title: A fast method for the quantification of fat fraction and relaxation times: Comparison of five sites of bone marrow.
abstract: Bone marrow is found either as red bone marrow, which mainly contains haematopoietic cells, or yellow bone marrow, which mainly contains adipocytes. In adults, red bone marrow is principally located in the axial skeleton. A recent study has introduced a method to simultaneously estimate the fat fraction (FF), the T1 and T2* relaxation times of water (T1w, T2*w) and fat (T1f and T2*f) in the vertebral bone marrow. The aim of the current study was to measure FF, T1w, T1f, T2*w and T2*f in five sites of bone marrow, and to assess the presence of regional variations.
  
  
  
  MRI experiments were performed at 1.5T on five healthy volunteers (31.6±15.6years) using a prototype chemical-shift-encoded 3D multi-gradient-echo sequence (VIBE) acquired with two flip angles. Acquisitions were performed in the shoulders, lumbar spine and pelvis, with acquisition times of <25seconds per sequence. Signal intensities of magnitude images of the individual echoes were used to fit the signal and compute FF, T1w, T1f, T2*w and T2*f in the humerus, sternum, vertebra, ilium and femur.
  
  
  
  Regional variations of fat fraction and relaxation times were observed in these sites, with higher fat fraction and longer T1w in the epiphyses of long bones. A high correlation between FF and T1w was measured in these bones (R=0.84 in the humerus and R=0.84 in the femur). In most sites, there was a significant difference between water and fat relaxation times, attesting the relevance of measuring these parameters separately.
  
  
  
  The method proposed in the current study allowed for measurements of FF, T1w, T1f, T2*w and T2*f in five sites of bone marrow. Regional variations of these parameters were observed and a strong negative correlation between the T1 of water and the fat fraction in bones with high fat fractions was found.
authors.affiliation: INSERM, UMR 1099, Rennes, France; LTSI, Université de Rennes 1, Rennes, France; Siemens Healthcare, Saint-Denis, France. Electronic address: herve.saint-jalmes@univ-rennes1.fr.
authors.forename: Caroline
authors.initials: C
authors.lastname: Le Ster
authors.affiliation: INSERM, UMR 1099, Rennes, France; LTSI, Université de Rennes 1, Rennes, France.
authors.forename: Jérémy
authors.initials: J
authors.lastname: Lasbleiz
authors.affiliation: Siemens Healthcare, Erlangen, Germany. Electronic address: stephan.kannengiesser@siemens.com.
authors.forename: Stephan
authors.initials: S
authors.lastname: Kannengiesser
authors.affiliation: Department of Imaging, Rennes University Hospital, Rennes, France. Electronic address: raphael.guillin@chu-rennes.fr.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Guillin
authors.affiliation: INSERM, UMR 1099, Rennes, France; LTSI, Université de Rennes 1, Rennes, France.
authors.forename: Giulio
authors.initials: G
authors.lastname: Gambarota
authors.affiliation: INSERM, UMR 1099, Rennes, France; LTSI, Université de Rennes 1, Rennes, France; CRLCC, Centre Eugène Marquis, Rennes, France. Electronic address: herve.saint-jalmes@univ-rennes1.fr.
authors.forename: Hervé
authors.initials: H
authors.lastname: Saint-Jalmes
mesh_terms: D017667:Adipocytes / Q000473:pathology; D000328:Adult; D001853:Bone Marrow / Q000000981:diagnostic imaging*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D006811:Humerus; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000000981:diagnostic imaging; D014867:Water / Q000737:chemistry; D055815:Young Adult
chemical_list: D014867:Water
keywords: Bone marrow; Relaxometry; Water-fat imaging