title: Density of organic matrix of native mineralized bone measured by water- and fat-suppressed proton projection MRI.
abstract: Water- and fat-suppressed projection MR imaging (WASPI) utilizes the large difference between the proton T(2) (*)s of the solid organic matrix and the fluid constituents of bone to suppress the fluid signals while preserving solid matrix signals. The solid constituents include collagen and some molecularly immobile water and exhibit very short T(2) (*). The fluid constituents include mobile water and fat, with long T(2) (*). In WASPI, chemical shift selective low-power pi/2 pulses excite mobile water and fat magnetization which is subsequently dephased by gradient pulses, while the magnetization of collagen and immobile water remains mostly in the z-direction. Additional selective pi pulses in alternate scans further cancel the residual water and fat magnetization. Following water and fat suppression, the matrix signal is excited by a short hard pulse and the free induction decay acquired in the presence of a gradient in a 3D projection method. WASPI was implemented on a 4.7 T MR imaging system and tested on phantoms and bone specimens, enabling excellent visualization of bone matrix. The bone matrix signal per unit volume of bovine trabecular specimens was measured by this MR technique and compared with that determined by chemical analysis. This method could be used in combination with bone mineral density measurement by solid state (31)P projection MRI to determine the degree of bone mineralization.
authors.affiliation: Laboratory for the Study of Skeletal Disorders and Rehabilitation, Department of Orthopaedic Surgery, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. yaotang.wu@tch.harvard.edu
authors.forename: Yaotang
authors.initials: Y
authors.lastname: Wu
authors.forename: Jerome L
authors.initials: JL
authors.lastname: Ackerman
authors.forename: David A
authors.initials: DA
authors.lastname: Chesler
authors.forename: Lila
authors.initials: L
authors.lastname: Graham
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.forename: Melvin J
authors.initials: MJ
authors.lastname: Glimcher
mesh_terms: D000273:Adipose Tissue / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D015519:Bone Density / Q000502:physiology*; D002417:Cattle; D003094:Collagen / Q000032:analysis*; D005109:Extracellular Matrix / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D005240:Feasibility Studies; D005269:Femur / Q000033:anatomy & histology / Q000737:chemistry* / Q000378:metabolism; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013710:Tendons / Q000737:chemistry / Q000378:metabolism; D014867:Water / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism
chemical_list: D014867:Water; D003094:Collagen