Brittle Bones & Stiff Disks
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Wednesday May 11th
Room 710A  13:30 - 15:30 Moderators: Laura M. Fayad and Roland Krug

13:30 418.   Morphologic and quantitative mapping of biological disc contructs in a rat tail model 
Sarah Pownder1, Matthew F Koff1, Andrew James2, Harry H Gebhard2, Roger Hartl2, Robby D Bowles3, Lawrence J Bonassar3, and Hollis G Potter1
1Department of Radiolgy and Imaging - MRI, Hospital for Special Surgery, New York, NY, United States, 2Department of Neurological Surgery, Weill Cornell Brain and Spine Center, 3Department of Biomedical Engineering, Cornell University

This study used a clinical magnet (3T) to assess morphologic and quantitative MR features (T1rho and T2 mapping) of a rat tail with a tissue engineered disc replacement. The disc construct was shorter, wider and had a thicker annulus than the normal disc. The T2 values of the nucleus, annulus, and endplate of the disc construct were significantly shorter than the normal disc. T1rho values of the disc tended to be shorter than normal disc. This study demonstrates the feasibility of quantitative MRI, at clinically relevant field strengths, to assess preclinical intervertebral disc morphology and biochemical composition.

13:42 419.   In Vivo T2 and T1rho Mapping of Rabbit Disc using Spin-Lock sequence at 3T  -permission withheld
Chan Hong Moon1, Lloydine Jacobs2,3, Jung-Hwan Kim1, Xiang He1, James Kang2,3, and Kyongtae Ty Bae1
1Radiology, University of Pittsburgh, Pittsburgh, PA, United States, 2Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA, United States, 3Ferguson Laboratory for Orthopaedic and Spine Research

We successfully obtained high-resolution, high-contrast T2 and T1rho images and measured T2 and T1rho in normal rabbit spine discs using in-house dual-tuned RF coil and SL sequence at 3T. Further study is necessary to demonstrate difference in T2 and T1rho between normal and degenerative disc models in rabbits in order to validate these imaging biomarkers for degenerative disc disease.

13:54 420.   Improving Predictability of Painful Discs by using T1ρ MRI and Disc Height 
Rachelle Berger1, Matthew Fenty2, Bryan Fry1, Philip M. Maurer3, Dawn M. Elliott4, and Ari Borthakur2
1Department of Biochemistry & Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA, United States, 2CMROI, Department of Radiology, University of Pennsylvania School of Medicine, Philadelphia, PA, United States, 33B Orthopaedics, Philadelphia, PA, United States, 4McKay Orthopaedic Lab, Department of Orthopaedic Surgery, University of Pennsylvania School of Medicine, Philadelphia, PA, United States

The hypothesis was tested that T1ρ relaxation time combined with the disc height in patients with disc degenerative disease (DDD) can detect painful discs non-invasively. Mean values for both biomarkers individually exhibited significant differences between non-painful and painful discs. The combination of biomarkers improved the predictive value to 95% (area under the curve from a ROC analysis). The long-term objective of this study is to evaluate quantitative and non-invasive biomarkers of disc degeneration in patients with lower back pain.

14:06 421.   in vivo sodium MRI of Intervertebral Disc at 7 T 

Intervertebral disc degeneration is a common and sometimes painful condition. The initial sign of intervertebral disc degeneration involves the breakdown of proteoglycans and the accompanying depletion of Na+. Sodium MRI has previously been used to study the depletion of Na+ in intervertebral disc ex vivo. In this study, we carried out in vivo sodium MRI of intervertebral disc on a 7 T MRI scanner. The tissue [Na+] value calculated from the sodium MR images were correlated with intervertebral disc degenerative grade, in order to elucidate the trend in [Na+] content in IVDs undergoing degeneration.

14:18 422.   Association between spinal disc degeneration and deficits in endplate perfusion 
L. Tugan Muftuler1, Yen K Hong2, Hon J Yu1, Vance O Gardner3, Anton N Hasso4, and Nitin N Bhatia5
1Center for Functional Onco-imaging, University of California, Irvine, CA, United States, 2Microbiology & Molecular Genetics, University of California, 3Orthopaedic Education and Research Institute, Orange, CA, 4Radiological Sciences, University of California, Irvine, CA, 5Orthopaedic Surgery, University of California, Irvine, CA

The majority of chronic back pain is associated with degeneration of the intervertebral disc (IVD), which can manifest itself in many different clinical conditions. The factors that lead to disc degeneration and its pathophysiology are still not completely understood. IVD is avascular; nutrition is supplied via diffusion mechanism from the capillary beds of the cartilaginous vertebral body endplates. Disruption in subchondral bone/endplate perfusion has long been suspected as a factor in pathogenesis of IVD degeneration. In the presented study we used dynamic contrast-enhanced MRI (DCEMRI) to investigate the endplate perfusion and its association with spinal disc degeneration.

14:30 423.   MR imaging after spinal fusion using Slice Encoding for Metal Artifact Correction (SEMAC) 
Kathryn Jane Stevens1, Pauline W Worters1, Garry Evan Gold1, Jarrett K Rosenberg1, and Brian A Hargreaves1
1Department of Radiology, Stanford University Medical Center, Stanford, CA, United States

MRI of the lumbar spine is often of limited value in patients after instrumented spinal fusion due to the extensive associated metal artifact. Slice Encoding for Metal Artifact Correction (SEMAC) is an MRI technique that corrects for spatial distortions by performing extra slice encoding and using view-angle tilting. MRI in 8 patients with previous spinal fusions demonstrated significantly decreased in-plane and through-plane artifact on SEMAC images compared to 2D FSE. This allowed improved visualization of the spinal canal, spinal nerve roots and neural foramina, which we hope will translate to improved diagnostic capabilities in patients with failed back surgery syndrome.

14:42 424.   Trabecular bone elastic properties depend on lower case Greek muMRI-derived measures of bone volume fraction and fabric 
Michael J Wald1, Chamith S. Rajapakse1, Jeremy F. Magland1, and Felix W. Wehrli1
1Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States

Even though bone volume fraction is predictive of bone strength, the variation in mechanical properties with test direction requires inclusion of measures of structural orientation. Here, we examine whether the inclusion of trabecular bone fabric can improve the bone volume fraction-based prediction of the elastic constants derived from linear lower case Greek muFE analysis of lower case Greek muMR images of the distal tibia in specimens and live subjects. A strong power-law dependence of elastic moduli with bone volume fraction was observed, however the exponents depended on test direction and anatomical location. Inclusion of fabric information establishes a general model of the elastic constants independent of anatomical location and test direction.

14:54 425.   Quantification of Bone Marrow Types from High-Resolution MR Images in the Proximal Femur using Three Class Clustering 
Jenny Folkesson1, Julio Carballido-Gamio2, Dimitrios C Karampinos1, Thomas Baum1, Thomas M Link1, Sharmila Majumdar1, and Roland Krug1
1Radiology and Biomedical Imaging, University of California, San Francisco, CA, United States, 2Grupo Tecnologico Santa Fe, Mexico City, Mexico

The purpose of this work was to evaluate the feasibility of marrow composition quantification in high resolution proximal femur bone MRI. Automatic volume of interest placement was performed using an atlas built from IDEAL images . Separation of trabecular bone, red and yellow marrow was performed using 3-class fuzzy clustering. In the test cohort (2 fracture, 8 non-fracture females), fracture subjects had lower red marrow fraction (p<0.05). These initial results suggest that marrow composition analysis is feasible using HR MRI, and could potentially help understand underlying factors related to aging and fracture history.

15:06 426.   Initial Results from Baseline Structural and Computational Biomechanics µMRI Study in Postmenopausal Women 
Yusuf A Bhagat1, Chamith S Rajapakse1, Jeremy F Magland1, Michael J Wald1, Theresa M Scattergood2, Peter J Snyder2, and Felix W Wehrli1
1Laboratory for Structural NMR Imaging, University of Pennsylvania, Philadelphia, PA, United States, 2Division of Endocrinology, Diabetes and Metabolism, University of Pennsylvania, Philadelphia, PA, United States

Recent advances in high-resolution structural imaging of trabecular and cortical bone and the use of these data as input into micro-finite-element (µFE) models have shown potential for assessing the effect of treatment in patients with osteoporosis. Here, we report initial baseline and select follow-up data in an ongoing investigation of women with low bone density (N=30) receiving either zoledronic acid or teriparatide, conducted at 3T and 7T. The baseline data show moderate associations with pQCT bone density while µFE-derived axial stiffness is strongly correlated with bone volume fraction at the same site. Finally, repeat data in select subjects indicate large anabolic effects.

15:18 427.   In Vivo 31P Solid State MRI of Human Wrists: Short-T2 MRI Using the Scanner 1H Channel 
Jerome L Ackerman1,2, Yaotang Wu2,3, Timothy G. Reese1,2, Haihui Cao2,3, Mirko I. Hrovat4, Steven P. Toddes5, and Rostislav A. Lemdiasov5
1Martinos Center, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 2Harvard Medical School, Boston, MA, United States,3Department of Orthopedic Surgery, Children's Hospital, Boston, MA, United States, 4Mirtech, Inc., Brockton, MA, 5InsightMRI, Inc., Leominster, MA, United States

Solid state MRI requires fast recovery of the scanner receiver in order to capture short T2 signals with good fidelity. To circumvent the unacceptably long 31P receiver recovery time of a clinical scanner, we developed a frequency converter utilizing the fast recovery of the proton channel to acquire solid state 31P images of high quality. In effect, a special RF “front end” is interposed between the scanner and the 31P RF coil. Isotropic 3D 31P images of the bones of the wrists of volunteers were obtained with SNR ~30 in typically 37 min at 3T, exhibiting spatial resolution of ~5mm.