Quantitative imaging of proteoglycan in cartilage using a gadolinium probe and microCT

Objective: Micro-computed tomography (microCT) imaging has the potential to allow the three-dimensional (3D) visualization of cartilage morphology. However, cartilage intensity on a microCT image is weak because cartilage does not strongly attenuate X-rays. This work was designed to demonstrate that exposure of cartilage to charged gadolinium compounds modifies the intensity to allow an improved visualization of cartilage morphology and the determination of proteoglycan content. Design: Trypsin was used to deplete proteoglycan in bovine nasal cartilage disks. Disks were then exposed to Gd3+, gadopentetate (Gd-DTPA(2-)), or gadoteridol (Gd-HP-DO3A), and imaged with microCT. The intensities of the disks were measured from the images and compared to the actual proteoglycan content determined with a dimethylmethylene blue assay. Results: Treatment of naive disks with 200 mM Gd3+ for 24 h at room temperature produced a 2.8-fold increase in intensity on microCT images. Similar treatment with 200 mM Gd-DTPA2- produced a 1.4-fold increase. After 2 h of trypsin treatment at room temperature, the intensities of cartilage disks exposed to 200 mM Gd3+ decreased by 12%. Conversely, the intensities of trypsin-treated disks exposed to 200 mM Gd-DPTA(2-) increased by 15%. Trypsin treatment caused a 4% increase in the intensities of disks exposed to neutral Gd-HP-DO3A. The correlation between proteoglycan content and the microCT intensity of cartilage treated with Gd3+ was very good (r(2) = 0.81). Conclusions: Gadolinium and microCT allow an improved 3D visualization of cartilage and quantification of its proteoglycan content. (c) 2005 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.