title: A simple analytic method for estimating T2 in the knee from DESS.
abstract: To introduce a simple analytical formula for estimating T2from a single Double-Echo in Steady-State (DESS) scan.
  
  
  
  Extended Phase Graph (EPG) modeling was used to develop a straightforward linear approximation of the relationship between the two DESS signals, enabling accurate T2estimation from one DESS scan. Simulations were performed to demonstrate cancellation of different echo pathways to validate this simple model. The resulting analytic formula was compared to previous methods for T2estimation using DESS and fast spin-echo scans in agar phantoms and knee cartilage in three volunteers and three patients. The DESS approach allows 3D (256×256×44) T2-mapping with fat suppression in scan times of 3-4min.
  
  
  
  The simulations demonstrated that the model approximates the true signal very well. If the T1is within 20% of the assumed T1, the T2estimation error was shown to be less than 5% for typical scans. The inherent residual error in the model was demonstrated to be small both due to signal decay and opposing signal contributions. The estimated T2from the linear relationship agrees well with reference scans, both for the phantoms and in vivo. The method resulted in less underestimation of T2than previous single-scan approaches, with processing times 60 times faster than using a numerical fit.
  
  
  
  A simplified relationship between the two DESS signals allows for rapid 3D T2quantification with DESS that is accurate, yet also simple. The simplicity of the method allows for immediate T2estimation in cartilage during the MRI examination.
authors.affiliation: Department of Radiology, Stanford University, Stanford, CA, United States. Electronic address: bragi@stanford.edu.
authors.forename: B
authors.initials: B
authors.lastname: Sveinsson
authors.affiliation: Department of Radiology, Stanford University, Stanford, CA, United States.
authors.forename: A S
authors.initials: AS
authors.lastname: Chaudhari
authors.affiliation: Department of Radiology, Stanford University, Stanford, CA, United States.
authors.forename: G E
authors.initials: GE
authors.lastname: Gold
authors.affiliation: Department of Radiology, Stanford University, Stanford, CA, United States.
authors.forename: B A
authors.initials: BA
authors.lastname: Hargreaves
mesh_terms: D002358:Cartilage, Articular / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007717:Knee / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D012016:Reference Values; D015203:Reproducibility of Results
keywords: Cartilage; DESS; Osteoarthritis; T(2)