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Reduction of residual dipolar interaction in cartilage by spin‐lock technique
Author(s) -
Akella Sarma V.S.,
Regatte Ravinder R.,
Wheaton Andrew J.,
Borthakur Arijitt,
Reddy Ravinder
Publication year - 2004
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.20241
Subject(s) - cartilage , laminar flow , nuclear magnetic resonance , magic angle , flip angle , relaxation (psychology) , scanner , materials science , chemistry , biomedical engineering , magnetic resonance imaging , anatomy , physics , optics , nuclear magnetic resonance spectroscopy , medicine , mechanics , radiology
The influence of radiofrequency (RF) spin‐lock pulse on the laminar appearance of articular cartilage in MR images was investigated. Spin‐lock MRI experiments were performed on bovine cartilage plugs on a 4.7 Tesla small‐bore MRI scanner, and on human knee cartilage in vivo on a 1.5 Tesla clinical scanner. When the normal to the surface of cartilage was parallel to B 0 , a typical laminar appearence was exhibited in T 2 ‐weighted images of cartilage plugs, but was absent in T 1ρ ‐weighted images of the same plugs. At the “magic angle” orientation (when the normal to the surface of cartilage was 54.7° with respect to B 0 ), neither the T 2 nor the T 1ρ images demonstrated laminae. At the same time, T 1ρ values were greater than T 2 at both orientations throughout the cartilage. T 1ρ dispersion (i.e., the dependence of the relaxation rate on the spin‐lock frequency ω 1 ) was observed, which reached a steady‐state value of close to 2 kHz in both parallel and magic‐angle orientations. These results suggest that residual dipolar interaction from motionally‐restricted water and relaxation processes, such as chemical exchange, contribute to T 1ρ dispersion in cartilage. Further, one can reduce the laminar appearance in human articular cartilage by applying spin‐lock RF pulses, which may lead to a more accurate diagnosis of degenerative changes in cartilage. Magn Reson Med 52:1103–1109, 2004. © 2004 Wiley‐Liss, Inc.