Histological correlation of 7 T multi-parametric MRI performed in ex-vivo Achilles tendon

Abstract

IntroductionThe goal of this in vitro validation study was to investigate the feasibility of biochemical MRI techniques, such as sodium imaging, T2 mapping, fast imaging with steady state precession (FISP), and reversed FISP (PSIF), as potential markers for collagen, glycosaminoglycan and water content in the Achilles tendon. Materials and methodsFive fresh cadaver ankles acquired from a local anatomy department were used in the study. To acquire a sodium signal from the Achilles tendon, a 3D-gradient-echo sequence, optimized for sodium imaging, was used with TE=7.71ms and TR=17ms. The T2 relaxation times were obtained using a multi-echo, spin-echo technique with a repetition time (TR) of 1200ms and six echo times. A 3D, partially balanced, steady-state gradient echo pulse sequence was used to acquire FISP and PSIF images, with TR/TE=6.96/2.46ms. MRI parameters were correlated with each other, as well as with histologically assessed glycosaminoglycan and water content in cadaver Achilles tendons. ResultsThe highest relevant Pearson correlation coefficient was found between sodium SNR and glycosaminoglycan content (r=0.71, p=0.007). Relatively high correlation was found between the PSIF signal and T2 values (r=0.51, p=0.036), and between the FISP signal and T2 values (r=0.56, p=0.047). Other correlations were found to be below the moderate level. ConclusionThis study demonstrated the feasibility of progressive biochemical MRI methods for the imaging of the AT. A GAG-specific, contrast-free method (sodium imaging), as well as collagen- and water-sensitive methods (T2 mapping, FISP, PSIF), may be used in fast-relaxing tissues, such as tendons, in reasonable scan times.