title: Comprehensive analysis of the Cramer-Rao bounds for magnetic resonance temperature change measurement in fat-water voxels using multi-echo imaging.
abstract: OBJECTIVE
  The aim of this paper is to characterize the noise propagation for MRI temperature change measurement with emphasis on finding the best echo time combinations that yield the lowest temperature noise.
  
  
  METHODS
  A Cramer-Rao lower-bound (CRLB) calculation was used to estimate the temperature noise for a model of the MR signal in fat-water voxels. The temperature noise CRLB was then used to find a set of echo times that gave the lowest temperature change noise for a range of fat-water frequency differences, temperature changes, fat/water signal ratios, and T2* values. CRLB estimates were verified by Monte Carlo simulation and in phantoms using images acquired in a 1.5 T magnet.
  
  
  RESULTS
  Results show that regions exist where the CRLB predicts minimal temperature variation as a function of the other variables. The results also indicate that the CRLB values calculated in this paper provide excellent guidance for predicting the variation of temperature measurements due to changes in the signal parameters. For three echo scans, the best noise characteristics are seen for TE values of 20.71, 23.71, and 26.71 ms. Results for five and seven echo scans are also presented in the text.
  
  
  CONCLUSIONS
  The results present a comprehensive analysis of the effects of different scan parameters on temperature noise, potentially benefiting the selection of scan parameters for clinical MRI thermometry.
authors: Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710, USA. cory.wyatt@duke.edu
authors: Cory
authors: C
authors: Wyatt
authors: Brian J
authors: BJ
authors: Soher
authors: Kavitha
authors: K
authors: Arunachalam
authors: James
authors: J
authors: MacFall
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000465:Algorithms; D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy; D015233:Models, Statistical; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water