Accelerated MRI of the knee. Quality and efficiency of compressed sensing

Purpose: To evaluate potential clinical acceleration factors of Compressed SENSE (CS)(1) in direct comparison with SENSE for fat saturated (fs)(2), proton density-weighted (PD)(3) 2D and 3D sequences of the knee. Method: Twenty healthy volunteers were scanned with a 3 T scanner, all receiving a standard, fs 2D PD, three CS (CS 2, CS 3, CS 5) as well as time-equivalent SENSE accelerations (5 2, 5 3, 5 5). The fs 3D PD sequence was acquired with four CS (CS 6, CS 8, CS 10, CS 15) and equivalent SENSE (5 5.72, 5 7.69, 5 9.57, 5 14) factors. Three independent readers rated the images. Signal-to-noise, contrast-to-noise, root-mean-square error and structural similarity index were analyzed for objective evaluation. Results: Scan time decreased with increasing CS factor (2D CS 2: 145 s, 2D CS 3: 95 s, 2D CS 5: 57 s, 3D CS 6: 293 s, 3D CS 8: 220 s, 3D CS 10: 176 s, 3D CS 15: 119 s). The 2D standard sequence was rated best for diagnostic certainty and overall image impression with an average of 4.97 +/- 0.10 and 4.80 +/- 0.24 (all p < 0.05), except for 2D CS 2 and 2D 5 2. For the 3D sequences, the standard sequence performed better for both parameters for CS 15, 5 9.57 and 5 4, as well as 5 7.69 for overall image impression while CS 8 was non-inferior for all tested criteria and CS 10 only inferior for delineation of the anterior cruciate ligament, both outperforming the time-equivalent SENSE accelerations. Conclusion: Compressed SENSE can significantly decrease (34.39 % for 2D CS 2 and 54.17 % for 3D CS 10) scan time in knee imaging with unchanged diagnostic certainty and overall image impression compared to the clinical reference.