Formalin fixation affects equilibrium partitioning of an ionic contrast agent-microcomputed tomography (EPIC-μCT) imaging of osteochondral samples.
OBJECTIVE
Equilibrium Partitioning of an Ionic Contrast agent with microcomputed tomography (EPIC-μCT) is a non-invasive technique to quantify and visualize the three-dimensional distribution of glycosaminoglycans (GAGs) in fresh cartilage tissue. However, it is unclear whether this technique is applicable to already fixed tissues. Therefore, this study aimed at investigating whether formalin fixation of bovine cartilage affects X-ray attenuation, and thus the interpretation of EPIC-μCT data.


METHODS
Osteochondral samples (n=24) were incubated with ioxaglate, an ionic contrast agent, for 22h prior to μCT scanning. The samples were scanned in both formalin-fixed and fresh conditions. GAG content was measured using a biochemical assay and normalized to wet weight, dry weight, and water content to determine potential reasons for differences in X-ray attenuation.


RESULTS
The expected zonal distribution of contrast agent/GAGs was observed for both fixed and fresh cartilage specimens. However, despite no significant differences in GAG concentrations or physical properties between fixed and fresh samples, the average attenuation levels of formalin-fixed cartilage were 14.3% lower than in fresh samples.


CONCLUSIONS
EPIC-μCT is useful for three-dimensional visualization of GAGs in formalin-fixed cartilage. However, a significant reduction in X-ray attenuation for fixed (compared to fresh) cartilage must be taken into account and adjusted for accordingly when quantifying GAG concentrations using EPIC-μCT.
Department of Orthopaedics, University Medical Center Utrecht, The Netherlands.
K E M
KE
Benders
J
J
Malda
D B F
DB
Saris
W J A
WJ
Dhert
R
R
Steck
D W
DW
Hutmacher
T J
TJ
Klein
D000818:Animals; D002358:Cartilage, Articular / Q000737:chemistry* / Q000000981:diagnostic imaging*; D002417:Cattle; D003287:Contrast Media / Q000737:chemistry; D005557:Formaldehyde; D006025:Glycosaminoglycans / Q000032:analysis*; D007485:Ioxaglic Acid / Q000737:chemistry*; D016707:Tissue Fixation / Q000379:methods*; D055114:X-Ray Microtomography / Q000379:methods
D003287:Contrast Media; D006025:Glycosaminoglycans; D005557:Formaldehyde; D007485:Ioxaglic Acid