Contrast-enhanced micro-computed tomography of articular cartilage morphology with ioversol and iomeprol

Abstract

Non-ionic, low-osmolar contrast agents (CAs) used for computed tomography, such as Optiray (ioversol) and Iomeron (iomeprol), are associated with the reduced risk of adverse reactions and toxicity in comparison with ionic CAs, such as Hexabrix. Hexabrix has previously been used for imaging articular cartilage but has been commercially discontinued. This study aimed to evaluate the efficacy of Optiray and Iomeron as alternatives for visualisation of articular cartilage in small animal joints using contrast-enhanced micro-computed tomography (CECT). For this purpose, mouse femora were immersed in different concentrations (20%-50%) of Optiray 350 or Iomeron 350 for periods of time starting at five minutes. The femoral condyles were scanned ex vivo using CECT, and regions of articular cartilage manually contoured to calculate mean attenuation at each time point and concentration. For both CAs, a 30% CA concentration produced a mean cartilage attenuation optimally distinct from both bone and background signal, whilst 5-min immersion times were sufficient for equilibration of CA absorption. Additionally, plugs of bovine articular cartilage were digested by chondroitinase ABC to produce a spectrum of glycosaminoglycan (GAG) content. These samples were immersed in CA and assessed for any correlation between mean attenuation and GAG content. No significant correlation was found between attenuation and cartilage GAG content for either CAs. In conclusion, Optiray and Iomeron enable high-resolution morphological assessment of articular cartilage in small animals using CECT; however, they are not indicative of GAG content.

Keywords: CECT; EPIC-µCT; Iomeron; Optiray; cartilage imaging.

FIGURE 1

Chemical structure of the contrast agent compounds (a) Optiray and (b) Iomeron (National Center for Biotechnology Information, National Center for Biotechnology Information)

FIGURE 2

An overview of the sample preparation, scan timeline, and data processing and analysis tasks for assessing cartilage morphology using Optiray and Iomeron

FIGURE 3

An overview of the sample preparation, DMMB assay, and micro‐CT scanning and analysis tasks for assessing GAG correlation with CECT attenuation for Optiray and Iomeron

FIGURE 4

Mean CECT attenuation against time for each concentration of (a) Optiray 350 and (c) Iomeron 350. Mean CECT attenuation for the earliest equilibrium time(s) for each (b) Optiray and (d) Iomeron concentration, compared with bone (solid) and no‐contrast cartilage (dashed). * and † indicate significant difference to bone and no‐contrast cartilage attenuation values, respectively (p < 0.05)

FIGURE 5

Representative CECT images of mouse cartilage using 20%, 30%, 40% and 50% of (a) Optiray 350 and (b) Iomeron 350. Dashed region of interest insets is used to create histograms in Figure 6

FIGURE 6

Histograms of mouse cartilage using 20%, 30%, 40% and 50% of (a) Optiray 350 and (b) Iomeron 350 from dashed region of interest insets in Figure 5

FIGURE 7

Linear regression plots of CECT attenuation using (a) Optiray and (b) Iomeron vs GAG content of bovine articular cartilage. The light blue‐shaded curve shows the 95% confidence intervals for individual points, and the dark blue‐shaded curve shows the 95% confidence interval curve for the mean