Yang Xia uses magnetic resonance imaging to study articular cartilage

Reading scientific papers can often be difficult, because they tend to be technical and full of jargon. But the best papers begin with an introduction that outlines the significance and goals of the paper in clear simple language, and the last sentence of the introduction often contains a concise statement of the purpose of the study. A recent article by CBR member Yang Xia, of the Department of Physics, and his former postdoc Shaokuan Zheng provides an excellent example of an effective introduction. You will find the entire article in the September 2010 issue of the Journal of Magnetic Resonance Imaging (Volume 32, Pages 733-737), but I reproduce the introduction below. The second paragraph has a bit of unavoidable jargon, but hopefully the links provide the necessary background.

“DEGENERATIVE JOINT DISEASES such as osteoarthritis currently affect a large proportion of the senior population and have elicited extensive investigation through nondestructive imaging techniques such as magnetic resonance imaging (MRI). Current MRI procedures, however, cannot satisfactorily detect the subtle changes in the early stages of the tissue’s degradation (1,2). One major factor preventing the successful development of an early detection procedure in MRI is the complex structure of the tissue. In particular, the collagen fibril changes its spatial orientation significantly across the tissue thickness: parallel to the surface in the superficial zone, mostly random in the transitional zone, and perpendicular to the surface in the radial (deep) zone (3). This depth-dependent organization of the collagen matrix in cartilage is the origin of tissue’s anisotropic appearance as viewed by many imaging tools, such as the magic angle effect in MRI, birefringence in polarized light microscopy, amide anisotropy in Fourier-transform infrared imaging, diffusion tensor imaging in MRI, and anisotropic refraction angle in diffraction enhanced x-ray imaging.

The magic angle effect of articular cartilage in MRI (4,5) refers to the disappearing of a laminar appearance of cartilage when the normal axis of the tissue surface is oriented at 55 [degrees] with respect to the static magnetic field, B0. It has been well agreed that the laminar appearance of cartilage in spin echo MR images is caused by T2 anisotropy in articular cartilage (5), which is closely linked to the collagen matrix—the only known rigid and well-oriented network in the tissue. T2 anisotropy alone, however, cannot explain a slightly elevated signal lamina in the deep part of cartilage in images acquired by fast imaging sequences such as FLASH (fast-low-angleshot) or SPGR (spoiled-gradient-recalled-echo) (6–8). This phenomenon was commented on by McCauley and Disler (9) in a review article 10 years ago as ‘‘a thin band of intermediate signal intensity is sometimes seen in the deep radial zone; the etiology of this band is uncertain.’’ Since 3D FS-FLASH/SPGR sequences are efficient MRI protocols in clinical visualization of human cartilage, the objective of this project was to investigate the origin of this particular laminar phenomenon of articular cartilage by 3D FSFLASH/SPGR sequences and compare them to the spin-echo images.”

Xia’s laboratory is supported by two grants from the National Institutes of Health.