Toward An MRI-Based Method to Measure Non-Uniform Cartilage Deformation: An MRI-Cyclic Loading Apparatus System and Steady-State Cyclic Displacement of Articular Cartilage Under Compressive Loading

[+] Author and Article Information
C. P. Neu

Biomedical Engineering Graduate Group, University of California at Davis, Davis, CA

M. L. Hull

Biomedical Engineering Graduate Group, University of California at Davis, Davis, CADepartment of Mechanical and Aeronautical Engineering, University of California at Davis, Davis, CA

J Biomech Eng 125(2), 180-188 (Apr 09, 2003) (9 pages) doi:10.1115/1.1560141 History: Received December 01, 2001; Revised November 01, 2002; Online April 09, 2003
Copyright © 2003 by ASME
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Electro-pneumatic schematic (A) of the cyclic loading apparatus depicting the relationship between electronic (gray dashed arrows) and pneumatic (black solid arrows) components. Details of the loading mechanism are also shown (B), including the pneumatic cylinder, cantilever section, and sample holder. Rubber diaphragms (not shown) were used to provide a low-friction seal between the Delrin piston and the cylinder. A laser displacement measurement system (not shown) was also mounted to the apparatus.
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Photographs of a cartilage sample within the sample holder (A) and affixed to a Delrin mount (B)
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Timing diagram of the compressive load application and MRI signaling for two arbitrary loading cycles. Load is applied once during each cycle with variable total cycle duration, recovery time, and interval of constant loading. A TTL signal is sent to the MRI scanner prior to the onset of compression to trigger the DANTE pulse sequence and image the cartilage sample both prior to and after deformation.
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Response of a typical cartilage sample to cyclic loading. Data for every third cycle was recorded and depicted. The slopes of two groups of cycles (3–30 and 57–84) are shown and were used to determine the cycle at which the cartilage sample reached a steady-state response. Based on a predetermined slope criterion described in the text, steady-state was determined to begin at cycle 57. An expanded view of cycle 198 shows a small amount of creep resulting from the period of constant loading.
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Graph illustrating the highly correlated relationship between the load developed by the apparatus and the command signal sent to the pressure servovalve by the computer
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Images of phantom material in undeformed (A) and deformed (B) states. DANTE tag lines are seen to deform with the tissue, thus permitting the calculation of deformation on the material surface and throughout the interior. DANTE imaging parameters were radiofrequency (RF) pulses=20; RF pulse duration=4 μs; inter-pulse duration=100 μs; magnetic field gradient strength=20.0 Gauss/cm. Fast spin echo imaging parameters were: TR=5000.0 ms;TE=6.8 ms; number of echoes per TR=8; field of view=2.00×2.00 cm2; image matrix size=256×256 pixels2; number of excitations=1; slice thickness=0.5 mm.
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Graph illustrating the relationship between the number of cycles needed to reach steady-state response in the cartilage samples and the total cycle duration




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