title: Evaluation of the articular cartilage of the knee joint with vastly undersampled isotropic projection reconstruction steady-state free precession imaging.
abstract: OBJECTIVE
  To determine the feasibility of the vastly undersampled isotropic projection reconstruction steady-state free precession (VIPR-SSFP) sequence for evaluating the articular cartilage of the knee joint.
  
  
  METHODS
  A magnetic resonance (MR) examination of the knee was performed on 33 subjects using a GE 1.5T scanner and a phased-array extremity coil. VIPR-SSFP, proton density-weighted fast spin-echo (PD-FSE), fat-suppressed T2-weighted fast spin-echo (T2-FSE), and three-dimensional fat-suppressed spoiled gradient recall-echo (SPGR) sequences were performed on three asymptomatic volunteers and 10 patients with osteoarthritis of the knee joint. Signal-to-noise efficiency, and contrast-to-noise ratio (CNR) measurements were calculated for all sequences and compared with the use of paired t-tests. The VIPR-SSFP sequence was then performed on 20 consecutive patients who were undergoing a routine MR examination of the knee.
  
  
  RESULTS
  The cartilage signal-to-noise efficiency of the VIPR-SSFP sequence was not significantly different from that of the PD-FSE and SPGR sequences. The cartilage signal-to-noise efficiency of the VIPR-SSFP sequence was significantly higher (P < 0.05) than that of the T2-FSE sequence. The VIPR-SSFP sequence produced images with significantly higher (P < 0.05) CNR between cartilage and synovial fluid than the PD-FSE and SPGR sequences, and significantly higher (P < 0.05) CNR between cartilage and subchondral bone than the T2-FSE sequence. The VIPR-SSFP sequence allowed excellent visualization of the articular cartilage of the knee joint in all subjects. All articular cartilage defects identified on the PD-FSE, T2-FSE, and SPGR images were well visualized on the VIPR-SSFP images.
  
  
  CONCLUSIONS
  VIPR-SSFP images had high cartilage signal-to-noise efficiency and high CNR between cartilage and adjacent synovial fluid and subchondral bone; therefore, the sequence is well suited for evaluating the articular cartilage of the knee joint.
authors.affiliation: Department of Radiology, University of Wisconsin Hospital, Madison, Wisconsin, USA. rkijowski@mail.radiology.wisc.edu
authors.forename: Richard
authors.initials: R
authors.lastname: Kijowski
authors.forename: Aiming
authors.initials: A
authors.lastname: Lu
authors.forename: Walter
authors.initials: W
authors.lastname: Block
authors.forename: Thomas
authors.initials: T
authors.lastname: Grist
mesh_terms: D000328:Adult; D002356:Cartilage / Q000473:pathology; D002357:Cartilage Diseases / Q000473:pathology*; D002358:Cartilage, Articular / Q000473:pathology*; D005260:Female; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged