title: T1ρ and T2 mapping of the intervertebral disk: comparison of different methods of segmentation.
abstract: OBJECTIVE
  Intervertebral disk biochemical composition could be accessed in vivo by T1ρ and T2 relaxometry. We found no studies in the literature comparing different segmentation methods for data extraction using these techniques. Our aim was to compare different manual segmentation methods used to extract T1ρ and T2 relaxation times of intervertebral disks from MR imaging. Seven different methods of partial-disk segmentation techniques were compared with whole-disk segmentation as the reference standard.
  
  
  METHODS
  Sagittal T1ρ and T2 maps were generated by using a 1.5T MR imaging scanner in 57 asymptomatic volunteers 20-40 years of age. Two hundred eighty-five lumbar disks were separated into 2 groups: nondegenerated disk (Pfirrmann I and II) and degenerated disk (Pfirrmann III and IV). In whole-disk segmentation, the disk was segmented in its entirety on all sections. Partial-disk segmentation methods included segmentation of the disk into 6, 5, 4, 3, and 1 sagittal sections. Circular ROIs positioned in the nucleus pulposus and annulus fibrosus were also used to extract T1ρ and T2, and data were compared with whole-disk segmentation
  
  
  RESULTS
  In the nondegenerated group, segmentation of ≥5 sagittal sections showed no statistical difference with whole-disk segmentation. All the remaining partial-disk segmentation methods and circular ROIs showed different results from whole-disk segmentation (P < .001). In the degenerated disk group, all methods were statistically similar to whole-disk segmentation. All partial-segmentation methods, including circular ROIs, showed strong linear correlation with whole-disk segmentation in both the degenerated and nondegenerated disk groups.
  
  
  CONCLUSIONS
  Manual segmentation showed strong reproducibility for T1ρ and T2 and strong linear correlation between partial- and whole-disk segmentation. Absolute T1ρ and T2 values extracted from different segmentation techniques were statistically different in disks with Pfirrmann grades I and II.
authors.affiliation: From the Division of Radiology (R.M.-R., G.P.B., C.S.C., M.H.N.-B.), Ribeirão Preto Medical School rafaelmenezesreis@gmail.com.
authors.forename: R
authors.initials: R
authors.lastname: Menezes-Reis
authors.affiliation: Department of Physics (C.E.G.S.), Ribeirão Preto Philosophy and Sciences School, University of São Paulo, São Paulo, Brazil.
authors.forename: C E G
authors.initials: CE
authors.lastname: Salmon
authors.affiliation: From the Division of Radiology (R.M.-R., G.P.B., C.S.C., M.H.N.-B.), Ribeirão Preto Medical School.
authors.forename: C S
authors.initials: CS
authors.lastname: Carvalho
authors.affiliation: From the Division of Radiology (R.M.-R., G.P.B., C.S.C., M.H.N.-B.), Ribeirão Preto Medical School.
authors.forename: G P
authors.initials: GP
authors.lastname: Bonugli
authors.affiliation: Department of Radiology (C.B.C.), VA San Diego Healthcare System, San Diego, California.
authors.forename: C B
authors.initials: CB
authors.lastname: Chung
authors.affiliation: From the Division of Radiology (R.M.-R., G.P.B., C.S.C., M.H.N.-B.), Ribeirão Preto Medical School.
authors.forename: M H
authors.initials: MH
authors.lastname: Nogueira-Barbosa
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000737:chemistry* / Q000473:pathology; D055959:Intervertebral Disc Degeneration / Q000473:pathology; D008159:Lumbar Vertebrae; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D055815:Young Adult