pilot clinical feasibility study. This device was processed to slow its immune-mediated destruction by enzymatic elimination of α-gal epitopes and by partial crosslinking to slow the infiltration of macrophages into the biotransplant. RESULTS: Ten patients underwent reconstruction with the Z-Lig™ device. Five of 10 patients failed due to subsequent trauma (n = 3), arthrofibrosis (n = 1), and surgical technical error (n = 1). One patient was lost to follow-up after the 12-year evaluation. Each remaining patient reported a stable fully athletic knee. Physical exams are consistent with a score of less than one on the ACL stability tests. MRIs demonstrate mature remodeling of the device. There is no significant degradation in patient-reported outcome scores, physical exams, or MRI appearance from 12 to 20-year follow-ups. CONCLUSIONS: The studies in a small group of patients have demonstrated that implantation of porcine ligament bioprosthesis into patients with torn ACLs can result in the reconstruction of the bioprosthesis into autologous ACL that remains successful over 20 years. The possibility of humanizing porcine tissue opens the door to unlimited clinical material for tissue reconstructions if supported by additional clinical trials. LEVEL OF EVIDENCE: IV, case series.

A quantitative approach to sequence and image weighting.

Weighting is the term most frequently used to describe magnetic resonance pulse sequences and the concept most commonly used to relate image contrast to differences in magnetic resonance tissue properties. It is generally used in a qualitative sense with the single tissue property thought to be most responsible for the contrast used to describe the weighting of the image as a whole. This article describes a quantitative approach for understanding the weighting of sequences and images, using filters and partial derivatives of signal with respect to logarithms of tissue property values. Univariate and multivariate models are described for several pulse sequences including methods for maximizing weighting and calculating both sequence and image weighting ratios. The approach provides insights into difficulties associated with qualitative use of the concept of weighting and a quantitative basis for assessing the signal, contrast, and weighting of commonly used sequences and images.

Magnetic Resonance Imaging for Patellofemoral Chondromalacia: Is There a Role for T2 Mapping?

BACKGROUND: Patellofemoral pain is common, and treatment is guided by the presence and grade of chondromalacia. PURPOSE: To evaluate and compare the sensitivity and specificity in detecting and grading chondral abnormalities of the patella between proton density fat suppression (PDFS) and T2 mapping magnetic resonance imaging (MRI). STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: A total of 25 patients who underwent MRI of the knee with both a PDFS sequence and T2 mapping and subsequently underwent arthroscopic knee surgery were included. The cartilage surface of the patella was graded on both MRI sequences by 2 independent, blinded radiologists. Cartilage was then graded during arthroscopic surgery by a sports medicine fellowship-trained orthopaedic surgeon. Reliability, sensitivity, specificity, and accuracy were determined for both MRI methods. The findings during arthroscopic surgery were considered the gold standard. RESULTS: Intraobserver and interobserver agreement for both PDFS (98.5% and 89.4%, respectively) and T2 mapping (99.4% and 91.3%, respectively) MRI were excellent. For T2 mapping, the sensitivity (61%) and specificity (64%) were comparable, whereas for PDFS there was a lower sensitivity (37%) but higher specificity (81%) in identifying cartilage abnormalities. This resulted in a similar accuracy for PDFS (59%) and T2 mapping (62%). CONCLUSION: Both PDFS and T2 mapping MRI were reliable but only moderately accurate in predicting patellar chondromalacia found during knee arthroscopic surgery.

Osteochondral grafting for failed knee osteochondritis dissecans repairs.

BACKGROUND: Revision of failed surgical treatments of osteochondritis dissecans (OCD) lesions remains a challenge without an obvious solution. The aim of this study was to evaluate seven consecutive patients undergoing osteochondral grafting of a failed OCD repair. METHODS: The mean time from surgery to the latest evaluation was 7.0 years. IKDC, WOMAC, Tegner, and MRI studies were collected both preoperatively and during follow-up. Evaluation of the graft was assessed using the magnetic resonance observation of cartilage repair tissue (MOCART) grading system. RESULTS: Over the course of the study period, five patients required additional surgery with a study median of one additional surgery (range, zero to 3). At most recent follow-up, there was significant improvement from preoperative values in median IKDC (p=0.004), WOMAC (p=0.030), and Tegner (p=0.012). Complete cartilage fill and adjacent tissue integration of the paste graft were observed by MRI evaluation in five of the seven (71.4%) patients. Definitive correlation between clinical outcomes and MRI scores was not observed. CONCLUSIONS: This study shows promising results of osteochondral grafting as a viable option for the revision of failed OCD lesion repairs; however, more patients are needed to fully support its efficacy in these challenging failed revision cases.

Bone marrow edema is the most specific finding for rheumatoid arthritis (RA) on noncontrast magnetic resonance imaging of the hands and wrists: a comparison of patients with RA and healthy controls.

OBJECTIVE: To evaluate the sensitivity and specificity of magnetic resonance imaging (MRI) in detecting erosions, bone edema, and synovitis in the metacarpophalangeal and wrist joints for rheumatoid arthritis (RA). METHODS: MRI scans of bilateral hands and wrists of 40 healthy subjects and 40 RA patients were performed using 0.2 T extremity-MRI and read blindly using a modified RA MRI (RAMRIS) system (no contrast injection, imaging in 1 plane only). To determine interreader reliability, images of 10 randomly selected subjects were read independently by a musculoskeletal radiologist. RESULTS: A total of 3360 bones were evaluated. Patients with RA had significantly more erosions as well as higher scores for bone edema and synovitis than healthy subjects. Age had a significant effect on the number of erosions in both groups. However, when disease duration was factored in, age became insignificant in RA patients. Erosion number correlated with positive rheumatoid factor and higher C-reactive protein values. The intraclass correlation coefficient between the 2 readers was 0.76 for individual joints and 0.88 for total scores. When having a single erosion was used as a positive test for RA, the sensitivity of this test was 90%, but the specificity was only 35%. Presence of bone edema provided 65% sensitivity and 82.5% specificity. Eliminating the lunate from scoring for bone edema increased the specificity to 87.5% while decreasing the sensitivity to 62.5%. CONCLUSION: While MRI is a highly sensitive tool for identifying and tracking the progression of erosions, erosions detected by MRI with measures commonly used in a rheumatologist's office (no contrast, imaging in 1 plane) provide low specificity for RA. Bone marrow edema is the most specific MRI lesion for RA in this setting.

Complexities of MRI and false positive findings.

MRI is a robust technology that allows for superior contrast of muscles, tissues, and bones within the body, which enables visualization of soft tissue pathology that cannot be seen with CT or plain film radiography. In order to appreciate the subtle (and sometimes not so subtle) intricacies of MRI, one must have a basic knowledge of the MRI physics involved to acquire an image, which leads to better recognition and a clearer understanding of some of the more important artifacts seen with MRI, including incomplete fat suppression, chemical shift, magnetic susceptibility, magic angle, partial volume, wraparound, and motion artifact. There are, however, many complexities and pitfalls in imaging the rheumatoid wrist. Normal anatomy such as capsular insertion sites and nutrient vessels can mimic erosion sites. The magic angle phenomenon can mimic tendon tears. Alignment abnormalities can be simulated based on wrist positioning. By having a solid understanding of the physics of magnetic resonance, anatomy, and the disease processes involved, many of these pitfalls can be avoided.

Technical considerations and potential advantages of musculoskeletal imaging at 3.0 Tesla.

High field magnetic resonance imaging at 3.0 T is rapidly gaining clinical acceptance as the preferred platform for magnetic resonance (MR) imaging. This is spurred in part because advances in the manufacture of magnet technology have brought the cost of 3.0-T magnets into the range of previous 1.5-T machines, as well as ongoing research demonstrating numerous advantages of 3.0 T over 1.5 T in neurological imaging. Many factors are responsible for improved imaging at higher field strength, including increased signal-to-noise and contrast-to-noise ratios. The impact of 3.0-T imaging of the musculoskeletal system has been less dramatic because its optimization is more complicated in the musculoskeletal system than in the brain. Many issues must be considered beyond what might be expected from simply doubling the field strength, including hardware design, protocol modifications because of changes in tissue characteristics at higher fields, artifact reduction, and safety. This article addresses many of these concerns, focusing on techniques to optimize high field MR imaging of the musculoskeletal system.

Ironman triathletes: MRI assessment of the shoulder.

OBJECTIVE: The objective of this paper was to demonstrate the prevalence of shoulder magnetic resonance imaging (MRI) abnormalities, including abnormal bone marrow signal at the acromioclavicular (AC) joint in symptomatic and asymptomatic Ironman Triathletes. MATERIALS AND METHODS: The shoulders of 23 Ironman Triathletes, seven asymptomatic (group I) and 16 symptomatic (group II), were studied by MRI. A separate, non-triathlete group was evaluated specifically for AC joint marrow signal abnormalities to compare with the Ironman Triathletes. RESULTS: Partial thickness tears of the rotator cuff, rotator cuff tendinopathy, and AC joint arthrosis were common findings in both groups of triathletes. Tendinopathy was the only finding that was more prevalent in the symptomatic group, but this was not a statistically significant difference (p = 0.35). There were no tears of the glenoid labrum seen in group I or II subjects. Of note is that 71% (5/7) of group I subjects and 62% (10/16) of group II subjects had increased signal changes in the marrow of the AC joint (p = 0.68). The comparison group showed a lower prevalence (35%, p = 0.06) of this finding. CONCLUSIONS: No statistically significant difference was found among the findings for group 1, group 2, or the comparison group, although the difference between the comparison group and Ironman Triathletes approached statistical significance when evaluating for AC joint abnormal signal. Shoulder MRI of Ironman Triathletes should be interpreted with an appreciation of the commonly seen findings in asymptomatic subjects.

Low-field musculoskeletal MRI.

Since it was first introduced in the field of medical imaging in the early 1980s, MRI has become essential for the diagnosis and treatment of musculoskeletal conditions. Most imaging in the United States is performed on high-field (>1.0T), whole-body scanners. However, for reasons discussed below, imaging at low (<0.5T) and medium (0.5-1.0T) field strengths using small, low-cost, easily installed scanners in imaging centers and physicians' offices is gaining increasing popularity. Such scanners can be very useful for imaging the upper and lower extremities, from the shoulder to the fingers and the hips to the toes. In this review we provide an overview of the different available extremity scanners and their advantages and disadvantages, briefly review the literature regarding their use, and discuss our experience in using low-field extremity scanners to evaluate joints.

3.0 Tesla imaging of the musculoskeletal system.

High-field MRI at 3.0T is rapidly gaining clinical acceptance and experiencing more widespread use. The superiority of high-field imaging has clearly been demonstrated for neurological imaging. The impact of 3.0T imaging of the musculoskeletal system has been less dramatic due to complex optimization issues. Areas under consideration include coil technology, protocol modification, artifact reduction, and patient safety. In this article we review these issues and describe our experience with 3.0T musculoskeletal MRI. Fundamentally, an increased signal-to-noise ratio (SNR) is responsible for improved imaging at higher field strength. Increased SNR allows more headroom to adjust parameters that affect image resolution and examination time. It has been established that T1 relaxation time increases at 3.0T, while T2 time decreases. Consequently, scanner parameters require adjustment for optimization of images. Chemical shift and magnetic susceptibility artifacts are more pronounced and require special techniques to minimize the effect on image quality. Spectral fat saturation techniques can take advantage of the increased chemical shift. The specific absorption rate (SAR) and acoustic noise thresholds must be kept in mind at these higher fields. We additionally present some of the clinical issues we have experienced at 3.0T. A decision must be made as to whether to trade higher resolution for reduced scanning time. In general, we believe that routine imaging at 3.0T increases diagnostic confidence, especially for evaluations of cartilaginous and ligamentous structures.

Low field MRI: a review of the literature and our experience in upper extremity imaging.

Since its introduction to medical imaging in the early 1980s, MRI has become essential in diagnosis and treatment of musculoskeletal conditions. Most imaging in the United States is performed on high-field whole-body scanners (>1.0 T). Imaging on low (<0.5 T) and medium (0.5-1.0 T) field strengths using small, low-cost, easily installed scanners in physicians' offices or imaging centers has gained popularity. These scanners can be useful in imaging the upper extremity from the shoulder to the fingers. This article provides an overview of the different extremity scanners available and their advantages and disadvantages, a brief review of the literature regarding their use, and a discussion of our experience in using the low-field extremity scanners in evaluating the upper extremity.

Magnetic resonance imaging is more sensitive than radiographs in detecting change in size of erosions in rheumatoid arthritis.

OBJECTIVE: To evaluate the technological performance of magnetic resonance imaging (MRI) with respect to projection radiography by determining the incidence of changes in the size of individual bone lesions in inflammatory arthritis, using serial high-resolution in-office MRI over short time intervals (8 months average followup), and by comparing the sensitivity of 3-view projection radiography with in-office MRI for detecting changes in size and number of individual erosions. METHODS: MR examinations of the wrists and second and third metacarpophalangeal joints were performed using a portable in-office MR system in a total of 405 patients with inflammatory arthritis, from one rheumatologist's practice, who were undergoing aggressive disease modifying antirheumatic drug therapy. Of the patients, 156 were imaged at least twice, allowing evaluation of 246 followup examinations (mean followup interval of 8 months over a 2-year period). Baseline and followup plain radiographs were obtained in 165 patient intervals. Patients refused radiographic examination on 81 followup visits. RESULTS: MRI demonstrated no detectable changes in 124 of the 246 (50%) followup MRI examinations. An increase in the size or number of erosions was demonstrated in 74 (30%) examinations, a decrease in the size or number of erosions in 36 (15%), and both increases and decreases in erosions were seen in 11 (4%). In the 165 studies with followup radiographic comparisons, only one examination (0.8%) showed an erosion not seen on the prior examination and one (0.8%) showed an increase in a previously noted erosion. CONCLUSION: We showed that high-resolution in-office MRI with an average followup of 8 months detects changes in bony disease in 50% of compliant patients during aggressive treatment for inflammatory arthritis in a single rheumatologist's office practice. Plain radiography is insensitive for detecting changes in bone erosions for this patient population in this time frame.

The young adult with hip pain: diagnosis and medical treatment, circa 2004.

Hip pain in young adults (18-35 years old) often is characterized by nonspecific symptoms, normal imaging studies, and vague findings from the history and physical examination. In younger patients, pain is more likely to be caused by congenital hip dysplasia, athletic injuries, trauma, spondyloarthropathy, and by conditions that first appear during this stage of life, such as rheumatoid arthritis, osteoarthritis, intravenous drug use, alcoholism, or corticosteroid use. The history and physical examination may narrow the diagnosis to intraarticular, extraarticular, or referred sources of pain. Plain radiography and magnetic resonance imaging are the preferred initial imaging procedures. Analyses of the blood, urine, and synovial fluid can be helpful in diagnosing inflammation, infection, and systematic rheumatic disease. Fractures, infection, and ischemic necrosis should be ruled out early because they require immediate treatment to prevent damage to the joint. Hip trauma at a young age increases the risk of osteoarthritis with advancing age, and, unlike most older adults, young adults receiving total hip replacement can expect revision surgery. Medical treatment often involves patient education, physical therapy, and pharmacotherapy. Acetaminophen, nonsteroidal anti-inflammatory drugs, and opioids for pain and antibiotics for infection are the most often prescribed drugs for this population.

MR procedures: biologic effects, safety, and patient care.

The technology used for magnetic resonance (MR) procedures has evolved continuously during the past 20 years, yielding MR systems with stronger static magnetic fields, faster and stronger gradient magnetic fields, and more powerful radiofrequency transmission coils. Most reported cases of MR-related injuries and the few fatalities that have occurred have apparently been the result of failure to follow safety guidelines or of use of inappropriate or outdated information related to the safety aspects of biomedical implants and devices. To prevent accidents in the MR environment, therefore, it is necessary to revise information on biologic effects and safety according to changes that have occurred in MR technology and with regard to current guidelines for biomedical implants and devices. This review provides an overview of and update on MR biologic effects, discusses new or controversial MR safety topics and issues, presents evidence-based guidelines to ensure safety for patients and staff, and describes safety information for various implants and devices that have recently undergone evaluation.

Identification of wrist and metacarpophalangeal joint erosions using a portable magnetic resonance imaging system compared to conventional radiographs.

OBJECTIVE: To compare magnetic resonance (MR) images obtained using a portable MR system to radiographs for identifying bone erosions in the wrists and metacarpophalangeal (MCP) joints of patients with inflammatory arthropathy. METHODS: MR imaging and radiographs were performed in wrists (n = 227) and 2nd and 3rd MCP (n = 188) of 132 patients with inflammatory arthritis to identify erosions. MR imaging was performed using a portable MR system. Findings per body location and per patient were calculated and compared. Additionally, intraobserver and interobserver reliabilities were calculated. RESULTS: MR imaging identified bony erosions in 125 (95%) patients and in 315 (78%) body locations. By comparison, radiographs identified erosions in 78 (59%; p < 0.05) patients and in 156 (39%; p < 0.05) body locations. Intraobserver reliability (K = 0.564) and interobserver reliability (K = 0.429) exhibited moderate agreement, with reader agreement in 80% of the joints scored. CONCLUSION: There was superior sensitivity to bone damage using the portable MR system compared to radiographs of the wrists and MCP joints, suggesting that this scanner is extremely promising for assessment of inflammatory arthritis.