Morphologic analysis of normal human lumbar dorsal root ganglion by 3D MR imaging.

BACKGROUND AND PURPOSE: The dorsal root ganglion (DRG) of the spinal nerve has been considered a key structure in the mechanism of low-back pain and radicular symptoms. The purpose of this study was to clarify the normal morphologic features and variations of the lumbar DRGs in a healthy population by using 3D MR imaging. METHODS: 3D fast-field echo (FFE) with water selective excitation coronal MR images of lumbar spine obtained in 115 healthy volunteers were further reconstructed into a radial stack of 15 coronal images by using maximum intensity projection technique. The DRGs from L1 through L5 were assessed for the location, signal intensity, architecture, and dimensions. RESULTS: Most DGRs were foraminal in location. Only 5.7% of the L5 DGRs were located intraspinally. The sizes of L1, L2, and L5 DRGs in men were larger than those in women (P < .05). The dimensions of the DRGs gradually increased from L1 to L5 (P < .0001). The biganglia (2 ganglial components) frequently occurred in the L4 and L3 DRGs, whereas the singular ganglion (1 ganglial component), in the L5 and L1 DRGs. CONCLUSION: The normal anatomy and variants of the lumbar DRG could be better demonstrated by 3D MR imaging with water selective excitation technique. The relatively larger and more proximally located DRGs in the lower lumbar region may be more susceptible to compression. An appreciation of normal anatomy and variants of DRGs radiologically is helpful for the diagnosis and proper treatment for radiculopathy.

Structural Analysis of Highly Relaxed GaSb Grown on GaAs Substrates with Periodic Interfacial Array of 90° Misfit Dislocations.

We report structural analysis of completely relaxed GaSb epitaxial layers deposited monolithically on GaAs substrates using interfacial misfit (IMF) array growth mode. Unlike the traditional tetragonal distortion approach, strain due to the lattice mismatch is spontaneously relieved at the heterointerface in this growth. The complete and instantaneous strain relief at the GaSb/GaAs interface is achieved by the formation of a two-dimensional Lomer dislocation network comprising of pure-edge (90°) dislocations along both [110] and [1-10]. In the present analysis, structural properties of GaSb deposited using both IMF and non-IMF growths are compared. Moiré fringe patterns along with X-ray diffraction measure the long-range uniformity and strain relaxation of the IMF samples. The proof for the existence of the IMF array and low threading dislocation density is provided with the help of transmission electron micrographs for the GaSb epitaxial layer. Our results indicate that the IMF-grown GaSb is completely (98.5%) relaxed with very low density of threading dislocations (105 cm-2), while GaSb deposited using non-IMF growth is compressively strained and has a higher average density of threading dislocations (>109 cm-2).