To evaluate the diagnostic usefulness of synthetic T ₂ -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 T ₂ and M ₀ quantification (MARTINI) extended by generalized autocalibrating partial parallel acquistion (GRAPPA).
Overall, 58 individuals (26 female, mean age 23.3 ± 8.1 years) were examined at 3 Tesla with sagittal and axial T ₂ w turbo spin echo (TSE) sequences compared to synthetic T ₂ _- 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-to-noise ratios (CNR) of the nucleus pulposus and the annulus fibrosus.
Overall, the CR _T2w was 4.45 ± 1.80 and CR _T2synth was 4.71 ± 2.14. Both correlated (rsp = 0.768;p < 0.001) and differed (0.26 ± 1.38;p = 0.002) significantly. The CNR _T2w was 1.73 ± 0.52 and CNR _T2synth was 1.63 ± 0.50. Both correlated (rsp = 0.875;p < 0.001) and differed (-0.10 ± 0.25;p < 0.001) significantly. The inter-rater agreement was substantial to almost perfect (κ = 0.808-0.925) with the intra-rater agreement also substantial to almost perfect (κ = 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.
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 T ₂ w TSE.