title: The repeatability of T2 relaxation time measurement of human knee articular cartilage.
abstract: OBJECTIVE
  To assess short- and long-term repeatability of T2 relaxation time measurements of the knee articular cartilage.
  
  
  METHODS
  The right knees of nine asymptomatic volunteers (age 30-38 years, five male, four female) were imaged at 1.5 T in three sessions 1 and 2 weeks apart. To observe short-term repeatability, the measurements were repeated three times within one of the three imaging sessions for each volunteer. T2 relaxation time was mapped using a multi-slice multi-echo spin echo sequence in axial and sagittal planes. Cartilage was manually segmented and repeatability, as measured by root-mean-square coefficient of variation (CVRMS) was evaluated both for the entire bulk cartilage of each joint surface in the slice and separately for each region of interest (ROI) at different topographical locations and separately for the superficial and deep half of each ROI.
  
  
  RESULTS
  For bulk T2, the long-term repeatability was 3.2, 5.4, and 3.7%, and the short-term reproducibility was 3.9, 3.9, and 3.4% for bulk femoral, tibial, and patellar cartilage, respectively. There were no significant differences between long-term and short-term repeatability in superficial or deep cartilage when comparing CVRMS values (p = 0.338 and 0.700, respectively). For individual ROIs, the repeatability varied between 2.5 and 22.2% depending on the topographical location.
  
  
  CONCLUSIONS
  The current results show mostly good repeatability. However, there were remarkable variations of T2 between bulk cartilage and different ROIs, bulk cartilage showing better repeatability. With careful patient positioning T2 can be accurately determined for different cartilage surfaces.
authors.affiliation: Department of Diagnostic Radiology, Oulu University Hospital (OYS), Kajaanintie, POB 50, 90029, Oulu, Finland. ilkka.hannila@ppshp.fi.|Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland. ilkka.hannila@ppshp.fi.
authors.forename: Ilkka
authors.initials: I
authors.lastname: Hannila
authors.affiliation: Department of Diagnostic Radiology, Oulu University Hospital (OYS), Kajaanintie, POB 50, 90029, Oulu, Finland.|Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland.
authors.forename: Eveliina
authors.initials: E
authors.lastname: Lammentausta
authors.affiliation: Department of Diagnostic Radiology, Oulu University Hospital (OYS), Kajaanintie, POB 50, 90029, Oulu, Finland.|Center for Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland.|Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland.
authors.forename: Osmo
authors.initials: O
authors.lastname: Tervonen
authors.affiliation: Department of Diagnostic Radiology, Oulu University Hospital (OYS), Kajaanintie, POB 50, 90029, Oulu, Finland.|Center for Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland.|Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland.
authors.forename: Miika Tapio
authors.initials: MT
authors.lastname: Nieminen
mesh_terms: D000328:Adult; D002358:Cartilage, Articular / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007719:Knee Joint / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results
keywords: Cartilage; Magnetic resonance imaging (MRI); Repeatability; T2