Development and Testing of a Hybrid Synthetic-Biologic Phantom for the Optimization of MR Sequences for Articular Cartilage

Purpose To develop and validate a hybrid phantom for optimizing MRI sequences of knee articular cartilage. Methods MR study of the knee was performed in two patients prior to total knee arthroplasty (in-vivo MR). Osteochondral surgical resections of femur and tibia were used to set-up a phantom consisting in a transparent polyethylene box filled with echographic gel. Phantom assemblage and in-vitro MRI was performed in one patient within 20 minutes after surgery (fresh MR) and, for the other patient, after having preserved the tissues in formalin for 12 months (post-fixation MR). Morphological sequences (SE T1-weighted, DESS, TRUFI 3D) and compositional maps (SE T2, GR T2*) were obtained on sagittal plane. Phantom was validated by comparing MR data obtained in-vivo and in-vitro. Comparison of data obtained from fresh and fixed tissues allowed also to assess modifications in MR signal due to formalin preservation. Results MR imaging in-vitro allowed the evaluation of the whole articular surface of the femoral condyles and tibial plateau. Excellent concordance existed between in-vivo and in-vitro cartilage morphology in T1-weighted images. DESS and TRUFI 3D sequences showed limitations for in-vitro MR imaging because of their sensitivity to magnetic field inhomogeneities. Formalin fixation preserved tissue morphology and T2 relaxation times of the chondral tissue. Conclusions The proposed hybrid synthetic-biologic phantom allowed obtaining in-vitro MR data super-imposable to in-vivo data for both fresh and formalin-fixed tissues, proving its usability for the optimization of knee cartilage MRI.