title: Contrast agent-enhanced computed tomography of articular cartilage: association with tissue composition and properties.
abstract: BACKGROUND
  Contrast agent-enhanced computed tomography may enable the noninvasive quantification of glycosaminoglycan (GAG) content of articular cartilage. It has been reported that penetration of the negatively charged contrast agent ioxaglate (Hexabrix) increases significantly after enzymatic degradation of GAGs. However, it is not known whether spontaneous degradation of articular cartilage can be quantitatively detected with this technique.
  
  
  OBJECTIVE
  To investigate the diagnostic potential of contrast agent-enhanced cartilage tomography (CECT) in quantification of GAG concentration in normal and spontaneously degenerated articular cartilage by means of clinical peripheral quantitative computed tomography (pQCT).
  
  
  METHODS
  In this in vitro study, normal and spontaneously degenerated adult bovine cartilage (n=32) was used. Bovine patellar cartilage samples were immersed in 21 mM contrast agent (Hexabrix) solution for 24 hours at room temperature. After immersion, the samples were scanned with a clinical pQCT instrument. From pQCT images, the contrast agent concentration in superficial as well as in full-thickness cartilage was calculated. Histological and functional integrity of the samples was quantified with histochemical and mechanical reference measurements extracted from our earlier study.
  
  
  RESULTS
  Full diffusion of contrast agent into the deep cartilage was found to take over 8 hours. As compared to normal cartilage, a significant increase (11%, P<0.05) in contrast agent concentration was seen in the superficial layer of spontaneously degenerated samples. Significant negative correlations were revealed between the contrast agent concentration and the superficial or full-thickness GAG content of tissue (|R| > 0.5, P<0.01). Further, pQCT could be used to measure the thickness of patellar cartilage.
  
  
  CONCLUSIONS
  The present results suggest that CECT can be used to diagnose proteoglycan depletion in spontaneously degenerated articular cartilage with a clinical pQCT scanner. Possibly, the in vivo use of clinical pQCT for CECT arthrography of human joints is feasible.
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland. tuomo.silvast@uku.fi
authors.forename: T S
authors.initials: TS
authors.lastname: Silvast
authors.forename: J S
authors.initials: JS
authors.lastname: Jurvelin
authors.forename: A S
authors.initials: AS
authors.lastname: Aula
authors.forename: M J
authors.initials: MJ
authors.lastname: Lammi
authors.forename: J
authors.initials: J
authors.lastname: Töyräs
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000000981:diagnostic imaging* / Q000473:pathology; D002417:Cattle; D003287:Contrast Media; D066298:In Vitro Techniques; D007485:Ioxaglic Acid; D007719:Knee Joint; D011509:Proteoglycans / Q000032:analysis; D012372:ROC Curve; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D011509:Proteoglycans; D007485:Ioxaglic Acid