title: Short T2 tissue imaging with the Pointwise Encoding Time reduction with Radial Acquisition (PETRA) sequence: the additional value of fat saturation and subtraction in the meniscus.
abstract: OBJECTIVE
  The purposes of this study were (1) to compare single-echo PETRA with dual-echo PETRA using in vivo MR imaging, (2) to compare non-fat-saturated PETRA with fat-saturated PETRA using a 3-T clinical MR scanner, and (3) to determine the effect of the adequate sequence and post-processing method.
  
  
  METHODS
  Twenty-two patients underwent dual-echo 3D PETRA sequence knee MR imagining (TE of 70μs and 2.3ms) with and without fat-saturation using a 3T clinical MR scanner (Magnetom Trio, Siemens, Erlangen, Germany). The study population was classified into two groups: (1) normal meniscus on conventional MR images with no related physical examination on medical records and (2) meniscal degeneration or tear. We reformatted four image sets: (1) ultrashort TE signal without fat-saturation, (2) ultrashort TE signal with fat-saturation, (3) weighted-subtraction image of dual-echo PETRA images without fat-saturation, and (4) weighted-subtraction image with fat-saturation. For the weighted-subtraction images, the ultrashort TE image was rescaled relative to the second echo image with weighting factors from 0.6 based on SNR and CNR analyses. For quantitative assessment, the mean signal intensities inside user-drawn regions of interest (ROIs) were drawn and recorded. For statistical analyses, the t-test was used to compare the two groups and effect size was used for comparison of the discrimination power.
  
  
  RESULTS
  In all image sets, the mean signal intensity values were lower in patients with meniscal degeneration/tear compared to controls on both fat-saturated and non-fat-saturated MR images. The single-echo ultrashort TE images showed higher effect sizes than the weighted-subtraction image of dual-echo images.
  
  
  CONCLUSIONS
  We demonstrated that there was significantly lower signal intensity on ultrashort TE PETRA images in the patients with meniscal pathologies. In addition, the single-echo of the ultrashort TE PETRA images echo time could be a more sensitive indicator between normal and pathologic meniscus conditions in patients.
authors.affiliation: Department of Radiology, Research Institute of Radiological Science, Medical Convergence Research Institute, and Severance Biomedical Science Institute, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Young Han
authors.initials: YH
authors.lastname: Lee
authors.affiliation: Department of Radiology, Research Institute of Radiological Science, Medical Convergence Research Institute, and Severance Biomedical Science Institute, Yonsei University College of Medicine, Seoul, Republic of Korea. Electronic address: jss@yuhs.ac.
authors.forename: Jin-Suck
authors.initials: JS
authors.lastname: Suh
authors.affiliation: Siemens AG, Healthcare Sector, Erlangen, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Grodzki
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000328:Adult; D000368:Aged; D000465:Algorithms; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008592:Menisci, Tibial / Q000473:pathology*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D000070600:Tibial Meniscus Injuries
keywords: Fat saturation; Knee; Magnetic resonance imaging; Subtraction image; Ultrashort echo time