Neal K. Bangerter, Ph.D.

Graeme M. Bydder, M.B., Ch.B.

Alan C. Seifert¹, Suzanne L. Wehrli², and Felix W. Wehrli^1
1University of Pennsylvania, Philadelphia, PA, United States, ²Children's Hospital of Philadelphia, Philadelphia, PA, United States

Discrimination between bound and pore bone water is vital for quantification of bone matrix density and porosity. The two main approaches are T2-selective magnetization preparation and bi-exponential T2* fitting. T2* of pore water, however, is shortened by field gradients arising from the difference in susceptibility between water and bone. We scanned human cortical bone specimens at 4 field strengths, and validated bi-exponential fitting against µCT porosity and gravimetrically-determined matrix density. Our results indicate that T2* bi-exponential fitting of FIDs may be a suitable method for quantifying bound and pore water fractions at 1.5T, but may fail at higher field strengths.

Robert Nikolov¹, Jun Chen¹, Won Bae¹, Reni Biswas¹, Robert Healey¹, Eric Chang^1,2, Christine Chung^1,2, Graeme Bydder¹, and Jiang Du^1
1Radiology, University of California, San Diego, San Diego, California, United States, ²Radiology, VA San Diego Healthcare System, La Jolla, California, United States

Conventional long echo time (TE) imaging sequences are not applicable to short T2 tissues such as cortical bone. However, through use of high resolution imaging afforded by 11.7T we are able to detect water found in the pores of cortical human bone and measure pore sizes and water fraction which correlate to: cortical porosity (µCT), bound/unbound water ratio using UTE-MT (3T), and biomechanical properties. Average porosity (µCT) correlates positively with percent water content (R² = 0.47 ; p<0.001) and clusters of 5 voxels corresponding to a pore size of 8000 µm² (R² = 0.62 ; p<0.001).

Misung Han¹, Peder EZ Larson¹, Roland Krug¹, and Viola Rieke^1
1Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States

A variable flip angle method is a rapid T₁ mapping method by exploiting steady-state signals at multiple flip angles. When combined with ultrashort echo-time imaging, T₁ measurement for short T₂* tissues is also possible. However, flip angle errors due to miscalibration or B₁ inhomogeneities, and T₂* relaxation effects during RF excitation can degrade the accuracy of T₁ quantification. In this work, we propose the use of the actual flip imaging technique to correct flip angles to improve T₁ measurement for short T₂ tissues. Ex vivo study on bovine cortical bone and in vivo study on the Achilles tendon are presented.

Feliks Kogan¹, Audrey Fan¹, Sloane Brazina¹, Dawn Holley¹, Andrew Quon¹, and Garry Gold^1
1Department of Radiology, Stanford University, Stanford, CA, United States

New hybrid PET/MR systems allow for simultaneous, sensitive, and quantitative assessments of early bone activity in osteoarthritis (OA) with PET, which can be correlated with high-resolution quantitative MR methods of other tissues to study the pathogenesis of OA We demonstrate initial results of simultaneous time-of-flight PET/MR hybrid imaging of the knee OA. Results suggest that PET/MR may detect knee abnormalities unseen on MRI alone and is a promising tool for early detection of OA change in the bone.

Sergey Magnitsky¹, Geetha Mohan¹, Curtis Corum², Djaudat Idiyatullin², Nancy Lane³, and Sharmila Majumdar^1
1Radiology, UCSF, San Francisco, CA, United States, ²Radiology, University of Minnesota, MN, United States, ³UC Davis, CA, United States

Mesenchymal stem cells (MSC’s) have high potential for a treatment of bone loss disease. Progress in this promising area of research will require an in vivo technique to observe the grafted cells and engraftment pattern overtime. We implemented SWIFT pulse sequence to develop an in vivo imaging protocol to monitor MSC engraftment in the bone tissue. Our preliminary experiments have shown that SWIFT pulse sequence allowed to generate a positive MR signal from iron labeled cells and detect grafted cells in cortical bones. Proposed method will have a profound impact on stem cell treatment of bone degenerative diseases.