Feasibility of using real-time MRI to measure joint kinematics in 1.5T and open-bore 0.5T systems

Bringing MRI to low- and middle-income countries: Directions, challenges and potential solutions

The global disparity of magnetic resonance imaging (MRI) is a major challenge, with many low- and middle-income countries (LMICs) experiencing limited access to MRI. The reasons for limited access are technological, economic and social. With the advancement of MRI technology, we explore why these challenges still prevail, highlighting the importance of MRI as the epidemiology of disease changes in LMICs. In this paper, we establish a framework to develop MRI with these challenges in mind and discuss the different aspects of MRI development, including maximising image quality using cost-effective components, integrating local technology and infrastructure and implementing sustainable practices. We also highlight the current solutions-including teleradiology, artificial intelligence and doctor and patient education strategies-and how these might be further improved to achieve greater access to MRI.

Real-Time Magnetic Resonance Imaging

Real-time magnetic resonance imaging (RT-MRI) allows for imaging dynamic processes as they occur, without relying on any repetition or synchronization. This is made possible by modern MRI technology such as fast-switching gradients and parallel imaging. It is compatible with many (but not all) MRI sequences, including spoiled gradient echo, balanced steady-state free precession, and single-shot rapid acquisition with relaxation enhancement. RT-MRI has earned an important role in both diagnostic imaging and image guidance of invasive procedures. Its unique diagnostic value is prominent in areas of the body that undergo substantial and often irregular motion, such as the heart, gastrointestinal system, upper airway vocal tract, and joints. Its value in interventional procedure guidance is prominent for procedures that require multiple forms of soft-tissue contrast, as well as flow information. In this review, we discuss the history of RT-MRI, fundamental tradeoffs, enabling technology, established applications, and current trends. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY STAGE: 1.

Development and Evaluation of a Subject-Specific Lower Limb Model With an Eleven-Degrees-of-Freedom Natural Knee Model Using Magnetic Resonance and Biplanar X-Ray Imaging During a Quasi-Static Lunge

Musculoskeletal (MS) models can be used to study the muscle, ligament, and joint mechanics of natural knees. However, models that both capture subject-specific geometry and contain a detailed joint model do not currently exist. This study aims to first develop magnetic resonance image (MRI)-based subject-specific models with a detailed natural knee joint capable of simultaneously estimating in vivo ligament, muscle, tibiofemoral (TF), and patellofemoral (PF) joint contact forces and secondary joint kinematics. Then, to evaluate the models, the predicted secondary joint kinematics were compared to in vivo joint kinematics extracted from biplanar X-ray images (acquired using slot scanning technology) during a quasi-static lunge. To construct the models, bone, ligament, and cartilage structures were segmented from MRI scans of four subjects. The models were then used to simulate lunges based on motion capture and force place data. Accurate estimates of TF secondary joint kinematics and PF translations were found: translations were predicted with a mean difference (MD) and standard error (SE) of 2.13 ± 0.22 mm between all trials and measures, while rotations had a MD ± SE of 8.57 ± 0.63 deg. Ligament and contact forces were also reported. The presented modeling workflow and the resulting knee joint model have potential to aid in the understanding of subject-specific biomechanics and simulating the effects of surgical treatment and/or external devices on functional knee mechanics on an individual level.

Dynamic MRI for articulating joint evaluation on 1.5 T and 3.0 T scanners: setup, protocols, and real-time sequences

Dynamic magnetic resonance imaging (MRI) is a non-invasive method that can be used to increase the understanding of the pathomechanics of joints. Various types of real-time gradient echo sequences used for dynamic MRI acquisition of joints include balanced steady-state free precession sequence, radiofrequency-spoiled sequence, and ultra-fast gradient echo sequence. Due to their short repetition time and echo time, these sequences provide high temporal resolution, a good signal-to-noise ratio and spatial resolution, and soft tissue contrast. The prerequisites of the evaluation of joints with dynamic MRI include suitable patient installation and optimal positioning of the joint in the coil to allow joint movement, sometimes with dedicated coil support. There are currently few recommendations in the literature regarding appropriate protocol, sequence standardizations, and diagnostic criteria for the use of real-time dynamic MRI to evaluate joints. This article summarizes the technical parameters of these sequences from various manufacturers on 1.5 T and 3.0 T MRI scanners. We have reviewed pertinent details of the patient and coil positioning for dynamic MRI of various joints. The indications and limitations of dynamic MRI of joints are discussed.

Measuring three-dimensional tibiofemoral kinematics using dual-slice real-time magnetic resonance imaging

PURPOSE

The purpose of this study is to propose and evaluate a slice-to-volume registration (SVR) method integrating an advanced dual-slice real-time magnetic resonance image (MRI) and three-dimensional (3D) MRI volume of the tibiofemoral joint for determining their 3D kinematics.

METHODS

The real-time and 3D MRI of the knee were collected from 12 healthy adults at 5 static flexion positions and during dynamic flexion/extension movement. The 3D positions and orientations of the femur and tibia were obtained by registering their volumetric models constructed from the 3D MRI to dual-slice real-time MRI using an optimization process. The proposed method was quantitatively evaluated for its performance in terms of the robustness and measurement accuracy, and compared to those of a single-slice SVR method. Its repeatability in measuring knee kinematics during flexion/extension movement was also determined.

RESULTS

In comparison to the single-slice SVR method, the dual-slice method was significantly superior, giving a successful registration rate > 95%, a bias less than 0.5 mm in translations and 0.6° in rotations and a precision <0.7 mm in translations and 0.9° in rotations for determining the 3D tibiofemoral poses. For repeatability of the dual-slice SVR in measuring tibiofemoral kinematics during dynamic flexion/extension, the means of the time-averaged standard deviations were <0.9° for joint angles and 0.5 mm for joint translations.

CONCLUSION

A dual-slice SVR method in conjunction with real-time MRI has been developed and evaluated for its performance in measuring 3D kinematics of the tibiofemoral joint in 12 young adults in terms of the accuracy, robustness, and repeatability. The proposed MRI-based 3D measurement method provides a noninvasive and ionizing radiation-free approach for 3D kinematic measurement of the tibiofemoral joint, which will be helpful for future academic and clinical applications.

Real-Time Assessment of Femoroacetabular Motion Using Radial Gradient Echo Magnetic Resonance Arthrography at 3 Tesla in Routine Clinical Practice: A Pilot Study

PURPOSE

To compare femoroacetabular motion in a series of consecutive symptomatic patients with hip pain throughout the range of motion of the hip using a real-time radial gradient echo (GRE) sequence in addition to the routine hip protocol sequences for magnetic resonance (MR) arthrographic assessment of patients with and without clinical femoroacetabular impingement (FAI) syndrome. In particular, we sought to assess whether the additional dynamic sequence could differentiate between patients with and without a positive physical exam maneuver for FAI syndrome.

METHODS

Patients with hip pain referred for conventional hip MR arthrogram including those with and without a positive physical exam maneuver for FAI syndrome were imaged using routine hip MR arthrogram protocol and an additional real-time radial 2-dimensional GRE acquisition at 3 Tesla in an axial oblique plane with continuous scanning of a 9 mm thick slice through the center of the femoral head-neck axis. Patients who were unable to move through the range of motion were excluded (n = 3). Patients with acetabular dysplasia (defined by a lateral center-edge angle [CEA] of 20°) were also excluded, as were patients had Kellgren and Lawrence scores of > 0. The real-time cine sequence was acquired with the patient actively moving through neutral, flexion, flexion-abduction external-rotation, and flexion-adduction internal rotation (FADIR) positions aiming for 40° of abduction, then 25° of adduction at 80° to 90° flexion. Due to the placement of the coil over the hip, a true FADIR was precluded. Images were evaluated independently by 2 musculoskeletal radiologists measuring the joint space in the anterior, central, and posterior positions at each point during range of motion for femoroacetabular cortical space (FACS). Anterior FACS narrowing was calculated as the ratio of joint space in FADIR:neutral position, with lower ratios indicating greater narrowing. Static metrics including alpha angle, CEA, grade of cartilage loss according the Outerbridge classification, and patient demographics were also recorded.

RESULTS

Twenty-two painful hips in 22 patients (11 males and 11 females) with mean age 36 years (range, 15-67) were included. Twelve patients had a positive physical exam maneuver for FAI syndrome. The time to perform the dynamic sequence was 3 to 6 minutes. Interobserver agreement was strong, with intraclass correlation 0.91 and concordance correlation 0.90. According to results from both readers, patients with impingement on clinical exam had significantly lower anterior FACS ratios compared with those without clinical impingement (reader 1: 0.39 ± 0.10 vs 0.69 ± 0.20, P = .001; reader 2: 0.36 ± 0.07 vs 0.70 ± 0.17, P < .001). Decreased anterior FACS ratio was found to be significantly correlated to increased alpha angle by both readers (reader 1: R = -0.63, P = .002; reader 2: R = -0.67, P = .001) but not significantly correlated to CEA (reader 1: R = 0.13, P = .561; reader 2: R = 0.20, P = .378) or cartilage loss (reader 1: R = 0.03, P = .885; reader 2: R = -0.06, P = .784). Both readers found patients with an anterior FACS ratio of 1/2 to have significantly higher mean alpha angle (reader 1: 62.88 vs 52.79, P = .038; reader 2: 63.50 vs 50.58, P = .006); however, there were no significant differences in cartilage loss (reader 1: P = .133; reader 2: P = .882) or CEA (reader 1: P = .340; reader 2: P = .307).

CONCLUSIONS

A dynamic radial 2-dimensional-GRE sequence can be added to standard hip MR arthrogram protocols in <6 minutes, allowing assessment of dynamic femoroacetabular motion with strong interreader agreement. Patients with impingement on clinical exam had significantly lower anterior FACS ratios between FADIR and neutral positions, compared with those without clinical impingement.

LEVEL OF EVIDENCE

Level III, comparative diagnostic investigation.

A model-based tracking method for measuring 3D dynamic joint motion using an alternating biplane x-ray imaging system

PURPOSES

To propose a new model-based tracking method for measuring three-dimensional (3D) dynamic joint kinematics using a clinical alternating biplane x-ray imaging system; and to quantify in vitro its errors in measuring ankle and knee motions at different motion speeds.

METHODS

A new model-based tracking method based on motion component partition and interpolation (MCPI) was developed for measuring 3D dynamic joint kinematics based on a clinical alternating biplane x-ray imaging system. Two detectors of the biplane imaging system placed perpendicular to each other were operated to collect alternating fluoroscopic images of the targeted joint during tasks. The CT data of the joint were also acquired for the reconstruction of volumetric and surface models of each of the associated bones. The CT-based models of the bones were first registered to the alternating images using a model-to-single-plane fluoroscopic image registration method, and the resulting bone poses were then refined using a two-level optimization with motion component partition and model vertex trajectory interpolation. The MCPI method was evaluated in vitro for measurement errors for an ankle and a knee specimen moving at different speeds against a standard reference provided by a highly accurate motion capture system. The positional and rotational errors of the measured bone poses were quantified in terms of the bias, precision, and root-mean-squared errors (RMSE), as well as the mean target registration error (mTRE), a final mTRE less than 2.5 mm indicating a successful registration.

RESULTS

The new method was found to have RMSE of bone pose measurements of less than 0.18 mm for translations and 0.72° for rotations for the ankle, and 0.33 mm and 0.74° for the knee with a high successful registration rate (>97%), and did not appear to be affected by joint motion speeds. Given the same alternating fluoroscopic images, the MCPI method outperformed the typical biplane analysis method assuming zero time offset between the two fluoroscopic views. The differences in performance between the methods were increased with increased joint motion speed. With the accurate bone pose data, the new method enabled talocrural, subtalar, and tibiofemoral kinematics measurements with submillimeter and subdegree accuracy, except for an RMSE of 1.04° for the internal/external rotation of the talocrural joint.

CONCLUSIONS

A new model-based tracking method based on MCPI has been developed for measuring dynamic joint motions using an alternating biplane x-ray imaging system widely available in medical centers. The MCPI method has been demonstrated in vitro to be highly accurate in determining the 3D kinematics of the bones of both the ankle joint complex and the knee. The current results suggest that the MCPI method would be an effective approach for measuring in vivo 3D kinematics of dynamic joint motion in a clinical setting equipped with an alternating biplane x-ray imaging system.

Clinical Utility of Continuous Radial Magnetic Resonance Imaging Acquisition at 3 T in Real-time Patellofemoral Kinematic Assessment: A Feasibility Study

PURPOSE

To compare patellar instability with magnetic resonance imaging analysis using continuous real-time radial gradient-echo (GRE) imaging in the assessment of symptomatic patients and asymptomatic subjects.

METHODS

Symptomatic patients with suspected patellofemoral maltracking and asymptomatic volunteers were scanned in real time by a radial 2-dimensional GRE sequence at 3 T in axial orientation at the patella level through a range of flexion-extension. The degree of lateral maltracking, as well as the associated tibial tubercle-trochlear groove distance and trochlea depth, was measured. Patellar lateralization was categorized as normal (≤2 mm), mild (>2 to ≤5 mm), moderate (>5 to ≤10 mm), or severe (>10 mm). The patellofemoral cartilage was also assessed according to the modified Outerbridge grading system.

RESULTS

The study included 20 symptomatic patients (13 women and 7 men; mean age, 36 ± 12.8 years) and 10 asymptomatic subjects (3 women and 7 men; mean age, 33.1 years). The mean time to perform the dynamic component ranged from 3 to 7 minutes. Lateralization in the symptomatic group was normal in 10 patients, mild in 1, moderate in 8, and severe in 1. There was no lateral tracking greater than 3 mm in the volunteer group. Lateral maltracking was significantly higher in symptomatic patients than in asymptomatic subjects (4.4 ± 3.7 mm vs 1.5 ± 0.71 mm, P = .007). Lateral tracking significantly correlated with tibial tubercle-trochlear groove distance (r = 0.48, P = .006). There was excellent agreement on lateral tracking between the 2 reviewers (intraclass correlation coefficient, 0.979; 95% confidence interval, 0.956-0.990).

CONCLUSIONS

The inclusion of a dynamic radial 2-dimensional GRE sequence is a rapid and easily performed addition to the standard magnetic resonance imaging protocol and allows dynamic quantitative assessment of patellar instability and lateral maltracking in symptomatic patients. With a paucity of reported data using this technique confirming that these results reach clinical significance, future work is required to determine how much lateral tracking is clinically significant.

LEVEL OF EVIDENCE

Level III, case control.

Dynamic MRI to quantify musculoskeletal motion: A systematic review of concurrent validity and reliability, and perspectives for evaluation of musculoskeletal disorders

Purpose

To report evidence for the concurrent validity and reliability of dynamic MRI techniques to evaluate in vivo joint and muscle mechanics, and to propose recommendations for their use in the assessment of normal and impaired musculoskeletal function.

Materials and methods

The search was conducted on articles published in Web of science, PubMed, Scopus, Academic search Premier, and Cochrane Library between 1990 and August 2017. Studies that reported the concurrent validity and/or reliability of dynamic MRI techniques for in vivo evaluation of joint or muscle mechanics were included after assessment by two independent reviewers. Selected articles were assessed using an adapted quality assessment tool and a data extraction process. Results for concurrent validity and reliability were categorized as poor, moderate, or excellent.

Results

Twenty articles fulfilled the inclusion criteria with a mean quality assessment score of 66% (±10.4%). Concurrent validity and/or reliability of eight dynamic MRI techniques were reported, with the knee being the most evaluated joint (seven studies). Moderate to excellent concurrent validity and reliability were reported for seven out of eight dynamic MRI techniques. Cine phase contrast and real-time MRI appeared to be the most valid and reliable techniques to evaluate joint motion, and spin tag for muscle motion.

Conclusion

Dynamic MRI techniques are promising for the in vivo evaluation of musculoskeletal mechanics; however results should be evaluated with caution since validity and reliability have not been determined for all joints and muscles, nor for many pathological conditions.

Accuracy of model-based tracking of knee kinematics and cartilage contact measured by dynamic volumetric MRI

The purpose of this study was to determine the accuracy of knee kinematics and cartilage contact measured by volumetric dynamic MRI. A motor-actuated phantom drove femoral and tibial bone segments through cyclic 3D motion patterns. Volumetric images were continuously acquired using a 3D radially undersampled cine spoiled gradient echo sequence (SPGR-VIPR). Image data was binned based on position measured via a MRI-compatible rotary encoder. High-resolution static images were segmented to create bone models. Model-based tracking was performed by optimally registering the bone models to the volumetric images at each frame of the SPGR-VIPR series. 3D tibiofemoral translations and orientations were reconstructed, and compared to kinematics obtained by tracking fiducial markers. Imaging was repeated on a healthy subject who performed cyclic knee flexion-extension. Cartilage contact for the subject was assessed by measuring the overlap between articular cartilage surfaces. Model-based tracking was able to track tibiofemoral angles and translations with precisions less than 0.8° and 0.5mm. These precisions resulted in an uncertainty of less than 0.5mm in cartilage contact location. Dynamic SPGR-VIPR imaging can accurately assess in vivo knee kinematics and cartilage contact during voluntary knee motion performed in a MRI scanner. This technology could facilitate the quantitative investigation of links between joint mechanics and the development of osteoarthritis.

A target field design of open multi-purpose RF coil for musculoskeletal MR imaging at 3T

Musculoskeletal MR imaging under multi-angle situations plays an increasingly important role in assessing joint and muscle tissues system. However, there are still limitations due to the closed structures of most conventional RF coils. In this study, a time-harmonic target-field method was employed to design open multi-purpose coil (OMC) for multi-angle musculoskeletal MR imaging. The phantom imaging results suggested that the proposed OMC could achieve homogeneously distributed magnetic field and high signal-to-noise ratio (SNR) of 239.04±0.83 in the region of interest (ROI). The maximum temperature in the heating hazard test was 16°C lower than the standard regulation, which indicated the security of the designed OMC. Furthermore, to demonstrate the effectiveness of the proposed OMC for musculoskeletal MR imaging, especially for multi-angle imaging, a healthy volunteer was examined for MR imaging of elbow, ankle and knee using OMC. The in vivo imaging results showed that the proposed OMC is effective for MR imaging of musculoskeletal tissues at different body parts, with satisfied B1 field homogeneity and SNR. Moreover, the open structure of the OMC could provide a large joint movement region. The proposed open multi-purpose coil is feasible for musculoskeletal MR imaging, and potentially, it is more suitable for the evaluation of musculoskeletal tissues under multi-angle conditions.

In vivo articular cartilage deformation: noninvasive quantification of intratissue strain during joint contact in the human knee

The in vivo measurement of articular cartilage deformation is essential to understand how mechanical forces distribute throughout the healthy tissue and change over time in the pathologic joint. Displacements or strain may serve as a functional imaging biomarker for healthy, diseased, and repaired tissues, but unfortunately intratissue cartilage deformation in vivo is largely unknown. Here, we directly quantified for the first time deformation patterns through the thickness of tibiofemoral articular cartilage in healthy human volunteers. Magnetic resonance imaging acquisitions were synchronized with physiologically relevant compressive loading and used to visualize and measure regional displacement and strain of tibiofemoral articular cartilage in a sagittal plane. We found that compression (of 1/2 body weight) applied at the foot produced a sliding, rigid-body displacement at the tibiofemoral cartilage interface, that loading generated subject- and gender-specific and regionally complex patterns of intratissue strains, and that dominant cartilage strains (approaching 12%) were in shear. Maximum principle and shear strain measures in the tibia were correlated with body mass index. Our MRI-based approach may accelerate the development of regenerative therapies for diseased or damaged cartilage, which is currently limited by the lack of reliable in vivo methods for noninvasive assessment of functional changes following treatment.

Fluoroscopy-based tracking of femoral kinematics with statistical shape models

PURPOSE

Precise knee kinematics assessment helps to diagnose knee pathologies and to improve the design of customized prosthetic components. The first step in identifying knee kinematics is to assess the femoral motion in the anatomical frame. However, no work has been done on pathological femurs, whose shape can be highly different from healthy ones.

METHODS

We propose a new femoral tracking technique based on statistical shape models and two calibrated fluoroscopic images, taken at different flexion-extension angles. The cost function optimization is based on genetic algorithms, to avoid local minima. The proposed approach was evaluated on 3 sets of digitally reconstructed radiographic images of osteoarthritic patients.

RESULTS

It is found that using the estimated shape, rather than that calculated from CT, significantly reduces the pose accuracy, but still has reasonably good results (angle errors around 2[Formula: see text], translation around 1.5 mm).

Combined magnetic resonance imaging approach for the assessment of in vivo knee joint kinematics under full weight-bearing conditions

The development of detailed and specific knowledge on the biomechanical behavior of loaded knee structures has received increased attention in recent years. Stress magnetic resonance imaging techniques have been introduced in previous work to study knee kinematics under load conditions. Previous studies captured the knee movement either in atypical loading supine positions, or in upright positions with help of inclined supporting backrests being insufficient for movement capture under full-body weight-bearing conditions. In this work, we used a combined magnetic resonance imaging approach for measurement and assessment in knee kinematics under full-body weight-bearing in single legged stance. The proposed method is based on registration of high-resolution static magnetic resonance imaging data acquired in supine position with low-resolution data, quasi-static upright-magnetic resonance imaging data acquired in loaded positions for different degrees of knee flexion. The proposed method was applied for the measurement of tibiofemoral kinematics in 10 healthy volunteers. The combined magnetic resonance imaging approach allows the non-invasive measurement of knee kinematics in single legged stance and under physiological loading conditions. We believe that this method can provide enhanced understanding of the loaded knee kinematics.

A fast, accurate, and reliable reconstruction method of the lumbar spine vertebrae using positional MRI

In vivo measurement of lumbar spine configuration is useful for constructing quantitative biomechanical models. Positional magnetic resonance imaging (MRI) accommodates a larger range of movement in most joints than conventional MRI and does not require a supine position. However, this is achieved at the expense of image resolution and contrast. As a result, quantitative research using positional MRI has required long reconstruction times and is sensitive to incorrectly identifying the vertebral boundary due to low contrast between bone and surrounding tissue in the images. We present a semi-automated method used to obtain digitized reconstructions of lumbar vertebrae in any posture of interest. This method combines a high-resolution reference scan with a low-resolution postural scan to provide a detailed and accurate representation of the vertebrae in the posture of interest. Compared to a criterion standard, translational reconstruction error ranged from 0.7 to 1.6 mm and rotational reconstruction error ranged from 0.3 to 2.6°. Intraclass correlation coefficients indicated high interrater reliability for measurements within the imaging plane (ICC 0.97-0.99). Computational efficiency indicates that this method may be used to compile data sets large enough to account for population variance, and potentially expand the use of positional MRI as a quantitative biomechanics research tool.

Load-dependent variations in knee kinematics measured with dynamic MRI

Subtle changes in knee kinematics may substantially alter cartilage contact patterns and moment generating capacities of soft tissues. The objective of this study was to use dynamic magnetic resonance imaging (MRI) to measure the influence of the timing of quadriceps loading on in vivo tibiofemoral and patellofemoral kinematics. We tested the hypothesis that load-dependent changes in knee kinematics would alter both the finite helical axis of the tibiofemoral joint and the moment arm of the patellar tendon. Eight healthy young adults were positioned supine in a MRI-compatible device that could impose either elastic or inertial loads on the lower leg in response to cyclic knee flexion-extension. The elastic loading condition induced concentric quadriceps contractions with knee extension, while an inertial loading condition induced eccentric quadriceps contractions with knee flexion. Peak internal knee extension moments ranged from 23 to 33 N m, which is comparable to loadings seen in normal walking. We found that anterior tibia translation, superior patella glide, and anterior patella translation were reduced by an average of 5.1, 5.7 and 2.9 mm when quadriceps loading coincided with knee flexion rather than knee extension. These kinematic variations induced a distal shift in the finite helical axis of the tibiofemoral joint and a reduction in the patellar tendon moment arm. We conclude that it may be important to consider such load-dependent changes in knee kinematics when using models to ascertain soft tissue and cartilage loading during functional tasks such as gait.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation and progression of osteoarthritis. However, our understanding of which mechanical parameters are most important, and what their impact is on the disease, is limited by the challenge of measuring the most important mechanical quantities in living subjects. Consequently, comprehensive statements cannot be made about how mechanics should be modified to prevent, slow or arrest osteoarthritis. Our current understanding is based largely on studies of deviations from normal mechanics caused by malalignment, injury, and deformity. Some treatments for osteoarthritis focus on correcting mechanics, but there appears to be scope for more mechanically based interventions.

Dynamic MR imaging of a minipig's knee using a high-density multi-channel receive array and a movement device

OBJECT

To construct an optimised, high-density receive array and a movement device to achieve dynamic imaging of the knee in orthopedic large animal models (e.g., minipigs) at 1.5 T.

MATERIALS AND METHODS

A 13-channel RF receive array was constructed, and the crucial choice of the array element size (based on considerations like region of interest, geometry of the minipig's knee, achievable signal-to-noise ratio, applicability of parallel imaging, etc.) was determined using the Q factors of loops with different sizes. A special movement device was constructed to guide and produce a reproducible motion of the minipig's knee during acquisition.

RESULTS

The constructed array was electrically characterised and the reproducibility of the cyclic motion was validated. Snapshots of dynamic in vivo images taken at a temporal resolution (308 ms) are presented. Some of the fine internal structures within the minipig's knee, like cruciate ligaments, are traced in the snapshots.

CONCLUSION

This study is a step towards making dynamic imaging which can give additional information about joint injuries when static MRI is not able to give sufficient information, a routine clinical application. There, the combination of a high-density receive array and a movement device will be highly helpful in the diagnosis and therapy monitoring of knee injuries in the future.

Advances in musculoskeletal MRI: technical considerations

The technology of musculoskeletal magnetic resonance imaging (MRI) is advancing at a dramatic rate. MRI is now done at medium and higher field strengths with more specialized surface coils and with more variable pulse sequences and postprocessing techniques than ever before. These innumerable technical advances are advantageous as they lead to an increased signal-to-noise ratio and increased variety of soft-tissue contrast options. However, at the same time they potentially produce more imaging artifacts when compared with past techniques. Substantial technical advances have considerable clinical challenges in musculoskeletal radiology such as postoperative patient imaging, cartilage mapping, and molecular imaging. In this review we consider technical advances in hardware and software of musculoskeletal MRI along with their clinical applications.

Measurement of tibiofemoral kinematics using highly accelerated 3D radial sampling

This study investigated the use of dynamic, volumetric MRI to measure 3D skeletal motion. Ten healthy subjects were positioned on a MR-compatible knee loading device and instructed to harmonically flex and extend their knee at 0.5 Hz. The device induced active quadriceps loading with knee flexion, similar to the load acceptance phase of gait. Volumetric images were continuously acquired for 5 min using a 3D cine spoiled gradient-echo sequence in conjunction with vastly under-sampled isotropic projection reconstruction. Knee angle was simultaneously monitored and used retrospectively to sort images into 60 frames over the motion cycle. High-resolution static knee images were acquired and segmented to create subject-specific models of the femur and tibia. At each time frame, bone positions and orientations were determined by automatically registering the skeletal models to the dynamic images. Three-dimensional tibiofemoral translations and rotations were consistent across healthy subjects. Internal tibia rotations of 7.8±3.5° were present with 35.8±3.8° of knee flexion, a pattern consistent with knee kinematic measures during walking. We conclude that vastly under-sampled isotropic projection reconstruction imaging is a promising approach for noninvasively measuring 3D joint kinematics, which may be useful for assessing cartilage contact and investigating the causes and treatment of joint abnormalities.

Advances in musculoskeletal magnetic resonance imaging

The technology of musculoskeletal magnetic resonance imaging is advancing at a dramatic rate. Magnetic resonance imaging is now done at medium and higher field strengths with more specialized surface coils and with more variable pulse sequences and postprocessing techniques than ever before. These numerable technical advances are advantageous because they lead to an increased signal-to-noise ratio and increased variety of soft tissue contrast options. However, at the same time, they potentially produce more imaging artifacts when compared with past techniques. Substantial technical advances have considerable clinical challenges in musculoskeletal radiology such as postoperative patient imaging, cartilage mapping, and molecular imaging. In this review, we consider technical advances in hardware and software of musculoskeletal magnetic resonance imaging along with their clinical applications.

Joint mechanics measurement using magnetic resonance imaging

Magnetic resonance imaging-based methods for measuring the mechanics of human joints have been successfully applied to quantitatively evaluate biomechanics in a wide variety of joints, pathologies, and interventions. The objective of this review was to provide a detailed overview of methods in the literature for measuring joint kinematics, meniscal and ligament movement, and cartilage strain using MRI.

MRI of weight bearing and movement

Conventional, static magnetic resonance imaging (MRI) is able to provide a vast amount of information regarding the anatomy and pathology of the musculoskeletal system. However, patients, especially those whose pain is position dependent or elucidated by movement, may benefit from more advanced imaging techniques that allow for the acquisition of functional information. This manuscript reviews a variety of advancements in MRI techniques that are used to image the musculoskeletal system dynamically, while in motion or under load. The methodologies, advantages and drawbacks of stress MRI, cine-phase contrast MRI and real-time MRI are discussed as each has helped to advance the field by providing a scientific basis for understanding normal and pathological musculoskeletal anatomy and function. Advancements in dynamic MR imaging will certainly lead to improvements in the understanding, prevention, diagnosis and treatment of musculoskeletal disorders. It is difficult to anticipate that dynamic MRI will replace conventional MRI, however, dynamic MRI may provide additional valuable information to findings of conventional MRI.

The effect of a patellar brace on three-dimensional patellar kinematics in patients with lateral patellofemoral osteoarthritis

OBJECTIVE

Patellar bracing is a mechanical treatment strategy for patellofemoral osteoarthritis (OA) that aims to unload the lateral compartment of the joint by translating the patella medially. Our objective was to determine whether a patellar brace can correct patellar kinematics in patients with patellofemoral OA.

DESIGN

We assessed the effect of a patellar brace on three-dimensional patellar kinematics (flexion, spin and tilt; proximal, lateral and anterior translation) at sequential, static knee postures, using a validated magnetic resonance imaging (MRI)-based method, in 19 patients with radiographic lateral patellofemoral OA. Differences in kinematics between unbraced and braced conditions were assessed in the unloaded and loaded knee (15% bodyweight load) using hierarchical linear random-effects models. Random slope and quadratic terms were included in the model when significant (P<0.05).

RESULTS

Bracing with load caused the patellae to translate 0.46 mm medially (P<0.001), tilt 1.17° medially (P<0.001), spin 0.62° externally (P=0.012) and translate 1.09 mm distally (P<0.001) and 0.47 mm anteriorly (P<0.001) over the range of knee flexion angles studied. Bracing also caused the patellae to extend in early angles of knee flexion (P<0.001). The brace caused similar trends for the unloaded condition, though magnitudes of the changes varied.

CONCLUSION

Bracing changed patellar kinematics, but these changes did not appear large enough to be clinically meaningful because no reduction in pain was observed in the parent study.

Differences in patellofemoral kinematics between weight-bearing and non-weight-bearing conditions in patients with patellofemoral pain

Patellar maltracking is thought to be one source of patellofemoral pain. Measurements of patellar tracking are frequently obtained during non-weight-bearing knee extension; however, pain typically arises during highly loaded activities, such as squatting, stair climbing, and running. It is unclear whether patellofemoral joint kinematics during lightly loaded tasks replicate patellofemoral joint motion during weight-bearing activities. The purpose of this study was to: evaluate differences between upright, weight-bearing and supine, non-weight-bearing joint kinematics in patients with patellofemoral pain; and evaluate whether the kinematics in subjects with maltracking respond differently to weight-bearing than those in nonmaltrackers. We used real-time magnetic resonance imaging to visualize the patellofemoral joint during dynamic knee extension from 30° to 0° of knee flexion during two conditions: upright, weight-bearing and supine, non-weight-bearing. We compared patellofemoral kinematics measured from the images. The patella translated more laterally during the supine task compared to the weight-bearing task for knee flexion angles between 0° and 5° (p = 0.001). The kinematics of the maltrackers responded differently to joint loading than those of the non-maltrackers. In subjects with excessive lateral patellar translation, the patella translated more laterally during upright, weight-bearing knee extension for knee flexion angles between 25° and 30° (p = 0.001). However, in subjects with normal patellar translation, the patella translated more laterally during supine, non-weight-bearing knee extension near full extension (p = 0.001). These results suggest that patellofemoral kinematics measured during supine, unloaded tasks do not accurately represent the joint motion during weight-bearing activities.

Assessing the accuracy and precision of musculoskeletal motion tracking using cine-PC MRI on a 3.0T platform

The rising cost of musculoskeletal pathology, disease, and injury creates a pressing need for accurate and reliable methods to quantify 3D musculoskeletal motion, fostering a renewed interest in this area over the past few years. To date, cine-phase contrast (PC) MRI remains the only technique capable of non-invasively tracking in vivo 3D musculoskeletal motion during volitional activity, but current scan times are long on the 1.5T MR platform (∼ 2.5 min or 75 movement cycles). With the clinical availability of higher field strength magnets (3.0T) that have increased signal-to-noise ratios, it is likely that scan times can be reduced while improving accuracy. Therefore, the purpose of this study is to validate cine-PC MRI on a 3.0T platform, in terms of accuracy, precision, and subject-repeatability, and to determine if scan time could be minimized. On the 3.0T platform it is possible to limit scan time to 2 min, with sub-millimeter accuracy (<0.33 mm/0.97°), excellent technique precision (<0.18°), and strong subject-repeatability (<0.73 mm/1.10°). This represents reduction in imaging time by 25% (42 s), a 50% improvement in accuracy, and a 72% improvement in technique precision over the original 1.5T platform. Scan time can be reduced to 1 min (30 movement cycles), but the improvements in accuracy are not as large.

Clinical feasibility of a magnetic resonance tracking system to guide the position of the scan plane during physiologic joint motion

PURPOSE

Unrestricted physiologic joint motion results in multidirectional displacement of the anatomic structures. When performing real-time magnetic resonance (MR) imaging of such a joint motion, continuous adjustment of the scan plane position may be required. The purpose of this study was to evaluate the clinical feasibility of a method to guide the scan plane position during dynamic-motion MR imaging of freely moving joints.

MATERIALS AND METHODS

The location of a small tracker device (dedicated hardware) placed on the patient's skin overlying a joint was determined by an ultrashort MR sequence and used to automatically adjust the scan plane position prior to each dynamic-motion MR image. Using a vertically open MR unit, this MR tracking system was applied in ten dynamic-motion MR examinations to evaluate flexion/extension manoeuvres in the weight-bearing knee joint, and in ten dynamic-motion MR examinations of the shoulder joint to evaluate manoeuvres such as internal/external rotation of the humerus, stress testing of the glenohumeral joint and abduction/adduction manoeuvres. Average number of manoeuvre repetitions, total number of images and percentage of useful images per manoeuvre were calculated. Imaging time per scan plane for each manoeuvre was recorded.

RESULTS

Average repetition of manoeuvres varied between 1.6 and 5.8, with an average number of 7 to 18 images per manoeuvre. Average percentage of useful images varied between 61% and 89%. Total imaging time per scan plane ranged between 1 min 10 s and 4 min 51 s.

CONCLUSIONS

The MR tracking system to guide the slice position for each consecutive dynamic-motion MR image of the freely but slowly moving shoulder or knee joint was feasible for clinical use, providing a high percentage of useful images for each manoeuvre within a clinically acceptable time frame.

Using real-time MRI to quantify altered joint kinematics in subjects with patellofemoral pain and to evaluate the effects of a patellar brace or sleeve on joint motion

Abnormal patellofemoral joint motion is a possible cause of patellofemoral pain, and patellar braces are thought to alleviate pain by restoring normal joint kinematics. We evaluated whether females with patellofemoral pain exhibit abnormal patellofemoral joint kinematics during dynamic, weight-bearing knee extension and assessed the effects of knee braces on patellofemoral motion. Real-time magnetic resonance (MR) images of the patellofemoral joints of 36 female volunteers (13 pain-free controls, 23 patellofemoral pain) were acquired during weight-bearing knee extension. Pain subjects were also imaged while wearing a patellar-stabilizing brace and a patellar sleeve. We measured axial-plane kinematics from the images. Females with patellofemoral pain exhibited increased lateral translation of the patella for knee flexion angles between 0 degrees and 50 degrees (p = 0.03), and increased lateral tilt for knee flexion angles between 0 degrees and 20 degrees (p = 0.04). The brace and sleeve reduced the lateral translation of the patella; however, the brace reduced lateral displacement more than the sleeve (p = 0.006). The brace reduced patellar tilt near full extension (p = 0.001), while the sleeve had no effect on patellar tilt. Our results indicate that some subjects with patellofemoral pain exhibit abnormal weight-bearing joint kinematics and that braces may be effective in reducing patellar maltracking in these subjects.