title: Investigation of proton density for measuring tissue temperature.
abstract: OBJECTIVE
  To examine the temperature dependence of the proton density (PD) in both adipose and muscle tissues, and the application of the PD as a thermometry parameter in breast tissues.
  
  
  METHODS
  Porcine fat samples and bovine muscle samples were successively heated to temperatures ranging from 30 degrees C to 76 degrees C and then cooled. They were then imaged with a dual-echo spin-echo sequence. T1 and T2 effects were carefully corrected from the images. The apparent PD (APD) in regions of interest (ROIs) and the sum of the APD in all pixels (Sum_APD) were measured and analyzed by linear regression.
  
  
  RESULTS
  APD in adipose tissue is linear and reversible, and changes with a 0.3%/ degrees C to 0.45%/ degrees C temperature variation. The temperature coefficient of Sum_APD in adipose tissue is approximately 0.29%/ degrees C, as predicted from the Boltzmann distribution. However, the results in muscle tissue are more variable. There is an offset in both APD and Sum_APD between heating and cooling phases, as well as different temperature coefficients between these two phases.
  
  
  CONCLUSIONS
  The Sum_APD in adipose tissue validates the 1/T dependence on temperature. The APD is a potentially useful parameter for fat thermometry; however, its application in muscle tissue requires further investigation.
authors.affiliation: Department of Electrical Engineering, Stanford University, Lucas MRS Imaging Center, Rm. P064, 1201 Welch Road, Stanford, CA 94305-5488, USA. jeanchen@stanford.edu
authors.forename: Jing
authors.initials: J
authors.lastname: Chen
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Daniel
authors.forename: Kim Butts
authors.initials: KB
authors.lastname: Pauly
mesh_terms: D000273:Adipose Tissue; D000818:Animals; D002417:Cattle; D008279:Magnetic Resonance Imaging / Q000379:methods*; D018482:Muscle, Skeletal; D011522:Protons; D013552:Swine; D013696:Temperature
chemical_list: D011522:Protons