Publications

All Publications


  • Muscle velocity and inertial force from phase contrast MRI. Journal of magnetic resonance imaging Wentland, A. L., McWalter, E. J., Pal, S., Delp, S. L., Gold, G. E. 2015; 42 (2): 526-532

    Abstract

    To evaluate velocity waveforms in muscle and to create a tool and algorithm for computing and analyzing muscle inertial forces derived from 2D phase contrast (PC) magnetic resonance imaging (MRI).PC MRI was performed in the forearm of four healthy volunteers during 1 Hz cycles of wrist flexion-extension as well as in the lower leg of six healthy volunteers during 1 Hz cycles of plantarflexion-dorsiflexion. Inertial forces (F) were derived via the equation F = ma. The mass, m, was derived by multiplying voxel volume by voxel-by-voxel estimates of density via fat-water separation techniques. Acceleration, a, was obtained via the derivative of the PC MRI velocity waveform.Mean velocities in the flexors of the forearm and lower leg were 1.94 ± 0.97 cm/s and 5.57 ± 2.72 cm/s, respectively, as averaged across all subjects; the inertial forces in the flexors of the forearm and lower leg were 1.9 × 10(-3)  ± 1.3 × 10(-3) N and 1.1 × 10(-2)  ± 6.1 × 10(-3) N, respectively, as averaged across all subjects.PC MRI provided a promising means of computing muscle velocities and inertial forces-providing the first method for quantifying inertial forces. J. Magn. Reson. Imaging 2015;42:526-532.

    View details for DOI 10.1002/jmri.24807

    View details for PubMedID 25425185

  • T-2 Relaxation time quantitation differs between pulse sequences in articular cartilage JOURNAL OF MAGNETIC RESONANCE IMAGING Matzat, S. J., McWalter, E. J., Kogan, F., Chen, W., Gold, G. E. 2015; 42 (1): 105-113

    Abstract

    To compare T2 relaxation time measurements between MR pulse sequences at 3 Tesla in agar phantoms and in vivo patellar, femoral, and tibial articular cartilage.T2 relaxation times were quantified in phantoms and knee articular cartilage of eight healthy individuals using a single echo spin echo (SE) as a reference standard and five other pulse sequences: multi-echo SE (MESE), fast SE (2D-FSE), magnetization-prepared spoiled gradient echo (3D-MAPSS), three-dimensional (3D) 3D-FSE with variable refocusing flip angle schedules (3D vfl-FSE), and quantitative double echo steady state (qDESS). Cartilage was manually segmented and average regional T2 relaxation times were obtained for each sequence. A regression analysis was carried out between each sequence and the reference standard, and root-mean-square error (RMSE) was calculated.Phantom measurements from all sequences demonstrated strong fits (R(2)  > 0.8; P < 0.05). For in vivo cartilage measurements, R(2) values, slope, and RMSE were: MESE: 0.25/0.42/5.0 ms, 2D-FSE: 0.64/1.31/9.3 ms, 3D-MAPSS: 0.51/0.66/3.8 ms, 3D vfl-FSE: 0.30/0.414.2 ms, qDESS: 0.60/0.90/4.6 ms.2D-FSE, qDESS, and 3D-MAPSS demonstrated the best fits with SE measurements as well as the greatest dynamic ranges. The 3D-MAPSS, 3D vfl-FSE, and qDESS demonstrated the closest average measurements to SE. Discrepancies in T2 relaxation time quantitation between sequences suggest that care should be taken when comparing results between studies.J. Magn. Reson. Imaging 2014. © 2014 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.24757

    View details for Web of Science ID 000356625500012

    View details for PubMedID 25244647

  • MRI of the Hip for the evaluation of femoroacetabular impingement; past, present, and future. Journal of magnetic resonance imaging : JMRI Riley, G. M., McWalter, E. J., Stevens, K. J., Safran, M. R., Lattanzi, R., Gold, G. E. 2015; 41 (3): 558-572

    Abstract

    The concept of femoroacetabular impingement (FAI) has, in a relatively short time, come to the forefront of orthopedic imaging. In just a few short years MRI findings that were in the past ascribed to degenerative change, normal variation, or other pathologies must now be described and included in radiology reports, as they have been shown, or are suspected to be related to, FAI. Crucial questions have come up in this time, including: what is the relationship of bony morphology to subsequent cartilage and labral damage, and most importantly, how is this morphology related to the development of osteoarthritis? In this review, we attempt to place a historical perspective on the controversy, provide guidelines for interpretation of MRI examinations of patients with suspected FAI, and offer a glimpse into the future of MRI of this complex condition. J. Magn. Reson. Imaging 2014. © 2014 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.24725

    View details for PubMedID 25155435

  • MRI of the Hip for the evaluation of femoroacetabular impingement; past, present, and future. Journal of magnetic resonance imaging : JMRI Riley, G. M., McWalter, E. J., Stevens, K. J., Safran, M. R., Lattanzi, R., Gold, G. E. 2015; 41 (3): spcone-?

    Abstract

    The concept of femoroacetabular impingement (FAI) has, in a relatively short time, come to the forefront of orthopedic imaging. In just a few short years MRI findings that were in the past ascribed to degenerative change, normal variation, or other pathologies must now be described and included in radiology reports, as they have been shown, or are suspected to be related to, FAI. Crucial questions have come up in this time, including: what is the relationship of bony morphology to subsequent cartilage and labral damage, and most importantly, how is this morphology related to the development of osteoarthritis? In this review, we attempt to place a historical perspective on the controversy, provide guidelines for interpretation of MRI examinations of patients with suspected FAI, and offer a glimpse into the future of MRI of this complex condition. J. Magn. Reson. Imaging 2015;41:558-572. © 2014 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.24868

    View details for PubMedID 25693521

  • On high heels and short muscles: A multiscale model for sarcomere loss in the gastrocnemius muscle. Journal of theoretical biology Zöllner, A. M., Pok, J. M., McWalter, E. J., Gold, G. E., Kuhl, E. 2015; 365: 301-310

    Abstract

    High heels are a major source of chronic lower limb pain. Yet, more than one third of all women compromise health for looks and wear high heels on a daily basis. Changing from flat footwear to high heels induces chronic muscle shortening associated with discomfort, fatigue, reduced shock absorption, and increased injury risk. However, the long-term effects of high-heeled footwear on the musculoskeletal kinematics of the lower extremities remain poorly understood. Here we create a multiscale computational model for chronic muscle adaptation to characterize the acute and chronic effects of global muscle shortening on local sarcomere lengths. We perform a case study of a healthy female subject and show that raising the heel by 13cm shortens the gastrocnemius muscle by 5% while the Achilles tendon remains virtually unaffected. Our computational simulation indicates that muscle shortening displays significant regional variations with extreme values of 22% in the central gastrocnemius. Our model suggests that the muscle gradually adjusts to its new functional length by a chronic loss of sarcomeres in series. Sarcomere loss varies significantly across the muscle with an average loss of 9%, virtually no loss at the proximal and distal ends, and a maximum loss of 39% in the central region. These changes reposition the remaining sarcomeres back into their optimal operating regime. Computational modeling of chronic muscle shortening provides a valuable tool to shape our understanding of the underlying mechanisms of muscle adaptation. Our study could open new avenues in orthopedic surgery and enhance treatment for patients with muscle contracture caused by other conditions than high heel wear such as paralysis, muscular atrophy, and muscular dystrophy.

    View details for DOI 10.1016/j.jtbi.2014.10.036

    View details for PubMedID 25451524

  • Variability of CubeQuant T-1 rho, quantitative DESS T-2, and cones sodium MRI in knee cartilage OSTEOARTHRITIS AND CARTILAGE Jordan, C. D., McWalter, E. J., Monu, U. D., Watkins, R. D., Chen, W., Bangerter, N. K., Hargreaves, B. A., Gold, G. E. 2014; 22 (10): 1559-1567
  • Mechanisms of Osteoarthritis in the Knee: MR Imaging Appearance JOURNAL OF MAGNETIC RESONANCE IMAGING Shapiro, L. M., McWalter, E. J., Son, M., Levenston, M., Hargreaves, B. A., Gold, G. E. 2014; 39 (6): 1346-1356

    Abstract

    Osteoarthritis has grown to become a widely prevalent disease that has major implications in both individual and public health. Although originally considered to be a degenerative disease driven by "wear and tear" of the articular cartilage, recent evidence has led to a consensus that osteoarthritis pathophysiology should be perceived in the context of the entire joint and multiple tissues. MRI is becoming an increasingly more important modality for imaging osteoarthritis, due to its excellent soft tissue contrast and ability to acquire morphological and biochemical data. This review will describe the pathophysiology of osteoarthritis as it is associated with various tissue types, highlight several promising MR imaging techniques for osteoarthritis and illustrate the expected appearance of osteoarthritis with each technique.

    View details for DOI 10.1002/jmri.24562

    View details for Web of Science ID 000335460500002

    View details for PubMedID 24677706

  • Fiducial marker-based correction for involuntary motion in weight-bearing C-arm CT scanning of knees. II. Experiment MEDICAL PHYSICS Choi, J., Maier, A., Keil, A., Pal, S., McWalter, E. J., Beaupre, G. S., Gold, G. E., Fahrig, R. 2014; 41 (6)

    View details for DOI 10.1118/1.4873675

    View details for Web of Science ID 000337106300020

  • Fiducial marker-based correction for involuntary motion in weight-bearing C-arm CT scanning of knees. Part I. Numerical model-based optimization MEDICAL PHYSICS Choi, J., Fahrig, R., Keil, A., Besier, T. F., Pal, S., McWalter, E. J., Beaupre, G. S., Maier, A. 2013; 40 (9)

    Abstract

    Human subjects in standing positions are apt to show much more involuntary motion than in supine positions. The authors aimed to simulate a complicated realistic lower body movement using the four-dimensional (4D) digital extended cardiac-torso (XCAT) phantom. The authors also investigated fiducial marker-based motion compensation methods in two-dimensional (2D) and three-dimensional (3D) space. The level of involuntary movement-induced artifacts and image quality improvement were investigated after applying each method.An optical tracking system with eight cameras and seven retroreflective markers enabled us to track involuntary motion of the lower body of nine healthy subjects holding a squat position at 60° of flexion. The XCAT-based knee model was developed using the 4D XCAT phantom and the optical tracking data acquired at 120 Hz. The authors divided the lower body in the XCAT into six parts and applied unique affine transforms to each so that the motion (6 degrees of freedom) could be synchronized with the optical markers' location at each time frame. The control points of the XCAT were tessellated into triangles and 248 projection images were created based on intersections of each ray and monochromatic absorption. The tracking data sets with the largest motion (Subject 2) and the smallest motion (Subject 5) among the nine data sets were used to animate the XCAT knee model. The authors defined eight skin control points well distributed around the knees as pseudo-fiducial markers which functioned as a reference in motion correction. Motion compensation was done in the following ways: (1) simple projection shifting in 2D, (2) deformable projection warping in 2D, and (3) rigid body warping in 3D. Graphics hardware accelerated filtered backprojection was implemented and combined with the three correction methods in order to speed up the simulation process. Correction fidelity was evaluated as a function of number of markers used (4-12) and marker distribution in three scenarios.Average optical-based translational motion for the nine subjects was 2.14 mm (± 0.69 mm) and 2.29 mm (± 0.63 mm) for the right and left knee, respectively. In the representative central slices of Subject 2, the authors observed 20.30%, 18.30%, and 22.02% improvements in the structural similarity (SSIM) index with 2D shifting, 2D warping, and 3D warping, respectively. The performance of 2D warping improved as the number of markers increased up to 12 while 2D shifting and 3D warping were insensitive to the number of markers used. The minimum required number of markers for 2D shifting, 2D warping, and 3D warping was 4-6, 12, and 8, respectively. An even distribution of markers over the entire field of view provided robust performance for all three correction methods.The authors were able to simulate subject-specific realistic knee movement in weight-bearing positions. This study indicates that involuntary motion can seriously degrade the image quality. The proposed three methods were evaluated with the numerical knee model; 3D warping was shown to outperform the 2D methods. The methods are shown to significantly reduce motion artifacts if an appropriate marker setup is chosen.

    View details for DOI 10.1118/1.4817476

    View details for Web of Science ID 000324259800025

    View details for PubMedID 24007156

  • The Measurement of Joint Mechanics and Their Role in Osteoarthritis Genesis and Progression RHEUMATIC DISEASE CLINICS OF NORTH AMERICA Wilson, D. R., McWalter, E. J., Johnston, J. D. 2013; 39 (1): 21-?

    Abstract

    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.

    View details for DOI 10.1016/j.rdc.2012.11.002

    View details for Web of Science ID 000315170300004

    View details for PubMedID 23312409

  • Analysis of Three-dimensional Joint Space of the Tibiofemoral Joint 2013 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (NSS/MIC) Choi, J., McWalter, E. J., Pal, S., Maier, A., Gold, G. E., Fahrig, R. 2013
  • UTE T2* mapping detects sub-clinical meniscus degeneration OSTEOARTHRITIS AND CARTILAGE McWalter, E. J., Gold, G. E. 2012; 20 (6): 471-472

    View details for DOI 10.1016/j.joca.2012.02.640

    View details for Web of Science ID 000304733900002

    View details for PubMedID 22406647

  • The effect of a patellar brace on three-dimensional patellar kinematics in patients with lateral patellofemoral osteoarthritis OSTEOARTHRITIS AND CARTILAGE McWalter, E. J., Hunter, D. J., Harvey, W. F., McCree, P., Hirko, K. A., Felson, D. T., Wilson, D. R. 2011; 19 (7): 801-808

    Abstract

    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.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).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.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.

    View details for DOI 10.1016/j.joca.2011.03.003

    View details for Web of Science ID 000293323000005

    View details for PubMedID 21397707

  • The effect of load magnitude on three-dimensional patellar kinematics in vivo JOURNAL OF BIOMECHANICS McWalter, E. J., Hunter, D. J., Wilson, D. R. 2010; 43 (10): 1890-1897

    Abstract

    Studies of three-dimensional patellar kinematics done with little or no applied load may not accurately reflect kinematics at physiological load levels, and may provide different results to those acquired with greater applied loads or in physiologic weightbearing. We report the effect of load magnitude on three-dimensional patellar kinematics (flexion, spin and tilt; proximal, lateral and anterior translation) using a validated, sequential static, MRI-based method. Ten healthy subjects loaded their study knee to 0% (no load), 15% and 30% bodyweight (BW) using a custom designed loading rig. Differences between loading levels were determined as a function of knee flexion for each kinematic parameter using linear hierarchical random-effects models. Quadratic and random slope terms were included in the models when significant. We found that the patellae flexed less with knee flexion at 30% BW load compared to 0% BW load (p<0.001) and 15% BW (p=0.004) load. The patellae showed a slight medial tilt with knee flexion at 30% BW load which was significantly less than the medial tilt seen at 0% BW load (p=0.017) and 15% BW load (p=0.043) with knee flexion. Small but statistically significant differences were also observed for proximal and anterior translation; the patellae were in a more proximal and posterior position at 30% BW load than at 0% BW load (p=0.010 and p=0.005, respectively) and 15% BW load (p<0.001 and p=0.029, respectively). Since differences in three-dimensional patellar kinematics were observed between loading levels, magnitudes of prescribed loads must be considered when designing studies and comparing results between studies.

    View details for DOI 10.1016/j.jbiomech.2010.03.027

    View details for Web of Science ID 000280313300007

    View details for PubMedID 20413124

  • A single measure of patellar kinematics is an inadequate surrogate marker for patterns of three-dimensional kinematics in healthy knees KNEE McWalter, E. J., MacIntyre, N. J., Cibere, J., Wilson, D. R. 2010; 17 (2): 135-140

    Abstract

    Patellofemoral disorders, such as osteoarthritis and patellofemoral pain, are thought to be associated with abnormal patellar kinematics. However, assessments of three-dimensional patellar kinematics are time consuming and expensive. The aim of this study was to determine whether a single static measure of three-dimensional patellar kinematics provides a surrogate marker for three-dimensional patellar kinematics over a range of flexion angles. We assessed three-dimensional patellar kinematics (flexion, tilt and spin; lateral, anterior and proximal translation) at sequential static angles through approximately 45 degrees of loaded knee flexion in 40 normal subjects using a validated, MRI-based method. The surrogate marker was defined as the static measure at 30 degrees of knee flexion and the pattern of kinematics was defined as the slope of the linear best fit line of each subject's kinematic data. A regression model was used to examine the relationship between the surrogate marker and pattern of kinematics. The surrogate marker predicted 26% of the variance in pattern of patellar flexion (p<0.001), 27% of the variance in pattern of patellar spin (p=0.003), 11% of the variance in pattern of proximal translation (p=0.037) and 39% of the variance in pattern of anterior translation (p<0.001). No relationships were seen between the surrogate marker and tilt or lateral translation. The results suggest that a single measure of patellar parameters at 30 degrees knee flexion is an inadequate surrogate marker of three-dimensional patellar kinematics; therefore, a complete assessment of patellar kinematics, over a range of knee flexion angles, is preferable to adequately assess patterns of patellar kinematics.

    View details for DOI 10.1016/j.knee.2009.08.001

    View details for Web of Science ID 000275263000008

    View details for PubMedID 19720534

  • The Measurement of Joint Mechanics and Their Role in Osteoarthritis Genesis and Progression MEDICAL CLINICS OF NORTH AMERICA Wilson, D. R., McWalter, E. J., Johnston, J. D. 2009; 93 (1): 67-?

    Abstract

    Mechanics play a role in the initiation, progression, and successful treatment of osteoarthritis. However, we don't yet know enough about which specific mechanical parameters are most important and what their impact is on the disease process to make comprehensive statements about how mechanics should be modified to prevent, slow, or arrest the disease process. The objectives of this review are (1) to summarize methods for assessing joint mechanics and their relative merits and limitations, (2) to describe current evidence for the role of mechanics in osteoarthritis initiation and progression, and (3) to describe some current treatment approaches that focus on modifying joint mechanics.

    View details for DOI 10.1016/j.mcna.2008.08.004

    View details for Web of Science ID 000262339100006

    View details for PubMedID 19059022

  • The measurement of joint mechanics and their role in osteoarthritis genesis and progression RHEUMATIC DISEASE CLINICS OF NORTH AMERICA Wilson, D. R., McWalter, E. J., Johnston, J. D. 2008; 34 (3): 605-?

    Abstract

    Justifying and improving mechanically based approaches to the treatment and prevention of osteoarthritis (OA) requires a critical understanding of the methods used to study joint mechanics and the current evidence for the role of mechanics in OA. The objectives of this article are (1) to summarize methods for assessing joint mechanics and their relative merits and limitations, (2) to describe the current evidence for the role of mechanics in OA initiation and progression, and (3) to describe some current treatment approaches that focus on modifying joint mechanics.

    View details for DOI 10.1016/j.rdc.2008.05.002

    View details for Web of Science ID 000258964700007

    View details for PubMedID 18687275

  • Relationship between varus-valgus alignment and patellar kinematics in individuals with knee osteoarthritis. journal of bone and joint surgery. American volume McWalter, E. J., Cibere, J., MacIntyre, N. J., Nicolaou, S., Schulzer, M., Wilson, D. R. 2007; 89 (12): 2723-2731

    Abstract

    Abnormal varus-valgus alignment is a risk factor for patellofemoral osteoarthritis, but tibiofemoral alignment alone does not explain compartmental patellofemoral osteoarthritis progression. Other mechanical factors, such as patellar kinematics, probably play a role in the initiation and progression of the disease. The objective of this study was to determine which three-dimensional patellar kinematic parameters (patellar flexion, spin, and tilt and patellar proximal, lateral, and anterior translation) are associated with varus and valgus alignment in subjects with osteoarthritis.Ten individuals with knee osteoarthritis and varus (five subjects) or valgus (five subjects) knee alignment underwent assessment of three-dimensional patellar kinematics. We used a validated magnetic resonance imaging-based method to measure three-dimensional patellar kinematics in knee flexion while the subjects pushed against a pedal with constant load (80 N). A linear random-effects model was used to test the null hypothesis that there was no difference in the relationship between tibiofemoral flexion and patellar kinematics between the varus and valgus groups.Patellar spin was significantly different between groups (p = 0.0096), with the varus group having 2 degrees of constant internal spin and the valgus group having 4.5 degrees of constant external spin. In the varus group, the patellae tracked with a constant medial tilt of 9.6 degrees with flexion, which was significantly different (p = 0.0056) from the increasing medial tilt (at a rate of 1.8 degrees per 10 degrees of increasing knee flexion) in the valgus group. The patellae of the valgus group were 7.5 degrees more extended (p = 0.0093) and positioned 8.8 mm more proximally (p = 0.0155) than the varus group through the range of flexion that was studied. The pattern of anterior translation differed between the groups (p = 0.0011).Our results suggest that authors of future large-scale studies of the relationships between knee mechanics and patellofemoral osteoarthritis should not rely solely on measurements of tibiofemoral alignment and should assess three-dimensional patellar kinematics directly.

    View details for PubMedID 18056505

  • Use of novel interactive input devices for segmentation of articular cartilage from magnetic resonance images OSTEOARTHRITIS AND CARTILAGE McWalter, E. J., Wirth, W., Siebert, M., von Eisenhart-Rothe, R. M., Hudelmaier, M., Wilson, D. R., Eckstein, F. 2005; 13 (1): 48-53

    Abstract

    To study the effect of new interactive computer input devices on cartilage segmentation in terms of time, consistency between input devices, and precision in quantitative magnetic resonance imaging (qMRI).We compared two new input devices, an interactive digitizing tablet and an interactive touch-sensitive screen, to a traditional mouse. Medial tibial and patellar cartilage of six healthy and six osteoarthritic knees were segmented using each input device. Cartilage volume, surface area and mean thickness were assessed using a validated algorithm and used to determine consistency and precision. Segmentation time was also measured.Segmenting with an interactive touch-sensitive screen reduced segmentation time by 15% when compared to the traditional mouse but we found no significant difference in segmentation time between the interactive digitizing tablet and the traditional mouse. We found no difference in consistency or precision of cartilage volume, mean thickness or surface area between the three input devices tested.We conclude that measurements of cartilage made using articular cartilage segmentation from MR images are independent of the input device chosen for user interaction.

    View details for DOI 10.1016/j.joca.2004.09.008

    View details for Web of Science ID 000226546700007

    View details for PubMedID 15639637

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