title: Bath Concentration of Anionic Contrast Agents Does Not Affect Their Diffusion and Distribution in Articular Cartilage In Vitro.
abstract: OBJECTIVE
  Differences in contrast agent diffusion reflect changes in composition and structure of articular cartilage. However, in clinical application the contrast agent concentration in the joint capsule varies, which may affect the reliability of contrast enhanced cartilage tomography (CECT). In the present study, effects of concentration of x-ray contrast agents on their diffusion and equilibrium distribution in cartilage were investigated.
  
  
  METHODS
  Full-thickness cartilage discs (d = 4.0 mm, n = 120) were detached from bovine patellae (n = 24). The diffusion of various concentrations of ioxaglate (5, 10, 21, 50 mM) and iodide (30, 60, 126, 300 mM) was allowed only through the articular surface. Samples were imaged with a clinical peripheral quantitative computed tomography scanner before immersion in contrast agent, and after 1, 5, 9, 16, 25, and 29 hours in the bath.
  
  
  RESULTS
  Diffusion and partition coefficients were similar between different contrast agent concentrations. The diffusion coefficient of iodide (473 ± 133 µm(2)/s) was greater (P ≤ 0.001) than that of ioxaglate (92 ± 46 µm(2)/s). In full-thickness cartilage, the partition coefficient (at 29 h) of iodide (71 ± 5%) was greater (P ≤ 0.02 with most concentrations) than that of ioxaglate (62 ± 6%).
  
  
  CONCLUSIONS
  Significant differences in partition and diffusion coefficient of two similarly charged (-1) contrast agents were detected, which shows the effect of steric interactions. However, the increase in solute concentration did not increase its partition coefficient. In clinical application, it is important that contrast agent concentration does not affect the interpretation of CECT imaging.
authors.affiliation: SIB-Labs, University of Eastern Finland, Kuopio, Finland ; Department of Applied Physics, University of Eastern Finland, Kuopio, Finland ; Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Tuomo S
authors.initials: TS
authors.lastname: Silvast
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
authors.forename: Jukka S
authors.initials: JS
authors.lastname: Jurvelin
authors.affiliation: Institute of Biomedicine, Anatomy, University of Eastern Finland, Kuopio, Finland.
authors.forename: Virpi
authors.initials: V
authors.lastname: Tiitu
authors.affiliation: Department of Chemical Engineering, McGill University, Montreal, Canada.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Quinn
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland ; Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Töyräs
keywords: articular cartilage; computed tomography; contrast agent concentration; diffusion; steric hindrance