Improvement of gagCEST imaging in the human lumbar intervertebral disc by motion correction

To investigate whether motion correction improves glycosaminoglycan chemical exchange saturation transfer imaging (gagCEST imaging) of intervertebral discs (IVDs). Magnetic resonance gagCEST imaging of 12 volunteers was obtained in lumbar IVDs at 3 T using a prototype pulse sequence. The data were motion-corrected using a prototype diffeomorphism-based motion compensation technique. For both the data with and that without motion correction (data(c), data(uc)), CEST evaluation was performed using the magnetisation transfer ratio asymmetry (MTRasym) as a means of quantifying CEST effects. MTRasym and the signal-to-noise ratio (SNR) of the MTRasym map in the nucleus pulposus (NP) were compared for data(c) and data(uc). A visual grading analysis was performed by a radiologist in order to subjectively quantify the quality of the MTRasym analysis (score 1: best quality, score 5: worst quality). Furthermore, a landmark analysis was performed in order to objectively quantify the motion between CEST images using the mean landmark distance d(mean). MTRasym and SNR were significantly higher for the motion-corrected data than for the uncorrected CEST data (MTRasym(data(c)) = 3.77 % +/- A 0.95 %, MTRasym(data(uc)) = 3.41 % +/- A 1.54 %, p value = 0.001; SNR(data(c)) = 3.88 A +/- 2.04, SNR(data(uc)) = 2.77 A +/- 1.55, p value < 0.001, number of IVDs = 48). The visual grading analysis revealed a higher reliability for data(c) (maximum score = 2) compared with data(uc) (maximum score = 5). The landmark analysis demonstrated the superiority of the motion-corrected data (d(mean)(data(c)) =0.08 mm +/- 0.09 mm, d(mean)(data(uc)) = 0.36 mm +/- 0.09 mm, p value = 0.001). Our study showed significant improvements in the ability to quantify CEST imaging in IVDs after the application of motion correction compared with uncorrected datasets.