title: Diffusion-tensor imaging of the growing ends of long bones: pilot demonstration of columnar structure in the physes and metaphyses of the knee.
abstract: OBJECTIVE
  To determine the feasibility of using in vivo diffusion-tensor imaging and tractography of the physis to examine changes related to rate of growth, location, and age.
  
  
  METHODS
  This retrospective study was institutional review board approved and HIPAA compliant and the requirement for informed consent was waived. Diffusion-tensor imaging of the knee was performed at 3.0 T in 31 subjects (nine boys and 22 girls) with a median age of 13.6 years. The mean ages of boys and girls were 14.7 years (range, 12.0-18.3 years) and 13.2 years (range, 7.0-18.6 years), respectively. Regions of interest were placed in the physis of the tibia and femur, and in the epiphyseal and articular cartilage of these bones. Tractography was performed by using a fractional anisotropic threshold of 0.15 and an angle threshold of 40°. The tractographic patterns were qualitatively evaluated and changes related to age were described. The tract-based apparent diffusion coefficient, fractional anistropy, tensor eigenvalues, and tract length were measured. Diffusion parameters were compared between the center and periphery of the physis, and between the distal femur and proximal tibia.
  
  
  RESULTS
  Tractography resulted in parallel tracts in the physis and the adjacent metaphysis. Tractographic pattern changed with age, with individuals approaching physeal closure having shorter tracts in a random arrangement. Patterns of tractography varied with age in the femur (P < .001) and tibia (P < .001). Femoral tracts (median length, 6.5 mm) were longer than tibial tracts (median length, 4.3 mm) (P < .001). Tracts in the periphery of the physes were longer than those in the center (femur, P = .005; tibia, P = .004). In the physis of the femur and tibia, a significant age-related decrease was observed in apparent diffusion coefficient (P < .001 for both), axial diffusion (femur, P = .001; tibia, P < .001), and transverse diffusion [P < .001 for both]), and an age-related increase was seen in fractional anistropy (P < .001, for both).
  
  
  CONCLUSIONS
  Diffusion-tensor imaging shows the columnar microstructure of the physis and adjacent metaphysis, and provides further insight into normal growth.
authors.affiliation: From the Department of Radiology, The Children's Hospital of Philadelphia, 34th & Civic Center Blvd, Room 3NW, Philadelphia, PA 19104 (C.J., J.I.B., J.D., V.H.F., D.J.); and Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pa (J.I.B., V.H.F., D.J.).
authors.forename: Camilo
authors.initials: C
authors.lastname: Jaimes
authors.forename: Jeffrey I
authors.initials: JI
authors.lastname: Berman
authors.forename: Jorge
authors.initials: J
authors.lastname: Delgado
authors.forename: Victor
authors.initials: V
authors.lastname: Ho-Fung
authors.forename: Diego
authors.initials: D
authors.lastname: Jaramillo
mesh_terms: D000293:Adolescent; D002358:Cartilage, Articular / Q000033:anatomy & histology*; D002648:Child; D056324:Diffusion Tensor Imaging; D004838:Epiphyses / Q000033:anatomy & histology*; D005260:Female; D005269:Femur / Q000033:anatomy & histology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007719:Knee Joint / Q000033:anatomy & histology*; D008297:Male; D010865:Pilot Projects; D012189:Retrospective Studies; D059629:Signal-To-Noise Ratio; D013977:Tibia / Q000033:anatomy & histology*