Extract
Following joint trauma and during the early stages of cartilage
degeneration, typical changes become apparent in tissue structure and
composition, including the loss of
glycosaminoglycan1,2.
These changes often are not apparent on conventional magnetic resonance
imaging or visible at arthroscopy, thereby precluding diagnosis. Delayed
gadolinium-enhanced magnetic resonance imaging of cartilage, or dGEMRIC, is an
emerging in vivo method for the assessment of the biochemical composition of
articular cartilage and provides a surrogate measure of glycosaminoglycan
content3,4.
When injected intravenously, the anionic contrast agent gadolinium diethylene
triamine penta-acetic acid (Gd-DTPA2—) penetrates cartilage
both from the synovial surface and from the subchondral
bone3,5.
Given sufficient time, the anionic contrast agent distributes inversely to the
fixed negative charge associated with the cartilage glycosaminoglycan content
in accordance with the Donnan principle of equilibrium.
Gd-DTPA2-therefore
distributes in relatively higher concentrations in regions of low
glycosaminoglycan, and vice versa.
Gd-DTPA2-has a
concentration-dependent effect on the magnetic resonance imaging parameter T1;
therefore, T1 imaging in the presence of Gd-DTPA2—
(T1Gd) reflects the cartilage
Gd-DTPA2—concentration and, hence, glycosaminoglycan
concentration.