Contrast-enhanced CT of articular cartilage: experimental study for quantification of glycosaminoglycan content in articular cartilage.

To investigate the diagnostic potential of delayed contrast material-enhanced computed tomography (CT) of articular cartilage in quantification of glycosaminoglycan (GAG) concentration in normal and degenerated articular cartilage ex vivo by using a clinical CT scanner. This study was exempted by the institutional and animal review boards, and informed consent was not required. Forty intact porcine patellae were extracted and assigned to either a control (n = 20) or a trypsin-treated group (ie, GAG-depleted group) (n = 20). Ten patellae in each group were immersed in anionic contrast agent (ioxaglate, 40%) and the other ten in neutral contrast agent (iopromide, 35%) for 2 hours. To determine the contrast agent concentration within cartilage, samples were scanned with a clinical CT scanner immediately after the immersion time, and the x-ray attenuation of cartilage was measured. CT images were compared with safranin O-stained histologic sections, and actual GAG contents were determined with a dimethylmethylene blue assay. Ioxaglate was taken up by GAG-depleted cartilage to a greater extent than by normal cartilage (P = .01). In contrast, the penetration of iopromide was not significantly different between GAG-depleted and normal cartilage (P = .1). The loss of GAGs in trypsin-treated cartilage was confirmed microscopically by using safranin O-stained sections, and a dimethylmethylene blue assay also confirmed that GAG content was markedly decreased in trypsin-treated cartilage (P = .003). This study showed that contrast-enhanced CT images of articular cartilage could reflect the GAG content within the cartilage by allowing measurement of the concentration of anionic iodine-based contrast agent accumulated in the cartilage.