Pia M. Jungmann

Objective The aim of this study was to longitudinally determine the prognostic value of early postoperative quantitative 3T-MRI (magnetic resonance imaging) parameters of subchondral bone marrow for 2-year clinical and MRI outcome after matrix-associated autologous chondrocyte implantation (MACI) with autologous bone grafting (ABG) at the knee. Design Consecutive subjects who received MACI with ABG for treatment of focal osteochondral defects received MRI follow-up 3, 6, 12, and 24 months postoperatively. Quantitative MRI included bone marrow edema-like lesion (BMEL) volume measurements and single-voxel magnetic resonance spectroscopy (MRS; n = 9) of the subchondral bone marrow. At 2-year follow-up, morphological MRI outcome included MOCART (magnetic resonance observation of cartilage repair tissue) 2.0 scores. Clinical outcomes were assessed using Lysholm scores. Results Among a total of 18 subjects (mean age: 28.7 ± 8.4 years, n = 14 males) with defects at the medial or lateral ( n = 15 and n = 3, respectively) condyle, mean BMEL volume decreased from 4.9 cm 3 at 3 months to 2.0 cm 3 at 2-year follow-up ( P = 0.040). MRS-based bone marrow water T2 showed a decrease from 20.7 ms at 1-year follow-up to 16.8 ms at 2-year follow-up ( P = 0.040). Higher BMEL volume at 6 months correlated with lower 2-year Lysholm (R = −0.616, P = 0.015) and MOCART 2.0 scores (R = −0.567, P = 0.027). Larger early postoperative BMEL volumes at 3 months (R = −0.850, P = 0.007) and 6 months (R = −0.811, P = 0.008) correlated with lower MRS-based unsaturated lipid fractions at 2-year follow-up. Furthermore, patients with early postoperative bony defects showed worse MOCART 2.0 ( P = 0.044) and Lysholm scores ( P = 0.017) after 24 months. Conclusion Low subchondral BMEL volume and optimal restoration of the subchondral bone at early postoperative time points predict better 2-year clinical and MRI outcomes after MACI with ABG.

Purpose To accelerate the Pointwise Encoding Time Reduction with Radial Acquisition (PETRA) sequence using compressed sensing while preserving the image quality for high‐resolution MRI of tissue with ultra‐short values. Methods Compressed sensing was introduced in the PETRA sequence (csPETRA) to accelerate the time‐consuming single point acquisition of the k‐space center data. Random undersampling was applied to achieve acceleration factors up to Acc = 32. Phantom and in vivo images of the knee joint of six volunteers were measured at 3T using csPETRA sequence with Acc = 4, 8, 12, 16, 24, and 32. Images were compared against fully sampled PETRA data ( Acc = 1) for structural similarity and normalized‐mean‐square‐error. Qualitative and semi‐quantitative analyses were performed to assess the effect of the acceleration on image artifacts, image quality, and delineation of anatomical structures at the knee. Results Even at high acceleration factors of Acc = 16 no aliasing artifacts were observed, and the anatomical details were preserved compared with the fully sampled data. The normalized‐mean‐square‐error was less than 1% for Acc = 16, in which single point imaging acquisition time was reduced from 165 to 10 s, reducing the total scan time from 7.8 to 5.2 min. Semi‐quantitative analyses suggest that Acc = 16 yields comparable diagnostic quality as the fully sampled data for knee imaging at a scan time of 5.2 min. Conclusion csPETRA allows for ultra‐short imaging of the knee joint in clinically acceptable scan times while maintaining the image quality of original non‐accelerated PETRA sequence.