Synthetic T-2-weighted images of the lumbar spine derived from an accelerated T-2 mapping sequence: Comparison to conventional T(2)w turbo spin echo

Objectives: To evaluate the diagnostic usefulness of synthetic T2-weighted images of the lumbar spine derived from ten-fold undersampled k-space data using GRAPPATINI, a combination of a model-based approach for rapid T2 and M0 quantification (MARTINI) extended by generalized autocalibrating partial parallel acquistion (GRAPPA). Materials and methods: Overall, 58 individuals (26 female, mean age 23.3 +/- 8.1 years) were examined at 3 Tesla with sagittal and axial T2w turbo spin echo (TSE) sequences compared to synthetic T2_weighted contrasts derived at identical effective echo times and spatial resolutions. Two blinded readers graded disk degeneration and evaluated the lumbar intervertebral disks for present herniation or annular tear. One reader reassessed all studies after four weeks. Weighted kappa statistics were calculated to assess inter-rater and intra-rater agreement. Also, all studies were segmented manually by one reader to compute contrast ratios (CR) and contrast-tonoise ratios (CNR) of the nucleus pulposus and the annulus fibrosus. Results: Overall, the CRT2w was 4.45 +/- 1.80 and CRT2synth was 4.71 +/- 2.14. Both correlated (rsp = 0.768;p < 0.001) and differed (0.26 +/- 1.38;p = 0.002) significantly. The CNRT2w was 1.73 +/- 0.52 and CNRT2synth was 1.63 +/- 0.50. Both correlated (rsp = 0.875;p < 0.001) and differed (-0.10 +/- 0.25;p < 0.001) significantly. The interrater agreement was substantial to almost perfect (Kappa = 0.808-0.925) with the intra-rater agreement also substantial to almost perfect (Kappa = 0.862-0.963). The area under the curve of the receiver operating characteristics assessing disk herniation or annular tear ranged from 0.787 to 0.892. Conclusions: This study concludes that synthetic images derived by GRAPPATINI can be used for clinical routine assessment with inter-rater and intra-rater agreements comparable to conventional T2w TSE.