Ex vivo validation of delayed gadolinium-enhanced magnetic resonance imaging (MRI) of cartilage (dGEMRIC) and T2 mapping for quantifying cartilage thickness in normal and naturally occurred osteoarthritic distal interphalangeal joints using a high-field MRI

Determination of measurements of cartilage thickness on dGEMRIC, T2 maps and histology of pre-determined sites in normal and naturally occurring osteoarthritic Warmblood cadaver distal interphalangeal joints (DIPJs), correlation of histological and MRI measurements, and testing of the effect of cartilage health and cartilage position within the joint on the cartilage thickness (histological and MRI measurements). From 12 Warmblood DIPJ cadavers cartilage thickness was obtained from dGEMRIC images after intra-articular gadolinium administration (T1(postGd)) and from T2(maps) using a 3 tesla magnet at predetermined sites in the DIPJ. Corresponding cartilage sites underwent histologic evaluation to determine cartilage health and cartilage thickness was measured by 2 observers. Interobserver agreement was calculated using intraclass correlation coefficients. Mean T1(postGd) and T2(map) cartilage thickness was correlated with histological cartilage thickness. Mixed generalised linear models were created to evaluate the effects of cartilage site, articular surface, and cartilage health on cartilage thickness. 122 cartilage specimens were analysed. T1(postGd) (r = 0.42-0.43; P < 0.001) and T2(map) (r = 0.34-0.35; P < 0.001) cartilage thickness correlated positively with histological cartilage thickness. T1(postGd) cartilage thickness significantly decreased as osteoarthritis progressed. There were topical variations in cartilage thickness. Whereby articular cartilage was thinnest situated in the dorsal DIPJ zone (T1(PostGd), T2(map) and histology), on the condyles (T2(map)) and on the distal aspect of the middle phalanx (histology). In conclusion T1(PostGd) and T2(map) are reliable to evaluate the thickness of normal and osteoarthritic equine articular cartilage, whereby T1(PostGd) is superior. Topographical variations of DIPJ cartilage thickness should be appreciated by clinicians to avoid misinterpretation of cartilage thinning secondary to cartilage disease. Volume averaging should be appreciated as a complicating factor, especially in the joint periphery.